Soil Carbon and Nitrogen Dynamics of Integrated Crop-Pasture Systems with Annual and Perennial Forages

Increased demand for food and bioenergy crops and the subsequent intensification of crop production creates a challenge for the conservation of natural resources in Latin America and the world. In Uruguay, no-till cash-crop production area has increased from 0.4 to 1.5 million ha in the last decade (DIEA 2011) mostly at the expense of pastureland through expanding grain production to soils with lower land use capability. Production systems based on crop-pasture rotations shifted to a longer annual cropping phase with a shorter pasture phase, or to continuous annual crop-ping. Long-term experiments in the country have shown that the rotation of annual crops and perennial pastures minimizes soil erosion in tilled systems, maintaining a positive long-term soil carbon (C) and nitrogen (N) balance that contrasts with C and N losses in annual cropping systems (García-Préchac et al. 2004). Research and extension on soil conservation in crop-pasture systems have led to a massive adoption of no-tillage practices, reaching about 90% of cash crop area by the 2009 growing season (DIEA 2011). However, the gradual increase in no-till adoption by farm operators has been associated with a dramatic increase in continuous annual cropping to the detriment of the pasture phase of the rotation. Our overarching question is: What is the impact of an increased frequency of annual crops in the C and N cycling of these systems? The objective of this study was to assess the impact of the pasture phase and cropping intensity on the soil C and N cycling of an Oxyaquic Argiudoll soil of eastern Uruguay using long term field experimental data and a cropping systems simulation model

Cover Crops Alternatives for Sustainable Agriculture Systems in Uruguay

In Uruguay, the increase of cropland area during the last decade was based on rotation systems intensification and soybean expansion, achieving 1.321.000 ha (Souto, 2014). Diaz (2007) demonstrated the value of the ley-farming systems where the integration of livestock and crop production achieved benefits on sustainability. Despite the advantages of crop-pasture rotation systems (García Prechac et al., 2004), grain market prices and food demand resulted in pasture phase losses in rotation with crops. Recently, Livestock Agriculture and Fisheries Ministry implemented a national soil conservation plan, that regulates cropping rotation systems based on soil erosion estimations and other key soil quality indicators. Although, no-till was full adopted, climatic and soil conditions determine that soil must be cover by residues or vegetation all year to reduce erosion and degradation (Thorup-Kristensen et al., 2003). Cover crops contribute to protect soils during fallow periods. The 17% of total soybean area cultivated is in Eastern Uruguay, being soils with erosion risk , fertility, structure and drainage limitations. This paper evaluates cover crops adaptation, subsequent effects on soybean productivity, and estimations of nitrogen supply and extraction from cover crops and soybean, respectively

Scouting Benefits and Developing Innovations in Temperate Grassland to Sustainable Agriculture Production

Agricultural intensification raises concern about land use and future effects to natural resources. The world demand for grain, meat and forest products is increasing constantly. Changes are occurring at large scale, being a compromise for policy makers to contribute to identify opportunities to readdress the productive scenario. There is available technology to reduce impacts, without restricting necessarily productivity. Grasslands provide a large series of economical and ecological benefits to the agricultural systems, being the literature exhaustive in examples. Ley-farming and cover crops technologies are good examples of environmentally sound soil management practices. The society is also worried about an improper use of the natural resources involved. The drastic increase in the grain crops area leaded by soybean in Uruguay, determined that the government implemented Sustainable Soil Use and Management Plans, based on erosion estimation using the USLE-RUSLE model adapted locally by research conducted over more than 50 years on a series of long term experimental platforms. There is an opportunity for this type of local innovative initiatives to be widely diffused, adopted or adapted. In essence, grasslands will continue playing a key role in maintaining a sustainable production

O índice de nutrição de nitrogênio no GS 3.3 é uma ferramenta eficaz para ajustar o nitrogênio necessário para alcançar a produtividade de trigo atingível

