Evaluation And Analysis Of Competitive Ability Of Maize Cultivars

Competition is a common phenomenon in agriculture. In this study, three maize hybrids, ZD2(1970s), YD 13(1990s) and ZD909(2010s) which differed in the time of release were used as materials, with the reference to the research idea of competition in ecology, de Wit replacement series experiment was used, we studied whether maize hybrids differed in competitive ability and discussed the suitability of competitive indices for evaluating the competitiveness of maize hybrids; analyzed the change trend of competitiveness of maize hybrids in the process of yield improvement; we identified the effect of plant density and nitrogen rate on the competitive ability of maize hybrids. This study was conducted at the Gongzhuling Experimental Station of the Chinese Academy of Agricultural Science during 2012,2013 and 2014 growing seasons, The main results are as follows:(1) In the replacement series of YD 13 and ZD909, the single plant grain yield and biomass yield of YD13 and ZD909 both decreased with the increasing proportion of YD13,. Through the analysis of the competitiveness by using competitive indices, YD 13 was more competitive than ZD909, indicating that maize hybrids differed in competitive ability. Through the analysis of competitive indices, because of agressivity (AG) and competitive ratio (CR) were stable among different mixed ratios in the replacement series experiment of mazie hybrids, so these two indices were more suitbale for evalutating the competitive ability of maize hybrids(2) For the three maize hybrids, ZD2, YD13 and ZD909, in each replacement series, the single plant and population level grian yield were both decreased with the increasing proportion of the older cultivars. Through the analysis of agressivity (AG) and competitive outcome, the ranking of competitiveness was:ZD2> YD13> ZD909. The result indicated that the competitiveness of mazie hybrids was decreased in the process of yield improvement, the modern high yield maize hybrid was a weak competitor, however, the decreased competitiveness of maize cultivars was not in a straight line.(3) In each replacement series, the populaiton competitive pressure was increased as the proportion of the older cultivar increased. Through the related analysis, popualiton level biomass yield, grain yield and harvest index were all significantly decreased with the increasing proportion of population competitive pressure; thousand kernel weight and kernel number per plant were also decreased with the increasing proportion of population competitive pressure, but the correlated coefficients were not significant. The results indicated that there is a negative correlation between population level yield and population competitive pressure. In addition, population competitive pressure (PCP) was intrdoduced as a new index to measure the competitive ability of maize populaiton in a replacement series.(4) Plant density and nitrogen rate affect the competitive ability of maize hybrids, but it didn’t change competitive hierarchies of cultivars. Under the same population density, the competitive ability of YD 13 relative to ZD909 was increased under the condition of without nitrogen fertilization. However, with the increament of population density the competitiveness of YD 13 realtive to ZD909 was reduced under the same nitrogen rate. This is due mainly to the lower density tolerance of YD 13, comparing with ZD909. a higher plant density restricted the competitiveness of YD 13 raltive to ZD909. But nitrogen and plant density did not change the outcome that the competitivenenss of YD 13 was more competititive than ZD909.(5)The intra-cultivar competition of each cultivar was increased with the increasing population density. Under the same higher population density, the modern maize hybrid ZD909 has a lower competition intensity (CI) and absolute severity of competition (ASC) than YD 13 and ZD2, the CI and ASC of YD13 was also lower than ZD2. However, the relative reproductive efficiency was:ZD909> YD13> ZD2. The ranking of the maximum yield of the three maize hybrids was:ZD909> YD 13> ZD2, the ranking of density tolerance of cultivars showed similar trends. The results indicated that the improvement of density tolerance of modern maize cultivars was related to their decreased competitive ability, the modern maize hybrids decreased the competition among individuals in population, and increased the reproductive growth of population.The research proved that maize hybrids differed in competitiveness and modern high yield hybrds is weak competitor by reference to competitive theory and method in plant ecology. These results will provide a new thought for innovation of breeding materials and crop cultivation, and it also will give some references to the research of some other crops.