Organic Mulch Decomposition Kinetics in Semiarid Environment at Bare and Crop Field Conditions

Abstract

Scantly available knowledge of organic mulch decomposition kinetics is important to determine the best choice of mulching materials, and their application rate and frequency for crop production and soil protection in arid area. The kinetics was studied in two field experiments. In Experiment I, it was tested for sugarcane trash mulch (6 Mg ha-1) with and without enriching it with Mussoorie rock phosphate (MRP) at 600 kg ha-1 (obtained from M/s pyrites, Phosphates and Chemicals Ltd., Dehradun, India) and with industrial glue waste (GW) at 4 Mg ha-1, a solid granular waste material of subcutaneous animal origin, rich in N (obtained from Glue Industry, Juglan, Haryana, India) at ratoon sugarcane (Saccharum officinarum) on fine loamy soil for two years (1997-1998 and 1998-1999) at Hisar (29°058N, 75°388E, 222 m elevation). The GW and MRP were manually broadcast over the sugarcane trash mulch at the time of mulch application. Experiment II was conducted from December 1998 to April 1999 on sandy soil at Balsamand (29°078N, 75°288E, 225 m elevation), 35 km west of Hisar, at bare field conditions wherein three different types of mulches were tested: farmyard manure (FM), green neem (Azadiracta indica) leaves GM, and wheat straw (Triticum aestivum) (WM), with two mulch thicknesses (20 and 40 mm). Wheat straw mulch (WM) placed at surface was compared with wheat straw mixed into 0.0-0. 10 m soil depth (W-mixed) for decomposition kinetics. The loss in dry weight of mulches was taken as a measure for mulch decomposition as a function of time (t). First-order decomposition kinetics was followed in all the treatments at varying field moisture conditions in Experi ments I and II. T he decomposition percentage in 4 months (d4) was 40 % higher at enriched sugarcane trash (ESM) than that at sugarcane trash mulch (SM). It was higher at 20 mm mulch thickness than at 40 mm for all the types of mulch in Experiment II and followed the order GMg WMg FM. The d4 value of W-Mixed was two times higher than that of wheat straw mulch W M at 20 mm mulch thickness. Mulch decomposition rate constant k was 0.0071 d-1 for SM and 0.0115 d-1 for ESM averaged over the two years. The k values were 0.0021 d-1, 0.0032 d-1, and 0.0037 d-1 for FM, WM, and GM respectively at 20 mm mulch thickness and it was 0.0066 d-1 for W-mixed in Experiment II. The practical implications were: (a) enriched dry mulch should be preferred over dry mulch for annual crops in order to enhance their nutrient recycling and decomposition, and (b) dry mulch should be preferred over green mulch in the perennial fruit trees for their long persistence and durability in order to protect soils against wind erosion in arid areas.