8.1 Soils and Fertility
Fertility management is part of overall soil management involving proper tillage practices, crop rotation, cover crops, water management (irrigation and drainage), liming, and weed management. Although it is important in obtaining maximum economic yields, fertilization alone will not overcome shortcomings in the other areas mentioned above. Such problems should be corrected first so as to benefit fully from organic and inorganic fertilizer supplements and to sustain high yields and quality over the long term. Information on Soil Testing, Soil pH and Fertilizers is below in sections 8.8, 8.9 and 8.10.
8.2 Field and Soil Evaluation
Plan ahead when selecting new lands or fields. Soils for growing vegetables should be well drained, fairly deep, reasonably level, properly limed, and in good tilth (have good structure). Medium-textured soils (sandy to silty loams with good organic-matter content) are generally most satisfactory; well-drained, sandy soils with a slight to moderate southern slope are most favorable for early plantings and certain warm-season vegetables. For a summary of soil types and soil management groups in New York State, please see the general information section of the Cornell Guide for Integrated Field Crop Management. Detailed soil survey maps are available through local Cornell Cooperative Extension, NRCS and SWCD offices. For the soil types in your fields search online: Web Soil Survey from USDA-NRCS. After determining whether the soil is suitable, check for perennial weeds, correct pH, and soil nutrient levels before planting.
8.2.1 Soil Health
Soils in good health provide a desirable medium for root development, have pore space for both air and rapid percolation of excess water, have a high water-holding capacity so crops can withstand dry periods, are less prone to erosion, and resist the tendency to crust. Healthy soils have low levels of soil-borne disease organisms, and high levels of beneficial soil organisms. Many agricultural practices cause soil structure to deteriorate. Compaction, which results from the use of equipment on wet soils, is particularly damaging. Tillage tools break down soil aggregates, the tiny, basic building-blocks of good soil structure; intensive cultivation accelerates loss of organic matter and causes soil to crust. Obviously, all unnecessary operations should be avoided. Prepare the soil only enough to provide an adequate seedbed. Never plow, till, plant, or cultivate soils when they are wet. A ball of soil which crumbles when pressed with the thumb is likely dry enough. One mistake can reduce the yield of the crop regardless of the level of other inputs. For detailed information on soil health and the Cornell Soil Health Test search online: Cornell Soil Health
8.3 Crop Rotation
Vegetable crops within the same plant family (crucifers, legumes, vine crops, Solanaceous crops, etc.) tend to share the same diseases. As a rule of thumb, don’t include that plant family more than once every three years in the rotation. Include cover crops in the same family as well.
Rotation with forage, hay, and cereal crops is an effective way to maintain the organic matter and structure of soils used primarily for vegetables. A good stand of legume or grass-legume sod can also provide substantial nitrogen upon decomposition, thus reducing the nitrogen fertilizer requirement for the next vegetable crop planted. Grass and/or legume sods have a place in the rotation to maintain the porosity of fine-textured soils, improve the water-holding capacity of coarse soils, and may reduce the buildup of disease, insect, and weed pests. Note: All legumes, whether crops or cover crops, share many of the same diseases.
8.4 Cover Crops
Cover crops are planted to protect and improve the soil, suppress weeds and diseases, and help cycle nitrogen. Integrating cover crops into vegetable production systems offers many benefits, but provides some challenges as well. For cover cropping to be successful, it is important to know the intended purposes, consider key management factors, and understand the characteristics of different cover crop species.
Cover crops offer a way to add organic matter to soils; improve soil tilth and reduce compaction; protect soil from wind and water erosion; add or recycle plant nutrients; increase the biological activity of soil; retain soil moisture; and in some cases, suppress weeds and diseases. No single cover crop can do all of these things. Matching the need and opportunity to the right cover crop requires information and planning.
Cover crops need to be treated with the same care as cash crops in order to get the intended value. The best success will come with practices that favor a fast start, and that leave no gaps in the stand. These include: sufficient temperature, soil moisture, and soil fertility; practices such as preparing an adequate seedbed by drilling seed or broadcasting and cultipacking; inoculating legume seed with the proper Rhizobium inoculant; and, correcting pH or soil fertility problems. In some cases escaped weeds must be controlled with herbicides or by mowing the cover crop in midseason.
Cover crops must also be killed on time. Before planting, know when and how the cover crop will be killed, and have access to the means of termination. Cover crops that are killed too soon don’t deliver the benefit for which they were planted. If killed too late, they can reseed, leave clumps that make seedbeds impossible to form, or inhibit crop growth. Termination criteria and methods are available online. Search: Cover Crops for Vegetable Growers.
Despite the relatively short growing season in New York, there are many ways to integrate cover crops into vegetable rotations. Common examples include: planting small grains after vegetable crop harvest; interseeding ryegrass or clover into a standing vegetable crop; sowing buckwheat in mid-summer or crucifers in late summer; planting after early harvests of vegetables; planting barley windbreaks in muck-grown onions; or taking land out of production for a season.
