Sugarcane plays an important role in the Brazilian agribusiness. However, poor rainfall distribution and soil acidity directly affect its production in the Northeast Brazil. Gypsum improves the soil physical and chemical properties, attenuating the effects of water stress and acidity in the edaphic environment. This study aimed at determining the effect of gypsum doses on sugarcane growth and yield. A field experiment was conducted using a 3 x 5 factorial arrangement organized in a randomized block design, with four replications. Treatments consisted of a combination of three sugarcane varieties (RB011941, RB92579 and RB991536) with five gypsum doses (0 Mg ha-1, 2.5 Mg ha-1, 5.0 Mg ha-1, 10.0 Mg ha-1 and 20.0 Mg ha-1). RB92579 exhibited the highest stalk (157.90 Mg ha-1) and sugar (24.10 Mg ha-1) yield. Gypsum did not influence the sugarcane yield or plant growth in the vegetative growth stage, but, in the maturation phase, the leaf area declined and the number of shoots increased with the rise in gypsum doses. Applying gypsum increased the roots density along the soil profile, with a rise of around 1.10 g dm-3 at the most technically efficient dose (12.5 Mg ha-1), however, yield was not influenced, maybe due to the effect of high rainfall during the entire crop cycle. Thus, higher gypsum doses are recommended during periods of drought to benefit from the resulting increased root system.

The sugar-energy sector is highlighted in Brazilian agribusiness; however, poor water distribution and soil acidity have limited the yield and quality of cane fields. Gypsum improves the physical and chemical properties of the soil, attenuating the effects of water shortage and acidity in the edaphic environment. The aim of this study was to determine the effect of gypsum doses on the nutritional status, photochemical efficiency and technological quality of sugarcane. The experiment was conducted under field conditions using a randomized block design in a 3 x 5 factorial scheme with four replications. The treatments consisted of the combination of three sugarcane varieties (RB011941, RB92579, and RB991536) with five doses of gypsum (0 Mg ha-1 ; 2.5 Mg ha-1 ; 5.0 Mg ha-1 ; 10 Mg ha-1 ; and 20.0 Mg ha-1). The results showed that gypsum did not influence the evaluated variables. A varietal effect for leaf contents of P, K, Mg and S was observed. The RB92579 presented the highest levels of P (1.65 g kg-1) and K (14.55 g kg-1), while RB011941 showed the highest concentrations of Mg and S, 1.25 and 1.05 g kg-1 , respectively. The mean values of the macronutrients presented the following concentration order: N > K > Ca > Mg > P > S. Genotypes were similar in terms of photochemical efficiency, which in turn, was not influenced by gypsum application. The best technological quality was verified in RB92579, which showed the highest Brix percentage (22.35%), Pol (19.75%), and the highest levels of TRS (151.3 kg t-1) of sugarcane.

Drought associated with soil acidity and exchangeable Al3+ in depth are one of the main limiting factors in agricultural production in Northeast Brazil. Acidity correctives such as limestone, metallurgy slag, and gypsum are alternatives to minimize the effects of seasonal droughts on the crop. A field study was carried out to evaluate the effect of the slag and gypsum on the morphological aspects and productivity of sugarcane during two crop cycles. A randomized block design in subdivided plots scheme with four replications was used. The plot consisted of five rows of 10 m length each, spaced 1 m from each other. Treatments consisted of five levels of metallurgy slag (0; 1; 2; 3 and 4 Mg ha-1) and two levels of gypsum (0 and 1.9 Mg ha-1). Slag and gypsum had no effect on sugarcane plant yield. However, regarding sugarcane ratoon, slag increased the yield per hectare by 1.96 Mg ha-1 and sugar yield by 0.33 Mg ha-1 per Mg of applied slag. Slag and gypsum provided better biomass allocation to the root system and improved root distribution along the soil profile.

Sugarcane is one of the most important crops in the world, but subject to yield losses caused by sporadic droughts during the growing season. To mitigate the effects of drought stress, different strategies have already been used, including the foliar application of glycine betaine (GB). Thus, the present study aimed to evaluate the effect of GB spraying via leaf on gas exchange, chlorophyll fluorescence and on the sugarcane water status subjected to drought stress and rewatering. The experiment was carried out in a greenhouse, using the RB92579 sugarcane variety. A randomized block design was used, in a 3 9 2 factorial scheme, composed of three GB applications (G0-without GB, G1-one application and G2-two applications) and two water treatments: irrigated (Control) and non-irrigated (Drought Stress), with subsequent rewatering. The foliar application of GB minimized the impact of drought stress on gas exchange, on the photochemical efficiency of photosystem II (PSII) and leaf tissue water status in stressed plants. In addition, it favored the energy use in the PSII and reduced photoinhibition, a fact not observed in the G0 stressed plants. Thus, it can be inferred that the GB foliar application mitigates the negative effects of drought stress on gas exchange and photochemical apparatus of PSII in young sugarcane plants.

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