Crop rotation

Growing the same crop in the same place for many years in a row, known as monocropping, gradually depletes the soil of certain nutrients and selects for both a highly competitive pest and weed community.

Without balancing nutrient use and diversifying pest and weed communities, the productivity of monocultures is highly dependent on external inputs that may be harmful to the soil's fertility.

Additionally, crop rotations can improve soil structure and organic matter, which reduces erosion and increases farm system resilience.

Farmers have long recognized that suitable rotations such as planting spring crops for livestock in place of grains for human consumption make it possible to restore or to maintain productive soils.

Ancient Near Eastern farmers practiced crop rotation in 6000 BC, alternately planting legumes and cereals.

Since the spring crops were mostly legumes, which fix nitrogen needed for plants to make proteins, they increased the overall nutrition of the people of Europe.

Such practices aimed to increase yields, to prepare soil for specialist crops, and to reduce waste and inefficiency by simplifying planting, harvesting, and irrigation.

Crop rotation practices exist to strike a balance between short-term profitability and long-term productivity.

Legumes, like alfalfa and clover, collect available nitrogen from the atmosphere and store it in nodules on their root structure.

[12] When the plant is harvested, the biomass of uncollected roots breaks down, making the stored nitrogen available to future crops.

Grasses and cereals are key in weed management as they compete with undesired plants for soil space and nutrients.

Planning an effective rotation requires weighing fixed and fluctuating production circumstances: market, farm size, labor supply, climate, soil type, growing practices, etc.

Crop rotations can be applied to both monocultures and polycultures, resulting in multiple ways of increasing agricultural biodiversity (table).

These processes promote internal nutrient cycling and minimize the need for synthetic fertilizers and large-scale machinery.

As an additional benefit, the cattle, sheep and/or goat provide milk and can act as a cash crop in the times of economic hardship.

[10] Crop rotation is a required practice, in the United States, for farms seeking organic certification.

[20] The “Crop Rotation Practice Standard” for the National Organic Program under the U.S. Code of Federal Regulations, section §205.205, states that Farmers are required to implement a crop rotation that maintains or builds soil organic matter, works to control pests, manages and conserves nutrients, and protects against erosion.

This in tandem with greater short and long term yields makes rotation a powerful tool for improving agricultural systems.

With more SOM, water infiltration and retention improves, providing increased drought tolerance and decreased erosion.

Crop rotation, by nature, increases exposure to biomass from sod, green manure, and various other plant debris.

Thus rotation allows increased yields from nutrient availability but also alleviation of allelopathy and competitive weed environments.

[24] In Brazil, conversion to no-till methods combined with intensive crop rotations has been shown an SOC sequestration rate of 0.41 tonnes per hectare per year.

[26] It therefore makes good sense agriculturally to alternate them with cereals (family Poaceae) and other plants that require nitrates.

Under crop rotation, the number of viable seeds in the soil is reduced through the reduction of the weed population.

In areas that are highly susceptible to erosion, farm management practices such as zero and reduced tillage can be supplemented with specific crop rotation methods to reduce raindrop impact, sediment detachment, sediment transport, surface runoff, and soil loss.

Soil aggregates also reduce wind erosion, because they are larger particles, and are more resistant to abrasion through tillage practices.

In regions under relatively consistent climate conditions, where annual rainfall and temperature levels are assumed, rigid crop rotations can produce sufficient plant growth and soil cover.

In regions where climate conditions are less predictable, and unexpected periods of rain and drought may occur, a more flexible approach for soil cover by crop rotation is necessary.

Efficient fallow management is an essential part of reducing erosion in a crop rotation system.

[39][40] While crop rotation requires a great deal of planning, crop choice must respond to a number of fixed conditions (soil type, topography, climate, and irrigation) in addition to conditions that may change dramatically from year to the next (weather, market, labor supply).