The costs associated with cover cropping, which include the price of seed, amount of time and labor invested, use of equipment, and value of missed opportunities, should be taken into account. Some cover crops pose specific management challenges. For example, either grain rye left to grow into late spring or unmowed Sudan grass left into the fall can result in such rank growth that they are difficult to incorporate into the soil and may cause nitrogen immobilization. Cover crops can sometimes have detrimental effects. Direct-seeding a vegetable crop into soil with fresh organic residues invites seed-maggot damage. Some cover crops, such as hairy vetch, are hosts for common nematodes on soilborne diseases such as white mold. Many of these specific risks are detailed in the resources below.
For more details online search: Managing Cover Crops Profitably for general information,Cornell Cover Crops for Vegetable Growers for New York specific guidance, and the Cornell Cover Crop Decision Tool.
Oats. Seeding rate: 60 to 100 lb/acre. Timing: August through early September. Winter-killed small grain; if left untilled, will result in a dead mulch residue in spring that suppresses weeds. Easier than rye to incorporate in spring. Works well grown as a mixture with hairy vetch. Oats and other small grains are not hosts of most vegetable plant pathogens.
Wheat. Seeding rate: 80 to 110 lb/acre. Timing: mid-September through early October. Winter-hardy small grain; frequently used cover crop in New York. Spring regrowth is a week or more later than rye. May cause nitrogen immobilization and encourage seed maggots if vegetable crop is planted too soon following incorporation.
Rye. Seeding rate: 80 to 110 lb/acre. Timing: late August through mid-October. Winter-hardy small grain; can be planted later than any other cover crop in New York. Tolerates a wide range of growing conditions. Spring regrowth can be quite vigorous, making incorporation difficult. May cause nitrogen immobilization and encourage seed maggots if vegetable crop is planted too soon following incorporation. May also cause reduced growth in following. A mixture of rye and hairy vetch can result in significant biomass if left to grow until the vetch flowers in late May.
Barley. Seeding rate: 90 to 120 lb/acre. Timing: early spring or early fall. Nonwinter-hardy small grain. Does not tolerate wet soil, low pH, or low fertility well. Principally used as a windbreak for onions.
Ryegrass. Seeding rate: 18 to 20 lb/acre. Timing: August through September. Grass cover crop with an extensive root system which grows in compacted soils better than most. Forms a sod which can be difficult to kill chemically. Excellent erosion control. Shade tolerant, and used for overseeding into standing crops or between plastic mulch beds.
Brassica (arugula, spring mustard, fall mustard, forage radish, forage turnip and forage rape). Seeding rate: 10 to 12 lb/acre. Timing: mid-August. Broadleaf annuals and biennials, which grow rapidly in cool weather, with soil-improving root systems. There is great variation in winter hardiness among varieties and growth stage. Those that remain rosettes are the hardiest; those that have formed stalks (mustards) or swellings (radish, turnip) generally die. Radish and yellow mustard generally die early in winter, while forage rapeseed and turnip die late in winter, and canola regrows in spring. Excellent, deep-rooted nitrogen scavengers during the fall. Do not allow brassicas to set seed or weed problems may result.
Sudangrass and SorghumxSudangrass. Seeding rate: 30-50 lb/acre depending on seed size. Timing: Mid-June through July. Warm-season annual grasses that produce large amounts of biomass and penetrate compacted soils. Mowing when it reaches a height of three feet is recommended to manage top growth and stimulate roots. The mowed residue also smothers weeds. Incorporated green, sudangrass suppresses some diseases and nematodes. Extremely frost sensitive. Supplemental fertilizer (especially nitrogen) is needed if residual levels are low.
Buckwheat. Seeding rate: 50 lb/acre. Timing: June and July. Warm-season annual broadleaf characterized by rapid growth, moderate biomass accumulation, fine extensive root system, and ability to thrive on low-fertility soils. Two successive buckwheat cover crops in summer followed by winter rye can effectively reduce weed pressure in a field, particularly quackgrass. Mow or incorporate at early flowering to avoid seed set. Highly frost sensitive; decomposes rapidly.
Hairy vetch. Seeding rate: 35 to 40 lb/acre. Timing: late August through early September. Annual winter-hardy legume with the potential to fix up to 100 pounds of nitrogen per acre if left to grow well into May. Fall growth is typically modest; most growth occurs in May. Mixtures of vetch and rye or vetch and oats increase biomass production. Incorporate or mow closely at full flowering to maximize nitrogen contribution and avoid seed set and subsequent weed problems. Hairy vetch is a host for a number of plant diseases such as white mold, as well as several plant-pathogenic nematodes.
Clovers (red clover and white clover). Seeding rate: 10 to 15 lb/acre. Timing: early spring or late summer. Slow growing, shade-tolerant, perennial legumes which compete poorly with weeds. Of the clovers, only two are consistent performers in New York: Medium red clover as an annual or biennial, and Dutch white clover as a short-lived perennial. Red clover is often frost seeded into wheat in late winter, and contributes 40-75 pounds of nitrogen per acre after one year’s growth, depending on the stand and when it’s killed. It can also be interseeded because it is shade tolerant but will not grow quickly until the crop is removed. Dutch white clover can be particularly useful for walkways or alleys. Crimson clover, while not winter-hardy, can be used as a summer nitrogen-fixing cover crop.
