The Farm Bill of 1990 allowed limited fall and winter grazing on land enrolled in the CRP, it allowed " alley cropping " between hardwood tree stands in return for paying less money to the landowner, the 50 % cost share was expanded from only vegetative cover to include hardwood trees, shelterbelts, windbreaks, and wildlife corridors, and the Bill allowed for land already in the CRP that had been converted to vegetative cover to be converted to hardwood trees, windbreaks, shelterbelts, wildlife corridors, or wetlands under certain circumstances [ 7 ].
12.
Another form of immobilisation is when nutrients are locked up in organic matter that is slow to decay, such as wood, and some mycorrhizal fungi act directly as decay organisms, mobilising the nutrients and passing some onto the host plants; for example, in some dystrophic forests, large amounts of phosphate and other nutrients are taken up by mycorrhizal hyphae acting directly on leaf litter, bypassing the need for soil uptake . " Inga alley cropping ", proposed as an alternative to slash and burn rainforest destruction, relies upon mycorrhiza within the Inga Tree root system to prevent the rain from washing phosphorus out of the soil.
