Variation of leaf area index of the forage sorghum under different irrigation depths in dynamic of cuts

Abstract

The determination of leaf area index is a variable of great importance for predicting productivity, especially when it comes to forage species where the desired product is the leaves. This study aimed to determine the variation of the leaf area index of forage sorghum when subjected to different irrigation depths in four culture cuts. Treatments consisted of six irrigation depths, these being 0, 60, 80, 100, 120 and 140% of the reference evapotranspiration. Seven evaluations of leaf area index (LAI) were performed, which were in the four cuts, specifically at 50, 80, 110 and 140 days after sowing (DAS), and also 15 days after each cut to evaluate the culture's resprouting, that is, at 65, 95 and 125 DAS. The delineation was randomized blocks, with six treatments and four blocks, totaling 24 experimental units. The experiment was conducted in Santiago-RS. Sowing was done on November 18, 2014. Using an irrigation system sprinkler, with one main row and six lateral rows, of PVC, being the irrigation levels differentiated by the nozzle diameter difference of sprinkler each lateral row. Samples of 0.5 linear meters per plot were collected in each of the seven evaluations, totaling 24 samples for evaluation. The analysis of leaf area index was performed using the computer program ImageJ. Significant results were found for the influence of the different irrigation levels on the leaf area index in the four cuts (recommended periods for grazing) evaluated, as well as for resprouting evaluations in the intermediate periods between cuts. Quadratic equations were adjusted for all the evaluation dates, where the 100 and 120% reference evapotranspiration levels alternated the largest LAI for all evaluations. The results also characterize that the second cut, or second grazing period of the irrigated forage sorghum, was the most productive, being it possible to recommend an increase in the animal load, or increase in grazing period in the area in this period. In this way, irrigation by sprinkling in the sorghum culture was characterized as an alternative for producers to increase leaf area index, and, consequently, crop productivity.

Coupling Water Resources and Agricultural Practices for Sorghum in a Semiarid Environment

“…Cycles 2 and 3 were the ones showing better crop performance, with the highest crop productivity being observed for an ETc of 140%, providing yields of 12.3 and 15.6 Mg ha −1 , which were above production obtained for the ID of 60% of ETc in 15.3% and 24.7%, respectively (Figure 6c). Increased sorghum productivity for the second cycle was also observed by [60], working with irrigation depths of 60%, 80%, 100%, 120%, and 140% of ETo, as already mentioned.…”

“…A field investigation points out that high sorghum crop LAI values result from suitable crop management, where appropriate interception of solar radiation occurs, which reflects positively on crop productivity [60]. In their study with Sorghum bicolor L. (Moench) in the Rio Grande do Sul State, Brazil, over the 2014/2015 harvesting period, the authors obtained LAI of up to 4.8 for an ID of 120% of ETo.…”

“…Addressing the irrigation depth factor, [60] found an increase in LAI for higher depths and adopted five values of IDs (60%, 80%, 100%, 120%, and 140% of ETo) for forage sorghum. The highest index of 4.806 m 2 m −2 was reached for ID equal to 120% of ETo, in the south region of Brazil.…”

Water productivity and production function in irrigated millet crop

“…Water deficits significantly reduce the productivity of agricultural systems commensurate with their intensity and duration (RAY et al, 2015;VIVAN et al, 2015;. Irrigation is used to mitigate the effects of water deficits and ensure high forage yields (OLIVEIRA et al, 2015;KIRCHNER et al, 2017;KOETZ et al, 2017). Vital et al (2015) and Orth et al (2012) reported that several tropical forage species are used in Brazil, and one of the most prominent is millet (Pennisetum americanum L.), a grass with high forage potential, with yields of up to 20 tons.…”