Crop Rotation Effects on Soil Fertility and Plant Nutrition
Editor’s note: This article originally published in September 2019.
Soil organic matter and clay particles hold large stores of plant nutrients, writes Anusuya Rangarajan at SARE. These reservoirs, however, are not all available to the crop. In an organic crop rotation, the grower manages soil organic matter and nutrient availability by incorporating different crop residues, cycling among crops with different nutrient needs, using cover crops, and adding organic soil amendments. Most crops deplete soil nutrients during their growth cycle. Some of these nutrients leave the farm as harvested products, and the rest return to the soil as crop residues. The nutrients in residues may or may not be available to the next crop. Crop roots and residues improve soil fertility by stimulating soil microbial communities and improving soil aggregation. This improved soil physical environment facilitates water infiltration, water holding, aeration, and, ultimately, root growth and plant nutrient foraging.
Understanding the basics of how nutrients are added to and released from soil organic matter will help farmers and retailers in choosing crop sequences and amendments to optimize organic crop fertility. Certain fractions of soil organic matter contribute to plant nutrition more than other fractions. To effectively plan organic crop rotations to meet crop nutrient needs, several factors should be considered. Legume crops, which capture atmospheric nitrogen and “fix” it into forms available to plants, can be used strategically in rotations to meet the needs of nitrogen-demanding crops.
Cover crops used after a cash crop capture surplus plant-available nutrients and conserve these for following crops. Cash crops themselves vary in their nutrient demands; considering their needs helps make the most efficient use of the available soil nutrients in a rotation. Finally, other types of organic amendments, such as compost and manures or approved mineral fertilizers, can supplement nutrients at targeted times during a rotation.
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