Maize Yield Improvement in Argentina (1965-2010). Indirect Effect in Yield Components and Nitrogen Use Efficiency.

The retrospective analysis of the physiological basis of genetic gain in yield may provide an understanding of performance and indicate potential avenues for future increases. The yield gain on a breeding program could be explained by progress in the nitrogen use efficiency (NUE) during the improvement process. The objectives of this work are: a) compare the yield and grain yield components of maize hybrids managed at their selection conditions (SSMH), that represent the period of improvement in Dekalb/Monsanto from 1965-2010 evaluated through different level of nitrogen (N) and b) quantify changes in the efficiency of N uptake (NUpE) and nitrogen internal efficiency (NIE). Irrigated field experiment during the crop season 2010-2011 was conducted in order to measure i) grain yield, kernel number and kernel weight, ii) plant growth rate and kernel set during the grain filling, iii) biomass and harvest index and iv) nitrogen uptake and remobilizations. The experimental design was a split-plot with N treatments (0, 60, 120, 180 and 240 Kg N ha^-1) serving as the main plots arranged in a randomized complete block design. Six hybrids were evaluated in the small plot at their selection plant population allowing compare the yield at their “specific selection management”. Grain yield increased linearly in Argentina during the last 45 years, ranging from 44 kg year^-1 ha^-1 to 96 kg year^-1 ha^-1, according with the nitrogen doses (0 to 240 Kg N ha^-1 respectively). Harvest index increased from 1965 to 2010, but we did not find a relation with the year of hybrids release. The specific selection management increased the biomass production during the last 45 years and the increase in kernel number was the main yield component for the yield gain. The improvement in NUE was associated mainly with a change in NIE than from an increase in NUpE.