Assessment of Soil Losses, Runoff Estimates and Changes in some Physico-Chemical Properties of Soil under Different Cropping System

Abstract

The suitability of the soil for crops production is based on the quality of the soil physical, chemical and biological properties. One of the naturally occurring processes that may detrimentally affect oil properties and subsequent crop production is soil erosion. Nutrient loss is an important aspect of surface erosion since nutrients are concentration of plant nutrients and organic matter is high in eroded sediment as they are closely associated with finer fraction of soils. Erosion reduces soil quality through the loss of clay particles, nutrients and organic matter, degradation of soil structure, decreased rooting depth and decreased soil storage capacity for crop production. Various measures like crop and soil management practices can be adopted to control fertility of the soil on sloping lands. The type of inter –crops for a cropping system can be selected on account of their efficiency in controlling soil erosion and for their beneficial influence on the growth ad yield of major crops. Therefore, it I important to develop data for cropping pattern, management practices, erosion modeling and simulation to minimize soil and nutrients loss of sloping land. The purpose of this project was: 1. To study the effect of cropping system on soil erosion and nutrient losses through sediment and surface runoff. 2. To study the effect of cropping system on soil properties of the experimental soil. 3. To study the effect of rainfall erosivity on surface runoff, soil loss and critical distance of rill initiation and rill dimension. 4. To formulate recommendations to improve soil and water conservation through land management practices. The field was selected in village Thana, Malakand Agency for this piece of research work. The field was eroded and had past soil erosion. The field was located on sloppy land and was mainly used for rainfed agriculture. About one acre field with 6% slope as selected and permanent plots of 2 x 5 m2 size each were established. Cemented tanks measuring 1.5 x 1 x 1 m3 each were constructed at the bottom of plots to collect surface runoff and sediment from each plot. Experimental design was RCB with three replications. The treatments maintained were, wheat, barley + lentil and control (bare) in Rabi season and maize, maize + mung-beans and control (bare) in Kharif season. Sowing of wheat and barley was done on 20-06-2001. A fertilizer rate of 120-90-60 kg N-P2O5-K2O ha-1 was applied to both of the crops. Fertilizer sources were urea for N, SSP for P and potassium sulphate for K. Nitrogen fertilization was done in two splits, half at sowing time and the remaining half after few days of crop growth. All the usual cultural practices were being followed during the period of crops. Various field visits were made to the site to check the growth of the crops and to collect the necessary data. The result obtained showed that total runoff, soil loss and nutrient losses were much higher from bare plots as compared to cropped plots. In Rabi season, losses of N P K from bare plots were 57%, 53% and 49% higher respectively from the N P K losses from barley-legume inter-cropping whereas in Kharif season, losses of N P K from bare plots were 39%, 49%, and 38 higher respectively from the N P K losses from maize-legume inter-cropping. The losses of other nutrients were also higher from bare plots as compared to inter-cropping and mono- cropping. Losses of N P K in runoff were higher as compared to the losses of N P K in sediment. The loss of nutrients was closely related to the amount of sediment and runoff from the plots. More losses of nutrients from bare plots were the result of high loss of soil and runoff from bare plots. Soil erosion, total runoff, organic matter and nutrient losses were more in the early stage of the crops, when the surface cover was comparatively less. The losses of the above parameters decreased as the surface cover increased due to crop growth. Surfaced cover reduced soil erosion by more than 44% during Rabi season and by more than 51% during Kharif season. The increase in soil loss due to increase in rainfall was presumably due to increased kinetic energy associated with increasing intensity. The loss of organic carbon through sediment were higher from all the plots during both the seasons followed by the loss of K, Mn, N, Fe, P, Cu and Zn. Nutrient enrichment ratio of the sediment was greater than 1 for all nutrients, indicting higher losses of nutrients in the sediment. Very god correlation was observed for runoff and soil loss with organic matter and plant nutrient losses. The positive correlation for runoff and soil loss with organic matter and plant nutrient losses may be due to the fact that soil fertility is mainly associated with the surface soil because the surface soil contributes a large share of nutrients used by the plants. Due to their higher concentration in the surface soil, organic matter and plant nutrients can be easily washed away by surface runoff. Equation to represent the amount of sand, silt and clay for different treatments under different rainfall conditions were also developed, which can be helpful to understand the mechanism of surface erosion. The equation revealed that as compared to sand and clay particles, silt particles were higher in sediment due to their weak aggregation. As far as the effect of different cropping systems on the soil properties is concerned, so cropped plots maintained their soil properties more efficiently as compared to bare plots, as soil pH, electrical conductivity, lime content and bulk density of bare plots increased while copped plots showed no visible changes in these parameters. Further, soil organic matter and plant nutrients of the bare plots decreased whereas, cropped plots showed no prominent reduction in soil organic matter, N, P and K content. It can be concluded from this study that inter-cropping of barley-legume and maize-legume is an effective cropping system for reducing long term soil, runoff and nutrient losses from the slopping land. Furthermore, small reduction in runoff velocity due vegetation resulted in a major reduction in soil erosion. Generally, good soil cover is recommended to amend soil physico-chemical properties of the eroded soils and selection of proper cropping system and crop rotation is necessary for conservation oriented farming. Proper fertilizer management is needed to increase water and fertilizer use efficiency. Further, innovative management practices are required to buildup P level to enhance crop productivity in these areas. Data for the year 1999-2000 is presented in the first annual report while data for the year 2000-2001 is presented in second annual report submitted to the Pakistan Science Foundation. The present report contains data for the year 2001-2002. The data for Rabi and Kharif 2001 has been explained in detail while data for the Rabi 2002 has been given in Appendix-3 and this data is meant to check the results of the previous Rabi crops.