Building Soils for Better Crops, Third Edition

Improving Nutrient Cycling on the Farm

SARE Outreach
Fred Magdoff and Harold van Es | 2010 | 294 pages
PDF (6.8 MB)

This title is temporarily out of print. We expect to publish an updated edition in the spring/summer of 2021.

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 promoting “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. Ways organic matter can be built up and maintained include increased additions of a variety of sources of organic matter, plus methods for reducing losses via tillage and conservation practices. In addition, apply only the amount of irrigation water needed to refill the root zone. Applying more irrigation water than needed can cause both runoff and leaching losses of nutrients. (In arid climates occasional extra water applications will be needed to leach accumulating salts from the irrigation below the root zone.)
  • Enhance nutrient uptake efficiency by carefully using fertilizers and amendments, as well as irrigation practices. Better placement and synchronizing application with plant growth both 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 sources of 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). Although cycles, the removal of agriculturally usable nutrients from the “waste stream” makes sense and helps develop more environmentally sound nutrient flows.
  • Promote consumption of locally produced foods by supporting local markets as well as returning local food wastes to farmland. When people purchase locally produced foods, there are more possibilities 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, completing 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 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. This can be accomplished by renting or purchasing more land—to grow a higher percentage of animal feeds and for manure application—or by limiting animal numbers.
  • 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 farm has a need for nutrients and an inadequate land base for allowing a rotation that includes a forage legume. By cooperating on nutrient management and rotations, both farms win, sometimes in ways that were not anticipated (see “Win-Win Cooperation” box). Encouragement and coordination from an extension agent may help neighboring farmers work out cooperative agreements. It is more of a challenge as the distances become greater.
Essential Nutrients for Plants
 Element Common Available Form Source
Needed in large amounts
CarbonCO2atmosphere
OxygenO2, H2Oatmosphere and soil pores
HydrogenH2Owater in soil pores
NitrogenNO3, NH4+soil
PhosphorusH2PO4, HPO4-2soil
PotassiumK+soil
CalciumCa+2soil
MagnesiumMg+2soil
SulfurSO4-2soil
Needed in small amounts
IronFe+2, Fe+3soil
ManganeseMn+2soil
CopperCu+, Cu+2soil
ZincZn+2soil
BoronH3BO3soil
MolybdenumMoO4-2soil
ChlorineClsoil
CobaltCo+2soil
NickelNi+2soil
Sodium (Na) is considered an essential element for some plants.Although 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.Silica (Si) is considered essential for the normal growth and health of rice.

NUTRIENT MANAGEMENT GOALS

  • Satisfy crop nutrient requirements for yield and quality.
  • Minimize pest pressure caused by excess N fertilizer or deficiency of nutrients.
  • 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 exports of nutrients 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 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 landscape 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