Chapter 8 Soil Management
Contents
8.4.1 Manure and Produce Safety
8.8.1 Nitrogen, Phosphorus, and
Potassium
8.8.2 Secondary Nutrients and
Micronutrients
8.1 Soils and Fertility
Fertility management is part of an overall soil management program that involves 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 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.
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 Field Crops and Soils Handbook. Detailed soil survey maps are available through local extension and NRCS offices. After determining whether the soil is suitable, check for perennial weeds and correct pH level before planting.
Soils in good tilth provide a desirable medium for root development, absorb water and air rapidly, withstand erosion, and resist the tendency to crust. Many agricultural practices cause soil structure to deteriorate. Compaction, which results from the use of heavy equipment on wet soils, is particularly damaging. Tillage tools break down soil aggregation; 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. One mistake can reduce the yield of the planted crop regardless of the level of other inputs.
8.2
Crop Rotation
Rotation with forage, hay, and cereal crops is an effective way to maintain the organic matter and structure of mineral soils used primarily for vegetables. Ideally, grass or legume sods should appear in the rotation once every three years to maintain the porosity of fine-textured soils; improve the water-holding capacity of coarse soils; and reduce the buildup of disease, insect, and weed pests. Moreover, a good stand of legume or grass-legume sod can provide substantial nitrogen upon decomposition, thus reducing the nitrogen fertilizer requirement for the next vegetable crop planted.
8.3
Cover Crops
8.3.1
General
Cover crops are close-growing crops planted primarily for protecting and improving the soil. 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 remediate 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 other pests. 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 will perform best under good growing conditions, such as optimal temperatures, sufficient soil moisture, and adequate soil fertility. Practices, such as preparing an adequate seedbed; drilling seed or broadcasting and cultipacking; inoculating seed with the proper Rhizobium inoculant if using a legume; planting into sufficient soil moisture; correcting pH or soil fertility problems; and in some cases, controlling weeds with herbicides or mowing the cover crop in midseason, often further enhance cover crop performance. Access to appropriate equipment for incorporating the cover crop is also critical.
Despite the relatively short growing season in New York, there are many ways to integrate cover crops into vegetable rotations. Examples include planting grain rye or wheat after vegetable crop harvest; interseeding ryegrass or clover into a standing vegetable crop; no-till planting pumpkins into a herbicide-killed rye mulch; 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 summer 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 or soilborne diseases such as white mold. Before growing any new cover crop, try it first in small test strips.
8.3.2
Nonlegumes
Oats. Seeding rate: 60 to 100 lb/acre. Timing: August through early September. Nonwinter-hardy small grain; if left untilled, will result in a dead mulch residue in spring which suppresses weeds. Easier than rye to incorporate in spring. Works well grown as a mixture with hairy vetch. Like all small grains, oats are not a host 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, especially following a wheat crop. Spring regrowth is not as vigorous as 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 delayed growth in following crop (especially snap beans) if soils are wet during and following incorporation. A mixture of rye and hairy vetch can result in significant biomass if left to grow into 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.
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. Excellent erosion control; shade tolerant and used for overseeding into standing crops.
Brassicas. Seeding rate: 10 to 12 lb/acre. Timing: late August through mid-September. Broadleaf annuals and biennials, which grow rapidly in cool weather, with soil-improving root systems. Annuals such as oilseed radish and yellow mustard (Brassica hirta) die in winter, while biennials such as forage kale, forage turnip, and canola may regrow in spring. Excellent nitrogen scavengers during the fall. Do not allow brassicas to set seed or weed problems may result.
Sudan grass and Sorghum-sudan hybrids. Seeding rate: 50 lb/acre. Timing: late spring through summer. Warm-season annual grasses which produce large amounts of biomass and penetrate compacted soils. Mowing at a height of three feet is recommended to manage top growth and stimulate roots. Incorporated green, sudangrass may suppress some diseases and nematodes. Extremely frost sensitive. On poor soils, supplemental fertilizer (especially nitrogen) may be necessary.
Buckwheat. Seeding rate: 60 lb/acre. Timing: late spring through summer. Warm-season annual broadleaf characterized by rapid growth, moderate biomass accumulation, fine extensive root system, and ability to thrive on poor soils. Two successive buckwheat cover crops in summer followed by winter rye can effectively reduce weed pressure in a field. Mow or incorporate at early flowering to avoid seed set and subsequent weed problems. Highly frost sensitive; decomposes rapidly.
8.3.3
Legumes
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, typically modest; most growth occurs in the spring. 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. Note: lana vetch, a closely related cover crop but not winter-hardy, can be used as a summer nitrogen-fixing cover crop.
