Interference of Mexican Marlgold (tagetes minuta l) on growth and yield of maize (zea mays l)
Damage caused by weeds and the cost of their control constitute one of the largest losses in production of feed, food and fiber. This study was conducted to determine whether application of recommeded fertilizer rate influence the critical period of competition between Tagetes minuta and maize. Inter and intraspecific competition between the weed and the crop was determined in potted green house, replacement series experiments. The period when competition begins in the field was determined by allowing the weed to grow from crop emergence for varying lengths of time and then kept weed -free till harvesting. Length of required weed-free period for maximum yield was determined by keeping the crop weed-free for varying periods after emergence and then permiting weed growth the rest of the season. Both the weed and crop parameters were measured. The experiment was conducted at the University of Nairobi, Kabete Campus Field Station, on reddish brown Humic Nitosol. In greenhouse experiments increasing maize proportion in pots caused significant reduction in all growth and yield parameters. Plant relative yield (PRY) of maize was less than one under fertilization and no fertilization and decreased as the proportion of T minuta increased in pots, indicating that maize was more affected by interspecific than intraspecific competition. A mixture of maize and T.minuta significantly depressed plant height, irrespective of the proportion of the crop and the weed, below that of a single maize or T minuta plant per pot at both fertilization levels(fertilizer and no fertilizer). Also other parameters such as total, root, stem, and leaf dry weight ratios followed the same trend. The differences in the amount of total dry matter production in experiments(l and2) 'were attributed to differences in leaf area, leave area duration of the canopy and the total amount of solar radiation intercepted. As planting proportion increased the LA was decreased due to competition. All other parameters such as specific leaf weight, leaf area ratio, crop growth rate, relative growth rate and net assimilation rate followed the same trend. In field experiments maintaining maize free of T minuta for the first 30 days of growth during 1996 resulted in significant increase in grain yield relative to full season interference ( P=0.05) at both recommended and zero fertilization. In zero fertilizer application T minuta interference for 50 days or more significantly reduced grain yields. Weed dry matter yields were generally higher in 1996 than 1997. Linear regression predicted a significant maize yield increase of 160 Kg/ha and non-significant yield increase of Q.48 Kg/ha for each week of T minuta weed - free maintenance in 1996 and 1997 respectively. Linear regression predicted significant maize yield reduction of 252.2 Kg/ha and non-significant yield reduction of 40 Kg/ha for each week of T minuta interference in interference in maize with zero fertilizer application was found to be within the 50 days after planting. Uncontrolled Mexican marigold population decreased maize grain yields by 59 and 38% during 1996 and 1997 respectively. On the other hand, under recommended fertilizer application T minuta interference for 60 days or more significantly reduced grain yield Also weed dry matter yields were generally higher in 1996 than in 1997. No significantly yield increases or reductions were obtained in weed-free or weed-interference treatments respectively. Linear regression predicted a significant maize yield increase of 1J 5 and 109.5 Kg/ha for each week of T minuta weed -free maintenance in 1996 and 1997 respectively. Linear regression predicted a significant maize yield reduction of 152 Kg/ha and non-significant yield reduction of 51.1 Kg/ha for each week of T minuta interference in 1996 and 1997 respectively. The critical period of T minuta interference in maize with fertilizer application was found to be within the first 60 days after planting. Uncontrolled Trninuta populations decreased maize grain yield by 38 and 47% during 1996 and 1997 respectively. Maize plants were found to be more competitive during early stages of growth than the weed. Also this studies indicated that application of recommended fertilizer rates reduces competition between Tminuta and maize.