Effects of soil aggregate size on phosphorus extractability and uptake by rice (Oryza sativa L.) and corn (Zea mays L.) in two Ultisols from the Philippines(Soil Fertility)

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A number of recent studies suggest that soil aggregation may affect short- and long-term phosphorus (P) availability in highly weathered soils. We investigated the effect of natural soil aggregate sizes (from <0.212 to 4-5.6mm) on P extractability and plant P availability in low-P and high-P Siniloan soils (Typic Palehumults) from Laguna, Philippines. Mehlich-1 extractable P was always greatest in the smallest aggregates, regardless of whether or not it was extracted without P addition or extracted after 15 days incubation with newly applied P in both intact and ground aggregates. Grinding significantly increased the initial extracted P only in high-P soil. Soil aggregate size had little effect on the extractability of newly added P because the short-term Mehlich-1 P buffering coefficient (PBC), a change in Mehlich-1 extracted P (mg kg^<-1> soil) per unit of added fertilizer P (mg kg^<-1> soil), was not significantly correlated with aggregate size. In the greenhouse experiment, plant growth (shoot dry weight, root length and dry weight) and total P in the shoots of both corn (Zea mays L.) and rice (Oryza sativa L.) were markedly increased with decreasing aggregate diameters from 4-5.6mm to <0.212mm, even when the plant had adequate P in the rice experiment in the high-P soil. There was no interaction between P supply and aggregate size on the plant growth response and P uptake in both rice and corn grown in the two soils, suggesting that the effect of soil aggregation on plant P availability of newly added P was small. Although, the smaller aggregates themselves also contained higher total P, finer and longer root growth in these aggregates as a direct effect of aggregate size on root growth mainly contributed to better plant growth and P uptake in these aggregates. The findings of this study suggest that in Siniloan soil, soil aggregation had little effect on short-term PBC and plant P availability of the P newly added to soil over 5 weeks. However, in high-P soil, the current soil test procedures, which require grinding and shaking of soil sample, might overestimate the available P status of the soil.
社団法人日本土壌肥料学会の論文

Effects of soil aggregate size on phosphorus extractability and uptake by rice (Oryza sativa L.) and corn (Zea mays L.) in two Ultisols from the Philippines(Soil Fertility)

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