Nutritional resource use efficiency in rice production

Abstract

The chemical constraints for higher yields in laterite soils are identified as low cation exchange capacity and organic matter content, high acidity, iron and aluminium toxicity, high phosphorous fixation and poor nutrient status. Investigations carried out to identify the limiting factors and their mode of action in laterite soil revealed direct effect of excess iron absorption, their metabolic interference, unfavourable Ca + Mg / K ratio, and deficiency of certain elements manifested as negative effects of some others. Management of organic manuring modified by amelioration with suitable amendments was reported to be an ideal remedial measure for reducing the above chemical constraints. An experiment was conducted at Agricultural Research Station, Mannuthy during 2001-2002, to characterize and quantify the effect of organic sources on nutrient supply, amelioration and inactivation of the deleterious factors in rice , culture and to study the supplementary requirements of inputs and complementary effects on yield improvement. It was also intended to develop a technology by integrating various inputs and their levels to ensure high resource use efficiency and consequently higher productivity. The plant height and tiller production was highest in the treatment green manure + lime + ash at active t.illering, panicle initiation and 50 per cent flowering. The total dry matter production was highest in the green manuring + lime and green manuring + lime + ash treatment. All the growth parameters such as plant height, tiller count and total dry matter production showed a stepwise improvement with doubling of K, doubling of K along with addition of lime and ash and doubling of K with addition of lime, ash and sulphur over the treatment where K was given at normal rate and without any ameliorants. The highest chlorophyll content both 'a' and ob' was found as resulted in the fallow - green leaf manure treatment, however, this was not reflected in the

process of yield formation since the highest yield was observed for the treatment, green manure + lime + ash. The favourable cell sap pH around 6.21 was observed in the treatment green manure + lime + ash which resulted in the highest grain and straw yield. The highest grain and straw yield of 6.64 and 6.75 t ha-I, respectively was observed in the treatment combination green manure + lime + ash x N as NH4S04 + half P + lime + ash + double dose of K which indicate the importance of addition of lime, ash and sulphur as ammonium sulphate in the fertilizer package of rice in laterite soil. The following conclusionsare drawn from the results of the experiment. In the mundakan - summer - virippu rice cropping system in laterite soil leaving the land fallow' during summer may considerably reduce the yield during virippu if not supplemented with adequate organic manure and ameliorants like lime and ash. If the summer season is kept fallow, green leaf manu ring could be a better substitute for addition of organic matter to the laterite soil. Paddy straw incorporation at 15 days before the virippu cropping in laterite soil was found to reduce the yield of virippu rice probably due to high rate of immobilization ofN. The increase in acidity and consequent higher solubilization and uptake of Fe in virippu crop was evidently due to summer fallow which favour natural oxidation of Fe and Mn. Ameliorants like lime and ash added both during summer green manuring and virippu rice crop enhanced the rice growth and yield through modification of pH, supplementation of potash and calcium.

Enhancement ofN:K ratio to 1: 1 was found to enhance rice productivity in laterite soil. Addition of K application did not increase the K content in the plant but reduced Fe uptake. Changing the N source to ammomum sulphate and thereby sulphur I fertilization was found to increase growth and yield of rice. Ammonium sulphate treatment helped mainly to increase plant height but not tiller production. Among yield attributes spikelet production was very much influenced by sulphur fertilization. The physiological and uptake efficiency of the N derived from green manuring was higher compared to other organic sources and consequently resulted in better agronomic efficiency. This indicates the need for a green manure - rice system in laterite soil to enhance soil and crop productivity. The green manured rice with ameliorants such as lime and ash, and ammonium sulphate as N and S source resulted in the highest net return and B:C ratio of2.25.