Potassium fertilization and irrigation with treated wastewater on gas exchange of colored cotton

Abstract

The use of treated domestic wastewater in agriculture is promising because it contains essential nutrients for crops, especially for cotton plants. Information on leaf gas exchanges helps to understand the responses of plants to different water and nutrient managements, since they directly affect physiological processes. Thus, the objective of this study was to evaluate the effect of potassium fertilization and irrigation with treated wastewater on the gas exchange of naturally colored cotton plants grown in the semi-arid region of the state of Pernambuco, Brazil, providing a reference for evaluations of responses of cotton plants to abiotic factors. The experiment was conducted in a randomized block design, in a 5 × 5 factorial arrangement, with four replications. The treatments consisted of five potassium rates (0, 50, 100, 150, and 200% of the recommended rate for the crop) and five irrigation depths (50, 75, 100, 125, and 150% of the evapotranspiration of the crop). The highest stomatal conductance, transpiration, net assimilation rate, intercellular CO2 concentration, and carboxylation efficiency were found in irrigated plants with 110, 99, 117, 150, and 113% of ETc, combined with the potassium rates of 96, 113, 97, 100, and 100% of the recommendation rate for the crop, respectively. The increase in irrigation depths increased the diffusion of CO2 of the plants. The highest instantaneous water-use efficiency was found with the irrigation of 150% of ETc without potassium fertilization. According to the interaction between irrigation depths and potassium rates, the most efficient potassium rate for naturally colored cotton depends on the irrigation depth applied.

Irrigation with Wastewater and K Fertilization Ensure the Yield and Quality of Coloured Cotton in a Semiarid Climate

“…The increment in UHM caused by the increase in water replacement up to 98.7% of the ET C (Figure 8c) indicated that the soil could be enriched with various nutrients, including K, through the use of TDS as irrigation water [18,42,43]. In our study, this raised soil fertility of more Mg +2 , K + , and NO 3 − provided by the TDS water possibly favoured cell development and, consequently, a greater fibre elongation, in agreement with what was previously discussed by others [1,35].…”

“…Our results showed that the use of TDS in a full irrigation regime (100% ET C ) and at a deficit irrigation regime (75% ET C ), even without K fertilization, increased seed cotton productivity by 51 and 32%, and the lint cotton yield by 37 and 21%, respectively (Figures 4 and 5), compared to the control treatment (100% ET C with freshwater plus mineral fertilization). The higher availability of TDS in the soil probably allowed for greater absorption of water and nutrients by the roots, promoting better photosynthetic efficiency and increased crop yield [32,34,35]. It is important to emphasize that the application of fertilizers with nitrogen and phosphorus was carried out only in the control treatment as TDS water already contained 126 and 13.7 mg L −1 of total N and total P, respectively, further evidencing the beneficial effect of cotton irrigation with TDS, which had 1.4-fold more Ca +2 , 5-fold more Mg +2 , 4-fold more K + , and 2 mmol c L −1 of NO 3 − than freshwater [23,35].…”

“…The higher availability of TDS in the soil probably allowed for greater absorption of water and nutrients by the roots, promoting better photosynthetic efficiency and increased crop yield [32,34,35]. It is important to emphasize that the application of fertilizers with nitrogen and phosphorus was carried out only in the control treatment as TDS water already contained 126 and 13.7 mg L −1 of total N and total P, respectively, further evidencing the beneficial effect of cotton irrigation with TDS, which had 1.4-fold more Ca +2 , 5-fold more Mg +2 , 4-fold more K + , and 2 mmol c L −1 of NO 3 − than freshwater [23,35]. The highest values of seed cotton and lint yield were obtained with the highest TDS depth (150% ET C ), but this treatment showed a low water use efficiency (0.38), a value similar to that observed in the control treatment (0.34 kg m −3 ), and low values of fertilizer potassium use efficiency.…”