Soil Conservation Strategies Research Articles

Temporal variations in runoff and soil loss in relation to soil conservation practices in catchments in Shiwaliks of lower Himalayas

The soil conservation strategies adopted in the catchments of Shiwaliks, the most fragile region in the Himalayan ecosystem, failed to serve their purpose after a few years of their execution. A study was carried out in four differentially-treated catchments to monitor the variation in runoff and soil loss. The treatments imposed during 1988 included fencing,planting native vegetation and engineering structures in catchment I ; planting native vegetation and fencing in catchment II ; fencing alone in catchment III in addition to an untreated catchment IV. The soil loss during the initial years (1989 – 1995) of imposition of the treatments was lowest (25. 2tha-1) in catchment I, treated to the maximum extent and highest (43. 3tha -1) in untreated catchment IV. During the later period (1996 – 2006) the trends reversed, i. e., catchment IV recorded the lowest (14. 1tha-1) soil loss whereas catchment I recorded the highest (23. 4tha-1) soil loss despite the fact that there was no change in the status of soil conservation or the characteristics of the catchments. The runoff was 71% higher in untreated catchment than in treated catchments initially and this difference decreased to 27% during the later period.

A software coupling approach to assess low-cost soil conservation strategies for highland agriculture in Vietnam

Soil degradation is an environmental process mainly caused by land use decision-makers that has substantial feedback effects on livelihoods and the environment. To capture these feedback effects an...

Soil Erosion Estimation Based on GIS and Remote Sensing for Supporting Integrated Water Resources Conservation Management

Soil erosion is a crucial environmental problem in the Manjunto watershed, Bengkulu Province, Indonesia. It has economic implications and environmental consequences. Assessment of potential soil erosion rate is useful in designing soil conservation strategies within the framework of integrated watershed management. Information obtained from Remote Sensing (RS) and Geographic Information System (GIS) framework supports decision makers in preparing more accurate spatial maps in less time and cost. The aim of this research is to assess the average annual rate of potential soil erosion in Manjunto watershed for each soil mapping unit using remote sensing data, namely Normalized Difference Vegetation Index (NDVI) and Slope. The NDVI value obtained from satellite imagery processing while slope value obtained from Digital Elevation Model-Shuttle Radar Topographic Mission (DEM-SRTM) processing. The results showed that the eroded catchment area increased significantly. The average annual rate of potential soil erosion in Manjunto watershed in the year 2000 amounted to 3.00 tons ha-1 year-1 , while in the year 2009 there was a significant increase to 27.03 ton ha-1year-1 . The levels of erosion hazard in soil mapping unit numbers 41, 42 and 47 are classified in the very heavy category. Soil mapping unit numbers 41, 42 and 47 should be a first priority in soil and water conservation activities.

Greening summer fallow with legume green manures: On-farm assessment in north-central Montana

Replacing summer fallow practices with annual legumes as green manures (LGMs) may increase the sustainability of northern Great Plains wheat (Triticum aestivum L.) systems. Viability hinges on soil water use management and realizing biologically fixed nitrogen (N) benefits. Plot-scale research has shown that managing LGMs with first-flower stage termination and no-till practices conserves soil water and that rotational N benefits can increase wheat grain quality. Nonetheless, farmer adoption of LGMs has been negligible. To better understand this practice and its regional adoption potential, we conducted a participatory on-farm assessment of no-till LGM versus summer fallow–wheat rotations in north-central Montana. Soil water and nitrate (NO3) levels to 0.9 m (3 ft), potentially mineralizable N (PMN) to 0.3 m (1 ft), wheat yields, conservation potential, and producer adoption challenges were assessed at five farmer-managed, field-scale sites. Compared to fallow, LGM treatment diminished mean wheat yield by 6% (0.24 Mg ha−1 [3.7 bu ac−1]), diminished grain protein by 9 g kg−1 when wheat was fertilized with N (p = 0.01), and increased grain protein by 5 g kg−1 when wheat was unfertilized (p = 0.08). Small soil water depletions in LGM treatments below fallow at wheat seeding (17%; 30 mm [1.2 in]) and near-record high rainfall during the wheat growing season (280 to 380 mm [11 to 14 in]) suggest that LGMs likely did not limit soil water available to wheat in this study. Soil NO3 levels following LGMs were 29% to 56% less than summer fallow at wheat seeding, and conversely, greater PMN was detected in LGM treatments at 3 of 5 sites. We theorize that N mineralization from LGMs was insubstantial by wheat seeding due to dry soil conditions and low LGM biomass N contributions, consequently affecting wheat yield potential due to limited early season soil N availability. LGMs increased average use efficiency of available N by 24% during the wheat year and increased total residue carbon (C) and N returned to soils by 260 and 26 kg ha−1 (232 and 23 lb ac−1), respectively, after two years. Our results illustrated that farmers viably managed LGM soil water use with early termination and no-till practices but that LGM adoption may be hindered by a lack of immediate wheat yield or protein benefits from legume-N and seed costs for LGMs. Appropriate incentives, management strategies, and yield benefit expectations (short versus long term) should be fostered to increase the adoption potential of this N-economizing soil and water conservation strategy.

