Abstract
A study was conducted to compare the economics of four systems of weed management under three irrigation regimes and tillage systems. The effects of weed management system and irrigation regime and their interactions on peas and lettuce yields were investigated. The research project utilized a factorial design with type of weed management system crossed with irrigation regime and tillage system. The four weed management systems were chemical herbicides only, chemical herbicides and mechanical cultivation, mulch control and mechanical cultivation and mechanical cultivation only. The three irrigation regimes were 25% of the crop water requirements, 50% of the crop water requirements and 100% of the crop water requirements. The three tillage systems were chisel ploughing as primary tillage followed by disc harrow as secondary tillage, mouldboard ploughing as primary tillage followed by rotary tiller as secondary tillage and zero tillage. The average pea and lettuce yields for 2 years for each of the four weed management systems at the three irrigation regimes and tillage systems were analysed and reported. Machine and chemical costs were calculated by using current list prices of machinery and actual costs of chemicals. Based on results from field tests, it was found that weed management method affected pea and lettuce yields. Mechanical cultivation between the rows and using plastic mulch to cover the rows gave the highest pea and lettuce yields. Tillage system also affected yields of the two crops. It was found that zero tillage produced higher yields than chisel and mouldboard tillage systems. Percentage increases in yield between 8 and 31% were obtained with zero tillage treatments compared to the other two tillage systems. Irrigation regime significantly affected pea and lettuce yields. The irrigation regime (100% of the plant requirement) produced the highest yields. The results of this analysis showed that mechanical weed control with zero tillage practice was the alternative with the lowest machinery investment and total machinery and labour costs per hectare per year, followed by chisel tillage and finally mouldboard tillage.