Rafael Pivotto Bortolotto

Nitrogen fertilizer (15N) leaching in a central pivot fertigated coffee crop

Nitrogen has a complex dynamics in the soil-plant-atmosphere system. N fertilizers are subject to chemical and microbial transformations in soils that can result in significant losses. Considering the cost of fertilizers, the adoption of good management practices like fertigation could improve the N use efficiency by crops. Water balances (WB) were applied to evaluate fertilizer N leaching using 15N labeled urea in west Bahia, Brazil. Three scenarios (2008/2009) were established: i) rainfall + irrigation the full year, ii) rainfall only; and iii) rainfall + irrigation only in the dry season. The water excess was considered equal to the deep drainage for the very flat area (runoff = 0) with a water table located several meters below soil surface (capillary rise = 0). The control volume for water balance calculations was the 0 - 1 m soil layer, considering that it involves the active root system. The water drained below 1 m was used to estimate fertilizer N leaching losses. WB calculations used the mathematic model of Penman-Monteith for evapotranspiration, considering the crop coefficient equal to unity. The high N application rate associated to the high rainfall plus irrigation was found to be the main cause for leaching, which values were 14.7 and 104.5 kg ha-1 for the rates 400 and 800 kg ha-1 of N, corresponding to 3.7 and 13.1 % of the applied fertilizer, respectively.

Nitrogen Balance and Fertigation Use Efficiency in a Field Coffee Crop

Brazil is a major world coffee producer, using increasing quantities of nitrogen (N) fertilizer as the monoculture expands across the savannas. The fate and efficiency of this fertilizer N were evaluated for one complete cropping cycle using 15N tracer, permitting an N balance at harvest. Annual rates of 200, 400, 600, and 800 kg N ha−1 year−1 of 15N-labeled urea and an unfertilized control were applied every 14 days via fertigation. The N concentration, percentage of N derived from fertilizer, quantity of N derived from fertilizer, and percentage of nitrogen derived from fertilizer per N rate was assessed for 8-year-old coffee trees. The most efficient N use was with 200 kg ha−1 year−1 because it presented the lowest losses and highest N recoveries in the crop. Conversely, the least sustainable rate was 800 kg ha−1 year−1, which presented the greatest losses and the lowest N recovery in the whole plant.

RESPOSTA DA PRODUTIVIDADE DO ALGODOEIRO EM DIFERENTES DOSES DE NITROGÊNIO E EFICIÊNCIA DO SENSOR ÓPTICO EM ESTIMAR O POTENCIAL PRODUTIVO - DOI: 10.13083/1414-3984/reveng.v23n1p57-64

The development of the cotton crop is directly influenced by nitrogen nutrition, which is dependent on mineral fertilization. However, the management of nitrogen by this culture is complex, since large doses can also cause negative effects on crop yield. In this context, fine-tuning the dosage of N fertilizer, according to the crop demands, is essential to obtain high yields. This study sought to: I - establish the response curve of cotton yield to N fertilization, II – evaluate the capability of the optical sensor to estimate yield potential. The experiment was conducted in the agricultural year 2012/13 in an Oxisoil in the western region of the state of Bahia, in three areas with tropical climate, annual rainfall of 1600 mm yr-1 and a mean annual temperature of around 21 oC. The experiment was setup in a randomized block design with seven treatments and three replications. The treatments consisted of the following N doses: 0, 45, 90, 130, 150,180 and 220 kg ha - 1 applied at 43 days after sowing (DAS) in area 1 and 32 DAS in areas 2 and 3. The vegetation index (VI) readings were taken at three different times, corresponding to 63, 75 and 97 DAS in area 1 and 45, 57 and 80 DAS in areas 2 and 3, using the optical sensor N-Sensor ALS ® (YARA). For the different areas and VI readings the cotton yield was determined. The productivity of the cotton crop showed a quadratic fit with N doses studied in three experiments and the rates which achieved maximum economic efficiency were 164, 139 and 167 kg ha-1 of N for areas 1, 2 and 3, respectively.

Quantitative and qualitative analyses of weed seed banks of different agroecosystems

1 Department of Soil Science, Federal University of Santa Maria (UFSM), Avenida Roraima, 100, 97105-900, Santa Maria, Rio Grande do Sul, Brazil. 2 Departament of Crop Science and Plant Health, University of Ponta Grossa (UEPG), Avenida Carlos Cavalcanti, 4748, Campus Uvaranas, 84030-960, Ponta Grossa, Paraná, Brazil. 3 Center for Nuclear Energy in Agriculture, University de São Paulo (CENA/USP), Avenida Centenario, 303, bairro São Dimas, caixa postal 96, 13400-970, Piracicaba, São Paulo, Brazil. 4 University of Ponta Grossa (UEPG), Avenida Carlos Cavalcanti, 4748, Campus Uvaranas, 84030-960, Ponta Grossa, Paraná, Brazil.