THE STUDY OF HUMUS CHANGES IN SURFACE AND SUB-SURFACE LAYERS OF DESERTIFIED LANDS IN KHODABANDEH, IRAN.

Soil organic matters are considered as the animal and plant residues and active components of soils. the cultivation practices will cause the quick removal of organic matters in soils even in those which are not affected by erosion. this study was carried out to assess the level of soil humus in the pilot area, to investigate the positive or negative effect of humus level on soil and to introduce the most appropriate farming systemthe area is 12409 hectare located on the eastern north of khodabandeh city. in order to identify land uses, aerial photos and topographical maps were used and supported by field surveys. four stages were followed in khodabandeh in order to investigate on humus status in the regions. the results were compared using mstat statistical soft wares. in order to compare treatments, duncan test was applied. the results obtained from the studying surface and sub-surface layers of the area show that rangelands which have not been disturbed by anthropogenic activities are classified between irrigated and drylands. it can be said that the irrigated farming, especially alfalfa farming, enhances soil humus content due to nitrogen fixation done in the roots. but, the drylands especially those with high slope cause degradation of soil organic matters, fertility and production yield and also increase soil erodability.