สถานะและโพแทสเซียมบัฟเฟอร์ในดินปลูกยางพาราในภาคใต้ของประเทศไทย

Abstract

The soils in southern Thailand have low content of available K. The availability of soil K depends on the K speciation, K fixation, K release, and soil properties. The objectives of this study were 1) to compare soil K speciation based on its bioavailability (single leaching extraction; SLE) and sequential extraction process (SEP), 2) to assess the K buffer capacity in rubber growing soils, and 3) to investigate the K transformation in soil and soil K translocation in soil to plant. Soil profiles were selected different textural groups as follows; coarse, medium and fine texture. Soil K speciation was investigated by SLE and SEP and correlation with soil properties. K fixation, K release, and soil K transformation after rubber budding grown were evaluated. The results showed that the concentration of soil K speciation was high in fine > medium > coarse soil textural groups. Soil K speciation obtained by SLE and SEP not only exhibited a strong positive correlation with organic matter, cation exchange capacity, and clay particles, but also exhibited a high degree of correlation among themselves. The summation of Exch-K and Car-K was highly correlated with NH4OAc-K (r2=0.94). Moreover, the summation of Oxide-K and OM-K was highly correlated with Fixed-K (r2=0.84), and Res-K was highly correlated with Min-K (r2=0.83). K fixation was highest in fine textural soil. In all textural groups, the buffering coefficient for K (BCK ) was 0.7-0.8. Therefore, 70-80% of K applied were in Sol-K and Exch-K, while 20-30% was fixed in the soil. Rubber plantation soils were low K release potential. Fine soil texture had higher K fixation and release capacity than medium and coarse, respectively. K fertilizer application in soils promoted plant growth, and increased K and N uptake. While, high dosages of K fertilizer application inhibited Ca and Mg uptake in plant. Soil K speciation after rubber budding grown was high in Res-K > Exch-K > Car-K > Oxide-K > OM-K. The concentration of Exch-K and Car-K increased. Therefore, SEP can be used to evaluate availability K as SLE. Rubber plantation in southern Thailand, the combination of K fertilizer and organic fertilizer should be applied for soil K sufficiency level for rubber trees requirement.