Seasonal variations in the nutrient transformation in the lateritic alluvial rice soils of permanent manuurial trials

Abstract

A study was conducted during the first and second crop season of 1992 to find out the seasonal variations in nutrient transformations in the existing two permanent manorial trials (one with tall indica varieties and the other with dwarf indica varieties) at the Regional Agricultural Research Station, Pattambi. The experiment with tall indica variety was started in 1961 and the experiment with dwarf indica variety was started in 1973. The experiments were laid out in randomised block design with four replications and eight treatments. The treatments consisted of application of entire quantity of N as organic manure (cattle manure alone, green leaves alone and cattle manure + green leaves), inorganic fertilizers alone (ammonium sulphate alone and NPK fertilizers) and a combination of organics with inorganics (cattle manure + NPK fertilizers, green manure + NPK fertilizers and cattle manure + green leaves + NPK fertilizers). In both the experiments, the treatments are the same, but the dose of manures and fertilizers varied based on the nutrient requirements of all indica and dwarf indica varieties. For all indica the dose of NPK applied is 40:20:20 kg/ha whereas in the dwarf indica varieties the dose applied is 90:45:45 kg/ha. Soil samples were collected from all the replications of the various treatments at 11 stages from harvesting of second crop of 1991 to harvest of second crop of 1992. Plant samples were also collected at different stages of crop growth viz., tillering, 50 per cent flowering and harvest. Data on yield of grain and straw were collected from the Regional Agricultural Research Station, Pattambi. Soil and plant samples were analysed in the laboratory to find out the seasonal variations in the availability of nutrients in the soil and in the content and uptake of nutrients by the crop. Results of analysis of soil samples showed that significantly higher values of organic carbon, available N,P,K and Ca were recorded in the initial stages of crop growth namely transplanting, tillering and 50 per cent flowering in the first crop season but at harvest the trend reversed in both the experiments. In the case of magnesium significant difference between the seasons was noticed only at 50 per cent flowering and at this stage higher values were recorded in the first crop season in both the experiments. At the initial stages of crop growth, namely at tillering and 50 per cent flowering higher content of available nutrients namely N, P, K and Ca were recorded in the soil in the first crop season but higher contents of N, P and K in the plant were recorded in the second crop season for both tall and dwarf indica varieties. For magnesium content in plant comparatively higher values were recorded in the first crop season compared to second crop season for both tall and dwarf indica varieties at tillering and 50 per cent flowering. With regard to calcium higher contents were recorded in the first crop season at tillering but at 50 per cent flowering the trend reversed in the case of tall indica varieties. At both the stage higher contents were recorded in the first crop season in the dwarf indica varieties. In the grain significantly higher content of N, K and Mg were recorded in the second season. There was not much difference in the P content between the seasons. Similar trend was noticed in the nutrient content for both tall and dwarf indica varieties except for Ca. In the case of calcium no uniform trend was shown in both the experiments. Higher contents of P, K and Ca were noticed in the second crop season in the straw. Significantly higher values were recorded in the first crop season for nitrogen. No significant difference in magnesium content was noticed between the seasons. Similar trend was noticed in both the experiments for all the elements. Significantly higher uptake of N, P and K was noticed at all the growth stages in the second crop season in both the experiments. In the case of Ca and Mg though higher uptake was recorded in the initial growth periods, at the time of harvest the trend reversed and for these elements also higher values were recorded in the second crop season.