A software coupling approach to assess low-cost soil conservation strategies for highland agriculture in Vietnam

Soil degradation is an environmental process mainly caused by land use decision-makers that has substantial feedback effects on livelihoods and the environment. To capture these feedback effects and the resulting human-environment interactions, we used an agent-based modeling approach to couple two software packages that simulate soil, water and plant dynamics (LUCIA), and farm decision-making (MP-MAS). We show that such a software coupling approach has advantages over hard-coded model integration as applied by most other comparable studies, as it facilitates combining of increasingly sophisticated individual models and can achieve a well-balanced representation of agricultural systems. Using a numerical application for a small mountainous watershed in northwest Vietnam we show the challenges in model coupling, calibration and partial validation, and explore the properties of the coupled model system. Scenario analysis covering the introduction of low-cost soil conservation techniques indicates that some of these techniques would have an impact on soil erosion, maize productivity and household income levels in the study catchment area under current conditions. However, maize yields and the adoption of soil conservation appear to be sensitive to the price of mineral fertilizers, with lower fertilizer prices impeding the adoption of soil conservation measures. The software coupling approach was able to capture interactions between decision-makers and natural resources, as well as the level of spatial variability, in more detail than the individual models. Still, the greater number of endogenous variables and thus degrees of freedom increased the importance of validation and testing parameter sensitivity of the results.

Do atmospheric teleconnection patterns influence rainfall erosivity? A study of NAO, MO and WeMO in NE Spain, 1955–2006

Summary Rainfall erosivity is the ability of precipitation to erode soil. Raindrops impact on the surface—rainsplash—represents an important mechanism of soil particles detachment. If the soil is not perfectly flat rainsplash will also produce the movement of soil particles down the slope due to diffusion. But even in the case of flat soils the detached particles will be available for transport by other erosion agents such as surface runoff. Despite its importance as fundamental erosion process very few studies have addressed the climatology of rainfall erosivity. It is known fact rainfall erosivity in long term (e.g., cumulative annual values) is determined by a few number of heavy events. This study analyses the interannual variability of daily rainfall erosivity in NE Spain during the period 1955–2006, and its connection with atmospheric circulation patterns influencing rainfall in the region, namely the North Atlantic Oscillation (NAO), the Mediterranean Oscillation (MO) and the Western Mediterranean Oscillation (WeMO). It is found that the erosive power of rainfall is stronger during negative phases of the three atmospheric circulation indices, and weaker during positive conditions. Daily rainfall erosivity series were adjusted to a Generalized Pareto probability distribution for positive and negative days of the atmospheric circulation indices, for assessing their effects on rainfall erosivity extreme events. Results showed higher values expected for a given return period in most of the area under negative conditions of all indices, especially at the Mediterranean coast. Overall, MO and WeMO showed the strongest influence on daily rainfall erosivity extremes. These findings would be useful in the implementation of soil conservation strategies.

