Organic matter inputs by selected cropping systems on a Vertisol in the Semi-Arid Tropics of India

Soils of the Semi-Arid Tropics (SAT) are often low in organic matter. Conce rn about the maintenance of organic matter levels under conditions of inten sified land-use makes knowledge of organic matter returns to soil by differ ent crops and cropping systems important. In a two year field experiment, o rganic matter inputs of cropping systems for the SAT were studied on a deep vertisol. When the crops were not fertilized, Sorghum/Pigeonpea intercrop system for two years: ( S/PP S/PP) had higher root organic matter than the non-legume system of Sorghum, followed by Safflower for two years ( S+SAF S +SAF). But, when the crops were fertilized, the non-legume system also gave fairly high root organic matter. The lowest root organic matter inputs wer e found in the traditional Fallow + Sorghum Fallow + Chickpea (F+S F+CKP) s ystem. Most of the root organic matter was produced in the upper 0-30 cm la yer. In addition, pigeonpea dropped around 3 t ha(-1) a(-1) of dry leaves. Cowpea also dropped dry leaves, but its contribution was only around 140 kg ha(-1) a(-1). The improved SIPP S/PP and Cowpea/Piegonpea intercrop COW/PP S+SAF systems provided much higher organic matter inputs than the improved non-legume systems (S+SAF S+SAF), even where organic matter inputs of the latter were increased through fertilization. But, all improved systems were considerably better than the traditional system (F+S F+CKP). We concluded that longer crop cover, and greater biomass of improved cropping systems, h ave the potential to increase organic matter content over that of the tradi tional system. Particularly, the dropping of leaves by pigonpea after flowe ring increased organic matter addition in a situation where traditionally, all above-ground biomass is removed from the field.