Variabilidade no espaçamento de sementes reduz a produtividade de feijão-comum

An uneven seed spacing in the sowing row increases the plants intraspecific competition for environmental resources, potentially lowering grain yields. This study aimed to assess the yield and yield components of common bean plants, as a function of coefficients of variation (0 %, 20 %, 40 % and 60 %) of seeds in the sowing row. The main yield components, plant traits and grain yield were evaluated. The yield component that best explains the seed spacing variability on grain yield is the number of grains per plant (r = 0.94). Grain yield declines linearly as the seed spacing variability increases: 81.5 kg ha-1 (4.4 %) for every 10 % increase in the coefficient of variation. Thus, a less longitudinal seed spacing variability contributes to achieving higher grain yields.A distribuição irregular de sementes na linha de semeadura aumenta a competição intraespecífica das plantas por recursos ambientais, podendo reduzir a produtividade de grãos. Objetivou-se avaliar os componentes de rendimento e produtividade de feijão- comum, em função de coeficientes de variação (0 %, 20 %, 40 % e 60 %) das sementes na linha de semeadura. Avaliaram-se os principais componentes de rendimento, características da planta e produtividade de grãos. O componente de rendimento que melhor explica a distribuição das sementes na produtividade de grãos é o número de grãos por planta (r = 0,94). A produtividade de grãos reduz-se linearmente com o aumento da variação na distribuição das sementes: 81,5 kg ha-1 (4,4 %) para cada 10 % de aumento no coeficiente de variação. Dessa forma, uma semeadura com baixa variabilidade longitudinal contribui para a obtenção de maior produtividade de grãos

Sampling grids used to characterise the spatial variability of pH, Ca, Mg and V% in Oxisols

Knowledge of spatial variability is an important factor to be considered in planning a program of soil sampling and crop management under precision agriculture (PA). In this context, the aim of this work was to evaluate the efficiency of the dimensions of sampling grids used in the state of Rio Grande do Sul (RS), Brazil to characterise the spatial variability of the attributes pHwater, base saturation (V%), calcium (Ca) and magnesium (Mg) levels. The study was carried out on 30 agricultural sites located in the northern region of RS, having soils classified as Oxisols and managed using the tools of PA. The dimensions of the grids under study were: 100 x 100 m (10 areas), 142 x 142 m (10 areas) and 173 x 173 m (10 areas). Soil was collected at a depth of 0.00 to 0.10 m. The data for pHwater, V%, Ca and Mg were subjected to exploratory statistical analysis and to geostatistical analysis by means of semivariograms. The areas showed high Ca (>4.0 cmol c dm-3) and Mg (>1.0 cmol c dm-3) levels and localised problems of soil acidity (pHwater <5.5 or V<65%), justifying the carrying out of liming at specific sites. For the geostatistical procedures, the sample grids used at the sites of the Oxisols managed under PA in RS are not efficient in capturing the scales of spatial variability of the attributes pHwater, V%, Ca and Mg, which could compromise the accuracy of corrective prescriptions for specific sites