Combining sediment source tracing techniques with traditional monitoring to assess the impact of improved land management on catchment sediment yields

Summary This paper aims to demonstrate the potential value of combining sediment source tracing techniques with traditional monitoring approaches, when documenting the impact of improved land management on catchment sediment yields. It reports the results of an investigation undertaken in a small (1.19 km 2 ) agricultural catchment in southern Brazil, which was monitored before and after the implementation of improved land management practices. Attention focussed on 50 storm events that occurred between May 2002 and March 2006 and which reflected the behaviour of the catchment during the pre-change, transition and post-change periods. Improved land management, involving minimum-till cultivation and the maintenance of good crop cover, was introduced in early 2003. The traditional monitoring provided a basis for evaluating the changes in storm runoff volume, storm hydrograph peak and storm-period sediment load and mean suspended sediment concentration. The results indicate that both storm runoff volumes and peak flows associated with a given amount of rainfall provided evidence of a significant decrease after the introduction of improved land management. Storm-period sediment loads showed a similar reduction, with a reduction by as much as 80% for low magnitude events and of ca. 40% for events of intermediate magnitude. However, there was no significant change in mean suspended sediment concentrations, indicating that the reductions in sediment load were primarily the result of the reduced storm runoff volume. Sediment source fingerprinting was used to explore the changes in the relative and absolute contributions to the storm sediment loads from the three key sources, Journal of Hydrology (2008) 348, 546-563 a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l namely the surface of the fields under crops, the unpaved roads and the stream channels. A comparison of the load-weighted mean contributions for the pre-and post-treatment periods indicated that the contribution from the field surfaces and unpaved roads decreased from 63% and 36% to 54% and 24%, respectively, whereas the contribution from the stream channels increased from ca. 2% to 22%. By relating the absolute amounts of sediment mobilised from each individual source group to variables representing the runoff and precipitation associated with the events, it was possible to identify changes in the response of the individual sediment sources to the changes in land management that occurred within the catchment. Sediment mobilisation from the stream channel during individual events increased substantially over the whole range of flows after the introduction of improved land management in the study catchment, whereas the amounts of sediment mobilised from the surfaces of the fields and the unpaved roads showed a significant decrease during events of low and intermediate magnitude. The short monitoring period associated with the study, coupled with inter-annual variations in rainfall, necessarily limit the scope and rigour of the study reported, but it is seen to provide a useful demonstration of how the coupling of sediment source tracing with more traditional monitoring techniques can provide an improved understanding of the impact of improved management practices on the sediment response of a catchment, as well as important information to inform the design and implementation of effective sediment management and control measures.

Three rootstocks and six spacings on "Valência" orange production

Neste trabalho são estudados os efeitos da combinação de dois espaçamentos de plantio entre linhas, com três distâncias entre plantas, sobre a produção da laranjeira 'Valência' (Citrus sinensis (L.) Osbeck), em três porta-enxertos: limoeiro 'Cravo' (Citrus Iimonia Osbeck), laranjeira 'Caipira' (Citrus sinesis (L.) Osbeck) e 'Trifoliata' (Poncirus trifoliata Raff.). O experimento foi realizado na Estação Experimental Agronômica da Universidade Federal do Rio Grande do Sul, no período 1976 a 1981. Os menores espaçamentos testados não afetaram a produtividade das plantas, mas aumentaram o rendimento do pomar, proporcionalmente ao número de árvores por unidade de área. O limoeiro 'Cravo' proporcionou a maior produtividade por planta e o maior peso médio dos frutos, seguindo-se a laranjeira 'Caipira' e o 'Trifoliata', em ordem decrescente. Na primeira safra o 'Trifoliata' induziu maior produtividade do que a laranjeira 'Caipira', e foi por ela superado na segunda e na terceira safra. Na primeira safra, a distância de dois metros entre plantas, nas árvores enxertadas no limoeiro 'Cravo', proporcionou maior produtividade, por planta, do que os espaçamentos mais amplos.In this experiment the effects of the combination of two row widths with three plant spacings within row on the yield of 'Valência' Orange (Citrus sinesis (L.) Osbeck), grafted on three kinds of rootstocks:  'Rangpur' lime (Citrus limonia Osbeck) 'Caipira' orange (Citrus sinensis (L.) Osbeck), and 'Trifoliata' Orange (Poncirus trifoliata Raff.) were studied. The research was conducted at the Estação Experimental Agronômica da Universidade Federal do Rio Grande do Sul, from 1976 through 1981. The lowest spacings tested did not affect plant productivity, but they increased yield per area proportionately to the number of trees per area unit. The highest production per plant and the highest fruit weight were obtained by 'Rangpur' lime; 'Caipira' was the second. and ' Trifoliata' the third. In the first harvest, 'Trifoliata' induced higher productivity than the 'Caipira'; the opposite was observed on the second and third harvests. Also in the first harvest 'Valência' orange grafted on 'Rangpur' lime rootstocks produced higher yields per plant when these were spaced 2 m apart than by wider spacings

