18.4: Improving Nutrient Cycling on the Farm

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Fred Magdoff & Harold van Es
University of Vermont & Cornell University via Sustainable Agriculture Research and Education (SARE) program

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For economic and environmental reasons, it makes sense for plants to more efficiently utilize nutrient cycling on the farm. Goals should include a reduction in long-distance nutrient flows, as well as the promotion of “true” on-farm cycling, in which nutrients return in the form of crop residue or manure to the fields from which they came. There are a number of strategies to help farmers reach the goal of better nutrient cycling:

Reduce unintended losses by promoting water infiltration and better root health through enhanced management of soil organic matter and physical properties. Methods to increase and improve organic matter status include additions of a variety of sources of organic materials as well as methods for reducing losses from tillage and adopting conservation practices. Proper irrigation water management involves applying the right amount of irrigation water needed to refill the root zone. Applying excessive irrigation water can cause both runoff and leaching losses of nutrients. (In arid climates occasional extra water applications will be needed to leach accumulating salts below the root zone.) In addition, compared to conventional annual row crops such as corn and soybeans, rotations that include cover crops and perennial grass and legume crops tend to result in less leaching loss of nitrate as well as runoff phosphorus loss.

The ABCs Of Nutrient Management

a. Balance nutrient inflows and removals to maintain optimal levels and allow a little “drawdown” if nutrient levels get too high.

b. Enhance soil structure to increase plant capture of soil nutrients and reduce their loss in runoff by minimizing tillage, reducing compaction and promoting deeper rooting to access nutrients lower in the soil.

c. Build up and maintain high soil organic matter levels for biodiverse soils and to develop healthy plant roots.

d. Test manures and credit their nutrient content before applying fertilizers or other amendments.

e. If using liquid manure, consider soil injection to reduce N volatilization and potential loss of nutrients in runoff.

f. Test soils regularly to determine the nutrient status and whether or not manures, fertilizers or lime are needed.

g. Use regionally adapted nutrient recommendation tools.

h. Apply most nitrogen close to the time of crop uptake, and use recommendation tools that account for soil, weather and management practices.

i. Use forage legumes or legume cover crops to provide N to subsequent crops and to develop good soil structure.

j. Use cover crops to tie up nutrients during the off-season, enhance soil structure, reduce runoff and erosion, and provide microbes with fresh organic matter.

k. Maintain soil pH in the optimal range for the most sensitive crops in your rotation.

l. When P and K are very deficient, broadcast some of the fertilizer to increase the general soil fertility level, and band apply some as well.

m. To get the most efficient use of a fertilizer when P and K levels are at or below the medium or lower categories, consider band application at planting, especially in cool climates.

Table 18.1 Essential Nutrients for Plants
Element	Common available form	Source
Needed in large amounts
Carbon	CO₂	atmosphere
Oxygen	O₂, H₂O	atmosphere and soil pores
Hydrogen	H₂O	water in soil pores
Nitrogen	NO₃^–, NH₄⁺	soil (atmosphere for legumes)
Phosphorus	H₂PO₄^–, HPO₄^–2	soil
Potassium	K⁺	soil
Calcium	Ca⁺²	soil
Magnesium	Mg⁺²	soil
Sulfur	SO₄^–2	soil
Needed in small amounts
Iron	Fe⁺², Fe⁺³	soil
Manganese	Mn⁺²	soil
Copper	Cu⁺, Cu⁺²	soil
Zinc	Zn⁺²	soil
Boron	H₃BO₃	soil
Molybdenum	MoO₄^–2	soil
Chlorine	Cl^–	soil
Nickel	Ni⁺²	soil
Needed by some plants¹^{, 2}
Cobalt	Co⁺²	soil
Sodium	Na⁺	soil
Silicon	H₄SiO₄and H₂SiO₄^–2	soil
¹Cobalt has been shown to be essential only for legumes; sodium (Na) is considered an essential element for some plants; and silicon (Si) is considered essential for the normal growth and health of rice. ²Although selenium (Se) is not considered an essential element for plants, it is essential for animals, and so the Se content of plants is important for animal nutrition. On the other hand, plants growing on high-Se soils (such as locoweed, asters and saltbushes) accumulate enough Se to become toxic to grazing animals.

