6.5: Improving Nutrient Cycling on the Farm

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

Reduce 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

1. Balance nutrient inflows and removals to maintain optimal levels and allow a little “drawdown” if nutrient levels get too high.
2. 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.
3. Build up and maintain high soil organic matter levels for biodiverse soils and to develop healthy plant roots.
4. Test manures and credit their nutrient content before applying fertilizers or other amendments.
5. If using liquid manure, consider soil injection to reduce N volatilization and potential loss of nutrients in runoff.
6. Test soils regularly to determine the nutrient status and whether or not manures, fertilizers, or lime are needed.
7. Use regionally adapted nutrient recommendation tools.
8. Apply most nitrogen close to the time of crop uptake, and use recommendation tools that account for soil, weather, and management practices.
9. Use forage legumes or legume cover crops to provide N to subsequent crops and to develop good soil structure.
10. 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.
11. Maintain soil pH in the optimal range for the most sensitive crops in your rotation.
12. 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.
13. To get the most efficient use of fertilizer when P and K levels are at or below the medium or lower categories, consider band application at planting, especially in cool climates.

Enhance Nutrient Uptake Efficiency

Enhance the uptake of nutrients by carefully using fertilizers and amendments, as well as irrigation practices. Better placing and synchronizing nutrient applications with plant growth improve the 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

Seek 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). 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 the 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

Support local markets and return local food waste 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

Add 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 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 are discussed later, 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. The problem with using more technology to mitigate a nutrient flow problem is that it is not scale-neutral. That means that you have to be a farm of a certain size, usually something like 750 dairy cows, to make it cost-effective to install any type of nutrient export technology. If public tax dollars are put toward these solutions then they become a type of subsidy to a CAFO farm and make them more competitive at selling milk in volume, thus perpetuating the problem of too many cows on too few acres.

A better solution for large-scale farms, albeit lower-tech, is to move dairy heifers to outlying regions and pasture them there. Put cows back on landscapes that were formerly just supplying crops to the CAFO.

Farmers are finding that composting is an attractive alternative way to handle manure. During the composting process, volume and weight are greatly reduced, 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

... an economical use of fertilizers requires that they merely supplement the natural supply in the soil, and that the latter should furnish the larger part of the soil material used by the crop.

—T.L. Lyon and E.O. Fippin, 1909