• Authors:
    • Hensley, M.
    • Bennie, A. T. P.
    • Botha, J. J.
    • Rensburg, L. D. van
  • Source: Water SA
  • Volume: 37
  • Issue: 5
  • Year: 2011
  • Summary: This review provides an overview of Water Research Commission (WRC)-funded research over the past 36 years. A total of 28 WRC reports have been consulted, 13 of these compiled by the University of the Free State, 4 by the University of Fort Hare, and the remainder mainly by the ARC-Institute for Soil Climate and Water. This work has resulted in extensive capacity building in this field - numerous technical assistants and 58 researchers have been involved, of which 23 are still active in research. The focus on the water flow processes in the soil-plant-atmosphere continuum (SPAC), with particular emphasis on processes in the soil, has greatly enhanced understanding of the system, thereby enabling the formulation of a quantitative model relating the water supply from a layered soil profile to water demand; the formulation of logical quantitative definitions for crop-ecotope specific upper and lower limits of available water; the identification of the harmful rootzone development effects of compacted layers in fine sandy soils caused by cultivation, and amelioration procedures to prevent these effects; and management strategies to combat excessive water losses by deep drainage. The explanation of the way in which SPAC is expressed in the landscape in the form of the ecotope has been beneficial with regard to the extrapolation of studies on particular SPACs to the large number of ecotopes where detailed studies have not been possible. Valuable results are reported regarding rainfall and runoff management strategies. Longer fallow periods and deficit irrigation on certain crop ecotopes improved rainfall use efficiency. On semi-arid ecotopes with high-drought-risk clay and duplex soils and high runoff losses, in-field rainwater harvesting (IRWH), designed specifically for subsistence farmers, resulted in maize and sunflower yield increases of between 30% and 50% compared to yields obtained with conventional tillage. An indication of the level of understanding of the relevant processes that has been achieved is demonstrated by their quantitative description in mathematical and empirical models: BEWAB for irrigation, SWAMP mainly for dryland cropping, and CYP-SA for IRWH. Five important related research and development needs are identified. The WRC has played, and continues to play, an important role in commissioning and funding research on water utilisation in agriculture and has clearly made an excellent contribution to the progress made in addressing the needs and requirements of subsistence, emergent and dryland farmers in South Africa.
  • Authors:
    • Sanadze, E.
    • Weismiller, R.
    • Kirvalidze, D.
    • Kvrivishvil, T.
    • Korakhashvili, A.
  • Source: Communications in Soil Science and Plant Analysis
  • Volume: 42
  • Issue: 7
  • Year: 2011
  • Summary: In 2006, the International Organization of Christian Charities (IOCC) began a program in the country of Georgia to establish an improved dairy enterprise in the villages of Minadze and Ghreli in the Akhaltsikhe district. To correctly determine the fertility requirements for the use of either mineral or organic fertilizer materials for improving soil fertility for legume grain crops (beans, peas, soybeans, etc.) and perennial pastures (a mixture of perennial cereal grasses and perennial legumes) and for the proper management of these soils, it was necessary to understand the geomorphic, chemical, and physical characteristics of the soils of this region. Soils of this region belong to a sub-type of Cinnamonic Calcareous soils. The characteristics of these soils as well as their fertility and soil management needs were ascertained. Appropriate amounts of mineral and organic fertilizers needed for the proper growth of legume crops and perennial pastures as well as timing of application are presented.
  • Authors:
    • Laurent, F.
    • Ruelland, D.
