Nitrogen mass balance and uptake velocity for eutrophic reservoirs in the Brazilian semiarid region.

The nitrogen (N) cycle from the catchment to the downstream reservoir is complex, particularly the quantification of N losses. However, in order to assess the nitrogen impact in a reservoir ecosystem, simplified models may be applicable regarding the TN load production and the magnitude of lake TN removal. This study presented a methodology to perform and validate a TN mass balance to further calibrate a simplified coefficient for TN losses (vf.) in 29 tropical semiarid reservoirs. The study reservoirs were highly productive ecosystems with an average total nitrogen (TN) concentration, accounting for all measurements in all reservoirs, ranging from 0.59 to 3.84 mg L-1. Regarding the production of TN load, the median values ranged from 4.35 to 2,499.43 t year-1 with median of 80.34 t year-1. The TN loads were estimated through an annual mass balance over a 24-year period. The median of the estimates was compared with reference values obtained by using the export modelling coefficient. The correlation between the median estimated and reference loads resulted in satisfactory agreement (r2 0.88) and reinforced the reliability of the mass balance alternative. From the validated TN loads, the TN uptake velocity (vf) was estimated for all reservoirs (44.9 ± 20.1 m year-1) and could be described as a general function of the water residence time. The reservoirs of the study region have demonstrated higher vf than temperate lakes and reservoirs and similar vf with Latin America/Caribbean ones. As expected, reservoirs of warmer climates tend to present intensified N loss processes compared to lakes and reservoirs of temperate regions. The methodology proposed in the present study can be used to potentially improve water quality management in tropical semiarid reservoirs.

Zinc loading in urea-formaldehyde nanocomposites increases nitrogen and zinc micronutrient fertilization efficiencies in poor sand substrate.

Agricultural output needs significant increases to feed the growing population. Fertilizers are essential for plant production systems, with nitrogen (N) being the most limiting nutrient for plant growth. It is commonly supplied to crops as urea. Still, due to volatilization, up to 50 % of the total N application is lost. Slow or controlled release fertilizers are being developed to reduce these losses. The co-application of zinc (Zn) as a micronutrient can increase N absorption. Thus, we hypothesize that the controlled delivery of both nutrients (N and Zn) in an integrated system can improve uptake efficiency. Here we demonstrate an optimized fertilizer nanocomposite based on urea:urea-formaldehyde matrix loaded with ZnSO4 or ZnO. This nanocomposite effectively stimulates maize development, with consequent adequate N uptake, in an extreme condition - a very nutrient-poor sand substrate. Our results indicate that the Zn co-application is beneficial for plant development. However, there were advantages for ZnO due to its high Zn content. We discuss that the dispersion favors the Zn delivery as the nanoparticulated oxide in the matrix. Concerning maize development, we found that root morphology is altered in the presence of the fertilizer nanocomposite. Increased root length and surface area may improve soil nutrient uptake, potentially accompanied by increased root exudation of essential compounds for N release from the composite structure.

Conversion of ammonium to nitrate and abundance of ammonium-oxidizing-microorganism in Tropical soils with nitrification inhibitor

The use of nitrification inhibitors (NIs; dicyandiamide - DCD) is an alternative to reduce oxidation of ammonium (NH4+-N) to nitrate (NO3–-N) in the soil, reducing NO3–-N losses from fertilization practices. Based on the hypothesis that DCD reduces conversion of NH4+-N to NO3–-N in tropical soils and inhibits ammonia oxidizing microorganisms (AOM) abundance, soils from the Piracicaba region, São Paulo, with different textures (sand, loam and clay) were incubated with ammonium sulphate (AS) and DCD. Contents of NH4+-N, NO3–-N, soil pH, and AOM abundance were quantified periodically. Ammonium sulphate increased AOM abundance in all soils, but AS+DCD presented AOM abundances similar to the control. During 90 days of incubation, the effectiveness of DCD in reducing NO3–-N production was 1.8, 86.4, and 145.6 mg kg–1, while the effectiveness of DCD in reducing AOM abundance was 1.2, 3.0 and 2.3 × 10–3 g soil–1 for sandy, loamy, and clayey soils, respectively. DCD effectiveness was greater in loamy and clayey soils due to the naturally low nitrification in sandy soils. Application of AS treated with DCD showed potential not only to reduce NO3–-N production in loamy and clayey soils, but also to decrease the soil nitrification rate. Overall, DCD was effective in reducing AOM abundance and conversion of NH4+-N to NO3–-N in loamy and clay soils evaluated here. The increase in clay content directly influences DCD effectiveness in reducing conversion of NH4+-N to NO3–-N.