Clovers. 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, red varieties are tallest, Ladino white clover is medium, and Dutch white clover is low growing. Red clover can be frost seeded into wheat in late winter and can contribute up to 75-100 pounds of nitrogen per acre after one year’s growth. Dutch white clover can be useful for walkways or alleys. Note: crimson clover, while not winter-hardy, can be used as a summer nitrogen-fixing cover crop.
Annual sweetclover (Hubam). Seeding rate: 25 lb/acre. Timing: early spring. Annual legume which can reach five to six feet in height by early fall. Shade tolerant; grows poorly in compacted soils. Mowing makes incorporation easier and may improve growth. Susceptible to weevil damage.
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.
8.4
Manure
Most vegetable operations do not have a ready source of
manure, but it should be 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. An
excellent, thorough discussion of manure use in crop production is provided in
the Cornell Field Crops and Soils
Handbook.
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 during the 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.
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.
8.4.1 Manure and Produce Safety
The use of improperly aged or treated manure can increase microbial risks and contribute to foodborne illness. 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.
It is important that all farms using manure follow good agricultural practices to reduce any microbial risk that may exist. These include:
Consider the source, storage, and type of manure.
§ Store manure as far away as practical from areas where fresh produce is being grown and handled. If manure is not composted, age the manure at least six months prior to field application.
§ Where possible, erect physical barriers or wind barriers to prevent runoff and wind drift of manure.
§ Store manure slurry for at least 60 days in the summer and 90 days in the winter before applying to fields.
§ Compost manure. High temperatures achieved by a well-managed, aerobic compost can kill most harmful pathogens. Remember to optimize temperature, turning, and time to produce high quality, stable compost.
Plan manure application timing carefully.
§ Apply manure in the fall or at the end of the season to all planned vegetable ground, preferably when soils are warm, nonsaturated, and cover cropped.
§ Incorporate manure into soil.
§ If applying manure in the spring, spread the manure two weeks prior to planting, preferably to grain or forage crops.
§ DO NOT harvest vegetables until 120 days after manure application. If this is not feasible for short season crops like lettuce and leafy greens, apply only properly composted manure.
§ Document rates, dates, and locations of manure applications.
Choose appropriate crops
§ Avoid growing root or leafy crops in the year that manure is applied to a field.
§ Apply manure to grain or forage crops or to vegetables that will be heat processed.
§ Apply manure to perennial crops in the planting year or immediately following the last harvest of the season.
8.5
Sewage Sludges
Sewage sludges are a by-product of the purification of wastewater. Sewage sludges have a significant organic matter content and contain micro- and macronutrients essential for plant growth. Sewage sludges also contain contaminants such as heavy metals, toxic organics and pathogens. State and federal rules require that before being applied to agricultural lands, sludges must undergo further treatment for stabilization and disinfection. Restrictions on use depend on the level of treatment. Prior to using sludges, growers should carefully review the regulations. Many food processors will not accept vegetables grown on sludge-amended soils, so growers should check before applying sludges. Consumers may also be unwilling to accept such crops.
The quality of sewage sludges varies widely. Growers who are considering sludge use are urged to obtain analytic information from the supplier on the metal, toxic organic and nutrient concentrations in the particular sludge or sludge product they might apply. Regulations require testing only for a very limited list of regulated metals, nutrients and pathogens and only at intervals determined by the size of the sewage plant (infrequent testing at smaller plants). Testing for additional (unregulated) contaminants including antimony, beryllium, boron, chromium, molybdenum, selenium, silver, sulfur, and for dioxins and PCBs is recommended, as is testing of the particular load(s) to be applied, because composition and water contents may vary significantly. Application rates are generally calculated on the basis of nitrogen content and crop N requirements. The nitrogen mineralization rate of sludges is not well characterized and the nitrogen content of sludge from even one particular treatment plant varies widely, making it difficult to determine appropriate application rates.
Although many studies have been done on the land application of sludges, scientific uncertainties remain, particularly with respect to long-term soil productivity and ecologic safety. Other potential concerns include odors, airborne toxins and pathogens, and ground and surface water impacts. Further information on the use of sewage sludges on agricultural land can be obtained through your Cornell Cooperative Extension Association and through www.cfe.cornell.edu/wmi.
8.6
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 at least once every three years. The pH of most vegetable soils decreases gradually because of the removal of bases 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.