  • Source: Journal of Hydrology
  • Volume: 409
  • Issue: 1-2
  • Year: 2011
  • Summary: The SWAT model was used to model the impacts of climate, soils and agricultural practices on nitrate flows in a 1310 km 2 catchment in western France. Spatialized data were used for natural features (climate, soil, topography), while agricultural activities, finely represented by crop sequences over 3 years, and their associated cultural practices were mapped by remote sensing. The model was calibrated and validated for discharge and nitrate flows at a gauging station. Results are analyzed with respect to leaching for each crop sequence and for each soil type, as nitrate leaching is highly sensitive to the soil and the crop sequence. The lowest risks were found in clayey soils and the highest in sandy soils and/or in sequences including maize. In collaboration with local stakeholders, five scenarios of alternative practices were simulated to evaluate their consequences for nitrogen flows: reduced fertilization, catch crops, shallow cultivation, no-till with catch crops and filter strips. The impacts of the conversion of a pasture into wheat and rapeseed were also assessed. At the catchment gauging station, our 9-year simulations showed a reduction in nitrate flow of 8% with filters strips, 11% with catch crops, 12% with no-till with catch crops, and 15% with reduced fertilization. Shallow cultivation had no impact on nitrate flow. Inversely, the conversion of temporary pastures, which accounts for 32% of the catchment area, to cereals and rapeseed increased nitrate flow by 18%. The impacts of each scenario varied in accordance with leaching at the parcel scale and with the proportion of area affected by the practice. The results show that modelling can improve our understanding of the impacts of agricultural practices on water quality at different scales.
  • Authors:
    • Mchunu, C. N.
    • Lorentz, S.
    • Jewitt, G.
    • Manson, A.
    • Chaplot, V.
  • Source: Soil Science Society of America Journal
  • Volume: 75
  • Issue: 4
  • Year: 2011
  • Summary: Although no-till (NT) is now practiced in many countries of the world, for most smallholders, the crop residues are of such a value that they cannot be left on the soil surfaces to promote soil protection, thus potentially limiting NT benefits and adoption. In this study our main objective was to evaluate runoff, soil, and soil organic carbon (SOC) losses from traditional small-scale maize ( Zea mays) field under conventional tillage (T) and NT, with crop residues cover of less than 10% during the rainy season, in South Africa. Six runoff plots of 22.5 m 2 (2.25*10 m) under NT and T since 2002 were considered. At each plot, soil bulk density (rho b) and SOC content of the 0-0.02 m layer were estimated at nine pits. Top-soil SOC stocks were 26% higher under NT than under T ( P=0.001). The NT reduced soil losses by 68% (96.8 vs. 301.5 g m -2 yr -1, P=0.001) and SOC losses by 52% (7.7 vs. 16.2 g C m -2 yr -1, P=0.001), and differences in runoff were not significant. Dissolved organic carbon accounted for about 10% of total SOC losses and showed significantly higher concentrations under T than NT (1.49 versus 0.86 mg C m -2 yr -1). The less erosion in NT compared to T was explained by a greater occurrence under NT of indurated crusts, less prone to soil losses. These results showed the potential of NT even with low crop residue cover (<10%) to significantly reduce soil and SOC losses by water under small-scale agriculture.
  • Authors:
    • Ortega, A. L.
  • Source: Archives of Agronomy and Soil Science
  • Volume: 57
  • Issue: 6
  • Year: 2011
  • Summary: The permanent bed planting system for wheat ( Triticum aestivum L.) production has recently received additional attention. Studies using hard red spring wheat (cultivar Nahuatl F2000) were conducted at two locations in central Mexico. The studies included the installation of three furrow diking treatments, two granular N timing treatments and three foliar N rates applied at the end of anthesis. The objective was to evaluate the effect of these factors on wheat grain yield, yield components and grain N in a wheat-maize ( Zea maize L.) rotation with residues of both crops left as stubble. Results indicated that diking in alternate furrows increased both grain yield and the final number of spikes per m 2. The split application of N fertilizer enhanced the number of spikes per m 2 and grain N uptake, but the effect on grain yield was inconsistent. Similarly, grain protein increased with the foliar application of 6 kg N ha -1, depending upon the maximum temperature within the 10 days following anthesis. The normalized difference vegetative index (NDVI) readings collected at four growth stages were generally higher for the split N application than for the basal N application at planting. Grain N uptake was associated to NDVI readings collected after anthesis.
  • Authors:
    • Petersen, S. O.
    • Mutegi, J. K.
    • Hansen, E. M.
    • Munkholm, L. J.
