Balanço de potássio no sistema plantio direto em razão da adubação potássica na sucessão milheto-soja.

Trabalho publicado também nos Resumos do CONGRESSO BRASILEIRO DE SOJA, 6., 2012, Cuiabá

The water balance components of undisturbed tropical woodlands in the Brazilian cerrado

Deforestation of the Brazilian cerrado region has caused major changes in hydrological processes. These changes in water balance components are still poorly understood but are important for making land management decisions in this region. To better understand pre-deforestation conditions, we determined the main components of the water balance for an undisturbed tropical woodland classified as "cerrado sensu stricto denso". We developed an empirical model to estimate actual evapotranspiration (ET) by using flux tower measurements and vegetation conditions inferred from the enhanced vegetation index and reference evapotranspiration. Canopy interception, throughfall, stemflow, surface runoff, and water table level were assessed from ground measurements. We used data from two cerrado sites, Pé de Gigante (PDG) and Instituto Arruda Botelho (IAB). Flux tower data from the PDG site collected from 2001 to 2003 were used to develop the empirical model to estimate ET. The other hydrological processes were measured at the field scale between 2011 and 2014 at the IAB site. The empirical model showed significant agreement (<i>R</i>² = 0.73) with observed ET at the daily timescale. The average values of estimated ET at the IAB site ranged from 1.91 to 2.60 mm day⁻¹ for the dry and wet seasons, respectively. Canopy interception ranged from 4 to 20 % and stemflow values were approximately 1 % of the gross precipitation. The average runoff coefficient was less than 1 %, while cerrado deforestation has the potential to increase that amount up to 20-fold. As relatively little excess water runs off (either by surface water or groundwater), the water storage may be estimated by the difference between precipitation and evapotranspiration. Our results provide benchmark values of water balance dynamics in the undisturbed cerrado that will be useful to evaluate past and future land-cover and land-use changes for this region

V2Karst V1.1: a parsimonious large-scale integrated vegetation–recharge model to simulate the impact of climate and land cover change in karst regions

Karst aquifers are an important source of drinking water in many regions of the world. Karst areas are highly permeable and produce large amounts of groundwater recharge, while surface runoff is often negligible. As a result, recharge in these systems may have a different sensitivity to climate and land cover changes than in other less permeable systems. However, little is known about the combined impact of climate and land cover changes in karst areas at large scales. In particular, the representation of land cover, and its controls on evapotranspiration, has been very limited in previous karst hydrological models. In this study, we address this gap (1) by introducing the first large-scale hydrological model including an explicit representation of both karst and land cover properties, and (2) by providing an in-depth analysis of the model's recharge production behaviour. To achieve these aims, we replace the empirical approach to evapotranspiration estimation of a previous large-scale karst recharge model (VarKarst) with an explicit, mechanistic and parsimonious approach in the new model (V2Karst V1.1). We demonstrate the plausibility of V2Karst simulations at four carbonate rock FLUXNET sites by assessing the model's ability to reproduce observed evapotranspiration and soil moisture patterns and by showing that the controlling modelled processes are in line with expectations. Additional virtual experiments with synthetic input data systematically explore the sensitivities of recharge to precipitation characteristics (overall amount and temporal distribution) and land cover properties. This approach confirms that these sensitivities agree with expectations and provides first insights into the potential impacts of future change. V2Karst is the first model that enables the study of the joint impacts of large-scale land cover and climate changes on groundwater recharge in karst regions.</p

Translating aboveground cosmic-ray neutron intensity to high-frequency soil moisture profiles at sub-kilometer scale

Above-ground cosmic-ray neutron measurements provide an opportunity to infer soil moisture at the subkilometer scale. Initial efforts to assimilate those measurements have shown promise. This study expands such analysis by investigating (1) how the information from aboveground cosmic-ray neutrons can constrain the soil moisture at distinct depths simulated by a land surface model, and (2) how changes in data availability (in terms of retrieval frequency) impact the dynamics of simulated soil moisture profiles. We employ ensemble data assimilation techniques in a “nearly-identical twin” experiment applied at semi-arid shrubland, rainfed agricultural field, and mixed forest biomes in the USA. The performance of the Noah land surface model is compared with and without assimilation of observations at hourly intervals, as well as every 2 days. Synthetic observations of aboveground cosmic-ray neutrons better constrain the soil moisture simulated by Noah in root-zone soil layers (0–100 cm), despite the limited measurement depth of the sensor (estimated to be 12–20 cm). The ability of Noah to reproduce a “true” soil moisture profile is remarkably good, regardless of the frequency of observations at the semi-arid site. However, soil moisture profiles are better constrained when assimilating synthetic cosmic-ray neutron observations hourly rather than every 2 days at the cropland and mixed forest sites. This indicates potential benefits for hydrometeorological modeling when soil moisture measurements are available at a relatively high frequency. Moreover, differences in summertime meteorological forcing between the semi-arid site and the other two sites may indicate a possible controlling factor to soil moisture dynamics in addition to differences in soil and vegetation properties

