Fractionation of Phosphorus in Soil Profiles of Forest, Agroforestry, and Dryland in West Java

Abstract

ABSTRAK Penelitian ini bertujuan untuk mengevaluasi distribusi fraksi-fraksi fosfor (P) pada horison-horison atau profil tanah hutan, wanatani, dan tegalan di Jawa Barat, serta korelasinya dengan sifat-sifat kimia tanah. Evaluasi didasarkan atas hasil analisis contoh tanah yang diambil pada empat horison tanah (Ao atau Ap, A1 atau A2, B1, dan B2) di setiap tipe penggunaan lahan. Fraksionasi P tanah dilakukan menggunakan metode ekstraksi sekuensial untuk memperoleh fraksi-fraksi P-cepat tersedia (NaHCO3-P-inorganik (i)-P-organik (o)), P-agak tersedia (NaOH-Pi-Po), P-lambat tersedia (HCl-Pi), P-tidak tersedia (P-residual), dan P-total (HCl25%-P). Hasil penelitian menunjukkan bahwa rerata konsentrasi fraksi residual-P di ketiga tipe penggunaan lahan mencapai >99% dari total-P. Konsentrasi fraksi residual-P tertinggi terukur pada lahan tegalan, diikuti hutan dan wanatani. Hal ini mengindikasikan bahwa kapasitas jerapan P tanah sangat tinggi sehingga konsentrasi fraksi P-tersedia sangat rendah. Konsentrasi fraksi residual-P dan total-P tanah yang tinggi sangat mungkin berkaitan dengan aplikasi pemupukan P, khususnya di lahan tegalan. Distribusi fraksi-fraksi P pada horison-horison tanah di ketiga tipe penggunaan lahan berkorelasi nyata dengan konsentrasi bahan organik tanah. Oleh karena itu, konsentrasi fraksi NaHCO3-Po menurun dengan kedalaman tanah. Konsentrasi tertinggi dijumpai pada horison Ao atau Ap, meskipun tidak demikian halnya dengan fraksi NaOH-Po yang relatif konstan. Kata kunci: ekstraksi sekuensial, horison tanah, korelasi, penggunaan lahan ABSTRACT This study aims to evaluate the distribution of phosphorus (P) fractions within the soil horizons or profile of forest, agroforestry, and dryland in West Java and their correlations with soil chemical properties. Evaluation was based on the analytical results of soil samples taken from four soil horizons (Ao or Ap, A1 or A2, B1, and, B2) in each land use types. Fractionation of soil P was carried out using a sequential extraction method to get readily available-P (NaHCO3-P-inorganic (i)-P-organic (o)), rather available-P (NaOH-Pi-Po), slowly available-P (HCl-Pi), not available-P (residual-P), and total-P (HCl25%-P) fractions. The results showed that the average concentration of soil residual-P fraction in all land use types reached >99% of the total-P. The highest average concentration of residual-P fraction was measured in dryland, followed by forest and agroforestry. This indicated that soil P adsorption capacity was very high and resulted in a very low concentrations of the soil available-P fractions. The high concentrations of soil residual-P and total-P fractions were most probably related to P fertilizer application, particularly in dryland soil. Distributions of P fractions within the soil horizons at all land use types were significantly correlated with the concentration of soil organic matter content. It is therefore the concentration of soil NaOH-Po fraction was decreasing with the soil depths. The highest concentration was found at Ao or Ap horizon, although it was not the case for NaOH-Po fractions that was relatively constant.