Agricultural lands occupy 37% of the earth's land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO 2 , but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500-6000 Mt CO 2 -eq. yr K1 , with economic potentials of approximately 1500-1600, 2500-2700 and 4000-4300 Mt CO 2 -eq. yr K1 at carbon prices of up to 20, up to 50 and up to 100 US$ t CO 2 -eq. K1 , respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000 Mt CO 2 -eq. yr K1 at 0-20, 0-50 and 0-100 US$ t CO 2 -eq. K1 , respectively.

No abstract

. 1994. Root penetration profiles of wheat and barley as affected by soil penetration resistance in field conditions. Can. J. Soil Sci. 74: igZ-ZOO. e stuOy was conducted on three Manitoba soils (Marquette heavy clay, Fortier silty clay loam, and Souris loamy sand) with the objectives of: (a) assessing the effects of contrasting tillagesystems on various soil physical properties; and O) ielating root penetiation of cereals to these properties. The zero tillage (ZT) and conventional tif^fale (Cf) treatments hadbeen esta'blished between 3 (Marquette and Souris) and 10 (Fortier) years prior to the initiation of the stridy. Penetrometer resistance (PR), bulk density (BD) and pore size distribution (PSD) were measured at various depths and iimes during two growing ,"uronr. The effects of tillage systems on soil properties were generally small, particularly in the poorly strucirred S-ouris l6amy sand. PR in the top 10 cm of soil tended to be higher under ZT than^under C1.. pR uarleO mart 100^1m in diameter) near the soil surface tended to be higher under ZT ihan under CT. There was no evidence of any detrimenlal effect of poor aeration on the final root penetration p.oFtl.r of wheat. The proportion of roots penetrating the soil was inversely relatec to iR. Soil strength critical for root penetration was determined to be 2 MPa and was independent of soil type. In most situations' however, roots were able to grow inio soil with mechanical impedance greater than 2 MPa, possibly by making use of biochannels and spatial and temporal heterogeneity in the soil stmcture.

No abstract

No abstract