The expansion of Brazilian agriculture: Soil erosion scenarios

During the next 10 years Brazil’s agricultural area will expand to meet increased domestic and worldwide demand for food, fuel, and fiber. Present choices regarding land use will determine to what degree this expansion will have adverse effects that include soil erosion, reservoir siltation, water quality problems, loss of biodiversity and social conflict, especially around indigenous reservations. This paper presents an up-to-date inventory of soil erosion in Brazil caused by crop and livestock activities and provides estimates based on three different hypothetical land-use scenarios to accommodate the expansion of Brazilian agricultural activity by 2020: Scenario 1 – expansion of cropping into areas of natural vegetation, without adoption of conservation practices; Scenario 2 – expansion of cropping into areas of degraded pasture, without adoption of conservation practices; Scenario 3 – expansion of cropping into areas of degraded pasture, together with conservation practices in 100% of the expanded area. The worst-case scenario involves expansion of agriculture into areas of native vegetation in the Brazilian Savannah (Cerrado) and Brazilian rainforest (Amazon) biomes, and could increase total soil erosion in Brazil (currently about 800 million metric tons a year) by as much as 20%. In the best-case scenario, crop expansion under a conservation agriculture model would utilize currently degraded pasture, especially in the Savannah (circa 40 million hectares), reducing soil erosion in Brazil by around 20%. For this to occur, however, a national soil and water conservation policy needs to be implemented in Brazil to support a sustainable model of agriculture in which the environment can be preserved as much as possible

Use of the swat model for hydro-sedimentologic simulation in a small rural watershed

Mathematical models have great potential to support land use planning, with the goal of improving water and land quality. Before using a model, however, the model must demonstrate that it can correctly simulate the hydrological and erosive processes of a given site. The SWAT model (Soil and Water Assessment Tool) was developed in the United States to evaluate the effects of conservation agriculture on hydrological processes and water quality at the watershed scale. This model was initially proposed for use without calibration, which would eliminate the need for measured hydro-sedimentologic data. In this study, the SWAT model was evaluated in a small rural watershed (1.19 km²) located on the basalt slopes of the state of Rio Grande do Sul in southern Brazil, where farmers have been using cover crops associated with minimum tillage to control soil erosion. Values simulated by the model were compared with measured hydro-sedimentological data. Results for surface and total runoff on a daily basis were considered unsatisfactory (Nash-Sutcliffe efficiency coefficient - NSE < 0.5). However simulation results on monthly and annual scales were significantly better. With regard to the erosion process, the simulated sediment yields for all years of the study were unsatisfactory in comparison with the observed values on a daily and monthly basis (NSE values < -6), and overestimated the annual sediment yield by more than 100 %

Brazilian Agriculture in Perspective: Great Expectations vs Reality

Agronomists in most parts of the world are already, and will be increasingly in the next couple of decades, solicited to resolve pressing issues associated with global climate change and food security. For a number of reasons, it is most likely that in both of these areas, their research will be very tightly linked to what happens in Brazil. In that context, this chapter attempts to offer as complete a picture as possible of the events and influences that have shaped historically both Brazilian agriculture and its agricultural research efforts, as well as their relationships with other sectors of Brazilian society. An account is provided of the history of Brazilian agriculture and of the initially slow, then extremely rapid development of the agricultural research sector. This chapter also analyzes in detail the present contributions of agriculture to the economic and social consolidation of Brazil, describes the main actors of research and technological development, discusses the effect of agricultural production and expansion on the environment, tries to identify the various forces that are influencing Brazilian agriculture in the future, and lists the main challenges that will have to be faced in the future of Brazilian and world agriculture. Throughout the chapter, we try to make clear how Brazilians interpret as half-truths a number of statements commonly made about Brazilian agriculture, and how they see their agriculture evolve in the foreseeable future, with a discourse that often differs substantially from the one commonly put forth by the media or even scientists elsewhere in the world. This analysis results in the description of a proposed national agricultural policy that attempts to move Brazilian agriculture in the right direction within the context of the nation's economy