Assessment of sand encroachment in El-Qutaynah area, Sudan using remote sensing and geographic information system

Excavation involved in mining destroys useful soil for farming activities. Hence, this study was carried out to investigate the effect of mining on farming in Jos South Local Government Area of Plateau State. Random sampling technique was used to select 120 respondents from the area. The result reveals that 54.2% of the respondents identified low crop yield as the major consequence of mining on arable land in the area. Significant relationship existed at p < 0.05 between mining and the type of farming activities (χ 2 = 51.950), mining and consequences of mining (χ 2 = 94.583), mining and alternative work engaged in by the people (χ 2 = 45.300). The result revealed that tin mining activities reduced farm land through soil erosion problems, swampy nature of neglected mined excavation, mine dump and pits on the arable land. Consequently, the farmers experienced low productivity in crop farming, land fragmentation, land disputes and conflicts in the area. It is therefore recommended that definite measures should be taken to bring mining affected land back to productive farm land. Also, a soil conservation strategy should be planned for future mining.

Spatial Distribution of Soil Organic Matter Using Geostatistics: A Key Indicator to Assess Soil Degradation Status in Central Italy

Soil organic matter (SOM) content is one of the main factors to be considered in the evaluation of soil health and fertility. As timing, human and monetary resources often limit the amount of available data, geostatistical techniques provide a valid scientific approach to cope with spatial variability, to interpolate existing data and to predict values at unsampled locations for accurate SOM status survey. Using geostatistical and geographic information system (GIS) approaches, the spatial variability of some physical and chemical soil parameters was investigated under Mediterranean climatic condition in the Abruzzo region of central Italy, where soil erosion processes accelerated by human induced factors are the main causes of soil degradation associated with low SOM content. Experimental semivariograms were established to determine the spatial dependence of the soil variables under investigation. The results of 250 soil sampling point data were interpolated by means of ordinary kriging coupled with a GIS to produce contour maps distribution of soil texture, SOM content related to texture, and C/N ratio. The resulting spatial interpolation of the dataset highlighted a low content of SOM in relation with soil texture in most of the surveyed area (87%) and an optimal C/N ratio for only half of the investigated surface area. Spatial location of degraded area and the assessment of its magnitude can provide decision makers with an accurate support to design appropriate soil conservation strategies and then facilitate a regional planning of agri-environmental measures in the framework of the European Common Agricultural Policy.

Application of a RUSLE-based soil erosion modelling on Mauritius Island

Soil erosion by water is one of the most important natural resources management problems in the world. The damages it causes on-site are soil loss, breakdown of soil structure, and decline in organic matter content, nutrient content, fertility, and infiltration rate. Lands with the highest erosion risk on Mauritius Island are crop cultivations (sugarcane, tea, vegetables) on erosion-susceptible terrain (slopes &gt;20% coupled with highly erodible soils). The locations of such lands on Mauritius were mapped during previous, qualitatively based regional-scale erosion studies. In order to propose soil conservation strategies, there is a need to apply a more quantitative approach to supplement the previous, qualitatively based studies. This paper reports an application of the Revised Universal Soil Loss Equation (RUSLE) within a geographical information system in order to estimate soil loss on the island, and particularly for the high-erosion areas. Results show that total soil loss on the island is estimated at 298 259 t year–1, with soil loss from high-erosion areas summing 84 780 t year–1 (28% of total soil loss). If all of the high-erosion areas were afforested, their soil loss would be reduced to 10 264 t year–1, i.e. a reduction of 88% for the high-erosion areas and a reduction of 25% for the island. This study thus calls for soil and water conservation programs directed to these erosion-prone areas before the land degradation and environmental damage they are causing become irreversible. The methodological approach used in this work to quantitatively estimate soil loss from erosion-prone areas can be adopted in other countries as the basis for a nationwide erosion assessment in order to better inform environmental policy needs for soil and water conservation.

The role of social learning for soil conservation: the case of Amba Zuria land management, Ethiopia

Social learning plays key roles in sustainable natural resource management; however, studies on its role show mixed results. Even though most current studies highlight positive outcomes, there are also negative effects of social learning with respect to natural resource management. This paper explores the influence of social learning outcomes on the adoption of soil conservation practices in Amba Zuria, Ethiopia. Data were collected through semi-structured interviews, group discussions and in workshops. The interviews were transcribed and analysed with the qualitative data analysis software ATLAS.ti. In addition, a review of pertinent documents and literature complements the analysis. We found that social learning results in positive outcomes in interactions among the actors, broader understanding on soil conservation, trust and mutual understanding, and the creation of opportunities to apply both indigenous and scientific knowledge. These outcomes, in turn, foster the adoption of stone terraces to conserve soils. No such positive results were found for farmers who were not involved in the learning process and who did not adopt stone terraces. The non-adoption can partly be explained by their exclusion from sharing the positive outcomes of social learning. The study also shows limitations related to the short duration of the learning platforms, insufficient representation of women and irregular patterns of learning schedules. Hence, Ethiopian soil conservation strategies should put emphasis on social learning in order to strengthen the collective processes of soil conservation measures.

