The use of nitrogen fertilization in tropical grasslands is a strategy that may reduce the pressure of livestock production on biome areas with humid forests. The objective of this study was to assess the use of different doses of nitrogen in Guinea grass (Megathyrsus maximus (Jacq.) con. Mombasa) cultivated in the humid tropics. Doses of 0, 10, 20, 30, 40, and 50 kg of N ha⁻¹ application⁻¹ were applied during two consecutive years in experimental plots. The experimental area is located in the northeast of Pará, Brazil, with a predominantly tropical climate according to the Köppen classification. The morphogenic, production, and qualitative characteristics of the forage were evaluated. The morphogenic variables, rate of leaf appearance and rate of leaf elongation, in addition to daily accumulation of forage and crude protein content, increased with increasing doses of nitrogen. The morphological structure of the pasture was not modified. The number of cuts increased, whereas the number of days of recovery decreased, in the rainy season with increasing doses of nitrogen. The use of nitrogen fertilization does not alter the structure of the pasture; however, it improves the morphogenic, production, and chemical characteristics of Guinea grass.

The use of nitrogen fertilizers intensifies forage production, especially in tropical climates. This study aimed to evaluate the effects of nitrogen fertilization on the quantitative and qualitative characteristics of Massai grass grown in a humid tropical climate, specifically Am-type. A completely randomized design was used with six treatments and five replicates. The treatments used were a control treatment (without nitrogen application) and five doses of nitrogen fertilization (100, 200, 300, 400, and 500 kg N ha⁻¹year⁻¹). Urea was used as the nitrogen fertilizer for six applications, with an interval of 30 days. The leaf elongation rate increased by 69.1% at a dose of 500 kg N ha⁻¹ compared to that of the control. The leaf appearance rate and green leaves per tiller increased with nitrogen fertilization. Nitrogen fertilization did not affect the percentage of leaf blades and dead tissue. The average height of the canopies was 44.0 cm, regardless of fertilization. There was a quadratic response in total forage accumulation (TFA), with a maximum of 19,136 kg dry matter at a dose of 391 kg N ha⁻¹year⁻¹. Nitrogen utilization efficiency was the same as that of TFA. There was a reduction in the recovery of applied nitrogen and the agronomic efficiency of applied nitrogen with nitrogen fertilization. The number of cuts increased linearly with nitrogen fertilization, from 3.2 to 7.5 cuts. Crude protein content increased with nitrogen fertilization. Therefore, nitrogen fertilization favored the productivity and quality of Massai grass grown in a humid tropical climate.

Typical successions in land use affect the dynamics of carbon (C) and nitrogen (N) in the soil. This study aimed to determine the effects of land use change on soil organic carbon and N content and stocks in pastures, crops, and forests in the Amazon. Soil C and N stocks were assessed at depths of 30 and 100 cm to determine ¹³C isotopic abundance. The concentrations of C and N in crops were lower (p < 0.05) than those in other land use types. Soil organic C and soil N stocks for pasture (67.6, 144.8, 5.7, and 13.3) and forest (77.1, 137.5, 6.3, and 13.8) systems were similar, but greater than those of the crop area (36.4, 63.9, 3.0, and 6.0), regardless of depth (30 and 100 cm for C and N). Land use change for pastures in the Arc of Deforestation region of the Amazon maintains SOC and N stocks in the soil and is more sustainable than the agricultural system with black pepper, as long as the conditions of soil, climate, and cultivation are similar. Part of the C3-derived carbon from the forest was replaced by C4-derived C from grasses at soil depths up to 100 cm.

In this study, we aimed to determine the effects of cutting height (25 or 40 cm above ground) and bacterial inoculation (a combined inoculant of Lactobacillus plantarum and Propionibacterium acidipropionici) on the chemical and microbial compositions, fermentative profile, and aerobic stability of whole-plant corn silage and nitrogen balance, intake, and apparent nutrient digestibility by sheep. To evaluate silage characteristics and sheep metabolism, we performed analyses based on a completely randomized block design with a 2×2 factorial arrangement (two cutting [...] ABSTRACT In this study, we aimed to determine the effects of cutting height (25 or 40 cm above ground) and bacterial inoculation (a combined inoculant of Lactobacillus plantarum and Propionibacterium acidipropionici) on the chemical and microbial compositions, fermentative profile, and aerobic stability of whole-plant corn silage and nitrogen balance, intake, and apparent nutrient digestibility by sheep. To evaluate silage characteristics and sheep metabolism, we performed analyses based on a completely randomized block design with a 2×2 factorial arrangement (two cutting

Nitrous oxide (N₂O) is one of the main gases emitted from soils, and the changes in land use in the Amazon may alter gas emission patterns. The objective of this study was to evaluate the effects of land use, temperature, and nitrogen on N₂O emissions in soils in the Amazon. For this, three treatments randomized, with five repetitions, were incubated to quantify N₂O emissions: (i) three different land uses (wet rainforest, pasture, and agriculture); (ii) different temperatures (25, 30, 35, and 40 °C); and (iii) different nitrogen additions to the soil (0, 90, 180, and 270 kg of N ha⁻¹). Our results show that land use alters the flux of N₂O, with the highest emissions observed in agricultural soils compared to that in forest and pasture areas. The change in soil temperature to 30 °C increased N₂O emissions with land use, at which the emission of N₂O was higher in the pasture and agriculture soils. Our results showed that the emission of N₂O in the soil of the Amazon rainforest was low regardless of the temperature and nitrogen treatment. Therefore, the change in land use alters the resilience of the ecosystem, providing emissions of N₂O.