Nutrient recycling potential in rice–vegetable cropping sequences under in situ residue management at mid-altitude subtropical Meghalaya

Low native soil nitrogen (N) and very low phosphorus (P) coupled with apathy of farmers towards use of fertilizer are the major constraints limiting rice productivity in the North Eastern Hill (NEH) Region of India. Field experiment was undertaken in narrow valley wetland during Kharif and pre-Kharif (rainy) seasons of 2003, 2004, and 2005, respectively, at Umiam (950 m MSL), Meghalaya to evaluate the nutrient recycling and production potential of rice (Oryza sativa L.)—vegetables cropping sequences under low input in situ residue management under rainfed conditions. After rice, five vegetable crops, viz. tomato (Lycopersicon esculentum Mill), potato (Solanum tuberosum L.), frenchbean (Phaseolus vulgaris), cabbage (Brassica oleracea L. var. capitata), and carrot (Daucas carota L.) were grown during pre-kharif season on temporary raised and sunken beds. Minimum tillage was given to both rice and vegetables. No external input including fertilizer, organic manure, pesticides, etc. were applied to either crops. Only the economic parts of the crops were harvested and the rest of the biomass of the entire crop and weed residues were chopped and incorporated into the soil. Among the five cropping sequences, rice–tomato gave the highest rice equivalent yield (214.40 q/ha), followed by rice–carrot (206.4 q/ha). Highest net return (rupees Rs.] 66,635 ha⁻¹) was recorded in rice–carrot, closely followed by rice–tomato (Rs. 66,139 ha⁻¹). Rice–cabbage and rice–frenchbean were found to be on a par with each other in terms of yield and income. The highest amount of NPK recycling was recorded for the rice–potato sequence. Weed biomass production in the different sequences ranged from 37.5 q/ha for rice–tomato to as high as 50.6 q/ha in the case of rice–fallow. Soil fertility in terms of available NPK status was found to be stable in all the crop sequences except rice–cabbage, where fertility status declined slightly. The soil biological properties such as population of Rhizobium, bacteria, phosphorus-solubilizing microorganisms, and earthworm activity were all found to be remarkably higher in the experimental field compared to other adjacent plots that are managed inorganically. It was concluded that vegetables such as tomato, carrot, potato, etc. could be profitably grown after rice without the addition of fertilizer and manure, if residues are managed effectively under temporary raised beds without deteriorating soil fertility.