Effect of Variable Quality Residue on a Tropical Dryland Rice Soil

ABSTRACT

The experiment was designed to evaluate the effect of the quality of different plant residues (wheat straw, legume herbage, mixed herbage) on the microbial biomass and net nitrogen mineralization in bare plots and those planted to dryland rice. Soil organic C, total N and total P ranged, respectively, from 0.59 to 1.02%, 0.06 to 0.17% and 0.016 to 0.019%. Both fractions of inorganic N were more abundant in bare plots (NH₄-N 7.0-13.3 μg g⁻¹; NO₃-N 1.4-5.1 μg g⁻¹) compared to the vegetated plots (NH₄-N 5.2-9.3 μg g⁻¹; NO₃-N 0.8-4.1 μg g⁻¹), the maximum values being recorded for the legume treatment and minimum for the control plots. The rate of N-mineralization was higher in vegetated plots (4.7-14.8 μg g⁻¹ mo⁻¹) as compared to the bare plots (4.7-13.5 μg g⁻¹ mo⁻¹); the highest rates were recorded for the legume residue treated soils and lowest for the straw treated soil. Microbial biomass C was highest in the straw treatment (393.73-498.43 μg g⁻¹) and lowest in the control soil (250.60-275.63 μg g⁻¹). Plant biomass and grain yield were maximum in legume treated plots (biomass 273-363 g m⁻²; grain 225-285 g m⁻²) and were minimum for control (biomass 182.3-267 g m⁻²; grain 120-177 g m⁻²). Thus, the placement of legume residue substantially increased the nutrient supply rate and the yield of dryland rice.

KEYWORDS:

• Residue placement
• tropical soil
• dryland farming
• soil properties
• microbial biomass
• N-mineralization