Current nitrogen (N) fertilization schedule for spring wheat was developed under a dominant crop-pasture rotation. After the year 2002, this cropping system was converted to continuous annual cropping systems under no-till, reducing soil N supply capacity progressively. Additionally, highest grain yield of new varieties increased N demand. The required additional N fertilizer can be adjusted by monitoring nutritional status of the crop. Our objectives were: i) to determine optimal N status at different phenological stages; ii) to quantify the wheat yield gap explained by N supply deficit, and iii) to assess the critical nitrogen nutrition index (NNI) value as a predictor of response to N fertilizer applied at GS 3.3. We adjusted the nitrogen dilution curve (Nc=4.17DM-0.31), deriving a critical NNI at GS 3.3 (NNI=1.24). Depending on soil N supply capacity and NNI at GS 3.3, wheat yield gap attributed to N supply deficit varied from 0 to 2.74 Mg ha-1, averaging 0.76 Mg ha-1. The critical NNI proposed at GS 3.3 was effective to diagnose the N crop demand to reach the attainable yield under different scenarios.
Forty-six malting barley genotypes, including five commercial varieties, were evaluated in two years in order to characterize the genetic variability in breeding use in Uruguay, and its potential to over yield the varieties currently in use. The two analyzed years presented highly contrasting climatic characteristics. The genotypes were grouped according to their relative performance in the two years for a group of fourteen agronomic and grain quality traits. A cluster analysis was carried out, and the traits responsible for each cluster separation, were studied. The checks showed the ability to maintain a good grain yield and quality level in stressing climatic conditions. In the high yield year, several introduced genotypes exceeded the best checks, but they failed to maintain that superior performance in stressing climatic conditions. This performance was associated to longer cycles to anthesis and shorter grain-filling periods, which hinder the adaptation to national conditions. The use of introduced germplasm resulted in an inefficient way of reaching high yield potentials with high and stable grain quality.
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