• Authors:
    • Chaplot, V.
    • Mchunu, C.
  • Source: GEODERMA
  • Volume: 177
  • Year: 2012
  • Summary: Worldwide concerns with global change and its effects on our future environment require an improved understanding of the impact of land cover changes on the global C cycle. Overgrazing causes a reduction in plant cover with accepted consequences on soil infiltration and soil erosion, yet the impact on the loss of soil organic carbon (SOC) and its associated processes remain unaccounted for. In this study performed in South Africa, our main objective was to evaluate the impact of plant cover reduction on (i) SOC erosion by water in both particulate (POC) and dissolved (DOC) forms, and (ii) soil CO2 emissions to the atmosphere. The study performed under sandy-loam Acrisols investigated three proportions of soil surface coverage by plants (Cov), from 100% (Cov100) for the "non-degraded" treatment to 25-50% (Cov50) and 0-5% (Cov5). POC and DOC losses were evaluated using an artificial rainfall of 30 mm h(-1) applied for a period of 30 min on bounded 1 x 1 m(2) microplots (n = 3 per treatment). CO2 emissions from undisturbed soil samples (n = 9) were evaluated continuously at the laboratory over a 6-month period. At the "non-degraded" treatment of Cov100, plant-C inputs to the soil profile were 1950 +/- 180 gC m(-2) y(-1) and SOC stocks in the 0-0.02 m layer were 300.6 +/- 16.2 gC m(-2). While soil-C inputs by plants significantly (P<0.05 level) decreased by 38.5 +/- 3.5% at Cov50 and by 75.4 +/- 6.9% at Cov5, SOC, the losses by water erosion of 0.75 gC m(-2) at Cov100 increased from 66% at Cov50 (i.e. 3.76 +/- 1.8 gC m(-2)) to a staggering 213% at Cov5 (i.e. 7.08 +/- 2.9 gC m(-2)). These losses were for the most part in particulate form (from 88.0% for Cov100 to 98.7% for Cov5). Plant cover reduction significantly decreased both the cumulative C-CO2 emissions (by 68% at Cov50 and 69% at Cov5) and the mineralization rate of the soil organic matter (from 0.039 gC-CO2 gC(-1) at Cov100 to 0.031 gC-CO2 gC(-1) at Cov5). These results are expected to increase our understanding of the impact of land degradation on the global C cycle. Further in-situ research studies, however, need to investigate whether or not grassland degradation induces net C-emissions to the atmosphere.
  • Authors:
    • Raiesi, F.
  • Source: PLANT AND SOIL
  • Volume: 351
  • Issue: 1-2
  • Year: 2012
  • Summary: Land abandonment might be an alternative management for restoring soil conditions and C from prolonged cultivation and agricultural practices. In the present study, the influence of 18-22 years of land abandonment on soil properties, C dynamics and microbial biomass was evaluated in closely situated wheat and alfalfa farmlands, and abandoned lands on calcareous soils, Central Iran. Soil properties of the 0-15 and 15-30 cm depths from abandoned lands were compared to those from conventionally cultivated lands (i.e., continuous wheat-fallow and alfalfa-wheat rotation) common in calcareous soils of Central Zagros Mountains. Soil bulk density in the 0-15 and 15-30 cm layers decreased significantly while total porosity increased significantly in abandoned lands. Generally, soil aggregate stability tended to increase within the abandoned fields owing to increased water-stable macro-aggregates. Soil organic C (OC) contents (g kg(-1)) and pools (Mg ha(-1)) in the 0-15 cm soil layer increased significantly in abandoned lands compared with cultivated lands, with no effect in the 15-30 cm soil layer after 18-22 years of land abandonment, suggesting the restoration of C is pronounced in the upper 0-15 cm soil depth . The total C accumulation in abandoned lands was 7.0 Mg C ha(-1) for the entire sampling depth (0-30 cm) over the 18-22 years of land abandonment, which was 26% greater relative to cultivated lands. Carbon mineralization (Cmin) followed a trend similar to organic C, whereas C turnover (Cmin/OC ratio) was slightly greater in wheat fields. However, soil microbial biomass C (MBC) did not vary considerably among the three land uses. In brief, improvements, albeit slowly, in soil properties of the top layer with the cessation of cultivation indicated that land abandonment may result in enhanced soil C sequestration, and would maintain fertility and productivity of the farmlands of semi-arid climates.