Changing rainfall, seasonality and erosivity in the hyper‐arid zone of Sudan

AbstractA primary cause of soil erosion is the impact of rain. Therefore, understanding the altering rainfall characteristics and their effect on soil erosion is an issue of main concern. This is of utmost importance to contribute to developing suitable adaptation and mitigation strategies for soil and water resources conservation and crop management practices.The rainfall seasonality index (SI), precipitation concentration index (PCI) and modified Fournier index (MFI) for rainfall erosivity have been calculated and analysed in this study for the hyper‐arid region of Sudan. The data used consist of monthly rainfall measurements spanning over 60 years for three index meteorological stations, two on the Nile corridor and one on the Red Sea coast. The region is characterized by high year‐to‐year variability in rainfall leading to extreme seasonality/irregular distribution of rainfall over the year. Although prevalent diminishing rainfall amounts have been witnessed, there are marked tendencies for some months to become wetter, indicating changing intra‐annual rainfall variability and thus monthly rainfall erosivity. No statistically significant trends were observed in rainfall seasonality and concentration during the common data period of 1945–2007. Cases of high and very high erosion powers were detected. A significant decreasing trend in erosivity is shown for one inland station. A brief discussion on the implications of these results for risk of soil erosion, freshwater quality and agriculture is also given. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Impact of water and soil conservation (WSC) strategies in improving water balance and soil production in Algeria: options to alleviate the negative impacts of climate change

In Algeria, water and soil, vital resources of production, are currently experiencing degradation in terms of quantity and quality. The deficit of rainfall, the frequency and intensity of droughts, and torrential rains exacerbate growing water stress and erosion phenomenon. These conditions involve adaptation strategies and the development of management techniques for the scarcity of excess water. The strategies for the conservation and management of water and soil (WSC) will be one option, among others, to reduce the risks and impacts of climate change. In this sense and to highlight the strategies of WSC, we identified the different techniques of conservation of water and soil; we evaluated their effectiveness and suitability and identified some trends in these techniques. This evaluation has shown the positive role of these techniques in controlling water and conserving natural environments and suitability to the harsh conditions of semi-arid and arid areas.

Influence of Residue Management and Tillage Systems on Carbon Sequestration and Nitrogen, Phosphorus, and Potassium Dynamics of Soil and Plant and Wheat Production in Semi-arid Region

Reducing the tillage and application of mulch are important strategies for soil and water conservation and sustainability of agricultural systems. Soil can be a source or sink for carbon (C) depending on management strategies and plays a major role in the global C cycle. These interacting practices can alter nutrient movement and availability to the crops, reduce water loss, slow down organic-matter (OM) decomposition, and thus enhance C sequestration. A 2-year field study was conducted to quantify the tillage and mulching effect on soil organic C (SOC), OM, nitrogen (N), phosphorus (P), and potassium (K) at two depths (i.e., 0–15 and 15–30 cm deep) in the soil profile and N, P, and K concentrations (g kg−1) in plant shoots at harvest on a Typic Calciargids in wheat–maize rotation. The four tillage systems used were zero tillage (ZT), minimum tillage (MT), conventional tillage (CT), and deep tillage (DT), and four mulch rates [control, 2 (M2), 4 (M4), and 6 (M6) Mg ha−1 year−1 wheat (Triticum aestivum L.) straw] were applied in combination with each tillage system, keeping recommended rates of fertilizers. There was a linear positive response of mulch application on SOC for both years, but it was more pronounced during the second year. Greater values were found in ZT and the lowest in CT at all depths, although greater SOC content was found in upper layers than in deeper ones. Greater shoot N, P, and K concentrations were found in MT, CT, and DT, whereas the lowest concentration was found in ZT. Mulch application has no effect on N, P, and K concentrations in shoots. The soil N concentration was not affected by tillage and mulch, yet greater soil N content was found at 0–15 cm than 15–30 cm deep. There was significant effect of tillage on soil P and K during one year as greater P and K concentrations were found under MT, CT, and DT compared to ZT. More N, P, K, and OM concentrations were found at 0–15 cm deep than at 15–30 cm deep during the whole study period. Mulch effect was significant on K, and significantly greater amounts were found at greater levels of mulch application. The increases in the soil OM were 34.5, 35.75, and 24% at 0–8, 8–16, and 16–24 cm deep respectively from the first year to the second year. Tillage effect on soil organic-matter content was not significant. Tillage increased grain production for both years. For the first year, 22.9 and 27% greater yields were found in CT and DT, whereas in the second year yields were 10.6, 17.9, and 57% greater, respectively, in MT, CT, and DT as compared to ZT. Grain production was increased at a result of mulch application by 12.9, 20.3, and 10.6% during the first year and 11.45, 23.74, and 10.9% during the second year as compared to control (i.e., without mulch). Results show the importance of mulch application and crop residue retention. Both can increase the SOC content and water-holding capacity, which will result in improved production and soil physical health over long and continuous use of mulch.