Biennial sweetclover (yellow blossom and white). Seeding rate: 15 lb/acre. Timing: early spring to midsummer. Biennial, winter-hardy legume characterized by long, thick tap roots which can improve soil structure. Biomass production generally higher in second year. Mowing makes incorporation easier and may improve growth. Susceptible to weevil damage.
Field peas. Seeding rate: 100 lb/acre. Timing: early spring. To provide nitrogen for a late-planted vegetable crop, field peas can be sown in the spring. They perform best with an oat nurse crop. Seed cost is substantially higher than the other legumes in this list.
8.5 Reduced Tillage
Reduced tillage systems for large-seeded vegetable crops like beans, corn and vine crops, and transplanted crops, are gaining interest as strategies to improve soil health, to increase farm profitability, and to minimize the adverse effects of intensive agriculture on the environment. Zone tillage is one reduced tillage strategy that limits surface soil disturbance to 6-10 inches wide for the planting row, leaving the space between crop rows undisturbed through planting. The benefits of zone tillage can include improved soil health, reduced soil erosion, labor savings, lower fuel costs, and greater planting flexibility early in the season. Shallow surface zone tillage can perform well in soils without a subsurface compaction layer. However, in most vegetable soils, continuous plowing has created distinct layers of compaction, often between 8 and 12 inches deep. These layers can restrict root growth and water movement in the soil and severely limit the success of shallow surface zone tillage. For these soils, deep ripping where the crop row will be, with zone tillage, is necessary for successful crop production. Interested growers should try zone tillage first on a small area with mid-season sweet corn to be sure equipment is properly adjusted for your soil type for good crop emergence.
The following guidelines highlight key equipment, field preparation, weed management, fertility management and planter setup that should be considered for successful adoption of deep zone tillage for vegetables. For more online resources search: Cornell Reduced Tillage Vegetables
Zone builders are prevalent among Northeast growers using deep zone tillage for primary field preparation. They consist of straight-leg shanks to disturb the soil in narrow zones only where the crops will be planted, and can operate up to 20 inches deep. Narrow points and shanks are key to minimizing soil disturbance and soil inversion. The depth of compaction should be determined ahead of time in several places in the field with a penetrometer or a tile rod. The shanks are set to operate 2 inches below compacted soil layers. Each shank must be preceded by a residue-cutting coulter to prevent residue from binding on the shank. The zone builder should be equipped with a couple of coulters following each ripper to till a 6-10 inch wide strip and create a mini-mound over the ripped slot. Mini-mounds are adjusted by angling the coulters, with a 2-3 inch mound being best for planting and weed control. Six to 10 inch wide rolling baskets or culti-packer wheels follow the coulters to break up clods. For optimal performance three-point hitch units must be leveled by the top link, and the square frame must be parallel with the ground. Row cleaners preceding the ripping shank can help reduce residues in the planting row, or they can be mounted on the front of the planter. It is important that tractor horsepower be properly matched with zone building equipment. About 30–35 hp per ripper is needed in early years. Zone builders range from single to 12 row units with different manufacturers and custom-built options.
8.5.2 Weed Management
Control perennial weeds the fall prior to zone tillage. Cover crops can be used in reduced tillage systems for multiple benefits, possibly including weed control, but should be carefully planned. It is essential to kill a sod cover in the fall prior to zone tillage so the root clumps have time to break down. Legume cover crops are very difficult to kill with herbicides in the spring. Kill fall planted cover crops with herbicides 2-3 weeks before zone building. Avoid planting into live cover crops where competition for water and nutrients may limit crop growth and inhibition of crop growth may also occur. Concerning weed control for the growing season, herbicides that require incorporation are not likely to work well with strict zone tillage. Pre and post-emergence herbicides should be effective. Cultivation may be an option in some soils, if necessary. A major reason to start small with zone tillage is to fine-tune your weed control program.
8.5.3 Fertility Management
Be sure soils are tested for lime and nutrient requirements before starting zone tillage. Lime requirements especially must be met before limiting tillage, especially if high rates of lime are needed. Zone tillage will work some lime into the soil but full width lime incorporation will improve soil pH and nutrient availability throughout the root zone. Both liquid and dry fertilizer programs can be used in a zone tillage system. Fertilizers can be deep placed in the slot or banded at planting. Plan to supplement fertility with side-dress applications when necessary. If high rates of potassium (K20) are needed broadcast in the fall or ahead of zone tilling.
Plant the same number of rows as you zone till so you can line up the planter over the rip. Planter units may be preceded by a coulter to cut through heavy residues. An ideal planting unit for zone tillage has floating row cleaners, a seed firmer, spiked closing wheels and a closing drag chain. Planter or transplanter units should be preceded by row cleaners, preferably floating with depth bands, for best seedbed preparation when residues are present. These also remove lumps, rocks and root balls. They should only turn about 80% of the time, however, to avoid removing too much surface soil, or a depression will be left in the planting row where water can collect.
Note: Be sure to read the section on Produce Safety in section 8.6.1 below!
Most vegetable operations do not have a ready source of manure, but it should be judiciously used when available. Once applied to soil, manure is decomposed by microorganisms, forming humus. Manure provides both major and minor nutrients, and when used regularly, it contributes organic matter and helps to alleviate structural deterioration, an important consideration in maintaining the productivity of heavily worked vegetable soils. One drawback of using manure is that certain weed seeds maintain their viability after passage through animals, so a potential exists for adding a new weed species to a field. This threat is more likely with fresh than with composted manure.
