The study was initiated in 1977 on a Typic tropofluvent soil at the Cropping Systems Research Centre, Karamana, on a rice- rice (Oryza sativa cv. Aiswarya, medium duration) cropping system . The experiment was laid out in a partially confounded factorial design with three levels of N (40,80 and 120 kgha -1), 3 levels of P2O5 (0, 40, and 80 kgha -1), and two levels of K2O (0 and 40 kgha -1). op. After 30 years of cropping grain yield and dry matter production were markedly reduced in treatments continuously depleted of P, but with adequate N and K. The percent increase in grain yield over control increased with incremental additions of N and P but the magnitude of increase was more for P levels. The agronomic efficiency was higher at lower N and P levels but nutrient use efficiency decreased with increasing N, P and K levels. Skipping P significantly decreased N, P and K uptake. For each ton of grain produced, the total nutrient uptake increased with an increasing application levels. The N balance was always negative but phosphorus balance was negative only in control plots and increased to 13.52 kgha-1 annum-1 at P80. K balance was negative for both control and K added plots. Thus imbalanced and inadequate fertilization affects the yield response of wetland rice to nutrients. Though P is not generally a limiting nutrient in the acid entisols of India, its long term depletion was found to affect the crop response to N and K as well.

In Asia rice farming is confined to small farmers who are compelled to obtain higher productivity for their livelihood. In general there is an increase in area and production of rice in India. In the humid tropical region of Kerala State the area has been drastically reduced inspite of the efforts of the local Government. Crop diversification is a practical means to enhance the crop output. In conventional rice farming the usage of plant protection chemicals is very high and can cause an irreversible change in the wetland ecosystem. Diversified cropping of rice in rainy season and two subsequent vegetable crops viz cucumber and okra in the post rainy and summer seasons under organic farming practices was tested at the Cropping Systems Research Centre of Kerala Agricultural University for a consecutive period of five years from 2003-04. The experiment comprise of seven treatments in which five organic farming practices were compared with integrated nutrient management and full chemical nutrient practices. The study revealed that from the third year onwards organic farming and integrated nutrient management practice gave comparable yield as that of full nutrient as chemical inputs. The N and P content in the soil was enhanced while the K content was slightly reduced during the end of experimentation. There was an appreciable improvement in organic carbon in all the treatments through crop residue management.