Short-term effects of treated wastewater irrigation on Mediterranean calcareous soil

Water shortage and soil degradation are the two most important environmental problems in the Mediterranean area. For this reason, strategies for soil and water conservation are necessary. Our objective was to evaluate the use of treated wastewater as an irrigation source to help alleviate these problems. Short-term effects on several soil fertility properties were evaluated in an agricultural area located at Biar (Alicante, SE Spain), where grapes ( Vitis labrusca) are grown. Three treatments: fresh water (control), and treated wastewaters from secondary and tertiary treatment were evaluated for 2 years. We found a slight increase in soil organic carbon content in plots irrigated with the secondary treatment. These plots also had increased electrical conductivity (EC) and increased available Na content due to the high values of EC in wastewater. Laboratory analyses also show a decrease in aggregate stability for all treatments, presumably due to the wetting and drying (WD) cycles associated with each irrigation dose. These WD cycles may also explain changes in microbial biomass carbon and basal soil respiration. We recommend modifying the dose of irrigation in order to reduce the quantity applied and to increase the frequency of application to avoid the loss of aggregation. We also suggest long-term studies to assess the feasibility of wastewater reuse.

Soil conservation policies: Conditions for their effectiveness in the Czech Republic

AbstractConservation of agricultural soil is an important issue in the Czech Republic. This paper is focused on the assessment of the institutions and policies targeted at soil conservation in order to explain the degree to which they are effective and why. The study was carried out at both national and regional level (Svratka River basin) to document the performance of policies. The most important types of soil degradation in the case study area are soil erosion, soil compaction and loss of organic matter. Farming adds to soil degradation because soil protection practices are not applied. Farmers lack motivation to protect soil when they do not trust policies. Evidence from the case study area suggests that agri‐environmental schemes are the most effective policy. Land consolidation could be more successful if the process is better managed. The Law on Soil Protection is not a powerful tool to prevent land degradation because it is not enforced sufficiently. Farmers currently do not have partners in the case study area who could facilitate policy implementation. A lack of political support and the unfavourable division of responsibilities concerning soil conservation has not allowed the design of an integrated policy framework. Areas to be addressed in order to increase the effectiveness of policies are: (i) design e.g. the vague wording of legislation, (ii) implementation e.g. conflicts of interests and lack of advice, (iii) policy evaluation and (iv) policy integration. We suggest integrating the existing measures in an overarching soil conservation strategy. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Soil roughness, slope and surface storage relationship for impervious areas

