Biological Control of Soil Salinity and Fertility

Abstract

The objective of the research project was to study the relative efficiency of biological, chemical and combination (Biological + chemical) method of soil reclamation and to devise an efficient method for increasing the productivity of salt affected soils. The research work carried out for the purpose include 3 basic studies, pot experiments and a field experiment at Rakh Dera Chahl. In laboratory studies, It has been shown that the dynamics of solubilization of CaCo3 under the influence of different organic materials in 99line-sodic calcareous soils reveal that organic materials like kaller grass and kaller grass partially decompose by different fungi helped in the removal of exchangeable sodium from the soil. This reaction become possible due to solubilization of CaCo3 present in the soil under the test and some of the solubilization Ca was leached out in addition to the exchange of Na withCa on the soil complex. In order to selected salt tolerant plants for the efficient utilization of salt affected soils, a technique for conducting salt tolerance studies in pots was devised and utilized to study the salt tolerance of Diplachne fusca and sesbania aculeate, the two important plants used in the study. These studies indicate that a 50% reduction in dry matter yield of D.fusca occurred at an EC of 22 mmhos cm-1 and at an EC of 13mmhos/cm-1 in the case of the soil was also investigation in the case of D.fusca and S.aculeata. Both these plants proved highly tolerant to soil sodicity and therefore, were considered quite suitable for colonizing highly sodic and saline-sodic soils. An experiment to study the effect of sesbania green manuring on productivity and composition of soil indicate that green manuring no special edge over following as far as the yield of following wheat crop was concerned. However, green manured soils showed relatively higher water retaining capacity and they had a higher water infiltration rate. Apot experiment was carried out to study the effect of chemical, biological and combination treatments under relatively controlled conditions. Of the 10 treatment used it was found that growth of the kallar grass either alone or in combination with press-mud was instrumental better removal of salts in increased the organic-matter content of the soils but had very little beneficial effect on PH and SAR. Gypsum, as expected was very effective in improving all the soil parameters except organic-matter. Farm yard manure and sheep droppings increased the dicarbonate content of the soil even more was the case with the growth of kallar grass but gypsum depressed the solubilization of CaCO3 into the bicarbonate form, which the most probably due to the common ion effect. The field experiment to find a suitable biological, chemical or combination treatment for the utilization of salt-affected soil was carried out at Rakh Dera Chahl. The soil was in a highly deteriorated condition with a top layer pH of 10.5, ECx103 equal to 42.2 and SAR value 729. The soil texture varied from clay loam to sandy clay loam. Gypsum requirement was 13 tons acre 6-1 and the available tube-well water had an EC of 0.96 mmho cm and RCS 3.5 me/1-1. The feature, however, was that the SAR of the available was quite low (3.6). The experiment was carried out in two parts. In two blocks were irrigated with the tube-well water after it had been passed through gypsum blocks to reduce its RCS to 1.3. Out of the 6 treatments tested in the first part maximum reduction in pH was noted in plots receiving gypsum at the rate of 100% of the requirement. The next best was combination treatment comprising addition of press mud and growth of kallar grass. Simple leaching with water had very little effect on pH of the soil. Maximum reduction in the salt content was noted before transplanting rice and after its harvest but it appreciably increased in all treatments after the harvest of wheat. This phenomenon might have occurred due to stoppage of irrigation at that stage and the consequent migration of salts in the upward direction. Among the different treatments, the plots treated with gypsum and press mud + kallar-grass showed the lowest salt content throughout the profile. Salt content was high throughout the profile in the case of simple leaching while the growth of kallar grass reduced it in the top 30 cm, the lower horizons having progressively higher salt content. The behavior of SAR was akin to electrical conductivity being the lowest in the case of gypsum and press mud + kallar grass treatments and the highest in the case of simple leaching. The SAR values were higher after the harvest of wheat than after harvest of rice in the case of all treatments. This could again be due to the upward movement of salt in the absence of any irrigation. The maximum paddy yield was obtained from plots treated with press mud + kallar grass followed by kallar grass, gypsum and sheep droppings. The plots which were leached with simple water failed to support the growth of rice. In the case of plots receiving tube-well water passed through gypsum blocks, maximum reduction and pH was obtained were kallar grass was grown. Gypsum applied at 50% of the requirement did not lower the pH throughout the profile. The use of gypsum amended water was responsible for appreciably decreasing the salt content in the case of all treatments especially in the top 15 cm. Kallar grass treated plots were the ones where the reduction in EC took place throughout the profile. SAR value in the top layers was reduced to a maximum extent by whole, the beneficial effects of gypsum were observed at the earlier stages whereas the biological treatments produced gradual changes in various soil parameters observed. It can be safely concluded that for the farmers who cannot afford to apply expensive soil amendments like gypsum, the best policy could be to start a plant succession and improve the soil physico-chemical properties and its productivity by stages. This would have the added advantage of providing green fodder for his animals while the process of amelioration is in progress.