Increasing P-Availability and P-Uptake Using Sugarcane Filter Cake and Rice Husk Ash to Improve Chinesse Cabbage (Brassica Sp) Growth in Andisol, East Java

The production potential in Andisols is limited by the high P-retention capacity. Farmers commonly use organic matter. Sugarcane filter cake (blothong, Indonesian, SFC) and rice husk ash (RHA) are locally available in Coban Rondo, Malang, East Java and hence potentially used for soil amendment. To study the effects of SFC and RHA on P availability, P uptake and plant growth (Brassica sp.), soil samples were taken from 0-20 cm depth, incubated with SFC (21.37 Mg.ha-1) and RHA (44.64 Mg.ha-1). Total P, P-available, pH, organic carbon, exchangeable cations (K, Na, Ca, Mg), and P retention curve were determined at 0, 15, 30, and 45 days after incubation. Crop parameters (height, number of leaves, total dry weight) and P-uptake were also measured at 2, 4, 6 weeks after planting. The results showed that RHA was more effective than SFC to decrease P retention and increase P availability (120% on RHA; and 78% on SFC). Soils having higher organic matter tended to have higher P availability. As a consequence, RHA and SFC increased P-uptake respectively 3 and 2 times in soil rich in organic matter, and 1.9 and 2.7 times in soil low in organic matter compared to untreated soil. Increasing P-uptake was followed by plant growth improvement. RHA was more effective than SFC in soil rich in organic matter, but not soil low in organic matter.