ABSTRACT Phosphorus losses in runoff water and eroded sediment may increase the risk of eutrophication. Erosion prediction models can be used to assess and quantify nutrient losses and transport in different soil management scenarios. This study aimed to assess the performance of models to estimate the losses of available phosphorus in eroded sediments and assess their spatial variability pattern. The experiment was installed on a eutrophic Red Ultisol located in Tabapuã, northwestern São Paulo State, São Domingos Stream Watershed. Aiming at estimating and validating the models, measurements were made from 2007 to 2015 at 17 observation points (slopes), determining soil phosphorus content (Psoil), eroded sediments (Psed), and enrichment rate (ERsed). The models applied to estimate the enrichment rates of phosphorus in the eroded sediment and runoff are efficient when in use with the predictions of the model Water Erosion Prediction Project (WEPP). The enrichment rates obtained presented a Nash-Sutcliffe (NS) coefficient close to 1. Losses of soluble phosphorus in runoff above 0.02 mg L−1, a critical value for eutrophication, can be obtained in 81% of the watershed area with a probability higher than 75%.

ABSTRACT Considering the importance of nutrients in the soil for the plants development and the soil quality conservation and the quantification relevance of them for proper soil management, the aims of this research were: (i) to quantify the clay loss, adsorbed and soluble P from interrill erosion influenced by the presence of sugarcane residues on the ground surface; (ii) to determine the minimum percentage of residues to be maintained on the soil surface to not enrich the eroded sediment by clay and soluble P (Psed) and adsorbed (Pads). The experimental area is located in Guariba - SP, with soil classified as Red Dystrophic Oxisol. The experiment was designed based on results of previous experiments with residue analysis of variance for 40 plots. These experiments were conducted by our research group, which provided field representation and the establishment of a minimum number of degrees of freedom necessary to ensure normal distribution of results and variance homoscedasticity. The experimental design was completely randomized in a factorial design, 5 treatments with straw sugarcane and 3 repetitions, totaling 15 plots. In the treatments, the straw was manually distributed across the surface of the soil in amounts of 0; 0.16; 0.35; 0.52 to 0.7 Kg by plot, giving 0% coverage (SC0), 25% (SC25), 50% (SC50), 75% (SC75) and 100% (SC100), respectively. The experimental plots were subjected to simulated rain with average intensity of 60 mm h−1 for 65 minutes. To avoid enrichment ratio (ER) of the sediment eroded by Psed, Pads and clay, a minimum soil surface coverage (SC) of 42% is necessary.

RESUMO O trabalho foi desenvolvido em dois experimentos em casa de vegetação do CTRN/UFCG objetivando avaliar o uso de composto orgânico oriundo de lixo doméstico e irrigação com água residuária doméstica tratada no crescimento das culturas da mamona BRS-188/Paraguaçu e girassol EMBRAPA 122-V2000. Em ambos os experimentos utilizou-se o delineamento experimental em blocos casualizados em esquema fatorial 6 x 2 com 3 repetições sendo 6 doses de composto orgânico (0; 1,2; 2,0; 2,8; 3,6 e 4,4 kg vaso-1, correspondentes a 0, 60, 100, 140, 180 e 220 kg N ha-1) e 2 tipos de água (água de abastecimento e água residuária). Verificou-se que as doses de composto orgânico influenciaram significativamente o crescimento do girassol e da mamona, em todas as avaliações, exceto para o diâmetro do caule. As alturas máximas de planta foram de 91,7 cm para mamona e 85,2 cm para o girassol nas doses de 180 e 220 kg N ha-1, respectivamente. Os maiores valores de número de folhas foram obtidos para a dose de 220 kg N ha-1 em ambas as culturas. A influência da água residuária nas variáveis de crescimento só foi verificada nas avaliações finais, tanto para o girassol como para a mamona.

ABSTRACT The study was conducted in two experiments in greenhouse of the CTRN/UFCG, aiming to evaluate the use of organic compost from household garbage and irrigation with treated domestic wastewater on the growth of castor bean 'BRS-188/Paraguaçu' and sunflower 'Embrapa 122-V2000'. Both experiments were conducted a randomized block design in 6 x 2 factorial scheme, with three replicates, which corresponded to six doses of organic compost (0, 1.2, 2.0, 2.8, 3.6 and 4.4 kg pot-1, equivalent to 0, 60, 100, 140, 180 and 220 kg N ha-1) and two types of water (freshwater and wastewater). It was found that the organic compost doses significantly influenced the growth of sunflower and castor bean in all evaluations, except for stem diameter. The maximum plant heights were 91.7 cm for castor bean and 85.2 cm for sunflower at the doses of 180 and 220 kg N ha-1, respectively. The highest values of number of leaves were obtained for the N dose of 220 kg ha-1 in both crops. The influence of wastewater on growth variables was only observed in the final evaluations, for both sunflower and castor bean.