The identification of erosion-susceptible areas is fundamental for the adoption of soil conservation practices. Thus, the best way to estimate the spatial pattern of soil erosion must be identified, in which the process uncertainties are also taken into consideration. The purpose of this study was to evaluate the spatial and temporal uncertainty of soil loss under two scenarios of sugarcane harvest management: green cane (GC) and burnt cane (BC). The study was carried out on a 200-ha area, in Tabapuã, São Paulo State, Brazil. A regular 626-point sampling grid was established in the area, with equidistant intervals of 50 m and a final plant density of about 3.3 samples per ha. The probability that the soil loss would exceed the tolerable limit of 6.67 t ha-1 yr-1 was estimated for each management scenario and after the five harvests. The temporal uncertainty was determined by integrating the estimated annual probabilities, representing the harvests. Areas with soil loss risks above the threshold were identified based on probability maps, generated from the individual and combined dichotomous variables. Soil losses from the BC were highest, during all five harvests. With the exception of the 5 th harvest and the entire cultivation cycle under GC, all soil loss estimates were spatially dependent. From the 4 th harvest under GC, the probability of the soil loss exceeding the threshold was above 80 % in zero percent of the area, whereas, for BC, the probability exceeded 80 % in 40 % of the area. The production cycle allowed the delimitation of priority areas for the adoption of conservation practices in each management. In the BC, areas with steeper slopes were more likely to exceed the threshold with lower uncertainties.

No abstract

the assessment of spatial uncertainty in the prediction of nutrient losses by erosion associated with landscape models is an important tool for soil conservation planning. the purpose of this study was to evaluate the spatial and local uncertainty in predicting depletion rates of soil nutrients (p, K, ca, and Mg) by soil erosion from green and burnt sugarcane harvesting scenarios, using sequential gaussian simulation (SgS). a regular grid with equidistant intervals of 50 m (626 points) was established in the 200-ha study area, in tabapuã, São paulo, brazil. the rate of soil depletion (SD) was calculated from the relation between the nutrient concentration in the sediments and the chemical properties in the original soil for all grid points. the data were subjected to descriptive statistical and geostatistical analysis. the mean SD rate for all nutrients was higher in the slash-and-burn than the green cane harvest scenario (Student's t-test, p<0.05). in both scenarios, nutrient loss followed the order: ca>Mg>K>p. the SD rate was highest in areas with greater slope. lower uncertainties were associated to the areas with higher

O objetivo deste trabalho foi ajustar equações de regressão para estimativa da área foliar de <i>Tillandsia</i> spp. nativas do Brasil. Determinaram-se o comprimento ao longo da nervura principal (C), a largura máxima (L) e a área foliar real de, no mínimo, 100 folhas de cada espécie, mantidas intactas nas plantas. Calcularam-se relações lineares existentes entre a área foliar real e as dimensões C, L e CL (produto entre o comprimento e a largura da folha). O modelo de regressão linear com intercepto foi o mais adequado, e as equações recomendadas, sendo AFE= área foliar estimada, foram: para <i>Tillandsia carminea</i>, AFE= 0,281188 + 0,562219 CL (R2= 0,7296); <i>:Tillandsia dura</i>, AFE= 0,891231 + 0,412457 CL (R2= 0,8432); <i>Tillandsia gardneri</i>, AFE= 2,54412 + 0,445525 CL (R2= 0,8662); <i>Tillandsia geminiflora</i>, AFE= 0,674484 + 0,444418 CL (R2= 0,8474); <i>Tillandsia globosa</i>, AFE= 1,9494 + 0,3804 CL (R2= 0,8178); <i>Tillandsia grazielae</i>, AFE= 0,518512 + 0,530259 CL (R2= 0,7608); <i>Tillandsia kautskyi</i>, AFE= 0,59338 + 0,374353 CL (R2= 0,6931); <i>Tillandsia reclinata</i>, AFE= 0,0379111 + 0,641623 CL (R2= 0,9169); <i>Tillandsia stricta</i>, AFE= 0,3937 + 0,4277 C (R2= 0,8661), ou AFE= 1,21336 + 0,385727 CL (R2= 0,8607); <i>Tillandsia tenuifolia</i>, AFE= 0,991226 + 0,402221 CL (R2= 0,7523).