Conversion of ammonium to nitrate and abundance of ammonium-oxidizing-microorganism in Tropical soils with nitrification inhibitor

The use of nitrification inhibitors (NIs; dicyandiamide - DCD) is an alternative to reduce oxidation of ammonium (NH4+-N) to nitrate (NO3–-N) in the soil, reducing NO3–-N losses from fertilization practices. Based on the hypothesis that DCD reduces conversion of NH4+-N to NO3–-N in tropical soils and inhibits ammonia oxidizing microorganisms (AOM) abundance, soils from the Piracicaba region, São Paulo, with different textures (sand, loam and clay) were incubated with ammonium sulphate (AS) and DCD. Contents of NH4+-N, NO3–-N, soil pH, and AOM abundance were quantified periodically. Ammonium sulphate increased AOM abundance in all soils, but AS+DCD presented AOM abundances similar to the control. During 90 days of incubation, the effectiveness of DCD in reducing NO3–-N production was 1.8, 86.4, and 145.6 mg kg–1, while the effectiveness of DCD in reducing AOM abundance was 1.2, 3.0 and 2.3 × 10–3 g soil–1 for sandy, loamy, and clayey soils, respectively. DCD effectiveness was greater in loamy and clayey soils due to the naturally low nitrification in sandy soils. Application of AS treated with DCD showed potential not only to reduce NO3–-N production in loamy and clayey soils, but also to decrease the soil nitrification rate. Overall, DCD was effective in reducing AOM abundance and conversion of NH4+-N to NO3–-N in loamy and clay soils evaluated here. The increase in clay content directly influences DCD effectiveness in reducing conversion of NH4+-N to NO3–-N.(AU)

Volatilização da amônia da ureia estabilizada com NBPT na adubação em cobertura da Urochloa ruziziensis / Ammonia volatilization from stabilized urea with NBPT of the topdressing fertilization in Urochloa ruziziensis

A ureia é o principal adubo nitrogenado utilizado em pastagens. Nesse fertilizante, uma das principais perdas de nitrogênio (N) está relacionada com a volatilização da amônia. O uso de produtos que proporcionam redução das perdas de N da ureia pode contribuir para aumentar a eficiência de uso desse nutriente em pastagens. Assim, objetivou-se determinar o efeito de fontes e doses de N aplicado parcelado em cobertura na Urochloa ruziziensis, nas perdas de N pela volatilização de amônia (N-NH3). O experimento foi conduzido em Santo Antônio de Goiás, GO, em Latossolo Vermelho Distrófico. Utilizou o delineamento experimental de blocos ao acaso, com quatro repetições em arranjo fatorial 2 x 5 x 5. Os tratamentos foram compostos pelas fontes de N: ureia comum e ureia com inibidor de urease, doses de N: 0, 50, 100, 200 e 300 kg ha-1 (parceladas em 5 aplicações) e cinco períodos de crescimento da forrageira: 14/11 a 13/12 (1º período), 14/12 a 12/01 (2º período), 13/01 a 11/02 (3º período), 24/03 a 22/04 (4º período), e 10/07 a 08/08 (5º período). O uso de ureia com inibidor de urease proporcionou reduções nas perdas de amônia por volatilização em relação à ureia comum. O aumento das doses de N proporcionou aumento da volatilização de N-NH3. Ocorreram maiores perdas de N pela volatilização da amônia nos períodos mais secos do ano.(AU)

Urea is the major nitrogen fertilizer used in pastures. In this fertilizer, one of the main nitrogen (N) losses is related to ammonia volatilization. The use of products that provide reduced losses of N from urea can help to increase the use efficiency of this nutrient in pastures. This study aimed to determine the effect of nitrogen sources and doses split applied at topdressing in Urochloa ruziziensis in the N losses by ammonia N-NH3 volatilization. The experiment was conducted in Santo Antônio de Goiás, GO, in a in a Brazilian Oxisol. It was used the randomized blocks experimental design, with four replications, in a factorial arrangement 2 x 5 x 5. Treatments were composed by N sources: common urea and urea with urease inhibitor, N rates: 0, 50, 100, 200 and 300 kg ha-1 (split in 5 applications) and five forage growth period: 11/14 to 12/13 (1º period), 12/14 to 01/12 (2º period), 01/13 to 02/11 (3º period), 03/24 to 04/22 (4º period) and 07/10 to 08/08 (5º period). The use of urea with urease inhibitor provided reductions in ammonia loss by volatilization in comparison to the common urea. Increasing N rates led to increased NNH3 volatilization. In drier periods of the year it was found greater losses of N by ammonia volatilization.(AU)

Volatilização da amônia da ureia estabilizada com NBPT na adubação em cobertura da Urochloa ruziziensis / Ammonia volatilization from stabilized urea with NBPT of the topdressing fertilization in Urochloa ruziziensis

