SOM increases available water capacity, also AWC increases with increasingly fine Stextured soil, because fine textured soils have a greater occurrence of small pores that hold water against free drainage. If there is land converted from forest to cultivation, which led to significantly decrease in SOM and increase in clay% and bulk density. what is expected to happen to field capacity, wilting point and available water? both lands ( before and after conversion) were clay texture .
Dear colleague,
If the land has been converted to cultivation area, it is certainly affect the water holding capacity of soil because the environmental change.
As naturally decreasing SOM will occur when the forest shift to others land use that then automatically decrease the water holding capacity, SOM give a high stability aggregate for good soil drainage, the percent clay was not significantly change to much i think, while increasing bulk density can contribute to soil compaction, when soil is compacted the soil tend sustain to waterlogged condition on the surface, it is usually caused by vehicle traffic like tractor. Thus the water infiltration become low and it was not good for agricultural activity.
Organic matter and clay can be important for water retention in soil. When forests are cleared and converted to cropping the organic matter typically decays and uncovered cultivated fields can have high erosion rates. These processes degrade soil fertility and texture. Clay and organic matter both have overall negative electrical charge and can be dispersed in water and wind. The addition of lime can help cement the organo mineral complex which is important for maintains soil organic matter key to water dynamics and texture. Compost can be the way of achieving improving soil texture and fertility and is more stable than manure use. In sandy soils the addition of clay and organic materials are particularly useful. You may want to have soil analysis which includes the proportions of sand, silt and clay as well as the elemental analysis and pH and Organic matter to develop a plan for improving your results based on soil constraints and optimizing the soil conditions.
in addition what colleagues have mentioned above, both SOM and clay particles are cementing agents in soil aggregate formation, any changes to these cementing agents and others will affect soil structure, hence water retention and redistribution properties. This is well illustrated in the developed pedotransfer functions where soil texture, SOM, bulk density, EC and others are inputs to derive soil hydraulic properties.
When an area converted from forest cultivated to cultivated one .We expect that water holding capacity was very high due to its high OM content during the first years, followed by a decrease in this ability as a result of OM decrease from successive cultivation and increasing bulk density due to soil compaction as result of continuous use of heavy equipments .Clay% may be increased little due to OM decrease.
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