Poli Raghava Reddy and Alluri Padma Raju. Acharya N.G. Ranga Agricultural Univ, Rajendranagar, Hyderabad, India
Andhra Pradesh is one of the major rice producing states in India and aptly called as rice bowl of South India. Rice is cultivated in an area of about 2.8 – 4.2 lakh hectares with a production of 107-124 lakh tons and productivity of 2.6 to 3.0 t/ha. It is grown in all parts of the state and in all seasons and in all kinds of soils. About 24 per cent of gross cropped area and 48 per cent of the area under foodgrain crops is under rice cultivation in Andhra Pradesh. Rice accounts for almost a quarter of the State's GSDP and is the single largest contributor. The State with 6-7 per cent area generally accounts for 10-12 per cent of production in the country and contributes 3-4 million tons to the buffer stock of the country every year. Although rice is said to be irrigated to an extent of 97% in the state, about 50% of the area is under canals, tanks (17.0%), tube wells, other wells (25%) and other sources (5.0%), the dependability of which rests on the local rainfall. The research on rice is being carried out in Andhra Pradesh by fifteen Agricultural Research Stations located at Ragolu, Maruteru, Pulla, Machilipatnam, Bapatla, Nellore, Utukur, Warangal, Rudrur, Jagtial, Wyra, Rajendranagar, Nandyal, Chintapalli and Seethampet covering the entire state of Andhra Pradesh. Among these research stations, Andhra Pradesh Rice Research Institute (APRRI). Maruteru is the lead centre for rice research in Andhra Pradesh and this is located in deltaic alluvial soils. Majority of the rice in Andhra Pradesh is grown in deltaic alluvial soils. These soils are marine and reverine deposits and they are very deep medium to fine textured, neutral to alkaline in reaction (pH 7.0-9.0) and highly fertile. The soils are moderate to slowly permeable with moderate to poor drainage. The Godavari alluvial soils are found to be high in CEC with the clay minerals of smectite (40-50%), mica (20%), interstatified (20%), clorite (20%) and vermiculite (traces). Voluminous work has been done on different aspects of integrated nutrient management in rice. An attempt has been made to present the highlights of research work carried out. Incorporation of paddy straw @ 2 and 4 tons per hectare along with 100 and 80 N kg/ha respectively would result in rice yields comparable to that obtained with 120 kg N/ha in rabi season. Thus, there is a saving of about 20 to 40 kg N/ha. It was found that the paddy straw should be incorporated much in advance of planting of rice to overcome nutritional disorders and mortality of the planted seedlings. The long term soil fertility management studies indicated that substitution of 50 percent recommended nitrogen through organic sources like green manure (5037 kg/ha) or FYM (4967 kg/ha) could produce yields that were on par with the yield obtained by applying 100% recommended NPK through inorganic fertilizers (5387 kg/ha). Mere application of FYM at 10 tons/ha also produced on par rice yields (4247 kg/ha). The build up available N, P and K also followed similar trend. Studies on recycling of crop residues have shown that 50% of NPK requirement of kharif rice could be saved by Insitu incorporation of rice like Sesbania spp, grain legumes like Pillipesara and black gram and also application of paddy straw and FYM. Such saving was not observed in plots that were left as weedy fallow. The results of field experiments on the utilization of phosphate solubilizing bacteria in Godavari alluvial soils have revealed the significant positive role of phosphate biofertilizer in sollubilizing and making available the native soil phosphorus to the rice crop which otherwise is not readily available to the crop. Application of phosphate bio fertilizers at 2.5 (6096 kg/ha) or 5.0 (6184 kg/ha) alone was on par with 30 kg P2O5 applied through either SSP (6140 kg/ha) or rock phosphate (6038 kg/ha) alone with 2.5 kg phosphate bio fertilizer in respect of rice yield. Thus, there is a saving of 30 kg P2O5/ha by inoculating the soil with phosphate bio fertilizer. The studies on Azospillirum, a nitrogen fixing bacteria associated with nonleguminus plants showed that mere inoculation of rice fields with azospirillum at 500 kg was observed to produce more grain yield than control (5025 kg/ha). The integrated nutrient supply system through the judicious use of inorganic, organic and microbial fertilizer has been observed to lead to balanced nutrient supply and improved soil fertility. This has resulted in reduction of cost of production. Organic recycling was found to augment the crop productivity target and minimizing the environmental pollution. Severe campaigns were organized to popularize the integrated nutrient management in rice cultivation among the farmers. Impact studies on the adoption and evaluation of integrated nutrient supply are also being carried out.