October Shift

Rotation cropping, also known as crop rotation or rotation, is an agricultural practice in which different crop species are grown in a planned sequence on the same field. This practice is recognized as one of the key cultural methods influencing yield per unit area, with its primary objectives being the maintenance of soil fertility and the enhancement of productivity per unit area.

Example of Rotation Cropping (Generated by Artificial Intelligence)

Historical Context

Rotation cropping has long been a fundamental component of agricultural systems. In the 19th century, before the development of synthetic herbicides, rotation cropping was the primary method for combating pests and the spread of weed species. In Türkiye, particularly in arid and semi-arid regions such as Central Anatolia, research has been conducted on rotation cropping systems as alternatives to fallowing—the practice of leaving land uncultivated to accumulate soil moisture. The Nadas Area Reduction (NAD) Project, initiated in the 1980s, aimed to identify areas where fallowing could be entirely eliminated or its duration reduced—for example, to every three or four years—and to develop suitable rotation cropping systems for these areas.

Purposes and Effects of Rotation Cropping

Compared to monoculture farming, where a single crop is continuously grown, rotation cropping has various effects on soil structure, biological diversity, yield, and economic profitability.

Soil Fertility and Structure

Rotation cropping contributes to the preservation and improvement of soil quality through the following mechanisms:

Nutrient Management

Different plants consume different nutrients and in varying quantities from the soil. For example, maize depletes large amounts of nitrogen, alfalfa consumes phosphorus, and clover takes up calcium. Rotation cropping prevents the one-sided depletion of specific soil nutrients. Additionally, alternating deep-rooted and fibrous-rooted crops allows for the utilization of nutrients at different soil depths.

Organic Matter and Nitrogen

Incorporating leguminous plants into rotation systems plays a critical role in enhancing soil fertility. Legumes fix atmospheric nitrogen through nodules on their roots. The plant residues left in the soil after harvest increase the soil’s organic matter content and nitrogen (N) levels.

C/N (Carbon/Nitrogen) Ratio

The rate at which plant residues decompose into humus depends on their carbon-to-nitrogen (C/N) ratio. Residues from cereal crops, which have a high C/N ratio (e.g., 80:1), slow decomposition by creating nitrogen competition in the soil. In contrast, legume residues, with a low C/N ratio (e.g., 15:1), accelerate microbial activity and promote rapid breakdown of organic matter.

Soil Moisture

Rotation cropping aids in preserving soil moisture and improving the soil’s water-holding capacity. In arid regions, the primary purpose of fallowing within a rotation cycle is to accumulate soil moisture for the subsequent crop. Research has shown that in dry years, this moisture-conserving effect of fallowing positively impacts yield, particularly in deep-profile (subsoil) soils.

Disease, Pest, and Weed Management

Monoculture farming can lead to increased populations of diseases, pests, and weeds specific to a single crop. Rotation cropping disrupts the life cycles of these organisms, thereby reducing their populations.

In terms of weed management, rotation cropping is considered one of the most effective cultural practices. The inclusion of different crop types—for example, cover crops, competitive crops—and varying cultivation practices such as planting and harvesting times and tillage methods within the rotation cycle reduces weed populations and competitiveness, alters the weed seed bank in the soil, and decreases dependence on chemical control. This approach also helps manage the risk of herbicide resistance commonly observed in monoculture systems.

Yield, Quality, and Economic Effects

Rotation cropping practices have positive effects on crop yield and quality. For instance, soybean-maize rotation has been found to increase yield by 5–20% compared to monoculture maize, while rice-wheat rotation has increased grain yield by 20%.

In terms of quality, the use of legumes as a preceding crop tends to increase the crude protein content of subsequent cereal crops due to the nitrogen they leave in the soil.

For producers, rotation cropping supports the goal of identifying high-income crop patterns and minimizing financial risk by diversifying crops and reducing dependence on fluctuating market conditions. Some rotation systems, such as rice-wheat, can also reduce overall farm operating costs.

Rotation Cropping Systems and Concepts

Rotation cropping systems can be classified according to the sequence of crops:

1. Fixed Rotation System: Crops follow a regular sequence and the cycle is completed within a specific number of years (e.g., every four years).
2. Variable Rotation: Although crops follow a general sequence, the order may vary from year to year based on market conditions, climate, or other factors.

