Moisture release curves of agriculturally important soils of Chakwaldistrict [Pakistan]

This piece of research work was concerned using laboratory and fieldinvestigations for developing moisture characteristics curves for differentthree sites of Chakwal district. Two fields already established at Soil andWater Conservation Research Institute Chakwal (SAWCRI) and one farmer's fieldin village Balkasar, District Chakwal were selected for this research work. Soilsamples were collected from three pits in each field. From each pit six coresamples and six auger samples at the depth increments of 15 cm to a depth of90 cm was taken. Thus, fifty-four samples were collected. Dispersed soilsamples (auger sample) were analyzed for organic matter and texture whilebulk density and available water was determined on undisturbed samples (coresamples). For determining available water five pressures i.e. 0.01MPa, 0.03MPa,0.05MPa, 0.IMPa and 1.5MPa were used. The data analyzed for texture, organicmatter, bulk density and available water from three fields showed considerablevariation for different depths and among the fields. Statistical analysis showedthat organic matter contents ranged form a maximum of 0.93% at the depth of0.15 cm to a minimum of 0.52% at the depth of 75-90 cm with an average valueof 0.72% in field 1. In field 2, a maximum of 1% at the depth of 0-15 cm to aminimum of 0.67% at the depth of 75-90 cm with an average value of 0.82% wasobserved. In field 3, a maximum of 0.85% at the depth of 0.15 cm to a minimumof 0.61% at the depth of 75-90 cm with an average value of 072% was noted.Mean bulk density of field 1 was 1.52-g cm-1, while that of filed 2 and field 3was 1.36-g cm-1. Available water (0.90 cm depth) of field 1, field 2 and field 3was 6.12 cm, 2.25 cm and 3.70 cm, respectively. The coefficient of variation forfield 1 fields 2 and field 3 was 9.8% 16% and 19.4% respectively. Clay, silt andsand percentage also varied depth wise and among three fields. An averageclay content of field 1 field 2 and field 3 was 7.8% 55.2% and 32.82%respectively. Average silt contents of field 1 field 2 and field 3 was 33.1%,16.8% and 32.92%, respectively, while average sand contents of field 1 field 2and field 3 was 59.2% 29.33% and 34.26% respectively. It was observed thatrelationship between estimated and measured water contents of field 1 (r2=0.88), and field 2 (r2= 0.94) from six depths (0-90 cm) was significant, as thevalues were close to each other. However, in field 3 (r2= 0.10)' the relationshipwas poor. Curves between water contents versus pressure (0.01 MP2, 0.03 Mpa,0.05 Mpa and 0.1 Mpa) showed significant decrease in water contents with anincrease in pressure. The linearization of equation (psi = a0b) showed astraight linear relationship between water contents and pressure applied andwas significant. The coefficients for moisture characteristics curves for field 1at the depth of 0-15 cm was : a = 3.02 and b = -4.16 and r2 values for- thisequation was 0.99. The coefficients for moisture characteristics curve for field2 at the depth of 0-15 cm was : a = 1.3 and b = -6.62 and the r2' values forthis equation was 1.0. The coefficients of moisture characteristics carve forfield at the depth of 0-15 cm was a= 2.71 and b= -5.08 and the r2 values forthis equation was 1.0.