“… Green Manures-An Investment in Your Soil’s Fertility

There are many times during the season, and at different stages of plant growth, when you can till under a cover crop. Each time has virtues and drawbacks, and choosing a time is much like picking a savings plan. You can invest wisely or squander your capital, but no single plan is “the best” – for protection, use a number of plans, each for a specific situation.

Short-Term Investments, Rapid Return
Succulent young plant tissue has the highest amount of readily available nutrients. For a quick return on your investment, grow dynamic accumulators until just before they bloom, then turn them under as a green manure. They will release nutrients quickly for the crop that follows. However, you must wait three to four weeks before planting, while the soil digests the green manure. If you plant earlier, your crop will get less nitrogen, since much of the nitrogen will be tied up in the bodies of microorganisms. Once they digest the manure, large numbers die and decompose, releasing nitrogen for the crop.

Long-Term Investments, Slow Payback
Dry, dead plant material does not have as much nitrogen as green foliage, and the nitrogen is firmly bound up in a form that does not easily decompose. This can be a liability or an asset – depending on your investment strategy. If you need plenty of nitrogen in the next few months, do not till under dead cover crops. The soil’s bacteria will be so busy trying to digest what you tilled under that little, if any, nitrogen would reach your crops.

As a long-term deposit, however, tilling dead plants under is an ideal way to keep organic matter and nitrogen in the soil. In fact, nature uses this investment scheme often – the forest is littered with the branches and trunks of these “long-term accounts.” The slow decay and the billions of bacteria tying up nitrogen in their bodies ensure that this precious element does not leach or vaporize. …”

Urban Orchards : Grow Your Own Fertilizers.