A systematic approach technique has been introduced from Agro Service International (ASI), and further modified and developed to evaluate soil nutrients status in China. The systematic approach consists of 1) soil testing for availability of 11 nutrients by using a multi-elements extraction solution (ASI solution: 0. 25mol/L NaHCO3 -0.01mol/L EDTA-0.01mol/L NH4F); 2) determination of adsorption capacity of the soil for P. K, S, B, Mn, Zn and Cu: and 3) pot experiments to estimate the existing or potentially existing nutrient deficiency; 4) field trials to verify the finding in the laboratory and pot experiments.
The technique has been used for 140 soils taken from 17 provinces of China. Soil testing and pot experiments indicated that, among the 140 soils, the number of soils showed deficient in N, P, K, Zn, S, Cu. B, Mn, Mo, Mg, Ca and Fe were 137, 126, 84, 68, 45, 37, 36, 34, 28. 25, 20, and 17, respectively. By using the Cate-Nelson method, the adequate level of each nutrient under pot culture condition was estimated, which was in good agreement with that recommended by ASI.
Field trials were designed at the sites where soil samples were taken, based on the findings from the laboratory and pot experiments. Critical levels of soil P and K determined by using the ASI multi-nutrients extraction solution, were also estimated by using the Cate-Nelson method, and data from the field trials. The estimated critical level for P and K under field condition were 15mg/L and 90mg/L soil, respectively.
The systematic approach was used in Yutian county of Hebei province in a large scale for soil nutrients status evaluation. Based on the results of the soil testing, adsorption study, pot experiments, field experiments and field demonstration plots, a computer program was developed and used in a large scale for balanced fertilizer recommendation for major crops in the county.