|wheat and vetch|
The root matter of green manures adds organic matter to the soil. The organic matter helps both sandy and clay soils become more like a sponge that has air and can hold moisture after rain. Ken read a couple years ago that for each percentage of organic matter the soil has, the crops planted in that soil can go without rainfall - for example a field with five percent organic matter can support crops with no rainfall for a month. This enables Ken to spend less time irrigating crops.