Crescimento, desenvolvimento e produtividade de milho sob restrição de radiação solar

Abstract

Maize is the most cultivated cereal in the world and Brazil is the third largest producer. The crop plays an important socioeconomic role in Brazil and around the world, being used in animal and human food and in the production of bioethanol. With the projected increase in the world population to 9.6 billion people in 2050, cereals also have great importance in food security, being the main grain used in the production of animal feed. Projections of future climate change scenarios estimate a decline in the availability of solar radiation, which could negatively affect maize productivity potential. Therefore, it is necessary to understand at which stage of development the restriction of solar radiation negatively impacts grain productivity to allow the mitigation of its effects, making adaptations in crop management. Thus, the objectives of this study are: 1) to evaluate the growth variables of maize plants most affected by solar radiation restriction; 2) quantify the loss of maize grain productivity due to the restriction of solar radiation on different sowing dates; and 3) determine which stage of maize development presents the greatest loss of productivity due to restriction of solar radiation in a subtropical environment. To meet the objectives, an experiment was carried out in the 2019/19 harvest (Agudo), and the 2020/21 and 2021/22 harvest (Santa Maria). The treatments included a 50% restriction of incident solar radiation: (1) from emergence to the final number of leaves (vegetative); (2) bolting to bubble grain (reproductive); and (3) milky grain until physiological maturity (grain filling). The restriction of solar radiation caused lower accumulation of dry matter (ADM) in maize plants, mainly in the grain filling phase, reducing on average 30%, where the main productivity component affected was the weight of a thousand grains. The penalty in productivity due to the restriction of solar radiation was greatest in the grain filling phase, followed by the reproductive phase, and lastly, the least affected, the vegetative phase, reducing, on average, 4.84, 2.4 and 1 .0 Mg ha-1 , which corresponds to 36%, 18% and 4%, respectively, when compared to the control. The loss per cloudy day was greatest in the grain filling phase (356.4 kg ha-1day-1 ), followed by the reproductive phase (202.7 kg ha-1day-1 ) and vegetative phase (28.1 kg ha-1day-1 ). These results are important to optimize sowing time management and to direct genetic improvement programs in the search for cultivars that are more efficient in the use of solar radiation.