MSc

An investigation on soil fertility of coconut rootzone as influenced by long term inorganic fertilization was conducted at the College of Horticulture, Vellanikkara. Soil samples from coconut basins of NPK factorial experiment at the Coconut Research Station, Balaramapuram, which had been receiving inorganic fertilizers for the past 22 years were used for the present study.
It was found that both exchange acidity and exchangeable AI were increased following the application of ammonium sulphate. Ammonium sulphate x superphosphate and ammonium sulphate x muriate of potash interactions were found significant. Application of superphosphate in combination with ammonium sulphate was found to decrease exchangeable AI. Muriate of potash decreased the exchangeable AI content in the absence of ammonium sulphate.
Considerable build-up of P reserve in the soil following superphosphate application was observed. Soil k content was increased by muriate of potash application. Calcium reserve was improved as a result of superphosphate application while ammonium sulphate application reduced it. A decrease IN Mg content was noticed in plots which did not receive ammonium sulphate. Both ammonium sulphate and superphosphate application improved S status considerably whereas muriate of potash application was found to reduce total S.
Ammonium sulphate application decreased total Mn and total Zn. A reverse trend was noticed in the case of Cu, while total Fe content remained unaffected.
Generally exchange acidity, exchangeable AI, total K, total S and total Fe increased with depth while total P, total Ca and total Mn decreased with depth.
Application of ammonium sulphate increased exchange acidity and exchangeable AI in different soil layers and the increase was more conspicuous in the deeper layers. Application of muriate of potash decreased the exchange acidity and exchangeable AI down to a depth of 75 cm.
Continuous superphosphate application increased the Ca reserve upto a depth of 50 cm while total P content increased significantly to a depth of 75 cm, showing leaching of P to deeper layers as a result of superphosphate application. Application of muriate of potash resulted in large increase in K reserve to a depth of 100 cm and accumulation of K was more beyond 50 cm depth.
There were increases in all the P fractions in plots receiving superphosphate whereas in muriate of potash – fertilized plots, increase was seen only in insoluble P. All the fractions tended to decrease in plots which did not receive superphosphate.
Depth – wise distribution of soil P forms showed concentration gradients decreasing with depth. Among the five fractions the build – up of AI – P, especially in the upper layers was considerable. The various P forms decreased in the order of insoluble P> AI – P> Fe – P> Ca – P> saloid – bound P.
Significant positive correlations were obtained between AI – P, Fe – P, Ca – P saloid – P and available P. Step – wise regression and path coefficient analyses indicated that AI – P and saloid bound P were more important in explanting the variations in available P.
Easily reducible Mn and exchangeable Mn were found to be affected by the regular application of ammonium sulphate alone. Both these Mn forms gave significantly low values in ammonium sulphate applied plots. Depth – wise distribution showed concentration gradients decreasing with depth.
The comparison of the chemical characteristics of the uncropped and unfertilized area with cropped but unfertilized area revealed that chemical characteristics of the soil remained more or less same throughout the root zone upto a depth of 100 cm irrespective of whether the land is cropped to coconut or not.
Depth – wise comparison of soil P as well as soil Mn fractions between the two situations mentioned above showed no significant difference in both soil P and soil Mn forms studied.