Physical and chemical characterisation of the agricultural lands of the Soan–Sakesar Valley, Salt Range, Pakistan

Abstract

Soil samples (depth, 0–20 cm) from the Soan–Sakesar Valley were analysed for a variety of parameters: pH, electrical conductivity (ECe), alkalinity, Na, K, Ca, Mg, Cl, SO₄, Li, B, and NO₃ in saturation extracts; organic carbon (C), NaHCO₃-extractable phosphorus (P), and total P in whole soil; and mineralogical investigations in whole-soil and separated clay fractions. A Principal Component Analysis was carried out on the correlation matrix (i.e. on standardised attributes) and soil samples were subdivided into salinity groups. The mean ECe levels of Groups 1–4 were 1.27, 2.75, 2.07, and 5.67 dS/m, respectively; the corresponding sodium adsorption ratios were 5.36, 7.9, 15.7, and 29.6 mmol^0.5, respectively. In these soil groups, suitable crops were suggested on the basis of their salt tolerance and the salinity of the irrigation water. The low availability of P from phosphatic fertilisers and farmyard manure as a result of fixation by calcite, which is present in these soils to the extent of 7.8–15.2%, resulted in a lower yield of grain crops (wheat and maize). On the other hand, higher application rate of nitrogen (N) fertilisers together with farmyard manure to irrigated crops and vegetables resulted in N leaching from the crop rooting zone into groundwater. The soils investigated had mixed clay mineralogy with a dominance of chlorite, illite, and kaolinite, whereas major non-clay minerals are predominantly albite, calcite, and quartz.