Rotations are one dimension of the art and science of farm management. The biological principles of crop rotation intersect with many other aspects of the farm operation and farm business. Crop rotation is both a principle of production and a tool of management (see sidebar 2.3). Expert farmers balance market options and field biology. Labor, equipment, the layout of beds and fields, along with other logistics of planting and harvest, all influence how rotations are designed and executed.
Expert Farmers’ Definitions of Crop Rotation
The NEON expert panel did not formally define crop rotation, but individual farmers provided their own working definitions:
- Don Kretschmann—“Rotation is the practice of using the natural biological and physical properties of crops to benefit the growth, health, and competitive advantage of other crops. In this process the soil and its life are also benefited. The desired result is a farm which is more productive and to a greater extent self-reliant in resources.”
- Roy Brubaker—“[Rotation is] a planned succession of crops (cash and cover) chosen to sustain a farm’s economic and environmental health.”
- Will Stevens—“I’ve come to view crop rotation practices as a way to help me use nature’s ecological principles in the inherently non-natural world of agriculture. Striving to have as much ‘green’ on the ground as possible throughout the year is one step in that direction. I view crop rotation as a series of ‘rapid succession’ cycles, (ideally) minimally managed. Through this approach, the power and sustainability of natural systems can be expressed through the health and prosperity of the farm system.”
- Jean-Paul Courtens—“Rotations balance soil building crops (soil improvement crops) and cash crops, and can allow for bare fallow periods to break weed cycles and incorporate plant matter into the soil.”
Expert farmers’ rotations include key cash crops, “filler” or “break” crops, and cover crops. In every season, farmers must manage production across multiple fields and beds. Variation in the acreage of each crop, variation in field characteristics, and shifting business decisions result in multiple rotations or crop sequences on most organic farms. Consequently, farmers manage numerous crop rotations on the same farm.
“Model” rotations may suggest that every crop is grown on a fixed schedule on every field, with each crop rotating field to field around the entire farm. In reality, expert farmers in the northeast US rarely cycle every crop they grow through every field on any regular schedule. Instead, each field tends to have its own distinct sequence of crops, tillage, and amendments. Thus, each field tends to have a unique cropping history. On some farms, a few fields do follow an established, fixed rotation. Through trial and error the managers of these farms have settled on a cyclical rotation that works well for a particular field (see chapter 4 for real field examples).
Farm Size, Cover Crops, and Crop Rotations
Farm size affects cover cropping and the management of the crop rotation. Organic farmers plant cover crops to protect the soil, increase soil organic matter, improve soil physical properties, and accumulate nutrients. Cover crops may also provide habitat for beneficial insects or help crowd out weeds.
Most expert farmers integrate cover crops into their fields at every opportunity. Sometimes these opportunities come before or after a short-season crop or during the months between full-season summer crops. Many expert farmers use a full year of cover crops to restore the soil after intensive use. Large farms often have rotations that include multiyear perennial cover crops or hay.
Farmers with limited acreage (<5 acres) find that including cover crops and providing adequate rotation of crop families on a given field is challenging (see chapter 4). Many smaller farms rely on mulch, compost, and short-term winter cover crops in place of multi-season cover crops and hay rotations. Expert Brett Grohsgal advises that “smaller and more intensively managed farms don’t have nearly the cover crop dependence that [larger farms] do, yet these small systems can be extremely efficient, vigorous, and profitable.”
The challenge of a good crop rotation system is to grow the type and quantity of crops needed to ensure the farm’s profitability while continually building soil quality for long-term productivity. Most vegetable farms grow many different crops and crop families. Every crop is not equally profitable, and some crops are highly profitable but have limited markets. The rotation of botanical families of crops prevents the buildup of pest populations, by (1) interrupting pest life cycles, and (2) altering pest habitats. Alternatively, fields (or beds) may be deliberately rotated through a fallow to manage a weed or pest problem. Sometimes tillage, the use of mulch, or compost applications are also integrated into a field’s rotation plan (see chapter 4 for examples). Cover crops are often used for building soil fertility and health but make no direct contribution to cash flow. Farms with limited acreage may rely on compost or other soil amendments rather than cover crops (see sidebar 2.4).
On many successful farms, long-term, fixed, cyclical rotations are far less common than simple two- or three-year crop sequences. Expert farmers frequently rely on numerous “trusted” short sequences or crop couplets to achieve their crop rotation objectives. Instead of planning long, detailed cyclical rotations, experts use a suite of interchangeable short sequences to meet their farm’s goals for cash flow and soil quality. Biological principles are the main determinants of these short sequences. Samples of short sequences are shown in the “Real Fields on Real Farms” chart in chapter 4. Farmers with large land bases often include longer-term, soil-restoring perennial cover or hay crops in their rotations. After a period of intensive cropping, fields cycle out of annual production and into perennial hay or green manure cover crops. During the intensive cropping period, the season-to-season sequences vary with contingencies, and biological principles may be neglected. The perennial hay or cover crop is then expected to correct problems that may have built up during intensive cropping. These cycles often run six to ten years or more.
During a field season, a bed or field may be planted with a series of different short-season crops. Sometimes, because of market demand or other farm practicalities, growers make multiple plantings of a crop in the same bed within a given growing season, which is more problematic biologically. The same crop or sequence is rarely replanted in the same bed or field the following year, however, due to the likelihood of pest and disease outbreaks. Cover crops are often planted to follow or precede a cash crop and occupy a field only for the winter or a portion of the growing season. In all cases, experts are very conscious that such intensive cropping needs careful biological monitoring and management.