Full Length Research Paper
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
A drip irrigation system, managed by the method of simplified water balance based on Tank "Class A" (AGR) (Allen et al., 1998), in which, first determined the irrigation efficiency (Ie) system according to Keller and Karmeli (1975), measured daily evaporation (mm) using a micrometer and evapotranspiration of reference (ET0) was determined by multiplying the evaporation and the tank coefficient (Kp) equal to 0.65. Crop evapotranspiration (ETc) was determined by multiplying the ET0 the crop coefficient (Kc) determined by Oliveira et al. (2013). The 100% water depth was determined based on ETc and Ei, and then extrapolated to other blades used to compose the treatments. In each evaluation time (ET), measurements of plant height (PH) were taken, considering the distance from ground level to the plant apex. Afterwards, two plants were collected at ground level in each replicate, and were separated in plant organs: leaves, stems+branches and reproduction organ.The leaf area was determined using the equation proposed by Grimes and Carter (1969): y = 0.4322 x2,3002, where y is 1-leaf, x is the length of the main rib cotton leaf; and then the leaf area per plant was determined by the sum of leaf areas.
Plant material was placed in forced-air circulation greenhouse, at 65°C for 72 h and subsequently weighed to determine dry phytomass stem (DPS), dry phytomass leaf (DPL), dry phytomass of the reproductive organ (DPRO) anddry phytomass of aerial part (DPAP). AGR (absolute growth rate) per day, was calculated by the equation AGR = (Pn - Pn-1)/(Tn - Tn-1), in which Pn is the dry phytomass accumulated until evaluation to n; Pn-1 is the accumulated dry phytomass to evaluation n-1; Tn is the number of days after treatment when evaluation n; and Tn-1 is the number of days after treatment at the time of evalution n-1. The RGR (relative growth rate) growth in a certain time interval in relation to the phytomass accumulated at the beginning of this interval, the RGR was calculated by the equation RGR = (ln P2 - P1 ln) / T1 T2-g-1 g per day. The NAR (net assimilation rate) is dry phytomass produced per unit leaf area and time and was calculated using the following equation: NAR = [(Pn - Pn-1) / (Tn - Tn-1)] [(1nAn - 1nAn-1) / (An - An-1)], where An is the leaf area; and An-1 is area leaf of the plant during evaluation n-1. LAR (leaf area ratio) was calculated by the equation An = LAR/Pn, and the relationship between leaf area responsible for the photosynthesis and total dry phytomass produced. Results were submitted to analysis of variance and significant variances were compared at 5% probability level. Choice of the models was based on the significance of the regression coefficients using the t-test at 5% probability and the coefficient of determination.
RESULTS AND DISCUSSION
There was a significant effect for the interaction of evaluation time (ET) and water replacement (WR) for the following variables: plant height (PH), leaf area (LF),dry phytomass of the reproductive parts (DPRP), dry phytomass of aerial part (DPAP), absolute growth rate (AGR) and relative growth rate (RGR). The variables, dry stem phytomass (DPS), dry leaf phytomass (DPL), net assimilation rate (NAR) and leaf area ratio (LAR) showed significant variability for isolated factors. The coefficients of variation were low (2.09 - 10.82%), which shows relatively good experimental precision (Table 2). Several researchers have noted the importance of study related to irrigation levels on the growth, development and production of different cultures, because of this, allow the identification of the level that provides the best conditions to culture, as an example of Smith et al. (2015) found that variability in biomass and production of sunflower under the influence of irrigation levels, as Morais, et al. (2016) on growth and development of the bean crop and Zonta et al. (2015) in the production of cotton.
Changes in the performance of plants related to irrigation is explained to the stress caused by excess water in the soil, causing the death of root tissues due to lactic fermentation and acidosis in the cells, the moment that the soil is in lack of oxygen , which leads to lack of energy, and causes the plant to reduce the potential for absorption of nutrients.On the other hand, the soil water deficiency can lead to plant water stress and thus cause a reduction in cell growth, leaf area, ratio of the biomass of roots and shoots, lower nutrient absorption, stomatal closure and reduction in photosynthesis (Taiz and Zeiger, 2010). Figure 1 shows the positive linear adjustment of variables DPS and DPL due of WR and ET. DPS and DPL increased with WR (Figure 1A), with estimated increase of 0.22 and 0.35%, respectively, with a unit increase in WR. Still, for DPS and DPL (Figure 1B), there was an increase in the estimated daily from 15.69 and 1.92%, respectively, in a 20-days period.Thus, it is clear that even for ET of 101-120 days, the cotton plants is still able to assimilate production by stems and leaves. Increased water stress resulted in the formation of small leaves with reduced leaf area, and consequently reduction in light absorption by plant and lower production of assimilates (Souza, 2014).
The behavior of plant height and leaf area under the influence of water replacement levels, reveal that for a higher performance variables, it is important to consider in the design of the irrigation management, besides the crop coefficient (Kc) Results research as demonstrated by study. Its noted that DPRP was difference betwem WR only after 80 and 100 days and the regression equation as presented increments of 1.16 and 0.08% per unit increase in WR, respectively (Figure 2E). According to the equations EA scrolling regressions within each WR level, the largest accumulations of DPRP (58.8; 59.4; 60.1; 60.6; and 59.6 g) were scanned at 120 days in respective WR 25, 50, 75,100 and 125% (Figure 2F). There is difference between WR in all the DPAP and ET and at 60, 80, 100 and 120 days showed increases DPAP 0.47; 0.61; 0.14 and 0.10% per unit increase of WR, respectively (Figure 2G). At 100% WR, there was no significant difference between ET, but WR 25, 50, 75 and 125%, the DPAP accumulation in a 20 day interval was increased by 50.71; 51.81; 82.30 and 78.05%, respectively (Figure 2H).
The result of the largest responses for plants growth in height and leaf area between 100 and 120 days, the culture also showed greater assimilates productions shoot and thus the reproductive part linked to a water replacement of 100% of evapotranspiration. Studying the behavior of cotton cultivar Delta Opal under water stress in controlled environment, Baldo et al. (2009) found that smaller plant height, stem diameter, number of leaves and also the commitment of the formation of reproductive structures were water deficit of the consequences of 25% of the total pores, and even the best results for production of dry phytomass of aerial part and root were provided by replacement of 100%. Figure 3 showed the settings variables evaluated for WR unfolding in each level of ET. In time slots 40 to 60 and 61 to 80 days, it was found according to the regression equation, the highest absolute growth rates with 1.51 and 1.87 g per day, the WR 125 and 124%, respectively, since the period of 81 to 100 days greater AGR (2.72 g daily) was afforded by 25% WR (Figure 3A). The highest AGR (1.54, 2.26, 1.59, 1.94 and 2.12 g per day) in the WR 25, 50, 75, 100 and 125% were observed at 93.3, 97.4, 80.3, 85.0, 92.6 days, respectively (Figure 3B).
CONCLUSION
CONFLICT OF INTERESTS
ACKNOWLEDGEMENTS
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