Summary The study of the relationships between surface roughness, local slope gradient and maximum volume of water storage in surface depressions is a fundamental element in the development of hydrological models to be used in soil and water conservation strategies. Good estimates of the maximum volume of water storage are important for runoff assessment during rainfall events. Some attempts to link surface storage to parameters such as indices of surface roughness and, more rarely, local gradient have been proposed by several authors with empirical equations often conflicting between them and usually based on a narrow range of slope gradients. This suggests care in selecting any of the proposed equations or models and invites one to verify the existence of more realistic experimental relationships, based on physical models of the surfaces and valid for a larger range of gradients. The aim of this study is to develop such a relation for predicting/estimating the maximum volume of water that a soil surface, with given roughness characteristics and local slope gradient, can store. Experimental work has been carried out in order to reproduce reliable rough surfaces able to maintain the following properties during the experimental activity: (a) impervious surface to avoid biased storage determination; (b) stable, un-erodible surfaces to avoid changes of retention volume during tests; (c) absence of hydrophobic behaviour. To meet the conditions a–c we generate physical surfaces with various roughness magnitude using plasticine (emulsion of non-expansible clay and oil). The plasticine surface, reproducing surfaces of arable soils, was then wetted and dirtied with a very fine timber sawdust. This reduced the natural hydrophobic behaviour of the plasticine to an undetectable value. Storage experiments were conducted with plasticine rough surfaces on top of large rigid polystyrene plates inclined at different slope gradient: 2%, 5%, 10%, 20%, 30%. Roughness data collected on the generated plasticine surfaces were successfully compared with roughness data collected on real soil surfaces for similar conditions. A set of roughness indices was computed for each surface using roughness profiles measured with a laser profile meter. Roughness indices included quantiles of the Abbot–Firestone curve, which is used in surface metrology for industrial application to characterize surface roughness in a non-parametric approach ( Whitehouse, 1994 ). Storage data were fitted with an empirical equation (double negative exponential of roughness and slope). Several roughness indices resulted well related to storage. The better results were obtained using the Abbot–Firestone curve parameter P100. Beside this storage empirical model (SEM) a geometrical model was also developed, trying to give a more physical basis to the result obtained so far. Depression geometry was approximated with spherical cups. A general physical model was derived (storage cup model – SCM). The cup approximation identifies where roughness elevation comes in and how it relates to slope gradient in defining depression volume. Moreover, the exponential decay used for assessing slope effect on storage volume in the empirical model of Eqs. (8) , (9) emerges as consistent with distribution of cup sizes.

Modeling of Sediment Yield From Anjeni‐Gauged Watershed, Ethiopia Using SWAT Model1

Setegn, Shimelis G., Bijan Dargahi, Ragahavan Srinivasan, and Assefa M. Melesse, 2010. Modeling of Sediment Yield From Anjeni‐Gauged Watershed, Ethiopia Using SWAT Model.Journal of the American Water Resources Association(JAWRA) 46(3):514‐526. DOI: 10.1111/j.1752‐1688.2010.00431.xAbstract: The Soil and Water Assessment Tool (SWAT) was tested for prediction of sediment yield in Anjeni‐gauged watershed, Ethiopia. Soil erosion and land degradation is a major problem on the Ethiopian highlands. The objectives of this study were to evaluate the performance and applicability of SWAT model in predicting monthly sediment yield and assess the impacts of subbasin delineation and slope discretization on the prediction of sediment yield. Ten years monthly meteorological, flow and sediment data were used for model calibration and validation. The annual average measured sediment yield was 24.6 tonnes/ha. The annual average simulated sediment yield was 27.8 and 29.5 tones/ha for calibration and validation periods, respectively. The study found that the observed values showed good agreement with the simulated sediment yield with Nash‐Sutcliffe efficiency (NSE) = 0.81, percent bias (PBIAS) = 28%, RMSE‐observations standard deviation ratio (RSR) = 0.23, and coefficient of determination (R²) = 0.86 for calibration and NSE = 0.79, PBIAS = 30%, RSR = 0.29, andR² = 0.84 for validation periods. The model can be used for further analysis of different management scenarios that could help different stakeholders to plan and implement appropriate soil and water conservation strategies.