  • Authors:
    • Sharma, K. L.
    • Venkateswarlu, B.
    • Ramesh, V.
    • Wani, S. P.
  • Source: Communications in Soil Science and Plant Analysis
  • Volume: 43
  • Issue: 14
  • Year: 2012
  • Summary: The long-term effects of plant legume [horse gram (Macrotyloma uniflorum)] biomass incorporations were assessed in terms of carbon dioxide (CO2) emissions, soil quality parameters, and climatically influenced soil parameters in a dryland Alfisol under varying soil fertility conditions. Six selected treatments consisted of off-season legume incorporation (I) and no incorporation/fallow (F), each under three varying nitrogen and phosphorus fertilizer levels (viz., N0P0, N25P30, and N50P30). Soil moisture, soil temperature, soil surface carbon dioxide emission, soil dehydrogenases, and microbial biomass carbon (MBC) were monitored at three different crop situations [viz., Kharif period (KP), legume/fallow period (LP), and no crop period (NP)] at 14 different periods of the year. Incorporation practices resulted in greater rates of CO2 emission over fallow conditions during the Kharif and legume periods, whereas the emission rate was greater in fallow soils during the end of the legume and no crop periods. The increased rates of fertilizer doses also significantly increased the soil CO2 flux during the majority of the measurements. Beneficial effects of incorporation practices were observed in terms of high soil moisture (5-11%), low soil temperature (3-7%), and high content of MBC over without incorporations. Correlation studies indicated that the soil property MBC was found to be the greatest significant variable with CO2 emission in all the fertilizer treatments under biomass-incorporated soils. These results indicated the undesirable (in terms of CO2 fluxes) and desirable (soil biological and other parameters) effects of legume biomass incorporation and fertilizer application and their significance in improving soil quality and greenhouse gas (GHG) emissions in dryland Alfisols of semi-arid tropics.
  • Authors:
    • Kutu, F. R.
  • Source: African Journal of Agricultural Research
  • Volume: 7
  • Issue: 26
  • Year: 2012
  • Summary: Conservation agriculture experiment was conducted under irrigated and dryland conditions during 2007/2008-summer cropping season to determine a suitable soil-crop management practice for increase maize yield. The study consisted of tillage practices (conventional, minimum and zero), cropping systems (sole and intercrop plots) and fertilizer regimes (unfertilized control, low, adjusted low and optimum) as treatments. Minimum and zero tillage practices constituted the conservation agriculture tillage practices while supplementation of low fertilizer rate with seed inoculation using growth enhancing microbial inoculant constituted the adjusted low fertilizer rate. Fertilizer application gave a significant (P
  • Authors:
    • Mariga, I. K.
    • Molatudi, R. L.
  • Source: African Journal of Agricultural Research
  • Volume: 7
  • Issue: 20
  • Year: 2012
  • Summary: An experiment was conducted under dryland conditions at the University of Limpopo experimental farm at Syferkuil in Capricorn district in 2007/2008 and 2008/2009 growing seasons to determine the effect of maize density and dry bean variety on maize/bean intercrop performance. The trial was at 2*2*2 factorial consisting of eight treatments: two maize densities (24 700 and 37 000 plants/ha), two dry bean varieties (small white haricot and red speckled sugar bean) and two cropping systems (sole cropping and intercropping). Open pollinated maize variety ZM 523 (ex CIMMYT) was used in the trial. The results showed that maize density of 24 700 plants/ha yielded lower maize grain than the recommended 37 000 plants/ha and maize grain yields in sole cropping were significantly higher than in intercropping in both growing seasons. Intercropping of maize with red speckled sugar bean resulted in lower grain yield than intercropping of maize with small white haricot in both seasons. Increasing maize density to 37 000 plants/ha reduced number of branches per plant and grain yield of dry bean in both seasons. Sole cropping produced the highest dry bean grain yield component values. Intercropping maize and beans was advantageous at the different bean variety x maize density combinations with all, except one, achieving Land equivalent ratio (LER) values greater than 1. Intercropping of maize plant density of 37 000 plants/ha with red speckled sugar bean gave the highest total LER value in 2007/8 season but less than 1 in 2008/9 season. Intercropping was more advantageous than sole cropping in this study. The highest monetary values were achieved by the bean sole crops and their intercrops with 24 700 plants/ha maize. In this study maize densities of 37 000 plants/ha and 24 700 plants/ha were found to be suitable for sole maize and maize/bean intercropping, respectively.
