• Authors:
    • Portelli, M.
    • Rab, A.
    • Mock ,I.
    • Knight, A.
    • Blott, K.
    • Unkovich, M.
  • Source: Australian Journal of Agricultural Research
  • Volume: 54
  • Issue: 8
  • Year: 2003
  • Summary: Annual crops were grown in alleys between belts of perennial shrubs or trees over 3-4 years at 3 sites across low rainfall (<450 mm) south-eastern Australia. At the two lower rainfall sites (Pallamana and Walpeup), crop grain yields within 2-5 m of shrub belts declined significantly with time, with a reduction equivalent to 45% over 9 m in the final year of cropping. At the third, wetter site (Bridgewater), the reduction in crop grain yields adjacent to tree belts was not significant until the final year of the study (12% over 11 m) when the tree growth rates had increased. The reductions in crop yield were associated with increased competition for water between the shrub or tree belts and the crops once the soil profile immediately below the perennials had dried. At all 3 sites during the establishment year, estimates of water use under the woody perennials were less than under annual crops, but after this, trends in estimates of water use of alley farming systems varied between sites. At Pallamana the perennial shrubs used a large amount of stored soil water in the second summer after establishment, and subsequently were predominantly dependent on rainfall plus what they could scavenge from beneath the adjacent crop. After the establishment year at the Walpeup site, water use under the perennial shrubs was initially 67 mm greater than under the annual crop, declining to be only 24 mm greater in the final year. Under the trees at Bridgewater, water use consistently increased to be 243 mm greater than under the adjacent annual crop by the final year. Although the shrub belts used more water than adjacent crop systems at Walpeup and Pallamana, this was mostly due to the use of stored soil water, and since the belts occupied only 7-18% of the land area, increases in total water use of these alley farming systems compared with conventional crop monocultures were quite small, and in terms of the extent of recharge control this was less than the area of crop yield loss. At the wetter, Bridgewater site, alley farming appeared to be using an increasing amount of water compared with conventional annual cropping systems. Overall, the data support previous work that indicates that in lower rainfall environments (<350 mm), alley farming is likely to be dogged by competition for water between crops and perennials.
  • Authors:
    • Oenema, O.
    • Kuikman, P. J.
    • Velthof, G. L.
  • Source: Biology and Fertility of Soils
  • Volume: 37
  • Issue: 4
  • Year: 2003
  • Summary: Animal manures may differ strongly in composition and as a result may differ in the emission of N2O following application to soil. An incubation study was carried out to assess the effects of type of mineral N fertilizer and manure, application technique and application rate on N2O emission from a sandy soil with low organic matter content. Fluxes of N2O were measured 30 times over a 98-day period. The total N2O emission from mineral N fertilizer ranged from 2.1 to 4.0% of the N applied. High emissions were associated with manures with high contents of inorganic N, easily mineralizable N and easily mineralizable C, such as liquid pig manure (7.3-13.9% of the N applied). The emission from cattle slurries ranged from 1.8 to 3.0% and that of poultry manures from 0.5 to 1.9%. The total N2O emission during the experimental period tended to increase linearly with increasing N application rate of NH4NO3 and liquid pig manure. The N2O emission from surface-applied NH4NO3 was significantly smaller than that following the incorporation of NH4NO3 in the soil. The N2O emission from pig manure placed in a row at 5 cm depth was significantly higher than from surface-application and other techniques in which manure was incorporated in the soil. The results show that modification of the composition and application technique may be tools to mitigate emission of N2O.
  • Authors:
    • Pu, X. P.
    • Kang, M. Y.
    • Hu, Z. Z.
    • Long, R. J.
    • Dong, S. K.
  • Source: Grass and Forage Science
  • Volume: 58
  • Issue: 3
  • Year: 2003
  • Summary: Abstract The productivity and nutritive value of some cultivated perennial grasses, Bromus inermis (B), Elymus sibricus (S), E. nutans (N), Agropyron cristatum (A), Poa crymophila (P) and mixtures B + N, S + A, B + S + A, S + B + N, N + S + A, B + S + N + A, B + N + A + P, B + S +A + P and S + N + A + P, in the alpine region of the Tibetan Plateau were investigated. Elymus nutans and E. sibricus and the mixtures, B + S + N + A, B + S +A + P and S + N + A + P, were most productive with yields of dry matter (DM) of between 11 000 and 14 000 kg-1 of biomass annually in the second harvest year. Acid-detergent fibre (ADF) concentrations increased (P < 0·05), and crude protein (CP) concentrations and in sacco DM degradability values decreased (P < 0·05) with the maturity of the cultivated grasses. Swards, based on these species and mixtures, have the potential to be the main choices for cultivation in the Tibetan Plateau because they produce more nutrients than other grass species and mixtures. Late August (flowering stage of dominant grasses) is the optimum time for harvesting as the yield of rumen-degradable CP is highest that of DM relatively high and the DM degradability is satisfactory.
  • Authors:
    • de Caluwe, H.
    • Bobbink, R.
    • Hefting, M. M.
