Effect of submergence on the soil testing parameters of paddy soils

Abstract

Laboratory incubation studies were conducted to quantify the changes in pH, EC, lime requirement and availability of important nutrients such as N, P, K, Ca & Mg due to submergence of alluvial, acid saline acid sulphate and saline rice soils of Kerala, The study has revealed that pH of all the soil types increased Immediately after flooding of the air dried soils, reached a maximum and remained more or less steady throughout the period of three months submergence. Consequent to the increase in pH, a corresponding decrease in lime requirement was observed in all the soils. Maximum reduction in lime requirement was noticed for the saline and acid saline soils. A rise in EC was observed in all the soil types due to submergence during the first four to six weeks. It showed a decreasing tendency afterwards. All the soils showed a progressive increase in available nitrogen content with increase in the period of flooding. The increase was in the range of 75 - 395$ for the various soil types. Maximum increase was recorded by saline soils (395$) and minimum by alluvial soils (75%). The levels of available phosphorus recorded for the four soil types in the air dried state were in The low to medium range for rice. Submerging of these soils has resulted in a manifold increase in the content of available phosphorus. The increase was maximum for acid saline soils (700$) and minimum (55$) for alluvial soils. The availability of exchangeable cations like potassium, calcium and magnesium, however, showed a periodical increase and decrease on flooding in all the four soil types. The results of the study have clearly brought out the magnitude of the changes that result in the status of each nutrient upon flooding of soils for wetland paddy cultivation. The manifold increase in the status of major nutrients like N and P upon flooding of soils indicates that addition of fertilizer N and P under such conditions is not likely to produce any significant effect on rice unless the rice varieties are highly responsive to these nutrients. The feasibility of reducing The quantity of fertilizers to be applied or even skipping of fertilizers for one or two seasons may be considered taking into account the responsiveness of the rice variety as well as other economic factors.