  • Authors:
    • Moyo, B. H.
    • Chirwa, P. W.
    • Khumalo, S.
    • Syampungani, S.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 157
  • Year: 2012
  • Summary: This paper reviews the agroecosystems and agricultural biodiversity in Southern Africa and highlights the importance of the agricultural landscape in biodiversity conservation and the important role that the traditional farming systems play in conserving biodiversity. The review established that agrobiodiversity is of great importance to both small scale and large commercial farmers in Southern Africa through its provision of ecosystem services. The paper also highlights the significant loss of agrobiodiversity as a result of human population pressure and the transition from traditional mixed farming systems which is characterized with high agrobiodiversity, to modern monoculture farming resulting in decline of species diversity. Although concerted efforts are being made to promote the sustainable use and management of this agrobiodiversity, there need to have a multi-stakeholder approach so that conservation efforts are successful, a role that is currently played by the SADC Plant Genetic Resources Centre in Southern African conservation of agrobiodiversity.
  • Authors:
    • Du Preez, C. C.
    • Kotze, E.
    • Loke, P. F.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 94
  • Issue: 1
  • Year: 2012
  • Summary: Soil organic matter (SOM) degradation is common in semi-arid regions due to frequent and intensive cultivation, removal of crop residues after harvesting and warmer environmental conditions. Therefore, we evaluated the effects of long-term wheat production management practices on organic matter content of a Plinthosol in semi-arid South Africa. The treatments included two methods of straw management (unburned and burned), three methods of tillage (no-tillage, stubble mulch and ploughing) and two methods of weeding (chemical and mechanical). Soil samples were collected in 2010 at various depths and analysed for soil organic carbon (SOC), soil total nitrogen (STN) and soil total sulfur (STS) as organic matter indices. Treatments where straw was not burned had greater STN and STS, but lower SOC levels than those where straw was burned. No-tillage had higher SOC levels than the stubble mulch and ploughing treatments only in the 0-50 mm soil layer. Below 100 mm soil depth, higher SOC levels were recorded in the ploughed plots. No-tillage and stubble mulch enhanced STN throughout the soil profile compared to ploughing. Ploughing and stubble mulch treatments had greater STS levels than no-tillage treatments in the upper 250 mm soil layer, and STS in the 0-450 mm soil layer was higher in mechanically weeded plots than in chemically weeded plots. Treatment combinations also showed some significant interactions on these indices, but lack of consistency made it difficult to single out the combination that was superior to others. However, to maintain or improve SOM of this Plinthosol priority should be given to no-tillage and stubble mulch management practices. Wheat grain yields over the 32 years trial period were significantly influenced by straw management and tillage methods, but not by weeding methods.
  • Authors:
    • Lorentz, S.
    • Manson, A.
    • Mchunu, C. N.
    • Chaplot, V.