Manure contains two forms of nitrogen, the unstable form in the urine and the stable form in the feces. The unstable form may account for 50 percent or more of the total nitrogen in manure. This nitrogen decomposes rapidly to ammonium, which in turn converts quickly to extremely volatile ammonia that can be lost from the system. For this reason, much of manure’s unstable nitrogen may never be taken up by crops unless measures are taken to conserve it during the process of collection, storage, and application to the field. In general, about 35 percent of the stable nitrogen becomes available within a year of application, about 12 percent the second year, about five percent the third year, and about two percent the fourth year. Thus, repeated application to the same field results in an accumulation of a slow-release source of manure nitrogen.
Most potassium in manure is available for plant growth during the year applied; whereas, some of the phosphorus is in organic form and must decompose before it becomes available. Moreover, because phosphorus is not very mobile in the soil, broadcasting manure is not an efficient way of applying this element for crop establishment. Frequent manure application to meet crop nitrogen needs, inevitably results in excess phosphorus in the soil. A nutrient imbalance may result, in addition to the risk of stream and lake contamination and algae blooms.
A micronutrient deficiency in a field with a history of manuring is rare because manure contains small quantities of these elements. If a deficiency is observed on a nonmanured field, a commercial fertilizer should be added immediately because of the slower availability of micronutrients in manure. If soil pH is acceptable, manuring may eventually solve the problem.
For more information online about manure and nutrient cycling search: Cornell agronomy fact sheets.
8.6.1 Produce Safety
Improperly timed manure applications, or the use of incompletely composted manure, increase microbial risks of foodborne illness. Field and packinghouse workers may also carry pathogens that pose risk. The possibility that fecal matter may come into contact with produce, or that water might splash pathogens from the manure onto field produce are both important concerns. Pathogens such as E. coli O157:H7, Salmonella, and Campylobacter can be present in manure slurry for up to 3 months or more, depending on temperatures and soil conditions. Troubling for growers is that Listeria monocytogenes can survive in the soil for much longer than 3 months. Yersinia enterocolitica may survive, but not grow, in soil for almost a year. These pathogens can cause serious illness and even death, especially in the very young or old, or in people with weakened immune systems.
It is important that all farms follow Good Agricultural Practices (GAPs) to reduce microbial risk. For much more detail online search: Cornell GAPs and Cornell Produce Safety Alliance. Many produce buyers now require a third party audit of extensive grower records related to food safety. Trainings are available. The US Food & Drug Administration has proposed rules, and has been accepting comments, on the implementation of the Food Safety Modernization Act (FSMA). Updates available online by searching: FDA Food Safety Modernization Act.
Good Agricultural Practices related to manure include:
Consider the source, storage, and type of manure.
- Store manure far away from areas where fresh produce is being grown and handled.
- Erect physical barriers and wind barriers to prevent runoff and wind drift of manure.
- Properly and completely compost manure. High temperatures achieved by a well-managed, aerobic process that includes multiple turnings, as well as an aging period, can kill most harmful pathogens and produce a high quality, stable compost. For more information online search: Composting Manure NRCS
Plan manure application timing carefully.
- Apply manure in the fall or at the end of the season to all future vegetable ground, when soils are warm, nonsaturated, and will be promptly cover cropped.
- Incorporate manure into soil as soon as possible after spreading.
- DO NOT harvest vegetables until 120 days after manure application. If this is not feasible for short season crops apply only properly composted manure.
- Document type of manure, rates, dates, and locations of manure applications.
Choose appropriate crops.
- Apply manure to perennial crops in the planting year when they will not be harvested, or immediately following the last harvest of the season.
8.7 Sewage Sludges
Sewage sludges are by-products of the purification of municipal wastewater. Sewage sludges contain organic matter, and micro- and macronutrients essential for plant growth. They are extremely variable, however, and contain a wide range of contaminants such as heavy metals, toxic organics and human pathogens. The heavy metals remain indefinitely in soils where sludge is applied. The analysis of heavy metals and toxic organics in a sample is likely not complete, as many potential contaminants are not regulated. There are state and federal restrictions on use on agricultural land. Many food processors will not accept vegetables grown on soils where sewage sludge has ever been applied. Use of sewage sludge on vegetable land is not recommended.
8.8 Soil Testing
Fertilizer requirements for best economic yield should approximate the difference between what vegetables take up from the soil for best growth and quality, and what the soil can actually supply during the crop-growing period. The supply of essential nutrients in soil cannot be determined without conducting a soil test. Moreover, if pH is not in a desirable range, yields may be poor regardless of fertilizer added or already present in the soil.
