Soil Management for Pastures and Rangelands
Cover Crops and Grazing
Cover crops are used not only to prevent soil erosion and increase soil health, but they can also be used as a feed source for grazing livestock. Diverse mixtures of perennial plants are the backbone of most grazing systems. Pastures planted (or occurring naturally) with cover crops offer many benefits, including deep roots to maximize nutrient and water uptake, no need for replanting, tolerance, benefit from grazing the biomass, weed suppression, etc. The productivity of these forages fluctuates across the year due to the seasonality of forage production. Planting warm-season and cool-season annual cover crops provide ecosystem benefits to perennial-based pasture systems by introducing quality forage at opportune times of the year, creating a more diverse farm habitat, and providing opportunities to renovate overused or underutilized areas of the farm.
Types of Forage Crops
The most typically grown cover crops are grasses and legumes, including annual ryegrass, rye, wheat, oat, clovers, and vetch (Table 21.1). Some brassicas are gaining attention, such as forage radishes, turnips, and rapeseed. Legume cover crops (e.g., clover, hairy vetch, field pea) have a symbiotic association with nitrogen fixing bacteria to gain nitrogen from the atmosphere that will feed the plant.
Legumes in the Pasture
Legumes increase soil fertility, improve overall feed value of available forage, and extend the grazing season. Bacteria that live in nodules on the legume roots convert nitrogen in the air to a form the plant can use. Nitrogen can move from legumes into the rest of the pasture system through several different pathways. If the legume is eaten by livestock, they digest and absorb some of the nitrogen, but much of it is returned to the soil via manure or urine. If the plant goes uneaten and dies, nitrogen can enter the soil as the plant decomposes.
Grasses in the Pasture
Grasses are king when it comes to growing cover crops for supplemental grazing. They can provide excellent forage and some have the potential to be grazed in the winter and the spring. In addition to being the highest yielding family of cover crops, they are vital in reaching other cover cropping goals such as improving soil structure, reducing erosion, building organic matter, and suppressing weeds. Above all, grass cover crops are renowned for their capacity to prevent soil erosion by wind and water.
Brassicas in the Pasture
Brassicas are often deep-rooted, and can increase subsoil water storage capacity by enhancing aeration, increasing infiltration, and improving nutrient acquisition and redistribution.
Cover Crop Mixtures in the Pasture
When choosing cover crops for forages mixes, select species that are compatible in growth cycle and habit. Usually, more than 3 to 4 species in a mix is not recommended due to the reduce seeding rate that might impact plant establishment. Growing several crop species simultaneously may improve the efficiency of using above-ground and below-ground resources compared to growing them separately.
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