  • Source: Journal of Environmental Quality
  • Volume: 32
  • Issue: 4
  • Year: 2003
  • Summary: Riparian buffer zones are known to reduce diffuse N pollution of streams by removing and modifying N from agricultural runoff. Denitrification, often identified as the key N removal process, is also considered as a major source of the greenhouse gas nitrous oxide (N2O). The risks of high N2O emissions during nitrate mitigation and the environmental controls of emissions have been examined in relatively few riparian zones and the interactions between controls and emissions are still poorly understood. Our objectives were to assess the rates of N2O emission from riparian buffer zones that receive large loads of nitrate, and to evaluate various factors that are purported to control N emissions. Denitrification, nitrification, and N2O emissions were measured seasonally in grassland and forested buffer zones along first-order streams in the Netherlands. Lateral nitrate loading rates were high, up to 470 g N m-2 yr-1. Nitrogen process rates were determined using flux chamber measurements and incubation experiments. Nitrous oxide emissions were found to be significantly higher in the forested (20 kg N ha-1 yr-1) compared with the grassland buffer zone (2-4 kg N ha-1 yr-1), whereas denitrification rates were not significantly different. Higher rates of N2O emissions in the forested buffer zone were associated with higher nitrate concentrations in the ground water. We conclude that N transformation by nitrate-loaded buffer zones results in a significant increase of greenhouse gas emission. Considerable N2O fluxes measured in this study indicate that Intergovernmental Panel on Climate Change methodologies for quantifying indirect N2O emissions have to distinguish between agricultural uplands and riparian buffer zones in landscapes receiving large N inputs.
  • Authors:
    • Dennis, P. F.
    • Fukada, T.
    • Mühlherr ,I. H.
    • Bateman, A. S.
    • Hiscock, K. M.
  • Source: Environmental Science & Technology
  • Volume: 37
  • Issue: 16
  • Year: 2003
  • Summary: Diffuse pollution of groundwater by agriculture has caused elevated concentrations of nitrate (NO3 ) and nitrous oxide (N2O) in regional aquifers. N2O is an important "greenhouse" gas, yet there are few estimates of indirect emissions of N2O from regional aquifers. In this study, high concentrations of N2O (mean 602 nM) were measured in the unconfined Chalk aquifer of eastern England, in an area of intensive agriculture. In contrast, pristine ground waters from upland regions of England and Scotland, with predominantly natural vegetation cover, were found to have much lower concentrations of N2O (mean 27 nM). A positive relationship between N2O and NO3 concentrations and [sigma]18 O-NO3 values of between 3.36 and 16.00‰ suggest that nitrification is the principal source of N2O. A calculated emission factor (EF5-g) of 0.0019 for indirect losses ofN2O from Chalk groundwater is an order of magnitude lower than the value of 0.015 currently used in the Intergovernmental Panel on Climate Change (IPCC) methodology for assessing agricultural emissions. A flux of N2O from the major UK aquifers of 0.04 kg N2O Nha-1 a-1 has been calculated using two approaches and suggests that indirect losses of N2O from regional aquifers are much less significant ( 1%) than direct emissions from agricultural soils.
  • Authors:
    • Yang, H.
    • Walters, D. T.
    • Dobermann, A.
    • Cassman, K. G.
  • Source: Annual Review of Environment and Resources
  • Volume: 28
  • Issue: 1
  • Year: 2003
  • Summary: Agriculture is a resource-intensive enterprise. The manner in which food production systems utilize resources has a large influence on environmental quality. To evaluate prospects for conserving natural resources while meeting increased demand for cereals, we interpret recent trends and future trajectories in crop yields, land and nitrogen fertilizer use, carbon sequestration, and greenhouse gas emissions to identify key issues and challenges. Based on this assessment, we conclude that avoiding expansion of cultivation into natural ecosystems, increased nitrogen use efficiency, and improved soil quality are pivotal components of a sustainable agriculture that meets human needs and protects natural resources. To achieve this outcome will depend on raising the yield potential and closing existing yield gaps of the major cereal crops to avoid yield stagnation in some of the world's most productive systems. Recent trends suggest, however, that increasing crop yield potential is a formidable scientific challenge that has proven to be an elusive goal.
  • Authors:
    • Paustian, K.
    • Smith, G. R.
    • Conant, R. T.
  • Source: Journal of Environmental Quality
  • Volume: 32
  • Issue: 1
  • Year: 2003
  • Summary: The potential to sequester atmospheric carbon in agricultural and forest soils to offset greenhouse gas emissions has generated interest in measuring changes in soil carbon resulting from changes in land management. However, inherent spatial variability of soil carbon limits the precision of measurement of changes in soil carbon and hence, the ability to detect changes. We analyzed variability of soil carbon by intensively sampling sites under different land management as a step toward developing efficient soil sampling designs. Sites were tilled crop-land and a mixed deciduous forest in Tennessee, and old-growth and second-growth coniferous forest in western Washington, USA. Six soil cores within each of three microplots were taken as an initial sample and an additional six cores were taken to simulate resampling. Soil C variability was greater in Washington than in Tennessee, and greater in less disturbed than in more disturbed sites. Using this protocol, our data suggest that differences on the order of 2.0 Mg C ha(-1) could be detected by collection and analysis of cores from at least five (tilled) or two (forest) microplots in Tennessee. More spatial variability in the forested sites in Washington increased the minimum detectable difference, but these systems, consisting of low C content sandy soil with irregularly distributed pockets of organic C in buried logs, are likely to rank among the most spatially heterogeneous of systems. Our results clearly indicate that consistent intramicroplot differences at all sites will enable detection of much more modest changes if the same microplots are resampled.
