جستجوی مقالات مرتبط با کلیدواژه « Sensitivity coefficients » در نشریات گروه « کشاورزی »

Determining the intra-seasonal sensitivity of maize evapotranspiration to environmental stresses has an important effect on modeling of yield. In this research, the effect of drought and salinity stresses were investigated on the relative evapotranspiration (during initial, development, mid, and late stages) and relative yield of maize, in a field with sandy loam soil texture. Salinity treatments were applied by water with EC of 0.5(S0), 2.1(S1), 3.5(S2), and 5.7(S3)   dS.m-1. Drought treatments included four irrigation levels of 100% (I0), 80% (I1), 60% (I2), and 40% (I3) of the crop water requirement. The experiment was performed as factorial in a randomized complete block design, with three replications. The relative evapotranspiration of maize in the initial, development, middle and final stages was estimated between 63.5-100%, 62.6-100%, 55.2-100%, and 66.4-100%, respectively. The relative yield of maize in the I0S0 to I3S3 treatments was calculated between 42.6-100%. The results showed that salinity and drought stresses reduced both the evapotranspiration and maize yield. Also, evapotranspiration decreased with a steeper slope in sensitive growth stages compared to yield. Effect of the mentioned stresses at sensitive growth stages caused disruption in the flowering and fruiting of maize. In this study, the relative yield of maize was modeled by additive models of Blank, Stuart, Singh and multipliable models of Jensen, Rao, and Minhas. According to the results, Stewart model with sensitivity coefficients (in four growth stages) of 0.227, 0.416, 0.604, 0.14 and Jensen model with sensitivity coefficients of 0.301, 0.41, 0.608, and 0.147 were selected as the optimal models. However, Rao, Blank, Singh, and Minhas models were chosen as the next priorities. Therefore, under salinity and drought stress, the relative yield of maize was modeled based on the amount of evapotranspiration in the growth stages.

In order to determine the water production functions for winter wheat (Variety, C73,5), an experiment was conducted in through of a complete randomized block design with 9 treatments and 3 replications in Mashhad region. While the first treatment (as a control treatment) was selected on the basis of irrigation in all growth stages of growing season, six treatments were selected on the basis of an irrigation cut in the six stages of growth season and two remaining treatments were also selected on the basis of a constant reduction of irrigation to the amount of 20 and 60 percent. In general the water stress was caused that the amounts of depth percolation were calculated negatively which was an indication of the water uptake from below the root zone. According to results, models of the yield in per unit of area had a higher correlation coefficient of determination in relation to the models of the yield in per unit of water. The derived sensitivity coefficients indicated that the winter grain formation and flowering stages were respectively the most sensitive stages of the growth season stages to the water deficit. There are some differences between these computed sensitivity coefficients and the amounts reported by the other researchers. Probably the variety, degree of stress, the climatic conditions and some unknown factors may explain these differences.