Soils on which vegetables will be grown should be sampled and tested at least once every three years. The pH of most vegetable soils decreases (becomes more acidic) gradually because of the removal of calcium, magnesium and potassium ions by leaching and crop uptake, and from acid forming fertilizers. Testing every year gives a more complete evaluation and is appropriate when significant changes have been made in the fertilizer program (e.g., applying less phosphorus or potassium when the previous year’s test showed high levels). In general, when the Cornell-recommended rates of fertilizer are applied, low soil test values for phosphorus and potassium usually increase slowly and steadily in spite of crop removal. Medium soil test values tend to remain constant or increase slightly, whereas high values decrease gradually. The potassium level could decrease much more rapidly, however, if a light sandy soil with relatively low exchange capacity is coupled with a heavy potassium feeder such as potatoes or tomatoes. In such situations, yearly sampling is appropriate. The purpose of applying nutrients, however, is to benefit crop development, not to achieve a predetermined test result.
Soil testing in New York is now done by Dairy One/Agro One, in cooperation with Cornell University (730 Warren Rd. Ithaca NY 14850; 1-800-344-2697 x2172; or search online: soil testing Dairy One Agro One). Order sample boxes and Soil Submittal Forms by phone or online. New York growers interested in obtaining Cornell fertilizer guidelines for vegetable crop management should choose “New York samples - Cornell guidelines,” and “Commercial Vegetable - Modified Morgan Analysis,” to get the correct Soil Submittal Form - V or V2. Be sure to include the necessary field information (soil type and crop to be grown), or fertilizer guidelines can not be included with your results. Include your check with the sample box and form, and mail to Dairy One Agro-One.
The soil test results provide soil pH, percent of organic matter, and level of phosphorus, potassium, magnesium, calcium, and zinc. Levels of aluminum, iron, and manganese are also listed to identify potential toxicities rather than deficiencies. Other nutrients can be tested for an additional fee. See the nitrogen, phosphorus, and potassium recommendations under each crop to design a fertility program for your farm.
8.9 Soil pH
In general, vegetable crops grown on mineral soils will thrive at pH 6.0 to 6.5. Some vegetables do well at pH 5.5; potatoes will tolerate even greater acidity. In contrast to mineral soils, the desirable pH for muck soils is approximately 5.5, and they should not be limed above pH 5.7. This is largely because of the much greater amounts of calcium found in muck at pH 5.5 compared to mineral soils at similar pH. Specific pH ranges for individual vegetable crops are given under each crop’s fertility section.
When soil pH is adequate, the availability of both major and minor nutrients is maximized, and the accumulation of toxic metals is minimized. Clearly, one cannot expect to maximize dollars spent for nitrogen, phosphorus, and potassium fertilizer when soil pH is suboptimal. Thus, many people consider soil pH to be the most important part of the soil test.
For optimal vegetable production on New York’s acidic soils, soil pH should be adjusted with lime to fit the needs of the various crops. When soil pH is 6.0 or below, the laboratory will determine the exchangeable acidity on the sample. A lime requirement can be determined based on pH (actual acidity of the soil solution) and exchangeable acidity (reserve acidity for that soil). Two soils with the same low pH reading could require markedly different amounts of lime to correct the situation. A given amount of lime could overlime one soil, causing problems that did not exist previously, whereas the same amount of lime might be insufficient to correct the undesirable acidity in the other soil. This is one reason soil testing is so important.
Based on exchangable acidity, as determined by the soil test, an accurate lime recommendation can be given. When complete soil tests are not available, the general lime recommendations in Table 8.9.1 may prove useful. The lime rates given are based on an eight inch plow depth. If the plow depth is less than eight inches, decrease the rate given in the tables by 12 percent for every inch less than eight inches. If the plow depth is more than eight inches, increase the lime rate given by 12 percent for every inch greater than eight inches. For example, a plow depth of ten inches and a lime recommendation of four tons would require 24 percent more lime than given in the table. Therefore, the total rate to apply is approximately five tons (4 tons multiplied by 1.24 = 4.96).
The lime recommendations given in Table 8.7.1 and on the soil test result form are for limestones of 100 percent Effective Neutralizing Value (E.N.V.). These rates need to be increased or decreased according to the actual E.N.V. of the limestone being applied. The rate to be applied is calculated by dividing the recommended rate given in the tables or the test report (if necessary, correct for plowing depth) by the E.N.V. of the lime to be used. For example, if the recommended lime rate is four tons per acre and the E.N.V. of the limestone to be spread is 0.68, the rate to apply would be 5.88 tons (4.0 divided by 0.68), which would round off to six tons per acre. The delivery slip accompanying bulk spread limestone specifies the E.N.V. and the quantity required to equal limestone at 100 percent E.N.V.
Limestones vary in E.N.V. because of differences in purity (calcium carbonate equivalence) and particle size. Coarse limestone or limestone of lower purity is less effective than is more finely ground limestone or limestone of higher purity in neutralizing soil acidity. Cost per ton can be misleading if the limestones being compared do not have a similar E.N.V. Accordingly, the least expensive lime in terms of dollars per ton may not be the best value.
Limestones are mixtures of calcium carbonate and magnesium carbonate with calcium carbonate predominant. The magnesium content in limestones sold in New York varies from 1/5 percent to more than 12 percent. A dolomitic limestone contains a relatively high percentage of magnesium, although there is no legal definition. If pH is low, the magnesium soil test is low (below 65 pounds per acre), and a magnesium-sensitive crop such as melons or tomatoes is to be grown, using a dolomitic limestone is an excellent, economical way to provide the needed magnesium. If the soil test magnesium level exceeds 100 pounds per acre, there is no particular advantage to using lime with higher magnesium content. When magnesium levels are high, either a calcitic- or dolomitic-type limestone is appropriate.
