Interactive effects of weeding regimes and seed shapes on growth, yield and nutrient compononents of SC701 green mealies during summer and winter planting seasons under rain-fed condition.

Abstract

Maize and weeds interfere with growth activities of each other to a varying degree. Weeds compete for water, mineral nutrients, and light and hinder harvest operations. Maize plants are susceptible to weed competition and yield losses are estimated at 30% to complete crop failure. Seed shape and size can also be an important factor to consider for improving maize yield because it influences seedling vigour. The aim of this study was to evaluate the interactive effect of seed shape and size of SC701 maize hybrid on seed quality. Thereafter, the effect of seed shape and weed competition on yield of SC701 was evaluated in field trials planted during summer and winter, in KwaZulu-Natal. Germination test was carried out on SC701 differentiated on the basis of seed shape, (round and flat), and seed size (large and small). Seeds were germinated using four different temperature regimes: constant 20°C and 30°C as well as two alternating temperature regimes, 15/20°C and 20/30°C (12/12 hrs.). The experiment was laid out as a split-plot design with temperature being the main factor; variety was sub factor with four replications. Upon termination of the experiment, germination rate (GR), mean germination time (MGT), germination velocity index (GVI), vigour index (VI), seedling shoot and root lengths, seedling fresh and dry mass and seedling shoot: root ratio were determined. Field trials were used to evaluate the interactive effect of seed shape and weeding on SC701 harvested as green mealies during summer and winter seasons under rainfed conditions at Ukulinga and Umbumbulu in KwaZulu-Natal. At harvest, nutritional quality of the green mealies was determined. Results of seed quality showed no significant differences in final germination and MGT among seed sizes and shapes at different temperature regimes. Highly significant differences (P<0.001) were observed for daily germination, GR, GVI and VI. Results of daily germination, GR, and GVI showed that flat seeds germinated faster than round seeds at constant temperatures while in terms of seed size, small seeds germinated faster than large seeds. A similar trend was observed for VI. Alternating temperatures (20/30°C) produced higher VI when compared with constant temperatures for all varieties. Results from the field trials showed that emergence was faster during summer than during winter season. Flat seeds emerged better by 1.4% than round seeds. Maize plants were taller (P<0.001) in summer than in winter. Double weeding had the tallest (P<0.05) plants for both seasons. Double weeding had the highest leaf number followed by single weeding while no weeding had the lowest leaf number for both seasons. Weeding treatments had a significant (P<0.05) effect on days to tasseling (DTT) during both seasons and at both sites. Days to tasseling was faster by 29.1% during summer than winter while DTT in no weeding were 15.38% and 10.45% longer than DTT in double weeding during summer and winter respectively. Stomatal conductance (SC) and chlorophyll content index (CCI) were significantly higher (P<0.001) during the summer than winter season. Weeding frequencies had a significant (P<0.05) effect on harvest index, total biomass, ear prolificacy, kernel rows per cob, kernels per row and cob mass. Weeding frequency was shown to have an effect on nutritional quality of green mealies as indicated by results of total soluble sugars, starch and protein content; they were low with decreasing weeding frequency. Proline accumulation was highest in the no weeding treatment indicating the crop was stressed. It is concluded that although, standard germination test values showed that flat small seeds germinated faster at constant than alternating temperatures, this did not translate to better field emergence. In the field, seed shape of SC701 had no influence on improving crop vigour and ability to compete with weeds. Furthermore, the present study showed that season plays an important role in growth and development of green mealies in that winter planting of maize resulted in low yield production. Further research on the effect of weed competition on growth, yield and nutritional value of SC701 conducted under irrigated conditions during winter planting season for green mealies production is therefore recommended.