In this paper soil compaction is described in relation to soil physical factors, root growth, and nutrient uptake by crop plants; rice growth and yield.
In compaction, soil solids are rearranged with compression of liquid and gaseous phases accompanied by volume change. Soil compaction affects water retention characteristics, water intake rates, and gaseous exchange. In compacted soil, bulk density, microvoids, thermal conductivity, and nutrient mobility increase and macrovoids, hydraulic conductivity, and water intake rates decreases. Medium textured soils are most susceptible to compaction. Plants response in relation to root growth and nutrient uptake varies depending on particular stage of development under a particular environment.
Soil compaction, which cuts down percolation losses and reduces the water requirements of rice, appears to be a more practical and economical tillage practice than puddling for increasing rice growth and yield and water use efficiency. Compaction as a tillage practice is simpler, consumes less energy, is easily designed, and shows possibility of mechanization of wetland rice cultivation by replacing messy and difficult operation of puddling, especially on medium textured soils.
________________________________________________________________________________ 1 Scientific Officer, SRDI, Dhaka and PhD Fellow, Dept. of Agronomy, BSMRAU, Gazipur
The compaction of soil can be defined as an increase in its dry density,and closer packing of solid particles or reduction in porosity (McKyes,1985).In other words, soil compaction is a dynamic soil behavior by which the state of compaction is increased (Gill and Vanden Berg, 1967). Soehne (1958 ) determined that for arable soils compaction could be described by the following relationships: n = - A ln P + C Where, n = porosity, C = porosity obtained by compacting loose soil at a pressure of 10 psi, A = slope of the respective plotted curves, and P = applied pressure
Compaction can result from natural causes including rainfall impact, soaking, internal water tension and the like. Compaction of agricultural soils below the cultivated layer commonly results from the passage of vehicular traffic (Soane et al., 1982).
In agricultural fields compaction is produced more often in the surface layer and in the layer below the plow layer. Medium textured soils are most susceptible to compaction.
Compaction causes a rearrangement of the soil particles and many properties of the soil are influenced as a result. Pore size distribution is altered, total porosity is decreased, and there are changes in the movement and content of heat, air, water and nutrients in the soil (Grable and Siemer, 1968; Kemper et al., 1971; Tackett and Pearson, 1964a and 1964b; Warkentin, 1971; Wills and Raney, 1971). The restricted growth of roots commonly observed in compacted soil has been variously attributed to all these properties, and to the high mechanical resistance which compacted soil presents to plant roots (Taylor and Gardner, 1963; Taylor and Ratliff, 1969).
Compaction of soil decreases the number of large pores i.e. those similar in size to the diameter of plant roots, and since roots can not enter pores which have a smaller diameter than themselves (Goss, 1977 and Wiersum, 1962) they must exert force to deform or displace the soil particles (Whiteley and Dexter, 1981). The ability of roots to overcome the mechanical resistance of the soil varies with species (Taylor and Gardner, 1968) but how the differences in ability arise is not yet clear. The differences may be related to the diameter of the roots ( Barley, 1953; Phillips and Brown, 1965 ; Whiteley and Dexter, 1981) although data on this and the maximum forces which the roots of different species can exert are scarce (Goss,1977).
The effects of compaction on nutrient uptake by roots have recieved much less attention than effects on growth itself. While...