If pH is below 5.5 on mineral soil, lime should be applied long enough before seeding the more acid-sensitive vegetables to react with the entire plow layer. If there is insufficient time for an adequate reaction with the entire plow layer, a split application is recommended. At least half of the recommended lime should be added to the surface and disked in before seeding to provide a pH favorable for good seedling establishment in the zone near the seed. When soils require more than four tons per acre, split the lime application by plowing one-half down and disking the remainder into the surface. Smaller lime applications to maintain pH above 6.0 can be made anytime before seeding and can either be applied to the surface or plowed down. When rotations are used, the last summer or fall that a field is in sod is a good time to apply smaller maintenance applications of lime. At this time the soil is firm, and lime can be applied with less likelihood of soil compaction.
8.10.1 Nitrogen, Phosphorus, and Potassium
Although necessary for high-yielding crop production, fertilizer nutrients can escape from the agricultural system, thereby increasing the potential for environmental damage. Nutrients escape in various ways depending on the chemical and biological nature of the element involved. Obviously, this escape can be accelerated if fertilizers are added in excess of plant requirements or if they are applied or otherwise handled improperly.
Regardless of the chemical form added, nitrogen can convert rapidly to nitrate; in this form it does not bind to the soil but rather moves downward with water as the water moves through the soil. Thus, excessive nitrate-nitrogen poses a threat to the quality of ground water. Nitrogen is also lost to surface water as soils erode, removing soil organic matter.
Using nitrogen efficiently is probably the biggest challenge in fertility management. Vegetables are responsive to nitrogen, and no one wants to risk inferior yield or quality because of a deficiency. However, it is difficult to accurately determine the nitrogen contributions from soil organic matter, manure, or incorporated legumes because temperature and moisture can play a significant role. Also, sources of nitrogen convert to nitrate-nitrogen when conditions are optimal for plant growth, and in this form nitrogen moves with water and can be leached out of the system.
Guidelines for efficient use of nitrogen.
- Limit nitrogen applications prior to planting, and avoid deep plow-downs.
- Band either at planting or as a sidedressing to apply nitrogen most efficiently.
- Apply nitrogen close to the time the crop is most active in taking it up.
- Avoid “insurance” applications of nitrogen.
- Maintain the proper pH.
- Use plastic mulch to limit leaching and facilitate nitrogen release from nonfertilizer sources.
- Avoid over fertilization which will lead to leaching.
- Account for nitrogen from organic matter, cover crops, composts, manure, etc., which becomes available as the soils warm.
- Consider using the pre-sidedress soil nitrate test (PSNT) to determine nitrogen contributions from nonfertilizer sources.
- Use cover crops to retain nitrogen and other nutrients and limit leaching.
Phosphorus is usually tightly bound to soil particles with only small amounts in the soil water. Phosphorus may also occur in organic soil materials, some of which are water soluble. Most phosphorus loss is attributable to surface runoff and soil erosion. Techniques that help prevent nutrient loss to the environment include prevention of soil erosion, avoidance of overfertilization or insurance applications, and timing and placement of fertilizer applications in a manner to achieve efficient plant uptake.
Fertilizers are applied to improve plant growth by providing nutrients not adequately supplied by the soil. When the soil contains enough of a particular nutrient to support optimal plant growth, there is no need to supply additional quantities of that nutrient. See Section 8.8 on soil testing. The most common nutrients in commercial fertilizers are nitrogen (N), phosphorus (P), and potassium (K). Phosphorus and potassium are shown on fertilizer labels as the oxides P2O5 and K2O, respectively. For conversion multiply P2O5 by 0.44 to get P, and multiply K2O by 0.83 to get K. Calcium (Ca) and magnesium (Mg) are usually supplied by liming. See Section 8.9 on lime recommendations. New York soils in the proper pH range are not usually deficient in minor nutrients. See Section 8.9 for more details on minor nutrients.
Some common fertilizer materials and their analyses are given in Table 8.8.1. The materials shown in the table are used both for direct application to the soil and for the manufacture or blending of other complete fertilizers. Materials providing secondary nutrients and micronutrients are listed in Table 8.8.2.
Table 8.10.1 Common fertilizer materials supplying primary nutrients
|Common name||Chemical formula||Analysis Percent|
|Muriate of potash||KCl||0||0||60|
|Sulfate of potash||K2SO4||0||0||50|
|Sulfate of potash-magnesia (11% Mg)||K2SO4 • MgSO4||0||0||22|
8.10.2 Secondary Nutrients and Micronutrients
The secondary nutrients - calcium (Ca), magnesium (Mg), and sulfur (S) - are as important for normal growth as the primary nutrients but either are not required in large quantities or are usually supplied through means other than fertilizers. Micronutrients, often referred to as minor elements, include boron, zinc, manganese, copper, molybdenum, and iron. They are as important to normal plant growth and reproduction as are the primary and secondary elements. The difference is that micronutrients are required in small amounts because crops remove less than a pound per acre (less than an ounce per acre of some elements). Micronutrients are seldom deficient in New York soils when the pH is between 6.0 and 6.5 on upland soil and between 5.4 and 6.0 on muck. Response to micronutrients is rare on upland soils of reasonable organic matter content or on manured soils whose pH is in the proper range. In general, micronutrients should not be included in the fertilizer program. In a few specific cases, micronutrients may need to be added to achieve maximum marketable yield. See fertility recommendations under specific crops to determine potential deficiency problems.
