Title: The continuous and indiscriminate use of NPK fertilizers for longer periods resulted in the imbalance of nutrients in soil

Biography:

Kavitha Chandran is aproffesor from the Kerala Forest Research Institute and works in the Soil Science Department Peechi, Kerala.she published many papers and her resent research is on imbalance of nutrients in soil.

Abstract

The continuous and indiscriminate use of NPK fertilizers for longer periods resulted in the imbalance of nutrients in soil. This nutrient imbalance in soil gradually reflected in crops, animals and human beings, leading to various degenerative and deficiency related diseases now more than ever. This necessitates site specific nutrient management for crops, which essentially rely upon evaluation of soil fertility status. Geographic Information System is an advanced technology for storing and displaying of data and understanding the status of soil fertility spatially and temporally. GIS based soil fertility mapping for assessing spatial variation and site specific nutrient management in a region are not yet attempted in Kerala. The soil fertility status in various agro ecosystems was assessed by collecting 5120 soil samples @ one sample per ha. These samples were analyzed for pH, electrical conductivity (EC), organic carbon (OC), macro and micro nutrients using standard procedures. Results revealed that soil fertility of Thrissur district varied widely between various agro ecosystems across different agro ecological units. The soils of various agro eco systems in general were extremely acidic to slightly alkaline, non saline to highly saline, with low to high status of organic carbon and all the macro and micro nutrients. The soil fertility assessment based on soil reaction index indicated that in all the agro ecosystems, soils were acidic except arecanut and pepper, wherein the soils were in neutral condition. The value on salt index revealed normal non saline condition in all the cropping systems in the study area. The status of OC, which was evaluated by nutrient index values were high in soils of nutmeg and rubber. In all other crops its status was moderate. The nutrient index values revealed high N status in the soils of rubber based cropping system, and medium in all other crops. The status of P was high in the soils of all agro ecosystems. The status of K was low in arecanut, high in rubber, and medium in all the other crops. Mg was medium in all the agro ecosystems in the study area. The status of S was high in the soils of rubber, vegetables and pepper. The decreasing order of deficiency of macronutrients were K (9.2 % - 58.7 %) > Ca (17.8 % - 41 %) > Mg (17.7 % - 38.5 %) > S (3.7 % - 13.9 %) > P (1.9 % - 20.7 %). The nutrient index values revealed very high status of Zn in the soils of nutmeg and paddy, and high in other agro ecosystems. Status of B was very low in the soils of all the cropping systems. On the other hand, Cu was very high in the soils of paddy and coconut, and high in other cropping systems. The status of Fe and Mn were very high in the soils of all the crops grown in Thrissur district. The decreasing order of deficiency of micronutrients in Thrissur district were B (99.3 % – 100 %) > Cu (61.5 % – 84.3 %) > Zn (64.4 % – 75.9 %) > Mn (1.6 % – 18.5 %) > Fe (0.1 % - 1.8 %).

The spatial variation of nutrients in the study area was assessed by using semivariogram method in kriging interpolation. The characteristics of semivariogram such as range (m), nugget, sill, partial sill, relative nugget effect (%) and spatial dependence were calculated. The best fit model was applied to the kriging interpolation according to the determination coefficient, which is the correlation of measured and predicted values on space. Finally, spatial distribution maps of all the variables were prepared. Among the variables analyzed, K (7%) and B (24%) revealed strong spatial dependence, Zn (78%) with weak spatial dependence and others with moderate spatial dependence. The results from the present study call to develop a strategy for site - specific management for the parameters showing moderate spatial dependence and weak spatial dependence. But for K and B, showing strong spatial dependence, only uniform management is needed because it was greatly affected by the structural factors such as climate, topography and parent material. Spatial variability of soil properties is essential for precision agriculture because soil parameters with little or no spatial dependence will not be conducive to site-specific management, and will be managed on the average. The information on the spatial variability of soil nutrients is useful for refining soil management practices, and for improving sustainable land use in Thrissur district.

The third objective mainly focused on developing the soil fertility map depicting the extent of deficiency and toxicities of nutrients in the study area. From the map of pH prepared for Thrissur district, it was found that extremely acidic soils were mainly distributed in pokkali and kole lands (91.91 km²). A large portion (1146.6 km²) of the study area were with moderately acidic soils (pH 5.6-6.0). The saline soils were mainly located in pokkali lands to an area of 18.07 km² (0.6%) and the major area of the district extending to 2901.08 km² (95.75%) was non saline. High content of OC was mainly concentrated in northern and southern high hills in an area of 1544.39 km² (50.97%). High status of N was mainly located in the soils of high hills extending to an area of 1041.44 km² (34.37%). The high levels of P was noted in majority of the area extending to 2940 km² (97%). Low levels of K was mainly located in northern coastal plain and high levels in northern central laterite. Optimum level of Ca was noted in majority of the area extending to 2763.8 km² (91.2%) and its deficiency was pronounced in pokkali and kole lands. Deficiency of Mg was pronounced in all the agro ecological zones of the district. S deficiency was observed only in 19 % of the area. Among the micronutrients, deficiency of B was severe extending to 99 % of the area in the district. Deficiency of Cu was noted only in 14.8% of the area. Deficiency of Mn was less prominent in the district extending to an area of 6 % (182.5 km²) in northern central laterite. Adequate level of Fe was observed in 99.96 % of the district revealing negligible deficiency.

In general, low soil fertility status in the study area was mainly located in the coconut prominent areas of the northern coastal plain. 41% of the area showed optimum soil fertility, which was most suitable for farming practices. The information generated from this study can serve as base line data for future nutrient management in this region.