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Abstract: The objective of this work was to evaluate the effects of nitrogen fertilizers on the N dynamics and grain yield in flooded rice (Oryza sativa) cultivation in Brazilian tropical wetland. The experiment was carried out in a randomized complete block design with six treatments, as follows: common and protected urea; topdressing application of N doses (30, 70, and 150 kg ha-1); and one control treatment, without N fertilization. Emissions of N2O-N, global warming potential (pGWP), emission factors (EF) for mineral fertilizers, grain yield, emission intensity, nitrate, ammonium, pH, and potential redox were quantified. Gas sampling was carried out in two crop seasons of rice cultivation and in one off-season. During the flooded period of the two crop seasons, N2O fluxes did not exceed 862.41 μg m-2 h-1 N2O-N; in the off-season, the fluxes varied from -52.95 to 274.34 μg m-2 h-1 N2O-N. Consistent emission peaks were observed in soil draining before harvest, when the highest rate of both N sources was used, and also in the control treatment in the off-season. Protected urea does not reduce N2O emissions or EF. Nitrogen increases the grain yield. Protected urea does not have any effect on the pGWP. The concentrations of NO3- and NH4+ in the soil are not related to N2O fluxes.

The objective of this study was to report single season effects of wood biochar (char) application coupled with N fertilization on soil chemical properties, aerobic rice growth and grain yield in a clayey Rhodic Ferralsol in the Brazilian Savannah. Char application effected an increase in soil pH, K, Ca, Mg, CEC, Mn and nitrate while decreasing Al content and potential acidity of soils. No distinct effect of char application on grain yield of aerobic rice was observed. We believe that soil properties impacted by char application were inconsequential for rice yields because neither water, low pH, nor the availability of K or P were limiting factors for rice production. Rate of char above 16 Mg ha^(−1) reduced leaf area index and total shoot dry matter by 72 days after sowing. The number of panicles infected by rice blast decreased with increasing char rate. Increased dry matter beyond the remobilization capacity of the crop, and high number of panicles infected by rice blast were the likely cause of the lower grain yield observed when more than 60 kg N ha^(−1) was applied. The optimal rate of N was 46 kg ha^(−1) and resulted in a rice grain yield above 3 Mg ha^(−1).

The objective of this work was to evaluate the effect of eucalyptus biochar on the transpiration rate of upland rice 'BRSMG Curinga' as an alternative means to decrease the effect of water stress on plant growth and development. Two-pot experiments were carried out using a completely randomized block design, in a split-plot arrangement, with six replicates. Main plots were water stress (WS) and no-water stress (NWS), and the subplots were biochar doses at 0, 6, 12 and 24% in growing medium (sand). Total transpirable soil water (TTSW), the p factor - defined as the average fraction of TTSW which can be depleted from the root zone before water stress limits growth -, and the normalized transpiration rate (NTR) were determined. Biochar addition increased TTSW and the p factor, and reduced NTR. Consequently, biochar addition was able to change the moisture threshold (p factor) of the growing medium, up to 12% maximum concentration, delaying the point where transpiration declines and affects yield.