In planning rotation cropping, the concept of “self-tolerance” is a key factor:

• Non-self-tolerant Crops: Crops whose yields decline significantly when planted consecutively on the same field for multiple years (e.g., flax, sugar beet, oats, pea, sunflower).
• Self-tolerant Crops: Crops whose yield decline is minimal when grown in succession (e.g., maize, lentil, soybean, rice).
• Rotation Interval: The minimum time interval required before a non-self-tolerant crop can be replanted on the same field without experiencing yield loss.

Preceding Crop Value and Planning

The success of a rotation cropping system depends on the accuracy of crop selection, in which the concept of “preceding crop value” plays a central role.

Preceding crop refers to the crop grown before another in the rotation; subsequent crop is the crop grown after it. Preceding crop effect is the influence of a specific crop on the crop that follows it. Preceding crop value refers to the measurable effects—such as yield and quality—that different preceding crops have on the same subsequent crop.

The main factors determining the preceding crop value of a crop are:

1. Genetic Relatedness and Morphological Similarity: Planting crops from the same family or with similar morphology (e.g., two cereals) in succession leads to one-sided nutrient depletion, soil fatigue, and accumulation of similar diseases and pests, resulting in low preceding crop value. Selecting crops with different root systems (e.g., deep-rooted lentil and fibrous-rooted wheat) generally provides higher preceding crop value.
2. Vegetation Duration: The length of time a crop remains in the field affects its preceding crop value. For legumes that add nitrogen and organic matter to the soil, longer vegetation duration is preferred, whereas for crops like maize that extract large amounts of nutrients, shorter duration may be preferable.
3. Organic Matter Left in Soil: Crops that increase the soil’s organic matter content—especially legumes—have high preceding crop value for subsequent crops.
4. Soil Structure and Climatic Conditions: Crops with delayed harvests due to climatic conditions (e.g., late sugar beet) reduce preceding crop value because they delay soil preparation and planting of the subsequent crop.
5. Amount of Fertilizer Applied: Legumes that release substantial nitrogen or crops such as potatoes that receive manure application during cultivation leave nutrients for the subsequent crop, resulting in high preceding crop value.
6. Allelopathic Effect: Some crops (preceding crops) release chemical substances that negatively affect the germination or growth of the subsequent crop (allelopathy).
7. Competitiveness Against Weeds: Crops that effectively suppress weeds during their growth period (e.g., maize, sunflower, sorghum) or require intensive weeding leave the field cleaner for the next crop and thus serve as good preceding crops.
8. Disease and Pest Status: Some crops increase the incidence of diseases or pests affecting the subsequent crop (e.g., rapeseed and spinach increase sugar beet nematodes); others reduce them (e.g., barley, flax, and alfalfa are natural enemies of the same nematode). This directly affects preceding crop value.

In general rotation planning, in addition to these factors, regional climate and soil structure, characteristics of selected crops, marketing, storage, transportation facilities, and the farmer’s machinery fleet are also considered.

Application Areas

Relationship with Conservation Tillage

Rotation cropping is an integral component of conservation tillage systems, where tillage is minimized or eliminated (direct seeding). In such systems, the lack of soil disturbance makes weed control more difficult. A well-planned crop rotation helps manage weed problems through cultural methods (competition, allelopathy, etc.), increases soil organic matter, and improves the soil’s water-holding capacity.

Example from Central Anatolia (Arid/Semi-Arid Region)

In arid regions such as Central Anatolia, where fallowing is traditionally considered necessary, research has explored quadruple rotation systems as alternatives to the fallow-cereal system: Fallow – Post-fallow cereal – Alternative crop – Post-alternative crop cereal.

These studies found that the system Fallow – Cereal – summer lentil – Cereal was the most advantageous both in terms of yield and economic analysis (net income) compared to the traditional Fallow – Cereal – Fallow – Cereal system. Research demonstrated that in shallow (poor) soils, the traditional Fallow – Cereal – Fallow – Cereal system yielded the lowest net income, indicating that fallowing provides no economic benefit on such land. In contrast, on deep-profile (bottomland) soils, the system Fallow – Cereal – Wheat – Wheat (three consecutive years of cereals) was found to be an economically viable alternative.