Table 8.10.2 Fertilizer materials supplying secondary nutrients and micronutrients
|Common name||Element||Chemical formula||Analysis %|
|Calcium nitrate||calcium (Ca), N||Ca(NO3)2||22 Ca, 15.5 N|
|Magnesium sulfate¹||magnesium (Mg)||MgSO4||16 Mg, 14|
|Magnesium oxide¹||magnesium (Mg)||MgO||45 Mg|
|Superphosphate||sulfur (S)||Ca(H2PO4)2+CaSO4||8 S|
|Calcium sulfate (gypsum)¹||sulfur (S), Ca||CaSO4||15 S, 32 Ca,|
|Sulfate of potash-magnesia||sulfur (S), Mg||K2SO4 MgSO4||22 S, 11 Mg|
|Potassium sulfate||sulfur (S)||(NH4)2SO4||24 S|
|Borax¹||boron (B)||Na2BO4||12 B|
|Solubor||boron (B)||Na2BO4||20 B|
|Manganese sulfate¹||manganese (Mn)||MnSO4||28 Mn|
|Zinc sulfate¹||zinc (Zn)||ZnSO4||36 Zn|
|Zinc oxide¹||zinc (Zn)||ZnO||50 Zn|
|Zinc chelate||zinc (Zn||Zn-chelate||14 Zn)|
|Ferrous sulfate¹||iron (Fe)||FeSO4||20 Fe|
|Iron chelate||iron (Fe)||Fe-chelate||14 Fe|
|Copper sulfate||copper (Cu)||CuSO4||25 Cu|
|Sodium molybdate||molybdenum (Mo)||Na2MoO4||39 Mo|
|Ammonium molybdate||molybdenum (Mo)||(NH4)6Mo7O24||54 Mo|
8.10.3 Fertilizer Placement
To be used by plants, nutrients must be present in moist soil where roots are active. Nitrogen placed on the surface will leach down to roots if irrigation or rainfall is adequate. Phosphorus and potassium do not move extensively and therefore should be placed deeply enough to remain in moist soil throughout the growing season. All of the phosphorus and potassium and some of the nitrogen should be applied shortly before or at planting; the remaining nitrogen should be applied as sidedressings during the early part of the growing period. Band application of at least part of the fertilizer near the seed or plant row is recommended, especially when soil test levels are marginal and crop response to the fertilizer nutrients is likely. Beware of banding too close with rates above 80 to 100 pounds per acre of potassium and nitrogen combined because seeds or seedlings can be injured.
8.10.4 Fertilizer Injury
All nitrogen and potash materials add water-soluble ions to the soil. If the concentration of these ions is too high near the germinating seed or seedling, salt burn can result, reducing germination and retarding seedling growth. The problem occurs most often when the weather turns dry after seeding, a salt-sensitive vegetable such as beans is being grown, or the fertilizer band is being placed closer to the seed than the grower intended. To prevent salt burn when banding fertilizer, avoid using more than 80 to 100 pounds of N + K2O per acre in the band at planting. Potash can be broadcast and incorporated separately. This rule applies to fertilizer bands placed two inches below and two inches to the side of the seed. Check equipment when banding to ensure that the band is being placed where intended, especially on sloping fields. If more than 80 to 100 pounds of N + K2O per acre will be used, the band should be moved three inches to the side of the seed.
Materials containing nitrogen produce another type of germination or seedling injury associated with a high concentration of ammonia. Fertilizers producing this injury contain urea, diammonium phosphate (DAP), or anhydrous ammonia. Exceeding 30 pounds of nitrogen as urea, 30 pounds of phosphorus as DAP, or 30 pounds combined from fertilizers containing both materials may cause seedling injury in bands, especially when dry weather follows planting and the band is closer than two inches. Both urea and DAP can be used for plow-down applications without concern for injury. If anhydrous ammonia will be used as a preplant or preemergence source of nitrogen for sweet corn, it should be injected as far as possible from the seed.
8.10.5 Fertilizer/Transplant Solution
Adding a small amount of water-soluble or liquid fertilizer to transplant water can stimulate growth of young transplants such as cabbage, tomatoes, and peppers. Many grades are available for this purpose (e.g., 10-52-17, 14-28-14, 23-21-17, 20-20-20, 6-24-6, and 10-34-0). They are generally used at a concentration of about three pounds per 50 gallons of water and about one-third this strength on melon and cucumber plants. Transplants can be injured in hot weather if the soil is relatively dry. Reducing the concentration of starter fertilizer may help, but it is safer to irrigate before or immediately after transplanting.
Response to starter solutions is most likely when soils are cool and tests indicate low phosphorus and potassium. In tests at Cornell with transplanted tomatoes under these conditions, diluted 10-34-0 liquid fertilizer was as effective as complete grades. Tomatoes transplanted late (early June), however, into a warmer identical soil testing high in phosphorus and potassium did not respond to 10-34-0 or a complete starter fertilizer. If container-grown plants have been fertilized just before transplanting, the starter fertilizer may be diluted or eliminated from the transplant water.