Current nitrogen (N) fertilization schedule for spring wheat was developed under a dominant crop-pasture rotation. After the year 2002, this cropping system was converted to continuous annual cropping systems under no-till, reducing soil N supply capacity progressively. Additionally, highest grain yield of new varieties increased N demand. The required additional N fertilizer can be adjusted by monitoring nutritional status of the crop. Our objectives were: i) to determine optimal N status at different phenological stages; ii) to quantify the wheat yield gap explained by N supply deficit, and iii) to assess the critical nitrogen nutrition index (NNI) value as a predictor of response to N fertilizer applied at GS 3.3. We adjusted the nitrogen dilution curve (Nc=4.17DM-0.31), deriving a critical NNI at GS 3.3 (NNI=1.24). Depending on soil N supply capacity and NNI at GS 3.3, wheat yield gap attributed to N supply deficit varied from 0 to 2.74 Mg ha⁻¹, averaging 0.76 Mg ha⁻¹. The critical NNI proposed at GS 3.3 was effective to diagnose the N crop demand to reach the attainable yield under different scenarios.El esquema actual de fertilización con nitrógeno (N) para el trigo de primavera se desarrolló bajo una rotación dominante de cultivo-pastura. Después de 2002, este sistema se convirtió en un sistema de cultivo anual continuo con labranza cero, reduciendo progresivamente la capacidad de suministro de N del suelo. Además, el mayor rendimiento en grano de las nuevas variedades aumentó la demanda de N. El fertilizante nitrogenado adicional requerido se puede ajustar monitoreando el estado nutricional del cultivo. Nuestros objetivos fueron: i) determinar el estado óptimo de N en diferentes etapas fenológicas; ii) cuantificar la brecha de rendimiento del trigo explicada por el déficit de suministro de N, y iii) evaluar el valor crítico del índice de nutrición nitrogenada (INN) como predictor de respuesta al agregado de fertilizante nitrogenado en GS 3.3. Ajustamos la curva de dilución de nitrógeno (Nc=4,17MS-0,31), derivando un INN crítico en GS 3.3 (INN=1,24). Según la capacidad de suministro de N del suelo y el INN en GS 3.3, la brecha de rendimiento del trigo atribuida al déficit de suministro de N varió de 0 a 2,74 Mg ha⁻¹, con un promedio de 0,76 Mg ha⁻¹. El INN crítico propuesto en GS 3.3 fue efectivo para diagnosticar la demanda de N del cultivo y lograr el rendimiento alcanzable en diferentes escenarios.O esquema atual de fertilização com nitrogênio (N) para o trigo de primavera foi desenvolvido sob uma rotação dominante de cultivo e pastagem. A partir de 2002, esse sistema passou a ser um sistema de cultivo anual contínuo com plantio direto, reduzindo progressivamente a capacidade de suprimento de N do solo. Além disso, o maior rendimento de grãos das novas variedades aumentou a demanda por N. O fertilizante de nitrogênio adicional necessário pode ser ajustado monitorando o estado nutricional da cultura. Nossos objetivos foram: i) determinar o estado ótimo do N em diferentes estágios fonológicos; ii) quantificar a lacuna de produtividade do trigo explicada pelo déficit de oferta de N e iii) avaliar o valor crítico do índice de nutrição de nitrogênio (INN) como preditor de resposta à adição de fertilizante nitrogenado no GS 3.3. Ajustamos a curva de diluição de nitrogênio (Nc=4,17MS-0,31), derivando um INN crítico em GS 3,3 (INN=1,24). De acordo com a capacidade de suprimento de N do solo e do INN no GS 3.3, a diferença de produtividade do trigo atribuída ao déficit de suprimento de N variou de 0 a 2,74 Mg ha⁻¹, com média de 0,76 Mg ha⁻¹. O INN crítico proposto em GS 3.3 foi eficaz para diagnosticar a demanda de N da cultura para atingir o rendimento alcançável em diferentes cenários