    • Jewitt, G.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 159
  • Issue: September
  • Year: 2012
  • Summary: The acceleration of soil erosion by water in most regions of the world in response to the anthropogenic modification of landscapes is a serious threat to natural ecosystem functionalities because of the loss of invaluable constituents such as soil particles and organic carbon (OC). While soil OC erosion is likely to be a major component of the global C cycle, water erosion-induced CO2 emissions remain uncertain. In this study, our main objective was to compare the release of CO2 from eroded topsoils and from the sediments exported by diffuse erosion during an entire rainy season. Conventional tillage (CT) and no-tillage (NT) maize treatments were considered in an attempt to set up best management practices to mitigate gaseous OC losses from agricultural soils. The study was conducted in the KwaZulu-Natal province in South Africa, whereas in many other areas of the developing world, erosion is severe and crop residue scarcity is the main challenge. CO2 emissions from undisturbed 0-0.02 m soil samples collected within 2.25 m x 10 m runoff plots and from exported sediments by water erosion, were evaluated continuously at the laboratory over a 140-day period and compared to soil OC stocks. NT significantly reduced CO2 emissions from both soils and sediments. Overall NT, which exhibited a greater carbon density than CT (17.70 vs 13.19 kg C m(-3)), reduced soil gaseous emissions by 4.4% (10.40 vs 10.88 gCO(2)-C m(-2), P < 0.05) but had a much greater impact on the release of CO2 from eroded sediments (0.185 vs 0.778 gCO(2)-C m(-2)), which corresponded to a 76.3% decrease. For CT, cumulative 141-day emissions were, 19% greater in sediments (0.048 g CO2-C g C-1) compared to soils (0.040 gCO(2)-C g C-1), while for NT, emissions were 33% lower in sediments (0.024 g CO2-C g C-1) compared to soils (0.032 g CO2-C g C-1), these differences being significant at P < 0.05. The lower erosion-induced CO2 emissions under NT could be explained by a high soil aggregate stability (mean weight diameter of 2.29 +/- 0.05 mm for NT vs 1.59 +/- 0.07 mm for CT, P < 0.05) and the associated enhanced protection of SOC from the decomposers. These results on a land management control of water erosion-induced CO2 emissions, might allow improving the impact of terrestrial ecosystems on greenhouse gases concentration in the atmosphere and associated climate change. (C) 2012 Elsevier B.V. All rights reserved.
  • Authors:
    • Ghanati, F.
    • Sanavy, S. A. M. M.
    • Dolatabadian, A.
    • Gresshoff, P. M.
  • Source: South African Journal of Botany
  • Volume: 79
  • Year: 2012
  • Summary: Genistein, a major root-secreted isoflavone of soybean ( Glycine max (L.) Merr), is critical for the legume- Bradyrhizobium symbiosis as it induces several bacterial nod-gene systems. An experiment with soybean grown under salt stress was conducted to evaluate the effect of exogenous genistein addition to the Bradyrhizobium culture medium on subsequent nodulation, nitrogen fixation and selected plant physiological attributes. Five day-old plants (in pots) were inoculated with a liquid B. japonicum broth culture and irrigated with B&D solution containing either 0, 25, 50 and 100 mM NaCl. Four weeks after inoculation, maximum photochemical efficiency of PSII (Fv/Fm), photosynthetic rate, stomatal conductance, and transpiration rate were measured. Number of nodules per plant and apparent nitrogen fixation (as acetylene reduction activity) were determined. Salt stress decreased nodule number/plant and nitrogenase activity/plant and induced large changes of both photosynthetic parameters and antioxidant enzyme activity, compared to the control, genistein reversed the effect in each level of salinity tested. Moreover, pre-treatment of the microsymbiont with genistein enhanced maximum photochemical efficiency, photosynthetic rate, stomatal conductance and transpiration rate, while the enzymatic activities of catalase, superoxide dismutase and peroxidase in leaves and roots were not affected. It can be concluded that preincubation of the B. japonicum inoculant with genistein probably contributed towards growth in soybean via enhancement of nodulation and nitrogen fixation under both normal and salt stress conditions.
  • Authors:
    • Muchaonyerwa, P.
    • Chiduza, C.
    • Dube, E.
  • Source: Soil & Tillage Research
  • Volume: 123
  • Year: 2012
  • Summary: A study was conducted to determine the effects of oat (Avena sativa) and grazing vetch (Vicia dasycapa) winter cover crops and fertilization regimes on soil organic matter (SOM) in an irrigated maize-based (Zea mays L.) conservation agriculture (CA) system following four years of continuous practice. Separate plots of oat and grazing vetch cover crops were grown in winter and then maize was planted in all plots in the following summer season. The four fertilization regimes used were: (i) fertilizer applied to the cover crops and the maize crop (F1), (ii) fertilizer applied to cover crops only (F2), (iii) fertilizer applied to the maize crop only (F3) and (iv) no fertilizer applied (F4). Control plots (weedy fallows) were included and the treatments were laid out in a randomized complete block design with three replications. Soil samples from 0-5, 5-20 and 20-50 cm depths were analyzed for total SOM, particulate organic matter (POM) fractions, hot water soluble C (HWC) and C-associated with water stable macro- and micro-aggregates (WSAC). While total SOM was more concentrated in the 0-5 cm soil depth across treatments, a lack of maize fertilization (F2 and F4 regimes) significantly (P