Sustainable Weed Control and Enhancing Nutrient Use Efficiency in Crops through Brassica ( Brassica compestris L.) Allelopathy

Weed–crop competition and reduced soil fertility are some of the main reasons for decreased crop yields in Pakistan. Allelopathy can be applied to combat the problems of environmental degradation by reducing pesticide use and through reduction of herbicide-resistant weeds. A two-year field experiment (2014–2015) was conducted to assess the impact of incorporation of various levels of brassica residues and brassica water extract on the growth of mung bean and soil attributes. Two brassica water extract levels (10, 20 L/ha) and two residue levels (4, 6 t/ha) were tested, and a treatment with no water extract and residue incorporation was used as the control. The results showed that the water extract and residue incorporation had diverse impacts on soil fertility indices and weed dynamics, where treatment with 6 t/ha had more significant impacts. Compared with the control, reductions of 61% in dry weight of weeds and 52% in weed density were observed. After cropping, improved soil properties in terms of available potassium, available phosphorus, soil organic matter, and total nitrogen were higher in the rhizosphere (0–15 cm) soil after the treatments of residue incorporation, i.e., 59–91%, 62–84%, 29–45%, and 52–65% higher than the control, respectively. Meanwhile, alkaline phosphatase and dehydrogenase concentrations in the rhizosphere soil were 26–41% and 52–74% higher than with the control, respectively. The highest economic return with a high benefit–cost ratio was recorded with residue incorporation. In conclusion, addition of crop residues at 6 t/ha was the most effective and economical treatment with the highest net benefit rate of returns. This approach can provide a potential alternative for implementing sustainable weed control in mung bean with significant improvement in soil properties and can be a part of sustainable and eco-friendly agriculture.