Alternativas de fertilización nitrogenada en maíz bajo riego por pivot central

Título alternativo : Alternativas de fertilização com nitrogênio no milho sob irrigação por pivô centralIn the last 15 years, there has been an expansion of the use of center-pivots for irrigation in Uruguay. This equipment allows the application of diluted fertilizer in the irrigation water. The study aimed to generate information on fertilization strategies with nitrogen (N) in irrigated maize crops. A study was performed where five treatments were evaluated: T0, without additional nitrogen fertilization to the basal sowing fertilization; C0, cover fertilization with 150 Kg N ha⁻¹ split in three (V3) and seven leaves (V7); F1, idem “C0” but with liquid fertilizer in water; F2, 150 Kg N ha⁻¹ as liquid fertilizer in water split weekly from V3 to reproductive stage (R1); F3, idem "F2" but with 225 Kg N ha⁻¹. Irrigation was done according to water balance and the soil moisture was measured with an FDR probe. The N plant level and biomass were evaluated in states V3, V6, R1 and physiological maturity (R6). The grain yield was determined at harvest. The correlation between the color values and Color Index (InCol) was analyzed in R1 using aerial photography and software, with: % N; biomass; Nitrogen Sufficiency Index (NSI); and grain yield (kg ha⁻¹). The yield was higher in the treatment with the highest N dose, with no significant differences. No differences were found between the sources of N (sulfur urea and Fertec®) for the evaluated variables. A high correlation was obtained between the colors and the InCol and the cultivation variables.En los últimos 15 años, ha habido una expansión del uso de pivotes centrales para riego en Uruguay. Estos equipos permiten la aplicación de fertilizante con el riego. El objetivo fue generar información sobre estrategias de fertilización con nitrógeno (N) en maíz regado. Se instaló un experimento con 5 tratamientos: T0, sin fertilización nitrogenada adicional a la basal de la siembra; C0, fertilización en cobertura con 150 kg N ha⁻¹ fraccionado en tres (V3) y siete hojas (V7) de estado de desarrollo; F1, ídem a “C0” pero con fertilizante diluido en agua; F2,150 kg N ha⁻¹ como fertilizante diluido en agua, fraccionado semanalmente desde V3 hasta estado reproductivo (R1); F3, ídem a “F2” pero con 225 kg N ha⁻¹. Se manejó el riego a partir de un balance hídrico y se midió la humedad en el suelo con sonda FDR. Se evaluó contenido de N en planta y biomasa en los estados V3, V6, R1 y madurez fisiológica (R6). A cosecha se determinó el rendimiento en grano. En R1 mediante foto aérea del cultivo y software se analizó la correlación entre los valores de color e Índice de Color (InCol) con: %N; biomasa; Índice de Suficiencia de Nitrógeno (ISN); y rendimiento de grano (kg ha⁻¹). El rendimiento fue superior en el tratamiento con mayor dosis de N, sin detectar diferencias significativas. No se encontraron diferencias entre las fuentes de N (urea azufrada y Fertec®). Se obtuvo alta correlación entre los colores e InCol y las variables del cultivo analizadas.Nos últimos 15 anos, no Uruguai, houve uma expansão do uso de pivôs centrais para irrigação. Esses equipamentos permitem a aplicação de fertilizantes diluídos nas irrigaçãoes. O objetivo foi gerar informações sobre estratégias de fertilização com nitrogênio (N) no milho irrigado. Foram avaliados 5 tratamentos: T0, sem fertilização com nitrogênio adicional à fertilização de base da semeadura; C0, adubação em cobertura com 150 kg N ha⁻¹ dividido em três (V3) e sete (V7) folhas do estádio de desenvolvimento; F1, igual a “C0” mas com fertilizante diluído em água; F2, 150 kg N ha⁻¹ como fertilizante diluído em água, fracionado semanalmente de V3 ao estado reprodutivo (R1); F3, idem para “F2” mas com 225 kg N ha⁻¹. Foi regado de acordo com o balanço hídrico e a umidade do solo foi medida com uma sonda FDR. A concentração de N da planta e biomassa foram avaliadas nos estágios V3, V6, R1 e maturidade fisiológica (R6). Na colheita, foi determinado o rendimento de grãos. No R1, por meio de foto aérea e software, foi analisada a correlação entre os valores de cor e o Índice de Cor (InCol) com:% N; biomassa; Índice de Suficiência de Nitrogênio (ISN); e rendimento de grãos (kg ha⁻¹). O desempenho foi superior no tratamento com a maior dose de N, sem detectar diferenças significativas. Não foram encontradas diferenças entre as fontes de N (enxofre uréia e Fertec®). Uma alta correlação foi obtida entre as cores e o InCol e as variáveis de cultivo analisadas