  • Source: Soil Biology and Biochemistry
  • Volume: 43
  • Issue: 7
  • Year: 2011
  • Summary: Conservation tillage practices are widely used to protect against soil erosion and soil C losses, whereas winter cover crops are used mainly to protect against N losses during autumn and winter. For the greenhouse gas balance of a cropping system the effect of reduced tillage and cover crops on N2O emissions may be more important than the effect on soil C. This study monitored emissions of N2O between September 2008 and May 2009 in three tillage treatments, i.e., conventional tillage (CT), reduced tillage (RI) and direct drilling (DD), all with (+CC) or without (-CC) fodder radish as a winter cover crop. Cover crop growth, soil mineral N dynamics, and other soil characteristics were recorded. Furthermore, soil concentrations of N2O were determined eight times during the monitoring period using permanently installed needles. There was little evidence for effects of the cover crop on soil mineral N. Following spring tillage and slurry application soil mineral N was dominated by the input from slurry. Nitrous oxide emissions during autumn, winter and early spring remained low, although higher emissions from +CC treatments were indicated after freezing events. Following spring tillage and slurry application by direct injection N2O emissions were stimulated in all tillage treatments, reaching 250-400 mu g N m(-2) h(-1) except in the CT + CC treatment, where emissions peaked at 900 mu g N M-2 h(-1). Accumulated emissions ranged from 1.6 to 3.9 kg N2O ha(-1). A strong positive interaction between cover crop and tillage was observed. Soil concentration profiles of N2O showed a significant accumulation of N2O in CT relative to RI and DD treatments after spring tillage and slurry application, and a positive interaction between slurry and cover crop residues. A comparison in early May of N2O emissions with flux estimates based on soil concentration profiles indicated that much of the N2O emitted was produced near the soil surface.
  • Authors:
    • Preez, C.
    • Huyssteen, C.
    • Mnkeni, P.
  • Source: South African Journal of Science
  • Volume: 107
  • Issue: 5/6
  • Year: 2011
  • Summary: The decline of soil organic matter as a result of agricultural land use was identified for a review with the ultimate aim of developing a soil protection strategy and policy for South Africa. Such a policy is important because organic matter, especially the humus fraction, influences the characteristics of soil disproportionately to the quantities thereof present. Part 1 of this review dealt with the spatial variability of soil organic matter and the impact of grazing and burning under rangeland stock production. In this second part of the review, the impact of arable crop production on soil organic matter is addressed. A greater number of studies have addressed the degradation of soil organic matter that is associated with arable crop production than the restoration. However, cropping under dryland has been found to result in significant losses of soil organic matter, which is not always the case with cropping under irrigation. Restoration of soil organic matter has been very slow upon the introduction of conservational practices like zero tillage, minimal tillage, or mulch tillage. Reversion of cropland to perennial pasture has also been found to result in discouragingly slow soil organic matter restoration. Although increases or decreases in soil organic matter levels have occurred in the upper 300 mm, in most instances this took place only in the upper 50 mm. The extent of these changes was dependent inter alia on land use, soil form and environmental conditions. Loss of soil organic matter has resulted in lower nitrogen and sulphur reserves, but not necessarily lower phosphorus reserves. Depletion of soil organic matter coincided with changes in the composition of amino sugars, amino acids and lignin. It also resulted in a decline of water stable aggregates which are essential in the prevention of soil erosion. Although much is known about how arable crop production affects changes in soil organic matter, there are still uncertainties about the best management practices to maintain and even restore organic matter in degraded cropland. Coordinated long-term trials on carefully selected ecotopes across the country are therefore recommended to investigate cultivation practices suitable for this purpose.
  • Authors:
    • Purcell, P. J.
    • O'Brien, M.
    • Boland, T. M.
    • O'Kiely, P.
    • O'Donovan, M.
