RESUMO Apesar de sua relevância, o nitrogênio apresenta reduzido aproveitamento pela planta quando aplicado de forma inadequada. Assim, objetivou-se avaliar a produtividade e a eficiência do uso de nitrogênio (EUN) no milho em resposta a doses e parcelamentos da adubação nitrogenada. O delineamento experimental utilizado foi de blocos ao acaso, com três repetições. Foram aplicadas doses de 0, 30, 60 e 180 kg ha-1 de nitrogênio em semeadura visando criar diferentes condições nutricionais das plantas de milho e assim obter diferentes níveis de Índice de Vegetação por Diferença Normalizada (NDVI) medidos com sensor óptico “GreenSeeker®”. As subparcelas com doses de nitrogênio em cobertura de 0, 30, 60 e 90 kg ha-1 em V8 e uma dose de 60 kg ha-1 em V12 foram alocadas experimentalmente nas parcelas com doses de 0, 30, 60 e 180 kg ha-1 de nitrogênio em semeadura. Além disso, foi calculado no experimento a EUN através de índices agronômicos determinados a partir das aplicações de N em cobertura tardia (V8 e V12) e contrastado às possíveis combinações nas doses de 60, 90 e 120 kg ha-1 de nitrogênio total aplicado. Os resultados mostraram que houve relação linear entre dose de adubo nitrogenado e o NDVI, tanto no estádio V8, como em V12. As adubações em cobertura tardia (V12) não provocaram decréscimo na produtividade de grãos quando combinadas com as doses de nitrogênio na semeadura, inclusive apresentaram uma maior EUN. O parcelamento das doses de nitrogênio demonstrou melhores EUN que as combinações onde o nitrogênio não foi aplicado em semeadura ou cobertura. O atraso das coberturas nitrogenadas pode ser uma alternativa para o planejamento do momento da fertilização com N de acordo com a previsão climática em cada região.

ABSTRACT Despite its relevance, nitrogen is poorly utilized by the plants when improperly applied. Thus, the objective of this study was to evaluate the yield and nitrogen use efficiency (NUE) in corn in response to doses and split application of nitrogen fertilization. The experimental design was a randomized block design, with three replications. Doses of nitrogen of 0, 30, 60 and 180 kg ha-1 were applied at sowing in order to create different nutritional status of corn plants and to obtain different values of Normalized Difference Vegetation Index (NDVI) measured with “Greenseeker®” optical sensor. The subplots with nitrogen doses in topdressing of 0, 30, 60 and 90 kg ha-1 at V8 and a dose of 60 kg ha-1 at V12 were placed in experimental plots with doses of 0, 30, 60 and 180 kg ha-1 of nitrogen at sowing. Moreover, NUE was calculated in the experiment using agronomic indexes determined by applications of nitrogen in late topdressing (V8 and V12) and contrasted to the possible combinations at doses of 60, 90 and 120 kg ha-1 of total N applied. The results showed the occurrence of a linear relationship between nitrogen fertilizer dose and NDVI at V8 as well as at V12 stages. Late topdressing fertilizations (V12) did not cause a decrease in grain yield when combined with nitrogen fertilization at sowing, moreover resulted in higher NUE. Split the nitrogen dose showed better NUE than the combinations where nitrogen was not applied at sowing or in topdressing. The delay of nitrogen topdressing can be an alternative for the planning of the moment of the N fertilization according to the climate forecast in each region.

ABSTRACT Improvement of soil chemical properties in dystrophic Oxisols managed under long-term no-tillage system (NTS) with surface broadcast lime has been, frequently, restricted to a shallow topsoil layer. As a consequence, a sharply-defined chemical quality gradient is created, with deterioration from the surface towards deeper layers in Oxisols in southern Brazil. The aim of this study was to assess the temporal effects of gypsum, applied alone or in combination with lime, on Ca2+ content and Al3+ saturation in the rooting zone (RZ) (0.00-0.40 m). Four experiments were conducted from 2009 to 2014 in Typic Hapludox soils with distinct chemical qualities in the RZ managed under a long-term NTS (over 20 years) in Rio Grande do Sul (subtropical region). A randomized block experimental design with three replications was used. Experiments I and II were implemented in 2009, with treatments consisting of gypsum rates ranging from 0.0 to 6.5 Mg ha-1. The other two experiments were implemented in 2011. In experiment III, a split-plot design was used, with plots received gypsum rates ranging from 0.0 to 5.0 Mg ha-1, and the subplots received two lime rates (0.0 and 2.0 Mg ha-1). A split-plot design was also used in experiment IV, with plots receiving gypsum rates ranging from 0.0 to 6.0 Mg ha-1, and subplots receiving four lime rates, ranging from 0.0 to 4.8 Mg ha-1. Soil samples were stratified in layers at depth from 0.00 to 0.60 m and taken during the period of the experiment. The use of gypsum increased the Ca2+ and SO42−-S contents, proportional to the rate applied, and lowered Al3+ saturation throughout the soil profile evaluated. However, an increase in base saturation of the subsoil (0.25-0.60 m layer) was only observed at high rates of gypsum (>5.0 Mg ha-1) in the medium-term and through accumulation of a high rainfall volume. A faster and more pronounced effect of subsoil improvement was observed when the chemical quality of the topsoil layer was already high and when gypsum and lime were applied in combination. Greater improvement in subsoil chemical quality induced by gypsum, alone or in combination with lime, was found in a period exceeding 30 months (Experiments III and IV), remaining for up to 54 months (Experiments I and II). The combination of gypsum with lime was an effective strategy to increase vertical movement of bases in the RZ, mitigating the gradient of chemical quality in dystrophic Oxisol, avoiding discontinuity in the NTS.

ABSTRACT 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 de Ca2+, Mg2+, com pH em água, saturação e soma de bases, e com a capacidade de troca catiônica; e negativa com os valores de Al3+, saturação por alumínio e de H+Al3+. Na área com melhor qualidade química, a CEa apresentou relação com Ca2+, Mg2+, matéria orgânica do solo e teor de argila.

Abstract 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. The association of soil acidity attributes with corn yield and ECa was determined with correlation and principal component analyses. ECa was associated with the VI and corn yield. Moreover, in the area with low chemical quality, ECa had a positive relationship with Ca2+ and Mg2+ contents, pH in water, base saturation, sum of bases, and cation exchange capacity; and a negative relationship with Al3+, aluminum saturation, and H+Al3+ values. In the area with better chemical quality, ECa was related to Ca2+ and Mg2+ contents, soil organic matter, and clay content.