Purchase a soil test kit from your Cornell Cooperative Extension agent or order one from the Cornell Nutrient Analysis Laboratories, 804 Bradfield Hall, Cornell University, Ithaca, NY 14853-1901. The kit consists of a cloth mailing bag with a mailing envelope, plastic bag, information sheet, and instructions. Follow the instructions carefully since the results will only be as good as your sampling technique.
The soil test results provide soil pH, percent organic matter, and level of phosphorus, potassium, magnesium, calcium, zinc, and nitrate nitrogen. Levels of aluminum, iron, and manganese are also listed to identify potential toxicities rather than deficiencies. Boron 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.
8.7
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 8.1 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.
Table 8.1 General lime recommendations to raise pH to 6.5 for vegetables other than potatoes.1
Sands Sandy loams Loams and silt loams Silty clay loams
Initial soil pH (Values given in Tons/acre)
4.5 4.0 7.0 12.1 15.0
4.6 to 4.7 3.5 6.5 10.0 13.0
4.8 to 4.9 3.0 6.0 9.0 12.5
5.0 to 5.1 2.5 5.5 8.5 12.0
5.2 to 5.3 2.0 4.5 6.5 8.0
5.4 to 5.5 1.5 3.0 4.0 6.0
5.6 to 5.7 1.0 2.0 3.0 5.5
5.8 to 5.9 0.8 1.8 2.5 3.5
6.0 to 6.1 0.6 1.5 2.0 3.0
6.2 to 6.3 0.5 1.0 1.5 2.5
6.4 to 6.5 0.3 0.8 1.3 2.0
1 A guideline for muck is that 1,000 lb. of lime will
raise the pH about 0.1. These rates are based on an 8" plow depth and lime
with an effective neutralizing value (E.N.V.) of 100 percent.
8.8
Fertilizers
8.8.1
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.
1. Limit
nitrogen applications prior to planting, and avoid deep plow-downs.
2. Band
either at planting or as a sidedressing to apply nitrogen most efficiently.
3. Apply
nitrogen close to the time the crop is most active in taking it up.
4. Avoid
“insurance” applications of nitrogen.
5. Maintain
the proper pH.
6. Use
plastic mulch to limit leaching and facilitate nitrogen release from
nonfertilizer sources.
7. Avoid
over fertilization which will lead to leaching.
8. Account for nitrogen from organic matter, cover crops, composts, manure, etc., which becomes available as the soils warm.
9. Consider
using the pre-sidedress soil nitrate test (PSNT) to determine nitrogen
contributions from nonfertilizer sources.
10. 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 8.6 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 8.7 on lime recommendations. New York soils in the proper pH range are not usually deficient in minor nutrients. See Section 8.8.2 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.
8.8.2
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 8.8.1 Common fertilizer materials supplying primary nutrients.
Analysis
Percent
Common name Chemical
formula N P2O5 K2O
Nitrogen materials
Ammonium nitrate NH4NO3 34 0 0
Ammonium sulfate (NH4)2SO4 21 0 0
Ammonium nitrate-urea1 NH4NO3+(NH2)2CO 32 0 0
Anhydrous ammonia NH3 82 0 0
Aqua ammonia1 NH4OH 30 0 0
Calcium nitrate Ca(NO3)2 15.5 0 0
Sodium nitrate NaNO3 16 0 0
Urea (NH2)2CO 46 0 0
Phosphate materials
Ordinary superphosphate Ca(H2PO4)2 0 20 0
Concentrated superphosphate Ca(H2PO4)2 0 45 0
Ammoniated superphosphate1 Ca(NH4H2PO4)2 54 0 0
Monoammonium phosphate1 NH4H2PO4 13 52 0
Diammonium phosphate1 (NH4)2HPO4 18 46 0
Urea-ammonium phosphate (NH2)2CO+(NH4)2HPO4 28 28 0
Potash materials
Muriate of potash KCl 0 0 60
Sulfate of potash K2SO4 0 0 50
Potassium nitrate KNO3 13 0 44
Monopotassium phosphate1 KH2PO4 0 50 40
Sulfate of potash-magnesia (11%
Mg) K2SO4 • MgSO4 0 0 22
1: Analysis variable
Table 8.8.2 Fertilizer materials supplying secondary and micronutrients.
Common name Element Chemical
formula Analysis %
Secondary nutrients
Calcium nitrate calcium
(Ca), N Ca(NO3)2 22 Ca, 15.5 N
Magnesium sulfate1 magnesium
(Mg) MgSO4 16 Mg, 14 S
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
Micronutrients
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
1: Analysis variable
8.8.3
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.
8.8.4
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.
8.8.5
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.
8.8.6
Fertigation
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 10 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.
8.8.7
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.
8.8.8
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.
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