Enhance nutrient uptake efficiency by carefully using fertilizers and amendments, as well as irrigation practices. Better placing and synchronizing nutrient applications with plant growth improve efficiency of fertilizer nutrients. Sometimes changing planting dates or switching to a new crop creates a better match between the timing of nutrient availability and crop needs.
Tap local nutrient sources by seeking local organic materials, such as leaves or grass clippings from towns, aquatic weeds harvested from lakes, produce waste from markets and restaurants, food processing wastes and clean sewage sludges (see discussion on sewage sludge in Chapter 9). Caution always makes sense when receiving organic materials from off the farm; for example, grass might have been treated with herbicide, and municipal leaves may contain extraneous materials. Although some of these do not contribute to true nutrient cycles, the removal of agriculturally usable nutrients from the “waste stream” makes sense and helps develop more environmentally sound nutrient flows. The Food Safety Modernization Act (FSMA) requires greater care with use of certain organic materials, such as manures, when growing produce for the fresh market due to the potential for food to be contaminated with pathogens. Composting the materials from on or off the farm may be needed to comply with these regulations.
Promote consumption of locally produced foods by supporting local markets as well as by returning local food wastes to farmland. When people purchase locally produced foods, there are more opportunities for true nutrient cycling to occur. Some community supported agriculture (CSA) farms, where subscriptions for produce are paid before the start of the growing season, encourage their members to return produce waste to the farm for composting, and a portion of the nutrients in the produce complete a true cycle.
Reduce exports of nutrients in farm products by adding animal enterprises to crop farms. The best way to reduce nutrient exports per acre, as well as to make more use of forage legumes in rotations, is to add an animal (especially a ruminant) enterprise to a crop farm. Compared with selling crops, feeding crops to animals and exporting animal products result in far fewer nutrients and carbon leaving the farm. Keep in mind that, on the other hand, raising animals with mainly purchased feed overloads a farm with nutrients.
Bring animal densities in line with the land base of the farm. Renting or purchasing more land—to grow a higher percentage of animal feeds and to have increased area for manure application—or limiting animal numbers are ways to accomplish this.
Develop local partnerships to balance flows among different types of farms. As pointed out in Chapter 9 when we discussed organic matter management, sometimes neighboring farmers cooperate with both nutrient management and crop rotations. This is especially beneficial when a livestock farmer has too many animals and imports a high percentage of feed, and a neighboring vegetable or grain farmer has a need for nutrients and an inadequate land base for allowing a rotation that includes a forage legume. Both farms win by cooperating on nutrient management and rotations, sometimes in ways that were not anticipated (see “Win-Win Cooperation” box), but it is more of a challenge as the distances become greater. As of January 2020, the Food Safety Modernization Act requires a range of practices and documentation for all farms selling more than $25,000 worth of products. The implications of this legislation for farm practices is discussed in Chapter 12, on integrating livestock and cropping.

Nutrient Management Goals

Satisfy crop nutrient requirements for optimum economic yield and quality.
Minimize pest pressure caused by excess N fertilizer (such as from sap-feeding insects) or by a nutrient deficiency (low K causes less wheat resistance to rust and corn to stem rot).
Minimize the environmental and economic costs of supplying nutrients.
Use local sources of nutrients whenever possible.
Get full nutrient value from fertility sources.

—Modified from OMAFRA, 1997

Strategies For Improving Nutrient Cycles

Reduce unintended losses.
Enhance nutrient uptake efficiency.
Tap local nutrient sources.
Promote consumption of locally produced foods.
Reduce off-farm exports of nutrients and carbon in farm products.
Bring animal densities in line with the land base of the farm.
Develop local partnerships to balance flows among different types of farms.

Some livestock farms that are overloaded with nutrients would like to transfer manure to other farms but find that transportation costs are a factor (manures contain up to 90% water). Separating liquids (which are high in N) from solids using a settling or mechanical screw press system can be helpful. Also, farmers are finding that composting is an attractive alternative way to handle manure. During the composting process, volume and weight are greatly reduced (see Chapter 13), resulting in less material to transport. Organic farmers are always on the lookout for reasonably priced animal manures and composts. The landscaping industry also uses a fair amount of compost. Local or regional compost exchanges can help remove nutrients from overburdened animal operations and place them on nutrient-deficient soils.

Win-Win Cooperation

Cooperation between Maine potato farmers and their dairy farm neighbors has led to better soil and crop quality for both types of farms. As potato farmer John Dorman explains, after cooperating with a dairy farm on rotations and manure management, soil health “has really changed more in a few years than I’d have thought possible.” Dairy farmer Bob Fogler feels that the cooperation with the potato farmer allowed his family to expand the dairy herd. He notes, “We see fewer pests and better-quality corn. Our forage quality has improved. It’s hard to put a value on it, but forage quality means more milk.” —From Hoard’s Dairyman, April 10, 1999

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