Reproductive growth of maize, sunflower and soybean at different source levels during grain filling

Maize (Zea mays L.), sunflower (Helianthus annus L.) and soybean (Glycine max (L.) Merr.) are sometimes subjected to stress that affects source capacity during the grain filling period. Effects of variations in source capacity during grain filling on yield and its components in these crops were examined with shading and thinning treatments. Shading reduced grain yield in the three crops. Average percent reductions were greatest for sunflower and least for maize. In soybean and sunflower, the number of grains was more affected than weight per grain, whereas the opposite was true in maize. Average grain yield per plant was greatly increased in soybean and sunflower and slightly affected in maize when source per plant was increased by thinning. Grain number was the yield component most affected in soybean and weight per grain in sunflower. Neither treatment affected grain filling rate of maize, whereas shading reduced effective grain filling duration. Contrarily, the source treatments affected the rate of grain filling in sunflower and in soybean. Variations in source capacity during grain filling affected grain quality much more in sunflower and maize than in soybean. In general, thinning treatments resulted in the highest levels of sugars in stems and shading treatments the lowest. Maize would be the crop with the largest capacity to buffer source reductions during grain filling. In conclusion, modification of source capacity during grain filling had more impact on plant yield in sunflower and soybean than in maize and affected grain quality mainly in maize and sunflower.