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Es sabido que la soja intersembrada en trigo tiene bajo crecimiento inicial, lo cual podría afectar negativamente la formación de nódulos fijadores de nitrógeno (N) y limitar el crecimiento de la soja luego de la cosecha del trigo. En este trabajo se propuso: (i) corroborar si soja intersembrada en trigo tiene respuesta a la fertilización nitrogenada y (ii) evaluar la dosis de N óptima de una soja intersembrada. Se condujeron dos experimentos de soja intersembrada en trigo bajo riego en Balcarce, con tratamientos de niveles de fertilización nitrogenada. En el primer año los niveles de fertilización fueron cero y una dosis equivalente a los requerimientos de N del cultivo (530 kg N ha-1). En el segundo año se evaluaron cuatro niveles de fertilización calculados como una proporción de la dosis de indiferencia (204 kg N ha-1): 0, 51, 102 y 204 kg N ha-1. A la madurez del cultivo de soja, se midió rendimiento, índice de cosecha, peso/grano, peso seco total y número de granos m-2. Los resultados obtenidos muestran que existieron respuestas significativas de la soja a la fertilización nitrogenada. Bajas dosis de N (equivalentes a 1/4 de la dosis de indiferencia) fueron suficientes para maximizar el rendimiento. Ambos experimentos confirman que el aumento de rendimiento a causa del N aplicado generó un incremento en el aporte de biomasa al sistema.

In Argentina, wheat (Triticum aestivum L.) is cropped over a wide range of climatic conditions. Considerable variability in the ratio of dry weight produced per unit of transpired water, usually referred to as water-use efficiency (WUE), is expected as variation in climatic factors affects photosynthesis and transpiration in different ways. Also, previous studies have shown that water supply limitations may affect WUE in wheat. The objective of this study was to quantify the effects of climatic environment and water availability on WUE in wheat crops. Six experiments were conducted at different locations of the Argentine wheat belt and crop dry weight and water use were measured in periods when water use was dominated by transpiration. Three of the experiments included both irrigated and rainfed treatments. Mean daily values of (i) pan evaporation, (ii) relative humidity, (iii) potential water use, and (iv) vapor pressure deficit, were used to find a general relationship that explained effects of the climatic environment on WUE. For experiments with high water availability, daytime vapor pressure deficit was better related to WUE than the other climatic factors. WUE was greater for experiments with water limitation, probably because stomatal closure to restrict transpiration rate occurred around midday when vapor pressure deficit was highest. As a consequence, relative dry weight under water limitation was not linearly related to relative water use as proposed in previous studies. A quadratic relationship that better represented this response was derived., WATER SUPPLY is often the most critical factor limiting crop growth and yield in rainfed areas and the most expensive input of irrigated crops. Therefore, crop production usually requires maximizing [...]

This study analyzes differences in potential yield among six semidwarf awned spring bread wheat (Triticum aestivum L.) cultivars recently selected in Argentina. Yield was considered as the product of number of grain per square meter (NG) and weight per grain. The NG was analyzed in terms of (i) duration of the inflorescence growth period (excluding grains), (ii) crop growth rate during that period, (iii) partitioning of crop dry matter to spikes during the same period, and (iv) grain/spike weight ratio (i.e., number of grains per gram of spike). The data were obtained from two field experiments in the Province of Buenos Aires. Grain yield (range: 453-689 g [m.sup.-2]) was related more to NG (range: 13.3-21.3 x [10.sup.3] grain m z) than to weight per grain. Duration of spike growth period was the same (27 d) for all cultivars. During this period, intercepted photosynthetically active radiation, radiation-use efficiency (mean: 2.7 ± 0.28 g [MJ.sup.-1]), and crop growth rate (mean: 26 ± 2.5 g [m.sup.-2] [d.sup.-1]) were similar for all the cultivars examined. Differences among cultivars in partitioning to spikes (ranges: 28-34%) were significant. The NG, however, was not related to partitioning to the spike. There were clear differences among cultivars in the grain/spike weight ratio (range: 61-106 grain [g.sup.-1]); NG was more closely related to this ratio (r = 0.96, P [is less than] 0.01) than to dry weight of spikes at the end of their growth period (r = -0.30). Increments in potential yield by means of high grain/spike weight ratio were not previously reported and may be a path to future potential yield improvements., IN ARGENTINA, genetic selection has increased potential yield in wheat, mainly by reducing lodging and increasing the harvest index, with only small changes in total dry weight of the crop [...]