Assessing soil conservation strategies for upland cropping in Northeast Thailand with the WaNuLCAS model

Soil conservation approaches and agroforestry systems can play an important role in controlling erosion from tropical hillside cropping systems. Experimental testing of their potential application domain and design, however, is costly and time consuming. We, therefore, tested the ability of the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model. The specific objectives of the study were: (i) to evaluate the WaNuLCAS model for predicting water induced erosion under different soil conservation strategies, (ii) to use the model for a better understanding of various soil conservation measures in controlling erosion, and (iii) to assess the magnitude and dynamics of key processes influencing the efficiency of soil conservation measures. A 3-year-data set (2003–2005) from a field experiment from the Loei province in Northeast Thailand on the impact of soil conservation (Leucaena hedgerow, Jack bean relay cropping) under minimum tillage on runoff and soil loss was tested. Results indicated that WaNuLCAS was able to predict soil loss and runoff well at the test site; i.e. R 2 = 0.80 and 0.82, respectively. In the calibration procedure a sub data set was used, where adjusting crop development parameters was an important step for improving simulated soil loss (R 2 = 0.75) and runoff (R 2 = 0.89). Soil conservation measures such as Leucaena hedges were effective techniques to control runoff and soil loss. Implementing a dynamic soil structure module in combination with minimum tillage reduced runoff and soil loss via an increase in available macropores and hence drainage over time which improved simulation results. Relay cropping with Jack bean played an important role in the control treatment in reducing soil loss during the third year due to its additional soil cover and positive impact on soil fertility as suggested by the model. Hence, the WaNuLCAS model is a valuable tool to study and understand processes and to explore management options for improving tropical hillside cropping threatened by soil degradation.

Mapping and comparing the distribution of soil carbon under cropping and grazing management practices in Narrabri, north-west New South Wales

The reliable assessment of soil carbon stock is of key importance for soil conservation and mitigation strategies related to reducing atmospheric carbon. Measuring and monitoring soil carbon is complex because carbon pools cycle and rates of carbon sequestration vary across the landscape due to climate, soil type, and management practices. A new methodology has been developed and applied to make an assessment of the distribution of total, organic, and inorganic carbon at a grains research and grazing property in northern New South Wales at a high spatial resolution. In this study, baseline soil carbon maps were created using fine resolution, geo-referenced, proximal sensor data. Coupled with a digital elevation model and secondary terrain attributes, all of the data layers were combined by k-means clustering to develop a stratified random soil sampling scheme for the survey area. Soil samples taken at 0.15-m increments to a depth of 1 m were scanned with a mid-infrared spectrometer, which was calibrated using a proportion of the samples that were analysed in a laboratory for total carbon and inorganic carbon content. This combination of new methodologies and technologies has the potential to provide large volumes of reliable, fine resolution and timely data required to make baseline assessments, mapping, monitoring, and verification possible. This method has the potential to make soil carbon management and trading at the farm-scale possible by quantifying the carbon stock to a depth of 1 m and at a high spatial resolution.

Regeneración natural de plantas leñosas en una plantación costarricense de Vochysia guatemalensis (Vochysiaceae) y el efecto de la fertilización con P y NPK

Natural regeneration of woody species in a Costa Rican plantation of Vochysia guatemalensis (Vochysiaceae) and the effect of P and NPK fertilization. Forest plantation management strategies, including the selection of species, may have positive or negative effects over plant regeneration in the tropics. in this case, understory woody plants density and richness were studied in Tabarcia de Mora, Costa Rica, in a monoculture of Vochysia guatemalensis (ten year old plantation). Nineteen 80 m 2 plots, with several fertilization treatments (0-0; 0-50; 50-0, 50-50 g/plant of P, and NPK, during the first years, P placed once at the hole) in a completely randomized factorial design, were analyzed. Afterwards, the NPK fertilizer was increased from 150 to 200 g/ plant/year until the plantation was six year old. The plots, established after the coffee plantation was eliminated, had a minimum management schedule, basically the elimination of herbaceous vegetation once or twice a year during the first three years, and a tree thinning when the plantation was four year old, to increase spacing from 2x2 to 4x4 m. All woody vegetation taller than 0.5 m was tallied. A total of circa 10 000 ind/ha, distributed in 90 species, were found, mostly native of the region, some identified for forestry use, others important for the fauna. The majority of the species had low relative densities and frequencies. Sixteen percent of the plants reached heights greater than 2.5 m. Several factors seem to explain this regeneration pattern: a canopy with an intermedi - ate openness, a low intensity forestry management, the nearness of the plantation to a mature forest fragment, and that the Vochysia plantation substituted a coffee plantation where soil conservation strategies and an annual fertilization management plan were applied. Finally, plots with only P had significantly higher species richness and abundance (χ 2 =15.364, gl=3, p=0.002) probably because the trees in this treatment were less developed