|Soil and Water Conservation (SWC) Technologies and Agroforestry Systems (IIRR, 1992, 171 p.)|
In the woods
In the natural forest, most available nutrients are stored in plant materials. But in cultivated areas, where usually the amount of water from the rain is much more than the rate of evaporatranspiration, there will always be excess water. This water will cause a high rate of erosion and runoff, taking much of the highly soluble nutrients and will also leach nutrients out of the soil. In this situation, it becomes very difficult for nutrients to be stored.
The solution is to keep the nutrients in the plants and attach to it a vigorous nutrient recycling process. One often overlooked aspect in soil and water conservation is the role of lignin in organic matter, which really is a key issue to look at.
Plowing or tilling is actually one of the cardinal sins. The need to plow is a sign of the lack of lignin in the soil. It is the lignin contained in organic matter, especially twigs and stems, which improves the soil structure and determines the porosity of humus and reduces the need for tilling the soil.
There are several sources of lignin. One source is the original organic matter, that is, the cell walls of woody tissues, especially plentiful in mature plants. Another source is from the decomposition of insects that eat organic matter.
Some species that can be used for rapid fallowing are Flemengia congests, Desmodium gyroides, Cajanus cajan, Desmantus sp. These species provide a lot of stems and twigs. The twigs decompose slowly, gradually releasing the elements they are made of. Leaching is reduced while soil structure is improved. This, in turn reduces the need for tillage, the worst culprit causing erosion. The intention is to produce a great amount of organic matter from woody tissues with a high lignin content which will result in a soil that can hold more water for a longer period of time.
To balance the need for plant nutrients and organic matter, diversify plant species in the hedgerows to include species with different decomposition rates, i.e., Glincidia which rapidly decomposes and Flemengia which is slower.
It is true that, with all this wood in the soil, it is hard to weed, but it is a good idea to get lazy for a while. As long as the crops are above the weeds, it is okay. Of course, there is competition among plants for nutrients but it is also better to have many species of weeds rather than only one or two.
Note: Based on notes from a lecture delivered at the 1989 ATIK Workshop by Dr. Romeo S. Raros, Department of Forestry, Visayas State College of Agriculture, Baybay, Leyte, Philippines.