A ureia é o principal adubo nitrogenado utilizado em pastagens. Nesse fertilizante, uma das principais perdas de nitrogênio (N) está relacionada com a volatilização da amônia. O uso de produtos que proporcionam redução das perdas de N da ureia pode contribuir para aumentar a eficiência de uso desse nutriente em pastagens. Assim, objetivou-se determinar o efeito de fontes e doses de N aplicado parcelado em cobertura na Urochloa ruziziensis, nas perdas de N pela volatilização de amônia (N-NH3). O experimento foi conduzido em Santo Antônio de Goiás, GO, em Latossolo Vermelho Distrófico. Utilizou o delineamento experimental de blocos ao acaso, com quatro repetições em arranjo fatorial 2 x 5 x 5. Os tratamentos foram compostos pelas fontes de N: ureia comum e ureia com inibidor de urease, doses de N: 0, 50, 100, 200 e 300 kg ha-1 (parceladas em 5 aplicações) e cinco períodos de crescimento da forrageira: 14/11 a 13/12 (1º período), 14/12 a 12/01 (2º período), 13/01 a 11/02 (3º período), 24/03 a 22/04 (4º período), e 10/07 a 08/08 (5º período). O uso de ureia com inibidor de urease proporcionou reduções nas perdas de amônia por volatilização em relação à ureia comum. O aumento das doses de N proporcionou aumento da volatilização de N-NH3. Ocorreram maiores perdas de N pela volatilização da amônia nos períodos mais secos do ano.

Urea is the major nitrogen fertilizer used in pastures. In this fertilizer, one of the main nitrogen (N) losses is related to ammonia volatilization. The use of products that provide reduced losses of N from urea can help to increase the use efficiency of this nutrient in pastures. This study aimed to determine the effect of nitrogen sources and doses split applied at topdressing in Urochloa ruziziensis in the N losses by ammonia N-NH3 volatilization. The experiment was conducted in Santo Antônio de Goiás, GO, in a in a Brazilian Oxisol. It was used the randomized blocks experimental design, with four replications, in a factorial arrangement 2 x 5 x 5. Treatments were composed by N sources: common urea and urea with urease inhibitor, N rates: 0, 50, 100, 200 and 300 kg ha-1 (split in 5 applications) and five forage growth period: 11/14 to 12/13 (1º period), 12/14 to 01/12 (2º period), 01/13 to 02/11 (3º period), 03/24 to 04/22 (4º period) and 07/10 to 08/08 (5º period). The use of urea with urease inhibitor provided reductions in ammonia loss by volatilization in comparison to the common urea. Increasing N rates led to increased NNH3 volatilization. In drier periods of the year it was found greater losses of N by ammonia volatilization.

Resposta do arroz irrigado ao uso de inibidor de urease em plantio direto e convencional / Response of rice to the use of urease inhibitor in no-tillage and conventional

O objetivo do presente trabalho foi avaliar a volatilização de N-NH3 e a resposta do arroz irrigado ao uso de ureia com inibidor de urease em dois sistemas de cultivo, direto e convencional. Para tanto, desenvolveu-se um experimento em campo, no ano agrícola 2008/09, na UFSM em Santa Maria/RS. O delineamento utilizado foi de blocos ao acaso em esquema bifatorial (2x5), sendo o fator A constituído por ureia e ureia revestida com B e Cu (inibidor de urease) e o fator B composto por diferentes intervalos de entrada de água (0, 3, 6, 9, 12 dias) após a aplicação das fontes de nitrogênio (N). Os resultados demonstram que o inibidor de urease retarda e diminui a conversão de N para NH3, reduzindo as perdas por volatilização, comparativamente à ureia sem inibidor. Entre os sistemas, as perdas são potencializadas no sistema plantio direto. O inibidor de urease não traz benefícios à produtividade em qualquer um dos sistemas de cultivo utilizados e o estresse causado na planta de arroz pelo atraso no início da irrigação é mais prejudicial do que as perdas causadas pela volatilização de N-NH3.

The objective of this work was to measure the N-NH3 volatilization and the response of irrigated rice to the use of urea with urease inhibitor in two cropping systems, no-tillage and conventional. For this, an experiment in field was performed in the crop year 2008/09, at the UFSM in Santa Maria/RS. A random block in factorial scheme (2x5), with the factor A consisting of two nitrogen (N) sources, urea and urea coated with B and Cu (urease inhibitor) and the factor B consisting of different intervals of water intake (0, 3, 6, 9, 12 days) after the application of N sources. The results demonstrated that the urease inhibitor slows and decreases the conversion of N to NH3, reducing the losses by volatilization, comparatively to urea without inhibitor. Between the systems, the losses were increased in the no-tillage system. The urease inhibitor does not add benefits to the productivity in both cropping systems used and the stress caused on the rice plant by the delay of water intake is more harmful than the losses caused by the volatilization of N-NH3.