RESUMO
Sowing density is one of the most influential factors affecting corn yield. Here, we tested the hypothesis that, according to soil attributes, maximum corn productivity can be attained by varying the seed population. Specifically, our objectives were to identify the soil attributes that affect grain yield, in order to generate a model to define the optimum sowing rate as a function of the attributes identified, and determine which vegetative growth indices can be used to predict yield most accurately. The experiment was conducted in Chapadão do Céu-GO in 2018 and 2019 at two different locations. Corn was sown as the second crop after the soybean harvest. The hybrids used were AG 8700 PRO3 and FS 401 PW, which have similar characteristics and an average 135-day cropping cycle. Tested sowing rates were 50, 55, 60, and 65 thousand seeds ha-1. Soil attributes evaluated included pH, calcium, magnesium, phosphorus, potassium, organic matter, clay content, cation exchange capacity, and base saturation. Additionally, we measured the correlation between the different vegetative growth indices and yield. Linear correlations were obtained through Pearson's correlation network, followed by path analysis for the selection of cause and effect variables, which formed the decision trees to estimate yield and seeding density. Magnesium and apparent electrical conductivity (ECa) were the most important soil attributes for determining sowing density. Thus, the plant population should be 56,000 plants ha-1 to attain maximum yield at ECa values > 7.44 mS m-1. In addition, the plant population should be 64,800 plants ha-1 at values < 7.44 mS m-1 when magnesium levels are greater than 0.13 g kg-1, and 57,210 plants ha-1 when magnesium content is lower. Trial validation showed that the decision tree effectively predicted optimum plant population under the local experimental conditions, where yield did not significantly differ among populations.
RESUMO
RESUMO: A utilização de bioestimulantes pode auxiliar a mitigar os prejuízos ao milho, ocasionados pela má qualidade de estande. Este trabalho foi conduzido objetivando avaliar o efeito do tratamento de sementes com bioestimulante sobre o desempenho agronômico do milho, submetido a diferentes níveis de variabilidade na distribuição espacial das plantas na linha de semeadura. O experimento foi implantado em Lages, SC, durante o ano agrícola de 2013/2014. O delineamento experimental foi de blocos ao acaso, dispostos em parcelas subdivididas. Nas parcelas principais, testaram-se três níveis de desuniformidade espacial na linha: 0, 50 e 100% do Coeficiente de Variação (CV). No nível 0 % de CV, todas as sementes foram uniformemente distribuídas no sulco de semeadura, a uma distância de 17cm entre si. Nos demais níveis de CV, as distâncias entre sementes variaram conforme o tratamento. Nas subparcelas, testou-se a presença ou ausência do tratamento de sementes com bioestimulante. O aumento da variabilidade na distribuição espacial das plantas reduziu a área foliar e o teor de clorofila da folha índice no espigamento, bem como o diâmetro do colmo na colheita, independentemente do tratamento de sementes com bioestimulante. Isso contribuiu para reduzir o número de grãos por espiga e o rendimento de grãos dos tratamentos com 50 e 100% de CV na variabilidade espacial, tanto na presença quanto na ausência do bioestimulante. Portanto, o tratamento de sementes com bioestimulante não mitigou os prejuízos ao rendimento de grãos do milho ocasionados pela distribuição espacial irregular das plantas na linha de semeadura.
ABSTRACT: The use of biostimulants may help to mitigate damages to maize caused by poor stand quality. This research was carried out aiming to evaluate the effect of seed treatment with biostimulant on the agronomic performance of maize submitted to different levels of plant spatial distribution at the sowing row. The experiment was set in Lages, SC, during the 2013/2014 growing season. A randomized block design disposed in split plots was used. Three levels of plant spatial unevenness at the sowing row were tested in the main plots: 0, 50 and 100% of the variation coefficient (CV). At the level 0% of CV all seeds were evenly distributed with a distance of 17cm from each other. At the other levels of CV, the distance between seeds varied according to the treatment. The presence or absence of seed treatment with biostimulant was assessed in the split plots. The increase in plant spatial distribution variability at the sowing row decreased leaf area and leaf chlorophyll content at silking, as well as stem diameter at harvest, regardless of seed treatment with biostimulant. Such behavior contributed to decrease the number of kernels per ear and grain yield of treatments with 50 and 100% C.V. of spatial variability, with and without biostimulant seed treatment. Therefore, seed treatment with biostimulant did not mitigate damages to maize grain yield caused by irregular spatial plant distribution at sowing row.