Spatial distribution of wood volume in brazilian savannas

Here we model and describe the wood volume of Cerrado Sensu Stricto, a highly heterogeneous vegetation type in the Savanna biome, in the state of Minas Gerais, Brazil, integrating forest inventory data with spatial-environmental variables, multivariate regression, and regression kriging. Our study contributes to a better understanding of the factors that affect the spatial distribution of the wood volume of this vegetation type as well as allowing better representation of the spatial heterogeneity of this biome. Wood volume estimates were obtained through regression models using different environmental variables as independent variables. Using the best fitted model, spatial analysis of the residuals was carried out by selecting a semivariogram model for generating an ordinary kriging map, which in turn was used with the fitted regression model in the regression kriging technique. Seasonality of both temperature and precipitation, along with the density of deforestation, explained the variations of wood volume throughout Minas Gerais. The spatial distribution of predicted wood volume of Cerrado Sensu Stricto in Minas Gerais revealed the high variability of this variable (15.32 to 98.38 m3 ha-1) and the decreasing gradient in the southeast-northwest direction914COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESSem informaçã

Measured and modeled nitrogen balances in lowland rice-pasture rotations in temperate South America

Rotational rice systems, involving pastures, other crops and/or livestock, are common in temperate South America, exemplified by the rice-pasture-livestock system of Uruguay which combines very high rice yields with tight nitrogen (N) balances. The generally good nutrient use efficiency in these systems provides a template for nutrient management in other mixed farming systems, if the underlying processes can be sufficiently well quantified and understood. Here, we studied N balances in rice–non-rice rotations in a long-term experiment in Uruguay, with the aim of parameterizing and testing the DNDC model of N dynamics for such systems for use in future work. The experiment includes three rotations: continuous rice (RI-CONT), rice-soybean (RI-SOY) and rice-pasture (RI-PAST). We considered 9 years of data on N balances (NBAL), defined as all N inputs minus all N outputs; N surplus (NSURP), defined as all N inputs minus only N outputs in food products; and N use efficiency (NUE), defined as the fraction of N inputs removed in food products. We parameterized DNDC against measured yield and input and output data, with missing data on N losses inferred from the N balance and compared with literature values. The model performance was assessed using standard indices of mean error, agreement and efficiency. The model simulated crop yields and rice cumulative N uptake very well, and soil N reasonably well. The values of NBAL were +45 and−20 kg N ha−1 yr−1 in RI-CONT and RI-SOY, respectively, and close to zero in RI-PAST (−6 kg N ha−1 yr−1). Values of NSURP decreased in the order RI-CONT >> RI-SOY > RI-PAST (+115, +25 and +13 kg N ha−1 yr−1, respectively). Values of NUE (84, 54, and 48% for RI-SOY, RI-PAST, and RI-CONT, respectively) decreased as NBAL increased. The sensitivity of DNDC's predictions to the agronomic characteristics of the different crops, rotations and water regimes agreed with expectations. We conclude that the DNDC model as parameterized here is suitable for exploring how to optimize N management in these systems