Application of a universal soil extractant for determining the available NPK: A case study of crop planting zones in central China.

Being important parameters of crop growth the precise measurements of available nitrogen (N), phosphorus (P) and potassium (K) on site not only help the farmer to control his budget but also helps to keep the environmental pollution under control. Currently, the existing extractant cannot be applied to rapidly determine the concentrations of available NPK by soil chemical analysis methods, simultaneously. In the present paper, a universal extraction reagent consisting of 0.45 M NaHCO3 and 0.374 M Na2SO4 buffered at pH 8.5 in association with a portable multi-channel photoelectric system has been proposed. The present method provides the most useful indication for the rapid determination of available NPK concentrations in neutral and calcareous soil in field. A large number of soil samples were collected from crop planting zones in Henan province of central China for evaluating the effectiveness of this universal extractant. A portable multi-channel photoelectric system associated with this universal soil extractant was exclusively designed to provide reliable and reproducible available NPK concentrations in soil extracts. The experimental results showed that available NPK concentrations determined by this method are highly correlated with the laboratory-based methods. A '3414' fertilizer scheme was applied to optimize the fertilizer recommendation for achieving the high targeted yield. The recommendation fertilizer system worked with a high correlation coefficient and fertilizer utilization rate has been established by this '3414' fertilizer scheme. With advantage of portability, accuracy and low cost, the proposed method can help to cut down the economic burden of the farmer and also it helps to optimize the utilization of the fertilizers by limiting its excessive usage and hence control the environmental pollution.