The natural chemical qualities of the subsoil of Oxisols often restrict root growth, water use efficiency, and crop yield. The practice of continuous no-till farming creates a fertile topsoil but generally does not affect the subsoil. This study aimed to evaluate the effectiveness of gypsum in improving the chemical attributes of the subsoil and increasing crop yields. To this end, the experiment was conducted at two sites in distrophic Red Oxisols located in southern Brazil. The experimental design was a randomized complete block with three replications. Treatments consisted of broadcast gypsum rates of 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.5 Mg ha -1 . Soil samples were collected from the root zone at the beginning of the experiment and after six and 22 mo to evaluate soil pH and extractable P, K + , Ca 2+ , Mg 2+ , Al 3+ , and SO 4 -S concentrations. After 6 mo of gypsum application, an increase in exchangeable bases associated with a decrease in Al 3+ concentrations in the subsoil was noted, and this improvement was intensified further by 22 mo. An increase in crop yields was related to the increase in base saturation and Ca 2+ saturation and a decrease in Al 3+ saturation in the 25-to 40-cm soil depth. Surface application of gypsum was an effective method of improving the chemical quality of the rooting zone in Oxisols under continuous no-till farming and resulted in a higher impact on corn (Zea mays L.) grain yield than soybean [Glycine max (L.) Merr.] yield.

Modern maize, wheat, and soybean cultivars are usually characterized by a short cycle, high shoot-root ratio, and high responsiveness to nutrient input. Continuous no-tillage management (NTS) frequently leads to a steep gradient in soil chemical quality with depth, thus decreasing yield under conditions of acid subsoil and water stress. This study aimed to evaluate the effect of gypsum, applied separately or in combination with lime, on the yield of cultivars used in the state of Rio Grande do Sul, Brazil. The study consisted of four experiments conducted on a typic Hapludox under NTS. The experiment was arranged in a randomized block design with three replications. Experiments I and II were carried out on soils with a satisfactory chemical soil quality and tested treatments of gypsum applications ranging from 0.0 to 6.5 Mg ha -1 . The other experiments were carried out on acid soil (experiment III) and a soil with an abrupt drop in chemical quality (experiment IV). Experiment III was arranged in a split plot design, where plots corresponded to gypsum rates between 0.0 and 5.0 Mg ha -1 , and subplots to two lime rates (0.0 and 2.0 Mg ha -1 ). Experiment IV was conducted in a split plot design, with plots consisting of gypsum rates from 0.0 to 6.0 Mg ha -1 and subplots of lime rates from 0.0 to 4.8 Mg ha -1 . Of a set of 17 harvests investigated during the experimental period, 82 % responded with yield increases to gypsum and lime inputs. The gypsum rate that induced the highest grain yield was high (4.7 Mg ha -1 ) and similarly, the maximum technical efficiency of lime was higher than the currently recommended. Furthermore, the combined application of lime and gypsum increased yield. There was a correlation between grain yield with the chemical quality of the soil layer 0.25-0.40 m in experiment I, 0.00-0.40 m in experiment II, and the 0.00-0.25 m in experiment IV. Only in experiment III, where the surface layer was acidic, the diagnostic layer usually sampled (0.00-0.10 m) was correlated with grain yield. Therefore, the use of the 0.00-0.25 m soil layer with critical base saturation values of 65 % and maximum Al saturation of 5 % could improve the current recommendations for soil correction. To exploit the yield potential of modern grain cultivars on dystrophic Oxisol, the formation of a thicker layer with high chemical quality is an efficient strategy.

Resumo -O objetivo deste trabalho foi avaliar as relações da condutividade elétrica aparente (CEa), determinada por sensoriamento em tempo real, com os atributos do solo e com a produção vegetal, além de espacializar de forma indireta e em alta resolução os componentes da acidez de um Latossolo Vermelho distrófico no Sul do Brasil. O sensoriamento do solo foi realizado em duas áreas agrícolas, com o sensor Veris 3100. O solo foi amostrado à profundidade de 0,00-0,15 m, com trado calador. Avaliou-se o índice de vigor do milho (IV) com um sensor óptico, e a produtividade com sensores de produtividade e umidade. A associação dos atributos da acidez do solo com a produtividade do milho e com a CEa foi determinada por meio de análises de correlação e de componentes principais. A CEa relacionou-se ao IV e à produtividade de milho. Além disso, na área com qualidade química inferior, a CEa apresentou relação positiva com os conteúdos , matéria orgânica do solo e teor de argila.Termos para indexação: agricultura de precisão, condutividade elétrica, fertilidade do solo, manejo sítio-específico, matéria orgânica do solo, variabilidade espacial. High-resolution spacialization of an Oxisol's acidity attributes by on-the-go sensingAbstract -The objective of this work was to evaluate the relationships between the apparent electric conductivity (ECa), measured by on-the-go sensing, with soil attributes and plant production, besides indirectly mapping with high resolution, the main acidity attributes of an Oxisol in South Brazil. Soil sensing was performed in two crop fields using the Veris 3100 sensor. Soil was sampled at the 0.00-0.15-m soil depth using a hand auger. The corn vigor index (VI) was measured with an optical sensor, and yield was determined using grain yield and moisture sensors. contents, soil organic matter, and clay content.

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Rice culture can suffer great damages due to fungal diseases which affect seeds, roots, leaves and panicles, among which the blast disease stands out. In this context, the chemical control through fungicide use takes a key role, promoting healing, protecting and eradicative effects of the disease. The great majority of fungicides recommended include active ingredients of systemic action ways, that is, capable of penetrating and moving inside plants, being able to exert its effect in a different location from that applied. This study presents a review about the systemic fungicide use for blast disease control. For this disease, there are 25 registered commercial products which include 12 different active ingredients, considering seed treatment and foliar application, involving a total of 6 distinct ways of systemic action. The treatment with systemic fungicides has been shown efficient in chemical control for promoting healing, protecting and eradicating effects of the disease.