Pemanfaatan bagas dan daduk tebu untuk perbaikan status bahan organik tanah dan produksi tebu di Lampung Utara: pengukuran dan estimasi simulasi WanNulCAS

Sugarcane yields tend to drop rapidly along with soil fertility level on ultisols recently cleared from forest conversion if there is no fertilizer input. Ultisols in N. Lampung typically have a low content of soil organic matter (SOM), N, P, exchangeable cations and a high concentration of Al and Mn. Maintaining a high SOM content is considered to be one of the key factors in sustainable crop production, but availability of organic materials in the field is very limited and transferring organic materials from other places to the plot is too expensive for small farmers. One possibility to solve this problem is to return the sugarcane akibat dari usaha pengelolaan BO harvest residue (trash) to the soil in stead of burning it after harvest. Another potential source is Bagas (sugarcane processing waste) normally piled up around the sugarcane factory with a high risk of fire. A field experiment was carried out in 1998-2000 in the area of sugarcane plantation PTPN V Bunga Mayang, North Lampung. The following applications of organic materials were tested on a soil that had been cropped for more than 10 years after forest conversion: (1) Without organic materials as a control, (2) Bagas 8 Mg ha-1, (3) Bagas 16 Mg ha-1, (4) Sugarcane trash (harvest residue) 8 Mg ha-1. The treatments were arranged in a randomized block design (RBD) with four replicates. A mixed legume cover crops (LCC) Mucuna pruriens var. utilis and Centrosema pubescens (1:1) was planted in the first year, followed by sugarcane for another 2 years. Aim of this experiment is to study the impact of applying organic inputs on the SOM, N, P contents, biomass of LCC and subsequent yield sugarcane. Application of bagas to the top soil (0-5 cm) lead to an immobilization of N at 8 months after the start, but not for sugarcane trash application. At 5 months after applying trash to the soil, the highest net N mineralization was obtained but it declined for the next measurement. In the soil layer at 5-15 cm depth, however, application of all sugarcane residues to the soil increased mineral N content at 3 months after the start. No significant effect of application of sugarcane residues was observed on the SOM content, pH and available P level (P-Bray2). Application of sugarcane residues had no significant effect on Mucuna biomass production, but significantly (p

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