Daniel Santos Grohs

Modelo para estimativa do potencial produtivo em trigo e cevada por meio do sensor GreenSeeker

Areas with different yield potential within a field need to be managed separately as for nitrogen application in small grain cereals. Terrestrial remote sensing-based equipment such as the GreenSeeker sensor is one of the tools available to handle different management zones. To do this, the sensor allows the definition of classes to estimate yield potential. A model which correlated the Normalized Difference Vegetation Index (NDVI) to shoot dry biomass at the 6-leaf-stage was developed for estimating yield potential classes for wheat and barley. The model eliminated differences between species and cultivars as no correction for these factors is necessary. The effects of surface background (corn or soybean crop residues) were considered in this model. When readings are carried out before or after the recommended period, the model can be adjusted for under or overestimation. Spatial variability analysis may evaluate if yield potential zones estimated by the NDVI classes proposed in the model are related to spatial variability of shoot biomass, N rates applied and grain yield.

Padrão de afilhamento em arroz afetado pela presença dos íons amônio e nitrato

Rice development is affected by nitrogen, specially its tillering pattern which is determined by number of tillers. Tillers synchronism with main stem is related to leaves emission rate and both traits affect the number of productive culms potential. Tiller emission and synchronism of leaf development between main stem and tillers were studied in rice plants (cv IRGA 417) cultivated in a hydroponic solution (Hoagland) under three N concentrations (1, 5 e 10 mmol L-1), each with different proportion of N-NH4+ and N-NO3- (100:0; 75:25; 50:50; 25:75). The different proportions under 1 mmol L-1 were similar for tiller number, synchronism, and productive culms. All traits (tiller number, synchronism and productive culms) were negatively affected when higher levels of N-NH4+ ion (5 and 10 mmol L-1 - 100 and 75% of N ions) were supplied to plants. Nevertheless, when N-NO3- ion was present in at least 50% of the solution, the detrimental effects were not found. When N was at 1 mmol L-1, rice plants tolerate N-NH4+ ion presence, independently of the presence of N-NO3- ion. At higher N concentrations, it is necessary at least 50% of N-NO3- ion in order to avoid detrimental effects on tillering.

Validação de modelo para predição do potencial produtivo de trigo com sensor óptico ativo

The objective of this work was to validate a model based on the normalized difference vegetation index (NDVI) for the prediction of spatial variability of accumulated biomass in shoots and wheat grain yield. Georeferenced readings of NDVI and biomass, at the end of tillering, and of grain yield were carried out. The proposed method allowed relating classes of spatial variability of NDVI and biomass, with 81% of correspondence between them. However, the relation between spatial variability of yield and NDVI was lower, with 48% of correspondence.

Flutuação diária e estacional de nitrato e amônio em um Argissolo Vermelho distrófico típico

Os ions NH4+ e NO3- resultantes do processo de mineralizacao do N orgânico no solo sao as formas predominantes de N mineral disponiveis as plantas. A proporcao desses ions e sua distribuicao no solo e variavel, com flutuacoes diarias e oscilacoes sazonais ao longo do ano. Este trabalho avaliou a variacao dos teores de NH4+ e NO3- em duas areas adjacentes, sendo uma delas cultivada com graos (cevada, soja e cevada) no sistema de plantio direto ha mais de dez anos. Esta area recebeu, ao longo do tempo, fertilizantes a base de P e K e apresentava pH 6,0. A outra area foi mantida sem cultivo (campo limpo), com predominância de gramineas, com baixa fertilidade do solo e pH 4,8. O estudo foi realizado em um Argissolo Vermelho distrofico tipico na Estacao Experimental Agronomica da UFRGS, em Eldorado do Sul-RS, nos anos agricolas de 2002 e de 2003. As amostragens de solo, de carater estacional na area cultivada (31/05/2002 a 23/10/2003) e nao-cultivada (13/06/2002 a 17/10/2002), foram feitas, em media, a cada dez dias. Amostragens de carater diario (16/05 a 30/09 de 2003) foram realizadas em intervalos de um a tres dias. Em ambos os casos, as amostragens de solo foram feitas na camada superficial de 0-0,2 m de profundidade, em areas que nao receberam adubacao nitrogenada durante todo o periodo. As avaliacoes estacionais mostraram que o N mineral (NH4+ + NO3-) elevou-se da primavera ate o verao e decresceu no periodo outono/inverno tanto em 2002 quanto em 2003. As variacoes estacionais evidenciaram que a mineralizacao do N acompanhou, aproximadamente, as oscilacoes na temperatura media do periodo analisado. As avaliacoes diarias mostraram que os teores de N mineral variaram de um dia para outro, sendo as maiores variacoes ocasionadas pelas chuvas. Na area com vegetacao nativa, o N teve comportamento semelhante ao observado nas areas cultivadas com cevada e soja. A proporcao 1:1 dos ions NH4+ e NO3-, observada tanto no solo cultivado quanto naquele mantido sob vegetacao nativa, indica que ha um equilibrio entre as duas formas ionicas, independente do pH e do nivel de fertilidade do solo.

Teores de nitrogênio mineral do solo para predição do potencial produtivo de cevada

Soil N mineral content is not considered when recommending N for grain crops in southern Brazil due to the high variation according to environmental conditions. In the methodology described here soil N mineral is considered in adjusted N recommendations to increase efficiency and reduce production costs. The soil levels of NH4+ and NO3- were analyzed to a depth of 15 cm, in the pre-sowing and grain yield stage of 61 barley trials distributed in 20 counties in three regions of Rio Grande do Sul State (Depressao Central, Planalto Medio and Alto Uruguai) for four years (2002-2005). The yield potential was classified (very low, low, medium, high and very high) and related to the N mineral contents using the Gompertz regression model. The adjusted model indicated two N mineral values delimiting relative yields: 8 and 18 mg kg-1 soil. Low yields predominate below 8 mg kg-1 soil, indicating a direct effect of low N availability on yield potential very early in the season. At soil NH4+ and NO3- values over 18 mg kg-1 soil N was no longer decisive in the formation of yield, indicating a very high yield potential. These values may be useful in models of N recommendation.