- Authors:
- Cerri, C. C.
- Victoria, R.
- Bernoux, M.
- Jenkinson, D. S.
- Coleman, K.
- Cerri, C. E. P.
- Source: Soil Science Society of America Journal
- Volume: 67
- Issue: 6
- Year: 2003
- Summary: Conversion of tropical forest to agricultural management has important implications for C storage in soils and global climate change. The Nova Vida Ranch in the Western Brazilian Amazon basin provided a unique opportunity to study the conversion of tropical forests to pastures established in 1989, 1987, 1983, 1979, 1972, 1951, and 1911, in comparison with uncleared forest. Soils were analyzed for organic C, bulk density, total N, pH, clay content, and biomass C. The forest soil contained 34 Mg C ha(-1) in the 0- to 30-cm layer: modeling clearance and conversion to pasture caused an initial fall in the C stock, followed by a slow rise. After 88 yr, the pasture soil contained 53% more C than the forest soil. The increase in total N on conversion to pasture was less marked, which led to C/N ratios in the pasture soils being higher than in the forest soil. The Rothamsted C turnover model (RothC-26.3) was used to simulate changes in the 0- to 10- and 0- to 30-cm layer of soils when forest was converted to pasture. The model predicted that conversion to pasture would cause a 54% increase in the stock of organic C in the top 30 cm of soil in 100 yr. The modeled input of plant C to the 0- to 30-cm layer of soil under pasture was assumed to be 8.28 Mg C ha(-1) yr(-1). The model provided a reasonable estimate of the microbial biomass (BIO) C in the 0- to 10-cm soil layer. This was an independent test of model performance, because no adjustments were made to the model to generate output.
- Authors:
- Thornton, P. K.
- Jones, P. G.
- Source: Conservation Ecology
- Volume: 5
- Issue: 2
- Year: 2003
- Summary: Making decisions in natural resource management involves an understanding of the risk and uncertainty of the outcomes, such as crop failure or cattle starvation, and of the normal spread of the expected production. Hedging against poor outcomes often means lack of investment and slow adoption of new methods. At the household level, production instability can have serious effects on income and food security. At the national level, it can have social and economic impacts that may affect all sectors of society. Crop models such as CERES-Maize are excellent tools for assessing weather-related production variability. WATBAL is a water balance model that can provide robust estimates of the potential growing days for a pasture. These models require large quantities of daily weather data that are rarely available. MarkSim is an application for generating synthetic daily weather files by estimating the third-order Markov model parameters from interpolated climate surfaces. The models can then be run for each distinct point on the map. This paper examines the growth of maize and pasture in dryland agriculture in southern Africa (includes the southern part of Tanzania, Malawi, much of Mozambique, and all of Zimbabwe, and extends west from the Indian Ocean to include Zambia, the southeastern part of the Democratic Republic of Congo and small portions of Angola). Weather simulators produce independent estimates for each point on the map; however, we know that a spatial coherence of weather exists. We investigated a method of incorporating spatial coherence into MarkSim and show that it increases the variance of production. This means that all of the farmers in a coherent area share poor yields, with important consequences for food security, markets, transport, and shared grazing lands. The long-term aspects of risk are associated with global climate change. We used the results of a global circulation model to extrapolate to the year 2055. We found that low maize yields would become more likely in the marginal areas, whereas they may actually increase in some areas. The same trend was found with pasture growth. We outline areas where further work is required before these tools and methods can address natural resource management problems in a comprehensive manner at local community and policy levels.
- Authors:
- Anand, K. V.
- Katyal, V.
- Gangwar, B.
- Source: Indian Journal of Agricultural Science
- Volume: 73
- Issue: 9
- Year: 2003
- Summary: An experiment was conducted in Akola, Parbhani and Rahuri, Maharashtra, India to evaluate the productivity of various cropping sequences. In Akola (1987-88 to 1997-98) representing Vidharbha zone, the cropping sequence involving upland cotton ( Gossypium hirsutum)-groundnut ( Arachis hypogaea) was the most suitable and efficient, resulting in the highest grain-equivalent yield (10 079 kg ha -1 year -1), productivity (43.82 kg day -1 ha -1 wheat grain equivalent), profitability (49 539 rupees ha -1 year -1), economic efficiency (135.7 rupees day -1 ha -1) and land use efficiency (90.0%), and good benefit:cost ratio (16.57) and stability (0.68). However, in terms of energetics, soyabean ( Glycine max)-groundnut sequence was superior. In Central Maharashtra Plateaux Zone, cotton-groundnut sequence was also identified as the most efficient based on an 8-year study at Parbhani (1990-91 to 1997-98). This sequence gave the highest yield (12 060 kg ha -1 year -1 wheat grain equivalent), productivity (50.04 kg day -1 ha -1), profitability (62 053 rupees ha -1 year -1), economic efficiency (170.0 rupees day -1 ha -1) and land use efficiency (85%), with moderate system stability (0.59). In terms of energetics, soyabean-Indian mustard ( Brassica juncea) was superior. At Rahuri, representing western Maharashtra scarcity zone, sole sugarcane recorded the highest net return (93 429 rupees ha -1 year -1), economic efficiency (255.9 rupees ha -1 day -1) and benefit:cost ratio (19.96). Sorghum ( Sorghum bicolor)-cabbage ( Brassica oleracea var. capitata)-cowpea ( Vigna unguiculata) was equally profitable for fodder, resulting in a wheat grain yield equivalent of 22 793 kg ha -1 year -1, productivity of 94.2 kg day -1 ha -1, profitability of 81 733 rupees ha -1 year -1, economic efficiency of 223.9 rupees day -1 ha -1, and carbohydrate production of 4.69 g 10 6/ha.