  • Source: Animal Feed Science and Technology
  • Volume: 166/167
  • Year: 2011
  • Summary: This study determined in vitro rumen CH 4 production of perennial ryegrass grown within a well managed Irish dairy production system. Four strategies, consisting of two pre-grazing herbage mass (HM; high 2400 and low 1600 kg dry matter (DM)/ha) and two sward allowance (SA; high 20 and low 15 kg DM/cow/d) treatments, were compared throughout the grazing season using an in vitro rumen gas production technique. Samples were collected during five 22 d sampling periods (SP 1-5) throughout the growing season and analysed for in vitro rumen CH 4 output, and total gas and volatile fatty acid production following 24 h of incubation with rumen fluid and artificial saliva. High HM was associated with lower organic matter digestibility and crude protein concentration compared with low HM, whereas SA had no effect on herbage composition. Methane output as ml/g DM incubated or digested was higher (P<0.05) for the high HM treatment than for the low HM treatment (25.5 versus 24.6 and 32.2 versus 30.5, respectively). Sward allowance had no effect on CH 4 output, but CH 4 output/g DM incubated or digested was affected by sampling period. Sward allowance did not alter methanogenesis and, although HM affected CH 4 output in vitro, the biological scale of this effect was small. Thus, grass management strategy had little impact on in vitro rumen CH 4 output when herbage was consistently of high nutritional quality.
  • Authors:
    • Labreuche, J.
    • Richard, G.
    • Roger-Estrade, J.
  • Source: Cahiers Agricultures
  • Volume: 20
  • Issue: 3
  • Year: 2011
  • Summary: In this paper, we present a review of the literature on the effects of no-ploughing on soil structure, porosity and stability. In the second part, we discuss the consequences on soil erosion in a temperate environment. The effect of reduced tillage on soil physical properties has firstly to be evaluated on soil structure. If carbon accumulation on the soil surface improves aggregate stability, no-ploughing also greatly affects soil porosity. Not only does it decrease during the period following adoption of no-ploughing, but it also changes in nature and connectivity due to weathering, roots and biological activity. However, the efficiency of these factors is site-dependent and varies with the duration of no-ploughing and the crop sequence. Under tropical climates, reduced tillage systems have been proposed to prevent soil erosion while in temperate areas the present increase of no-till is motivated firstly by the decrease of production and mechanization costs. However, the efficiency of the numerous no-plough tillage systems on erosion control is not systematic. The soil must be sufficiently covered by crop residues and the infiltration rate has to remain high enough. This note critically assesses the available results on these two aspects of the effect of reduced tillage on soil physics.
  • Authors:
    • Corbeels, M.
    • Rufino, M. C.
    • Nyamangara, J.
    • Giller, K. E.
    • Rusinamhodzi, L.
    • van Wijk, M. T.
  • Source: Agronomy for Sustainable Development
  • Volume: 31
  • Issue: 4
  • Year: 2011
  • Summary: Conservation agriculture involves reduced tillage, permanent soil cover and crop rotations to enhance soil fertility and to supply food from a dwindling land resource. Recently, conservation agriculture has been promoted in Southern Africa, mainly for maize-based farming systems. However, maize yields under rain-fed conditions are often variable. There is therefore a need to identify factors that influence crop yield under conservation agriculture and rain-fed conditions. Here, we studied maize grain yield data from experiments lasting 5 years and more under rain-fed conditions. We assessed the effect of long-term tillage and residue retention on maize grain yield under contrasting soil textures, nitrogen input and climate. Yield variability was measured by stability analysis. Our results show an increase in maize yield over time with conservation agriculture practices that include rotation and high input use in low rainfall areas. But we observed no difference in system stability under those conditions. We observed a strong relationship between maize grain yield and annual rainfall. Our meta-analysis gave the following findings: (1) 92% of the data show that mulch cover in high rainfall areas leads to lower yields due to waterlogging; (2) 85% of data show that soil texture is important in the temporal development of conservation agriculture effects, improved yields are likely on well-drained soils; (3) 73% of the data show that conservation agriculture practices require high inputs especially N for improved yield; (4) 63% of data show that increased yields are obtained with rotation but calculations often do not include the variations in rainfall within and between seasons; (5) 56% of the data show that reduced tillage with no mulch cover leads to lower yields in semi-arid areas; and (6) when adequate fertiliser is available, rainfall is the most important determinant of yield in southern Africa. It is clear from our results that conservation agriculture needs to be targeted and adapted to specific biophysical conditions for improved impact.