Balance-sheet of soil nitrogen in rice (Oryza sativa) based cropping systems under integrated nutrient management

A field experiment was conducted at Rice Research Station, Kayamkulam, Alappuzha in Kerala to assess the impact of integrated nutrient management (INM) on four rice (Oryza sativa L.)-based cropping systems, compris- ing rice during the rainy (kharifj and winter (rabi) seasons; and four different crops during the summer season, in terms of their productivity, effect on the organic carbon of soil and nitrogen balance. Inclusion of legumes in the cropping system and integrated nutrient management improved the organic carbon status of the soil. The crop sequences rice-rice-cowpea [Vigna unguiculata (L.) Walp.] and rice-rice-groundnut (Arachis hypogaea L.) showed a positive nitrogen balance in the soil, the maximum being after rice-rice-groundnut crop sequence. The crop sequences rice-rice-sesame (Sesamum indicum L.) and rice-rice-okra (Abelmoschus esculentus L.) re- duced the available nitrogen status of the soil. Integration of nutrient sources made the predominant rice-rice- sesame cropping sequence more productive in the sandy-loam soil. Inclusion of groundnut and cowpea in rice- based crop sequences increased the yield of the succeeding crop of rice.