Nutrient status of aggregated and homogenized soil samples: implications for soil fertility evaluation
2002
Asio, V.B. | Navarrete, I. | Labra, J.P. | Macalde, S. | Suficiencia, G. (Leyte State Univ., Baybay, Leyte 6521A (Philippines). Dept. of Agronomy and Soil Science)
Soil analysis is the most popular method of soil fertility evaluation in agriculture. But this has been under increasing criticism because of the difficulty of interpreting the results (Landon, 1991) and the usually poor correlations between soil test results and nutrient uptake of many crops. The problem may not lie only in the diversity of extracting solutions and procedures, but may also be due to the use of ground or homogenized soil sample in the analysis. The authors conducted a series of studies using four different soils (1 Andisol, 1 Inceptisol and 2 utisols) from Leyte and Samar [Philippines] wherein the authors compared the nutrient status of homogenized samples and naturally aggregated samples. Results revealed that the two kinds of sample differed in terms of pH, OM, N, P and K as well as clay content. Results also showed that when the outer portion of the aggregates were separated from the inner portion and then analyzed, the two also differed in nutrient status. This observation explains why the ground or homogenized samples were different from the aggregated samples since there is mixing of outer and inner layers in the former. The results imply that the standard practice of homogenizing or grinding soil samples changes the properties of the soil sample making it non-reflective of the actual condition in the field. This is because roots in the soil are in contact with natural aggregates and that the nutrient dynamics in the soil occur normally on surfaces of aggregates. Finally, the results suggests that the long accepted practice of grinding soil samples may not be suitable for soil fertility evaluation purposes
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