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.

Excessive fertilization combined with unreasonable irrigation in farmland of the Hetao Irrigation Area (HIR), China, has resulted in a large amount of nitrogen (N) losses and agricultural non-point source pollution. Application of soil amendments has become one of the important strategies for reducing N losses of farmland. However, there is still no systematic study on the effects of various soil amendments on N losses in the HIR. In this study, three types of soil amendments (biochar, bentonite and polyacrylamide) were applied in a maize-wheat rotation system in the HIR during 2015-2017. Yields of maize and wheat, soil NH 3 volatilization, N 2 O emission and NO 3leaching were determined and soil N balance was estimated. The results showed that applications of biochar, bentonite and polyacrylamide significantly increased yields of maize by 9.2%, 14.3% and 13.3%, respectively, and wheat by 9.2%, 16.6% and 12.3%, respectively, compared with the control (fertilization alone). Applications of biochar, bentonite and polyacrylamide significantly reduced soil N leaching by 23.1%, 35.5% and 27.1%, soil NH 3-N volatilization by 34.8%, 52.7% and 37.8%, and soil N surplus by 23.9%, 37.4% and 30.6%, respectively. Applications of bentonite and polyacrylamide significantly reduced N 2 ON emissions from soil by 37.3% and 35.8%, respectively, compared with the control. Compared with application of biochar, applications of bentonite and polyacrylamide increased yields of maize and wheat by 5.1% and 3.5%, respectively. Our results suggest that soil amendments (bentonite and polyacrylamide) can play important roles in reducing N losses and increasing yield for the maize-wheat rotation system in the HIR, China.