The most efficient way to fertilize an established mulch row crop is through a trickle irrigation system which is usually installed during the mulching operation. See Chapter 7 for details on trickle irrigation. Due to the small holes in the trickle tubing, it is important that only completely soluble fertilizers are used. Best results have been achieved by using a 1-1-1 ratio of completely soluble fertilizer such as 20-20-20.
When applying soluble fertilizer, the system should first be fully charged with water. After the fertilizer has been injected, water should be applied only long enough to flush all of the fertilizer through the lines. A long irrigation immediately after fertigating will cause leaching of the fertilizer below the root zone and reduce, rather than increase, the efficiency of fertilizer. Drip fertigation schedules vary with the crop, soil conditions, and management practices. In general, preplant fertilizer should supply about 20 to 30 percent of the nitrogen and potassium and all of the phosphorous needs of the crop. The remainder of the nitrogen and potassium is supplied through the system during the growing season as needed by the crop. If equipment is available, applying the preplant fertilizer to the soil area to be covered with mulch is more efficient than a broadcast application. Some growers, particularly in initial years of experimenting, may supply up to 50 percent of the nitrogen and most of the potassium before planting.
To calculate fertilizer rates for trickle irrigation under mulch, base the amount applied on mulched acres rather than actual acres. For example, if the soil surface covered by the mulch is three feet wide and the row center is six feet wide, you should apply 1/2 or 50 percent of the rate that would have been calculated f or broadcasting on a per-field-acre basis. This is similar to reducing application amounts when banding fertilizers or herbicides.
The first soluble fertilizer should be applied through the drip system within one week of transplanting. The remainder should be split between three and five additional applications. Heavier soil may require fewer applications. See specific crops for details. There is little advantage in applying fertilizer more than once a week or once every other week, except on sandy soils where leaching or low cation exchange capacity may be a problem.
8.10.7 Foliar Feeding
When deficiency of a minor element is probable and corrective action was not taken in planning the soil fertilization program, foliar feeding can be useful. Such emergencies are infrequent, usually occurring when a vegetable has a high requirement for a micronutrient whose availability is restricted by undesirable soil pH. Routine use of foliar feeding products in vegetable production is not recommended.
Several foliar products are aggressively marketed and advertised. Many contain N, P2O5, and K2O and are basically diluted starter fertilizer materials supplemented with two to five micronutrients. The advertisements for these products try to create the impression that potential profits will be lost if foliar feeding is not a regular part of a fertility program. In reality, indiscriminate use of foliar nutrients and shotgun foliar mixtures, when soil deficiencies do not exist, wastes time and money and decreases profit margins. Once requirements have been met with a good soil fertility program, nutrient loading will not turn a good crop into a super crop. Marketers argue that foliar feeding can provide needed nutrients when environmental stresses limit feeding from the soil. When this happens, however, the stress itself limits growth (not just nutrient uptake), so that any response to foliar nutrients will be limited until the stress is removed, after which time sufficient feeding from the soil can resume.
If you are determined to use foliar nutrients, treat small areas and compare the results to untreated areas. In the unlikely event that a positive result is obtained, check the soil fertility program closely for problems that may need correction.
8.10.8 Plant Analysis
Plant analysis, which reports the concentration of all the essential elements in a growing crop, is now available at a reasonable cost. This information can identify nutrient deficiencies and toxicities from over fertilization. Plant analysis is best used in conjunction with other information such as the soil test, fertilizer program followed, cropping history, and observations on crop development. Once the results are obtained it is generally too late to make corrections on the existing annual crop; for this reason, plant analysis is used primarily in troubleshooting problem areas where insect, weed, or disease pests do not appear to be the culprit.
Despite the above limitation, analyses of healthy crops, along with good record keeping, can provide useful reference points and lead to better interpretive guidelines for local soil and climatic conditions. This information could help in investigating problems that may arise later, and it also provides a benchmark to assess how changes in the fertility program or in any other production practice affect the nutrition of the crop.
Another reason plant analysis has not been more widely used is that the results must be interpreted by an experienced person. Nutrient concentrations vary with the part of the plant sampled and the age of the plant. In addition, factors besides nutrients that limit growth, such as water stress, cool temperatures, and nematodes, can affect the uptake of nutrients and thus the results of the analysis. Moreover, there is often a lack of interpretive guidelines applicable to local growing conditions.
A specific analysis for nitrate-nitrogen in the petioles or leaves of vegetables that have the capacity to accumulate nitrate can provide guidelines on whether to sidedress. This is because the nitrate content of nitrate-accumulating vegetables is closely related to the supply of nitrate in the soil, provided that cool temperatures or low moisture are not inhibiting normal nitrogen uptake by the plant. Interpretive guidelines are currently being established for potatoes based on numerous nitrogen fertilizer rate experiments relating tuber yields to nitrate-nitrogen concentrations of petioles, fresh petiole sap, and whole leaves at specific stages of growth.
Maintained by Abby Seaman, New York State IPM Program. Last modified 2017.