- Authors:
- Source: Soil Science Society of America Journal
- Volume: 66
- Issue: 6
- Year: 2002
- Summary: Changes agricultural management can potentially increase the accumulation rate of soil organic C (SOC), thereby sequestering CO2 from the atmosphere. This study was conducted to quantify potential soil C sequestration rates for different crops in response to decreasing tillage intensity or enhancing rotation complexity, and to estimate the duration of time over which sequestration may occur. Analyses of C sequestration rates were completed using a global database of 67 long-term agricultural experiments, consisting of 276 paired treatments. Results indicate, on average, that a change from conventional tillage (CT) to no-till (NT) can sequester 57 +/- 14 g C m(-2) yr(-1), excluding wheat (Triticum aestivum L.)-fallow systems which may not result in SOC accumulation with a change from CT to NT. Enhancing rotation complexity can sequester an average 20 +/- 12 g C m(-2) yr(-1), excluding a change from continuous corn (Zea mays L.) to corn-soybean (Glycine mar L.) which may not result in a significant accumulation of SOC. Carbon sequestration rates, with a change from CT to NT, can be expected to peak in 5 to 10 yr with SOC reaching a new equilibrium in 15 to 20 yr. Following initiation of an enhancement in rotation complexity, SOC may reach a new equilibrium in approximately 40 to 60 yr. Carbon sequestration rates, estimated for a number of individual crops and crop rotations in this study, can be used in spatial modeling analyses to more accurately predict regional, national, and global C sequestration potentials.
- Authors:
- Albrecht, A.
- Sa, J. C. D.
- Ogle, S. M.
- Denef, K.
- Feller, C.
- Six, J.
- Source: Agronomie
- Volume: 22
- Issue: 7
- Year: 2002
- Summary: The long-term stabilization of soil organic matter (SOM) in tropical and temperate regions is mediated by soil biota (e. g. fungi, bacteria, roots and earthworms), soil structure (e. g. aggregation) and their interactions. On average, soil C turnover was twice as fast in tropical compared with temperate regions, but no major differences were observed in SOM quality between the two regions. Probably due to the soil mineralogy dominated by 1:1 clay minerals and oxides in tropical regions, we found a higher aggregate stability, but a lower correlation between C contents and aggregate stability in tropical soils. In addition, a smaller amount of C associated with clay and silt particles was observed in tropical versus temperate soils. In both tropical and temperate soils, a general increase in C levels (approximate to 325 +/- 113 kg C.ha(-1).yr(-1)) was observed under no-tillage compared with conventional tillage. On average, in temperate soils under no-tillage, compared with conventional tillage, CH4 uptake (approximate to0.42 +/- 0.10 kg C-CH4.ha(-1) yr(-1)) increased and N2O emissions increased (approximate to 1.95 +/- 0.45 kg N-N2O.ha(-1).yr(-1)). These increased N2O emissions lead to a negative global warming potential when expressed on a CO2 equivalent basis.
- Authors:
- Barrett, D. J.
- Galbally, I. E.
- Graetz, R. D.
- Source: Global Change Biology
- Volume: 7
- Issue: 8
- Year: 2001
- Authors:
- Zech, W.
- Guggenberger, G.
- Haumaier, L.
- Glaser, B
- Source: Naturwissenschaften
- Volume: 88
- Issue: 1
- Year: 2001
- Summary: Many soils of the lowland humid tropics are thought to be too infertile to support sustainable agriculture. However, there is strong evidence that permanent or semi-permanent agriculture can itself create sustainably fertile soils known as 'Terra Preta' soils. These soils not only contain higher concentrations of nutrients such as nitrogen, phosphorus, potassium and calcium, but also greater amounts of stable soil organic matter. Frequent findings of charcoal and highly aromatic humic substances suggest that residues of incomplete combustion of organic material (black carbon) are a key factor in the persistence of soil organic matter in these soils. Our investigations showed that 'Terra Preta' soils contained up to 70 times more black carbon than the surrounding soils. Due to its polycyclic aromatic structure, black carbon is chemically and microbially stable and persists in the environment over centuries. Oxidation during this time produces carboxylic groups on the edges of the aromatic backbone, which increases its nutrient-holding capacity. We conclude that black carbon can act as a significant carbon sink and is a key factor for sustainable and fertile soils, especially in the humid tropics.
- Authors:
- Ruiz-Suárez, L. G.
- González-Avalos, E.
- Source: Bioresource Technology
- Volume: 80
- Issue: 1
- Year: 2001
- Authors:
- Kaimowitz, D.
- Angelsen, A.
- Year: 2001