Soybean potassic fertilization in a Dark-Red Latosol sandy loam

Durante três anos foi conduzido um experimento em Latossolo Vermelho-Escuro fase arenosa, no qual foram estudados os efeitos de adubações anuais com 0,40, 80, 160 e 240 kg/ha de K2O, nas formas de cloreto de potássio e sulfato de potássio, aplicados no sulco de semeadura ou em área total com incorporação. Observou-se resposta à adubação potássica a partir do segundo ano de cultivo. As máximas produções sempre estiveram associadas a teores de potássio nas folhas acima de 1,5%. Em anos mais secos que o normal, as aplicações a lanço proporcionaram melhores resultados do que as aplicações em sulcos. Não foram observadas diferenças entre as fontes de potássio utilizadas. Notou-se acentuado decréscimo nos teores de potássio trocável do solo, com o transcorrer do tempo, sendo necessária a aplicação de doses maiores que 80 kg/ha de K2O por ano para manter o nível original. Por outro lado, a aplicação de doses elevadas de potássio levou a uma perda significativa do nutriente por lixiviação.During three years, an experiment was carried out in a Dark-Red Latosol (sandy loam) to study the effects of annual applications of 0, 40, 80, 160 and 240 kg/ha of K2O as potassium chloride and potassium sulphate, applied in the seed rows or spread and incorporated. There was a yield increase due to potassium fertilization since the second year. Maximum yields were associated to potassium levels in the leaves above 1.5% In drier than normal years, the spreading applications led to better results than row applications. There were no differences between potassium sources. A decrease in exchangeable potassium levels in the soil was observed; for this reason, the application of doses bigger than 80 kg/ha of K2O a year was considered necessary to maintain the original potassium level. On the other hand, the fertilization with higher potassium doses led to a significant loss of potassium by leaching

Effect of the soil Ca/Mg, Ca/K and Mg/K ratios on sweet sorghum production

Foi conduzido um ensaio em casa de vegetação, em vasos com capacidade para 25 litros de terra, com o objetivo de estudar a resposta do sorgo sacarino (Sorghum bicolor) ao magnésio na presença e ausência de calagem e de adubação potássica. Amostras de terra foram tomadas na época da emergência das plantas, onde foi determinado o efeito de quatro doses de Mg na forma de sulfato, duas de potássio na forma de cloreto e duas de cálcio na forma de calcário calcítico sobre as relações Ca/Mg, Ca/K e Mg/K do solo. Na época do emborrachamento foram colhidas folhas para a diagnose foliar, e ao final do ciclo foram analisadas as produções de colmos e de grãos. Os resultados obtidos demonstraram que com teores de Mg no solo variando de 0,15 a 0,52 meq/100 cm3 não houve resposta do sorgo sacarino em termos de produção de colmos, mas quando a relação Mg/K no solo foi menor que 0,6 ou a relação Ca/K no solo foi menor que 7,4, houve prejuízo na produtividade, em função das menores absorções de Mg e Ca, respectivamente. Não houve efeito da relação Ca/Mg sobre a produção de sorgo sacarino. Com relação à produção de grãos, houve resposta ao Mg apenas em um dos solos na ausência de potássio.A experiment was carried out in greenhouse conditions, in pots containing 25l of soil, to study the sorghum (Sorghum bicolor) response to magnesium with and without liming and potassium fertilization. Soil samples were taken at plant emergence and analysis of K, Ca and Mg were performed to determine the effect of four Mg doses as sulphate, two potassium doses as chloride and two calcium doses as calcite limestone upon the soil Ca/Mg, Ca/K and Mg/K ratios. At boot stage sorghum leaves were sampled for foliar diagnosis, and at harvest stalk and grain yields were evaluated. The results didn't show any difference in sorghum stalk yields when the magnesium level in the soil ranged from 0,15 to 0,52 meq/cm3, but when the Mg/K and Ca/K ratios in the soil were lower than 0.6 and 7.4 respectively, there was a decrease in sweet sorghum stalk yields, as a function of the lower Mg and Ca uptake. There was not any effect of the Ca/Mg ratio on sorghum yields. There was an increase in grain yields due to Mg application only in the absence of potassium in one of the soils

Translating aboveground cosmic-ray neutron intensity to high-frequency soil moisture profiles at sub-kilometer scale

Above-ground cosmic-ray neutron measurements provide an opportunity to infer soil moisture at the subkilometer scale. Initial efforts to assimilate those measurements have shown promise. This study expands such analysis by investigating (1) how the information from aboveground cosmic-ray neutrons can constrain the soil moisture at distinct depths simulated by a land surface model, and (2) how changes in data availability (in terms of retrieval frequency) impact the dynamics of simulated soil moisture profiles. We employ ensemble data assimilation techniques in a “nearly-identical twin” experiment applied at semi-arid shrubland, rainfed agricultural field, and mixed forest biomes in the USA. The performance of the Noah land surface model is compared with and without assimilation of observations at hourly intervals, as well as every 2 days. Synthetic observations of aboveground cosmic-ray neutrons better constrain the soil moisture simulated by Noah in root-zone soil layers (0–100 cm), despite the limited measurement depth of the sensor (estimated to be 12–20 cm). The ability of Noah to reproduce a “true” soil moisture profile is remarkably good, regardless of the frequency of observations at the semi-arid site. However, soil moisture profiles are better constrained when assimilating synthetic cosmic-ray neutron observations hourly rather than every 2 days at the cropland and mixed forest sites. This indicates potential benefits for hydrometeorological modeling when soil moisture measurements are available at a relatively high frequency. Moreover, differences in summertime meteorological forcing between the semi-arid site and the other two sites may indicate a possible controlling factor to soil moisture dynamics in addition to differences in soil and vegetation properties