Field experiments were conducted in the major rice growing area of Chile to evaluate the effects of nitrogen (N) fertilization and site on grain yield and some yield components, dry matter production, N uptake, and N use efficiency in rice cultivar 'Diamante'. Two sites (indicated as sites 1 and 2) and six N rates (0, 50, 100, 150, 200, and 300 kg N ha −1 ) were compared. Nitrogen fertilization increased yield, panicle density, spikelet sterility, dry matter production, and N uptake at maturity. 90% of maximum yield was obtained with 200 kg N ha −1 in site 1 (12,810 kg ha −1 ) and with 100 kg N ha −1 in site 2 (8,000 kg ha −1 ). These differences were explained by lower panicle density, and the resulting lower dry matter production and N uptake in site 2. Nitrogen use efficiency for biomass and grain production, and grain yield per unit of grain N decreased with N fertilization. While, agronomic N use efficiency and N harvest index were not affected. All N use efficiency indices were significantly higher in site 1, except grain yield per unit of grain N. The observed variation in N use efficiency indices between sites would reflect site-specific differences in temperature and solar radiation, which in turn, determined yield potentials of each site. On the basis of these results, cultivar 'Diamante' would correspond to a high-N use efficiency genotype for grain yield.

Factors regulating fine-root growth are poorly understood, particularly in fruit tree species. In this context, the effects of N addition on the temporal and spatial distribution of fine-root growth and on the fine-root turnover were assessed in irrigated sweet cherry trees. The influence of other exogenous and endogenous factors was also examined. The rhizotron technique was used to measure the length-based fine-root growth in trees fertilized at two N rates (0 and 60 kg ha(-1)), and the above-ground growth, leaf net assimilation, and air and soil variables were simultaneously monitored. N fertilization exerted a basal effect throughout the season, changing the magnitude, temporal patterns and spatial distribution of fine-root production and mortality. Specifically, N addition enhanced the total fine-root production by increasing rates and extending the production period. On average, N-fertilized trees had a length-based production that was 110-180% higher than in control trees, depending on growing season. Mortality was proportional to production, but turnover rates were inconsistently affected. Root production and mortality was homogeneously distributed in the soil profile of N-fertilized trees while control trees had 70-80% of the total fine-root production and mortality concentrated below 50 cm depth. Root mortality rates were associated with soil temperature and water content. In contrast, root production rates were primarily under endogenous control, specifically through source-sink relationships, which in turn were affected by N supply through changes in leaf photosynthetic level. Therefore, exogenous and endogenous factors interacted to control the fine-root dynamics of irrigated sweet cherry trees.

ORYZA2000 is a growth model for tropical lowland rice (Oryza sativa L.) developed by the International Rice Research Institute and Wageningen University. This model has been evaluated extensively in a wide range of environments. However, reports examining japonica cultivars growing in temperate climates are scarce. In this study, ORYZA2000 was calibrated and evaluated using data from experiments carried out in the South-Central area of Chile. These experiments were performed on a japonica rice cultivar growing under an irrigated Mediterranean environment at various N rates. ORYZA2000 was then applied to explore potential yield and grain yield response to N fertilization under likely weather conditions in the major rice-producing area in Chile. ORYZA2000 was sufficiently accurate to simulate grain yield and crop N uptake at the end of the season. Final crop N uptake was simulated with a root mean squared error (RMSE) of 20 kg ha -1 (15%) and grain yield with a RMSE of 1666 kg ha -1 (19%). However, the prediction of biomass and N uptake of individual organs throughout the season was poor. A long-term simulation study confirmed a potential yield as high as 12 000 kg ha -1 in the Parral area, as well as the existence of a scope for yield increase. The yield response to N fertilization was predicted even at rates of 300 kg ha -1 , although a significant probability of low yields was also observed. This trend supports the need to incorporate dynamic N management in Chilean rice production.

No abstract

C. Bonomelli, C. Bonilla, E. Acuña, and P. Artacho. 2012. Seasonal pattern of root growth in relation to shoot phenology and soil temperature in sweet cherry trees (Prunus avium): A preliminary study in central Chile. Cien. Inv. Agr. 39(1): 127-136. The period between flowering and harvest in the sweet cherry (Prunus avium L.) is shorter than most fruit trees; thus, competition for assimilate and nutrients occurs early in the season. To properly supply water and nutrients during this critical period, optimal growth and root development are necessary. To characterize the root growth pattern of cherry trees in relation to shoot growth and phenology, a study was conducted on a 'Bing' cherry orchard on Gisela 6 rootstock at fourth leaf, located in central Chile (34º70' S, 70º43' W). During the 2009-2010 season, the shoot length and fruit diameter were measured on eight trees, and the root length was quantified by installing rhizotrons on two trees. Additionally, a two-tone (black/white) plastic cover was placed in the row over one tree with a rhizotron to analyze the effects of the plastic cover on soil temperature and root growth. The results showed three peaks of root growth during the season. The first peak occurred 43 days after full bloom (DAFB), corresponding to the phenological stages of the fruit turning from green to straw color. This peak occurred at 326 accumulated degree days (ADD) in the soil and 212 ADD in the air. The second peak was observed after harvest at 97 DAFB, when the shoot growth had stopped, and the soil and air had accumulated 932 and 692 degree days, respectively. The third and last peak occurred at 167 DAFB, with 1887 ADD in the soil and 1361 ADD in the air. The plastic cover increased the average soil temperature by approximately 1 °C, thereby increasing the ADD by 105.2 units during the study period. However, this increase was not enough to affect the root growth pattern.