Source-efficacy relations of organics in wetland rice culture

Abstract

A field experiment was carried out during the Kharif season of 2000 at the Agricultural Research Station, Mannuthy to assess the efficacy of various sources of green leaf and organic manures in relation to nutrient accretion, rice growth and yield. The interactive effect of decomposition products on nutrient mineralization, chemical properties of the soil and subsequent elemental composition of the plant were studied in relation to rice growth. The changes in carbon: nitrogen relations in the soil and the pattern of nitrogen mineralization were monitored through an incubation study conducted at the College of Horticulture, Vellanikkara. The field experiment was laid out in randomized block design with three replications. The treatments consisted of twelve organic amendments of both plant and animal origin, three synthetic fertilizer combinations and an absolute control. All organic treatments were incorporated at 5tJha on dry weight basis. The short duration lNV, Matta Triveni was used in the experiment. Treatments had a significant effect on the content of major nutrients both in soil and plant. Micronutrients did not affect the yield by their inadequacy, however, Fe content in plants was found to be excess and may have negatively influenced the yield The growth characters of the plant like height of tillers, number of tillers, weight of roots, plant dry matter and total plant weight were largely affected by the . treatments. The height of tillers was highest in plots treated with poultry manure at all stages of the crop, while number of tillers especially after 25 DAT was maximum in FE treated plots and this was also the case in the number of productive tillers. Among the yield attributes, the number of spike lets per panicle and the length of panicle was maximum in poultry manure treated plots. The chaff percentage was highest in sesbania treated plots. The number of productive tillers was maximum in FE treated plots. The highest yield of grain (4.37 tIha) and straw (5.20 tJha) were from FE treated plots but the grain straw ratio (0.84) was the lowest in this treatment. In case

of FE treatment, the high yield was as a result of increase in number of productive tillers, while in case of pongamia and gliricidia, it was due to reduced chaff percentage and enhanced test weight. A higher yield was obtained in case of poultry manure treatment due to enhancement of number of spikelets per panicle The treatments in the field experiment were replicated as an incubation study to understand the pattern of nitrogen mineralization and to observe the variations in carbon nitrogen relations. A measured quantity of soil (lOOg) was placed in glass conical flasks and corresponding quantity of organic manures so as to maintain a ratio of 5 tJha and the fertilizer treatments also in the same ratio were incorporated and incubated for a period of 100 days. The mineralization of nitrogen was studied and in case of organic manures cow dung, gliricidia and sesbania were the first to do so. Straw and acacia treatments were the slowest to mineralize achieving peak levels at 70 days after incubation that were due to the quantities of lignin carbon and fibre in the organic manures. In case of phosphorus mineralization, it was noticed that mineralization in all the treatments irrespective of it being organic or inorganic in nature, tended to decrease rapidly after incubation up to 40 days and then gradually increase to levels higher than the initial level and in case of potassium mineralization, a slow and gradual increase in the levels ofK were observed which was noticed even after 70 days with a slight decrease being noticed towards the end in some treatments. The rate of decomposition and mineralization was affected by the CIN ratio, ligninIN ratio and also moisture content, content of fibre and nutrients 'present in the organic material. Substitution of a major quantity of inorganic fertilizers is possible by the use of organic manures. However, considering the mineralization patterns, a better option would be the combined use of inorganic and organic manures whereby the synthetic fertilizers would meet the initial nutrient need of the crop as they are readily available to the crop during the initial exponential growth phase and in the later stages the organic manures would provide the required nutrients.