INTEGRATED NUTRIENT MANAGEMENT FOR SUSTAINING PRODUCTIVITY AND FERTILITY BUILDING OF SOIL UNDER RICE (ORYZA-SATIVA) - BASED CROPPING SYSTEM

A field experiment was conducted during, pre-rainy season, rainy seaso n, winter season and summer season of 1989-91 to evaluate the producti vity, fertility build-up of soil and the economics involved in differe nt rice (Oryza saliva L.) - based cropping systems. The productivity o f rice was maximum (4.98 and 5.69 tonnes/ha) when both rainy- and summ er-season rice in sequence were green-manured in situ with prickly ses ban or dhaincha [Sesbania cannabina (Retz.) Pers.; syn S. aculeata (Wi lld.) Poir.], grasspea or khesari (Lathyrus sativus L.) respectively a long with 100% of the recommended dose of N, P and K (60, 14.2 and 25 kg/ha and 80, 22 and 41.5 kg/ha respectively in rainy- and summer-seas on rice). However, comparable yield (4.84 and 5.42 tonnes/ha) was obta ined when both rainy and summer-season rice in sequence were green-man ured in situ along with 75% of the recommended dose of fertilizers (N4 5P10.6K18.7 and N-60 P16.5K31 in rainy and summer season respectively) . Green-manuring twice in a year before transplanting of both rainy- a nd summer-season rice improved the soil-nutrient status (260 kg N/ha, 16.1 kg P/ha and 21 kg K/ha). Green-manuring with sesban and khesari w as found equivalent to 19.4 and 31.1 kg fertilizer N/ha during rainy- and summer-season rice respectively. Maximum net production value (2.1 1) was recorded in the sequence where both the rice crops were green-m anured with legume along with 75% recommended dose of N, P and K. Fert ilizer-use efficiency was improved (40.05)when any legume crop was inc luded in a cropping sequence involving 2 rice crops, and the improveme nt was maximum (41.42) when legume crop was buried into soil before tr ansplanting both rainy- and summer-season rice. Hence the recommended dose of N, P and K may safely be reduced by 25% if green-manure is pro vided to both the rice crops in sequence.