Chapter 16

The Use of Cover Crops to Manage Soil

Impact of Cover Crops on Soil Properties

Grasses as well as leguminous and non-leguminous broadleaves are the major categories of commonly grown cover crops. Cover crop management may provide a wide range of benefits to soil's physical, chemical, and biological properties. Grass cover crops are desirable for their decay and ability to provide substantial soil cover, broadleaf cover cops are used for their quick decomposition and capacity of releasing residues into the soil, while the leguminous cover crops are used for their ability to fix atmospheric nitrogen. Integrating cover crops into conventional cropping systems may reduce soil bulk density, improve soil structure and hydraulic properties to facilitate increased water infiltration and storage.

Impacts of Cover Crops on Soil Physical Properties

Cover crops have the potential to improve bulk density, porosity, and water retention. These properties, in turn, determine the water and nutrient-holding capacity of the soil. However, the extent to which cover crops may alter such properties may depend upon cover crop species, the duration of the growth period, cover crop biomass, soil texture, cover crop frequency in the crop rotation, and environmental conditions.

Cover Crops and Erosion Control

Planting a cover crop can reduce the effect of rainfall on the soil surface, and slows the breakdown of soil aggregates. Also, cover crops serve as a critical prerequisite for conservation tillage systems by improving soil structure and helping maximize this system’s benefits. So, using cover crops can provide a practical way for reducing soil erosion, improving soil health, and enhancing agricultural productivity.

Cover Crops and Soil Moisture Dynamics

Use of cover crops in cropping systems can help mitigate extreme soil moisture conditions, where soil water relationships of the cash crop can be controlled by cover crops. The effect of cover crops on soil water relationships can be positive, negative, or neutral. The effect depends on factors like the rate of infiltration or drainage of soil water, time of cover crops termination, irrigation after cover crop termination, soil texture, precipitation characteristics, infiltration, evaporation, amount of organic matter added to the soil by cover crops, and transpiration by cover crops.

Cover Crops and Soil Temperature

Cover crops can significantly alter soil temperatures. Cover crops decrease the amplitude of day and night temperatures resulting in less variability. Lower soil temperatures in the summer are beneficial because they reduce the rate of microbial decomposition of organic matter. Cover crops and mulches protect the soil from cold nights and slow down cooling. This may be a benefit in hot regions, but may slow growth in cooler regions.

Cover Crops and Soil Compaction

Soil compaction is a worldwide problem in modern agriculture associated with overuse of heavy machinery and intensification of cropping systems. Though tillage is traditionally used to alleviate compaction, increasing concerns about environmental impacts of tillage have led to interest in conservation tillage systems and incorporation of cover crops into crop rotations.

Impacts of Cover Crops on Soil Chemical Properties

Cover crops have the potential to influence soil organic matter or carbon, nutrient concentrations (especially nitrogen and phosphorus), pH, cation exchange capacity, and electrical conductivity.

Cover Crops and Organic Matter

The addition of cover crops in a production system furnishes organic matter that helps to boost soil quality. Hairy vetch or crimson clover cover crops may yield from 1.5 to more than 4 tons of dry weight per acre if allowed to grow long enough. Likewise, if a vigorous grass cover crop like cereal rye is grown to maturity, it can produce 3 to 5 tons of residue. However, the impact of cover crops on actual levels of organic matter and nutrient availability is highly dependent on the species, stage of termination, soil type, temperature, and rainfall.

Cover Crops and Soil Carbon

Soil organic carbon plays an important role for improved crop productivity and environmental sustainability. Within the soil ecosystem, organic carbon has been reported to improve microbial activity and soil homogenization, water availability, nutrient availability, and crop yield.

Cover Crops and Nitrogen

The nutrient that is most frequently required by crops is nitrogen, which can be supplied through commercial fertilizers, compost, manure, or cover crops. Cover crops (i.e., legumes) can be grown to supply nitrogen to crops and improve the soil structure and the movement of nitrogen through the soil root zone. Legume cover crops can provide 30 to 60 percent, and sometimes more, of the nitrogen needed by the following crop. But the amount of nitrogen supplied will vary widely depending on such factors as species, planting date, termination date, residual soil fertility, and growing conditions.

Cover Crops and Nutrient Leaching

Nitrogen and phosphorus are the two nutrients most likely to be lost from cropping systems through runoff, leaching and, in the case of nitrogen, volatilization. Catch crops can be used is used to reduce nutrient leaching from the soil profile. The best cover crops for scavenging nitrate are cereal rye, wheat, barley, annual ryegrass, winter canola, and brassicas such as daikon radish.

Impacts of Cover Crops on Soil Microbial Communities

Cover crops can improve soil biological health and alter the composition of soil microbial communities in agricultural systems. Soil microorganisms are very important for maintaining soil functions and ecosystem sustainability because they are involved in the cycling of nutrients and the turnover of organic matter. For example, cover cropping may enhance the mycorrhizal fungi population in a field.

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