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Intercropping forage grasses with upland rice is an alternative cropping system to improve agroecosystem diversification and could potentially enhance sustainability in tropical regions. However, nitrogen (N) immobilization and nutrient competition between rice and forage grasses could reduce rice grain yield and decrease overall productivity. Therefore, fertilizer N requirements of upland rice intercropped with forage grasses needs to be better defined. Field experiments were carried out during three growing seasons on a Typic Haplorthox soil in São Paulo state of Brazil. The experimental design was a randomized block design with a 3 × 4 factorial scheme with four replications. Treatments were cropping system [monocropped rice (Oryza sativa L.), rice intercropped with palisadegrass (Urochloa brizantha), and rice intercropped with guineagrass (Megathyrsus maximus) and sidedress N application rate (0, 40, 80, and 120 kg N ha−1). Intercropped grasses were sown between upland rice rows 30 days after rice emergence. On average, intercropping of rice with palisadegrass or guineagrass decreased rice shoot dry matter and grain yield by 11% and milled rice productivity by 10% compared with monocropped rice. Grain yield, grain protein, and milled productivity of rice increased as N application rate increased. Forage dry matter production (first and second cut) and crude protein (second cut) were greatest in the rice + palisadegrass intercropping system. Production of both forage grasses increased with up to 80 kg N ha−1 in the first cut and increased linearly with N in the second cut. Intercropping of rice with palisadegrass or guineagrass with 80 kg N ha−1 application resulted in the greatest land equivalent ratio (1.96 and 1.55, respectively). Relative N yield was greatest at 120 kg N ha−1 (220 and 173%, respectively). Although rice monocropping had greatest grain yield, intercropping systems with forage grasses were more favorable from both economic and environmental perspectives by enhancing plant diversification, nutrient cycling with forage grasses, land use production per unit area, and profitability throughout the year.

Thermomagnesium (TM), a byproduct of Ni ore mining, can be processed as a clean alternative to conventional fertilizers as a source of magnesium (Mg) and silicon (Si) for agriculture. TM positively impacts soil properties and provides nutrients that are available for uptake by plants; however, information on the effects of TM on plant physiology in cropping systems is limited. This study aimed to evaluate the impact of increasing doses of TM on crop yield; soil chemical attributes; and leaf contents of Mg, Si, reducing sugars, sucrose, and starch in a soybean-maize crop rotation system. The study was performed under rainfed conditions during three consecutive crop seasons in 2018/2019 (soybean), 2019 (maize), and 2019/2020 (soybean). Six TM doses (0, 350, 700, 1050, 1400, 1750 kg ha−1) with four replicates were applied prior to the first season. Responses to the application of TM were observed up to the highest doses (1,400 and 1750 kg ha−1), with increases in soil concentrations of Mg and Si, soil pH, leaf pigments, gas exchange parameters, and carbohydrate concentrations but decreases in starch content. The increases in photosynthetic rates and carbohydrate partitioning led to increases in the weight of 100 grains (W100G) and grain yield (GY). W100G increased by 11% in soybean at a TM dose of 1,050 kg ha−1 and 23% in maize at a TM dose of 1,400 kg ha−1 dose. For both crops, the greatest increases in GY were obtained at a TM dose of 1,050 kg ha−1, with increases of 1,068 and 3,658 kg ha−1 for soybean and maize, respectively, compared with the control. Therefore, TM can be used in agricultural systems as a viable source of Mg and Si and as soil acidity amendment to promote sustainable agriculture.