Dynamics of residue decomposition and N2 fixation of grain legumes upon sugarcane residue retention as an alternative to burning

Burning of sugarcane residues contributes to air pollution and sugarcane producers have been forced to abandon it. The change from burning to residue retention is likely to alter the cycling of nutrients. Additionally, there is often a time gap of 6–8 months between two different sugarcane cycles during which legumes could be planted. Thus, the objective of this study was to assess the effects of burning, mulching or incorporation of sugarcane residues on residue decomposition and N mineralization (sugarcane residue management period) and subsequently upon ploughing (legume period) on N dynamics, N₂ fixation, development and nutrient yields of groundnut and soybean grown between two sugarcane cycles on a sandy soil in Northeast Thailand.

Soil microbial biomass N increased when sugarcane residues were incorporated instead of burned or surface applied at 14 days after initiation of cane residue management. Thereafter, high net N mineralization was accompanied by a reduction in microbial biomass N, indicating that mineralized N was derived from microbial N turnover. However, upon ploughing after 96 days the different previous sugarcane residue management strategies had no significant (P > 0.05) effect on net mineral N and microbial biomass N during the subsequent legume period. Although, ¹⁵N enrichment in control reference plants and plant N uptake indicated significant N immobilization effects persisting into the legume crop phase, the proportion of N derived from N₂ fixation (%Ndfa) or amount of N₂ fixed were not significantly different between sugarcane residue management treatments. Soybean fixed more N₂ (78%Ndfa, 234 kg N fixed ha⁻¹) than groundnut (67%Ndfa, 170 kg N fixed ha⁻¹) due to its larger N demand and a poorer utilization of soil N (64 kg N ha⁻¹ vs. 85 kg N ha⁻¹). Groundnut led to a positive soil N balance while that of soybean was negative due to its high nitrogen harvest index. Legume residues returned 61 and 146 kg N ha⁻¹ to the soil for soybean and groundnut, respectively, compared to only 34–39 kg N ha⁻¹ by fallow weeds. Sugarcane residue retention improved soil organic carbon and N content. The results suggested that although a change from burning to sugarcane residues retention led to alterations in N cycling and improved soil organic matter it did not significantly affect N₂ fixation due to the uniforming action of ploughing and the extended time gap between sugarcane residue incorporation and legume planting.     

Effects of Butea superba on reproductive systems of rats

The effects of Butea superba on the reproductive system in male Wistar rats were investigated. The animals were fed daily with the powdered crude drug suspended in distilled water by a gastric tube at the dose of 2, 25, 250 and 1250 mg/kg body weight for 8 weeks. Rats fed with 1 ml of distilled water were used as a negative control. The weights of all vital organs in all treated groups were not different from the control. The percentage weight ratios of body weights of seminal vesicles and prostate glands were not different from the control, except that the testis of the group fed with 1250 mg/kg was significantly different from the control and the other treated groups. In addition, the sperm counts in this group showed about 16% more than the control group. Hematology as well as the liver and kidney function of all treated groups showed no difference from the control. B. superba, drug at 250 mg/kg which was 100 times more than the Thai FDA recommended dose for humans appeared to be safe in rats. The crude drug has demonstrated an increase tendency on testis weight and sperm counts in rat. The information from the present study can be used to explain the Thai folklore application of this plant in Thailand.