Brazil is one of the most important soybean producers in the world. Soybean is a very important crop for the country as it is used for several purposes, from food to biodiesel production. The levels of soybean yield in the different growing regions of the country vary substantially, which results in yield gaps of considerable magnitude. The present study aimed to investigate the soybean yield gaps in Brazil, their magnitude and causes, as well as possible solutions for a more sustainable production. The concepts of yield gaps were reviewed and their values for the soybean crop determined in 15 locations across Brazil. Yield gaps were determined using potential and attainable yields, estimated by a crop simulation model for the main maturity groups of each region, as well as the average actual famers' yield, obtained from national surveys provided by the Brazilian Government for a period of 32 years . The results showed that the main part of the yield gap was caused by water deficit, followed by sub-optimal crop management. The highest yield gaps caused by water deficit were observed mainly in the south of Brazil, with gaps higher than 1600 kg/ha, whereas the lowest were observed in Tapurah, Jataí, Santana do Araguaia and Uberaba, between 500 and 1050 kg/ha. The yield gaps caused by crop management were mainly concentrated in South-central Brazil. In the soybean locations in the mid-west, north and northeast regions, the yield gap caused by crop management was <500 kg/ha. When evaluating the integrated effects of water deficit and crop management on soybean yield gaps, special attention should be given to Southern Brazil, which has total yield gaps >2000 kg/ha. For reducing the present soybean yield gaps observed in Brazil, several solutions should be adopted by growers, which can be summarized as irrigation, crop rotation and precision agriculture. Improved dissemination of agricultural knowledge and the use of crop simulation models as a tool for improving crop management could further contribute to reduce the Brazilian soybean yield gap.

O trabalho foi conduzido em Piracicaba, SP, com o objetivo de avaliar o desenvolvimento de três cultivares de soja cultivados em épocas de semeadura normal e tardia, em cinco densidades de plantio. Foram utilizados os cultivares de soja IAC-17, IAC-12 e IAC-19 com ciclos de maturação precoce, semi precoce e médio, respectivamente, conduzidos no espaçamento de 0,50 m e nas densidades de 10, 15, 20, 25 e 30 plantas.m-1. Adotou-se o delineamento em blocos ao acaso com 15 tratamentos (3 cultivares x 5 densidades), repetidos três vezes. Cada parcela foi composta por 5 linhas com 5 metros, onde foram avaliadas as seguintes características: altura final de planta, diâmetro da haste principal, número de nós e número de ramificações por planta. As conclusões foram: a) a redução no ciclo dos cultivares com o atraso da época de semeadura, ocorreu principalmente na fase reprodutiva; b) independente da época de semeadura, quanto maior a densidade de plantas na linha, maior a altura final de planta, menor o diâmetro da haste principal e menor o número de ramificações por planta e c) com o atraso da época de semeadura ocorreu diminuição no número de nós.

SummaryOil and protein are the most valuable components of soybean seed. Evidence indicates that growth and composition of soybean seed are controlled by supplies of carbon and nitrogen provided by the maternal plant to the seed, but it is difficult experimentally to control and quantify the precise amount of carbon and nitrogen provided to the seed by the whole plant. To examine whether oil and protein concentrations are affected by the supply of nitrogen to the seed, immature soybean seeds (Glycine max cv. Williams 82) were grown in vitro in nutrient solutions containing 20, 40, 60 or 80 mM of glutamine. The seeds were incubated in Erlenmeyer flasks for 8 days at 25°C. The rate of dry matter accumulation changed from 7.2 to 8.3 mg seed−1 day−1 as the glutamine concentration increased from 20 to 80 mM but the differences were not significant (P 0.05). Seed protein concentration increased as glutamine concentration increased from 294 mg g−1 at 20 mM glutamine to as high as 445 mg g−1 at 80 mM glutamine. Typical in vivo protein concentration of mature soybean seeds is about 400 mg g−1. Oil and protein concentrations were negatively correlated (r2= 0.44), which indicates that oil and protein synthesis are interrelated. Protein synthesis was favoured over oil synthesis when nitrogen became more abundant. The seeds used in this study clearly demonstrated a capacity to respond to nitrogen availability with changes in seed protein concentration.

Much of the economic value of soybean (Glycine max) is based on the amount of protein and oil produced in the seeds. To examine the influence of temperature on seed oil and protein concentration, immature soybean seeds (cv. Williams 82) were grown in vitro at temperatures of 17°C, 21°C, 25°C, 29°C and 33°C. Dry growth rate (DGR) was calculated to be maximal at 23.7°C. Oil and protein concentration and seed growth rate did not show statistical difference (P > 0.05) within the temperature range from 21-29°C. Across all temperatures, however, a quadratic regression on oil concentration (R 2 = 0.66) showed a minimum at 24.1°C and a quadratic regression on protein concentration (R 2 = 0.59) showed a minimum at 24.3°C. Dilution by increased dry matter accumulation in the seed accounted for much of the variation in oil and protein concentration and the two concentrations were equally affected across temperatures. Consequently, oil and protein concentrations were positively related over the tested range of temperature. It was concluded that under these conditions the rate of dry matter accumulation by soybean seeds was critical in influencing seed oil and protein concentrations.

ABSTRACT:With the purpose to evaluate the effect of short (12 hours) and long (13 and 14 hours) photoperiods and air temperature regimes (winter and summer growing seasons) on soybean behaviour, greenhouse experiments were installed at the Federal University of Viçosa, Brasil, from June 1984 to December 1985. In each experiment, under a completely randomized design with 12 treatments (soybean cultivars) and eight replicates: duration of vegetative period from emergency to stage Rl or flowering (DVP, in days); plant height (PH, m); number of nodes per plant at stage Rl (NNP); and duration of soybean cycle from emergency to stage R7 or physiological maturity point (DC, days), were evaluated. The results permit to conclude that: the vegetative period from emergency to flowering and the juvenile period are significantly affected by the photoperiod and temperature differences; shorter photoperiods or higher temperatures anticipate flowering; longer photoperiods under the same temperature regime or higher temperature under the same photoperiod regime result in higher plants. Keywords: phenology, plant height, photoperiodism INFLUÊNCIA DO FOTOPERÍODO E DA TEMPERATURA DO AR NO CRESCIMENTO, FLORAÇÃO E MATURAÇÃO DA SOJA (Glycine max (L.) Merrill)RESUMO: Experimentos em casa-de-vegetacão visando estudar o comportamento de cultivares de soja perante fotoperíodo curto (12 horas) e longo (13 e 14 horas) e na presença de temperaturas variáveis em função de diferentes épocas de semeadura, foram instalados na Universidade Federal de Viçosa, MG, Brasil, durante o período de junho de 1984 a dezembro de 1985. Delineado inteiramente ao acaso, cada experimento contou com doze cultivares de soja repetidos oito vezes por época. Avaliaram-se as seguintes características: duração do subperíodo emergência -inicio do florescimento, altura de planta e número de nós vegetativos formados por planta e duração do subperíodo emergencia -maturidade fisiológica. Concluiu-se que a fase fenológica da soja compreendida entre a emergência e o inicio do florescimento é significativamente influenciada pelas variações do fotoperíodo e da temperatura do ar; fotoperíodo e temperatura interferem com a duração fenológica do período juvenil da soja e acréscimos de fotoperíodo e de temperatura antecipam o florescimento da soja e aumentam a altura de suas plantas. Descritores: fenología, altura de planta, fotoperiodismo