  • Authors:
    • Cadisch, G.
    • Cook, H.
    • Regar, A.
    • Pihlatie, M.
    • Stevenson, M.
    • Baggs, E. M.
  • Source: Plant and Soil
  • Volume: 254
  • Issue: 2
  • Year: 2003
  • Summary: Emissions of N2O were measured following combined applications of inorganic N fertiliser and crop residues to a silt loam soil in S. E. England, UK. Effects of cultivation technique and residue application on N2O emissions were examined over 2 years. N2O emissions were increased in the presence of residues and were further increased where NH4NO3 fertiliser (200 kg N ha(-1)) was applied. Large fluxes of N2O were measured from the zero till treatments after residue and fertiliser application, with 2.5 kg N2O- N ha(-1) measured over the first 23 days after application of fertiliser in combination with rye ( Secale cereale) residues under zero tillage. CO2 emissions were larger in the zero till than in the conventional till treatments. A significant tillage/residue interaction was found. Highest emissions were measured from the conventionally tilled bean ( Vicia faba) (1.0 kg N2O- N ha(-1) emitted over 65 days) and zero tilled rye (3.5 kg N2O-N ha(-1) over 65 days) treatments. This was attributed to rapid release of N following incorporation of bean residues in the conventionally tilled treatments, and availability of readily degradable C from the rye in the presence of anaerobic conditions under the mulch in the zero tilled treatments. Measurement of N-15-N2O emission following application of N-15-labelled fertiliser to microplots indicated that surface mulching of residues in zero till treatments resulted in a greater proportion of fertiliser N being lost as N2O than with incorporation of residues. Combined applications of N-15 fertiliser and bean residues resulted in higher or lower emissions, depending on cultivation technique, when compared with the sum of N2O from single applications. Such interactions have important implications for mitigation of N2O from agricultural soils.
  • Authors:
    • Diffey, S.
    • Good, A.
    • Mead, J.
    • Hocking, P.
  • Source: Australian Journal of Experimental Agriculture
  • Volume: 43
  • Issue: 11
  • Year: 2003
  • Summary: Land preparation for canola (oilseed rape; Brassica napus L.) by conventional cultivation can involve a number of workings, resulting in soil degradation and reduced crop growth. Minimum-tillage systems may help overcome these problems, but the placement of fertiliser at sowing must avoid chemical injury to germinating seed. The responses of canola cultivars to tillage and fertiliser placement were studied for 2 seasons at high (Breakfast Creek, 1997; Harden, 1998) and low (Ardlethan, 1997-98) rainfall sites. The tillage treatments were conventional cultivation, one-pass, and no-till (direct drill). The fertiliser treatments were 200 kg/ha 'starter' fertiliser (a compound fertiliser supplying 30 kg N, 26 kg P and 22 kg S/ha) either placed with the seed, or broadcast, or banded to the side and 3 cm below the seed. In 1997 the canola was sown after wheat, and in 1998 after pasture. Plant establishment of all cultivars was reduced by 40-65% when fertiliser was placed with the seed; tillage treatment did not alter this response. Placing fertiliser with the seed reduced dry matter/m 2 by up to 40% in plants at flowering, but by physiological maturity, there were no differences in dry matter/m 2 due to fertiliser placement. Analysis of the combined seed yields for both years showed that although plants in the with-seed placement compensated by producing more seed/plant, this compensation was sufficient only at Breakfast Creek for yields to be comparable to those of the other fertiliser placements. Tillage had little effect on seed yields. In 1997, no-till yielded more than one-pass at Ardlethan, but in 1998 at Ardlethan no-till yielded less than the other tillage systems. Fertiliser placement and tillage had no effect on seed oil concentration and meal protein content. Cone penetrometer measurements (1998) showed no differences in soil strength between tillage treatments at Ardlethan; while at Harden, one-pass had less soil strength than the other tillage treatments. Crop water extraction was not affected by tillage at any site. It is concluded that a conservation-farming system involving no-till or one-pass tillage, and separation of seed and fertiliser has the potential for producing high yielding canola crops, reducing the risk of soil degradation, as well as saving time and land-preparation costs.
  • Authors:
    • Simpfendorfer, S.
    • Backhouse, D.
    • Moore, K.
    • Verrell, A.
  • Source: Update of research in progress at the Tamworth Agricultural Institute 2002
  • Year: 2003
  • Summary: A replicated, fully phased, field trial was conducted in Tamworth, New South Wales, Australia, to determine the effects of the most common winter and summer break crops on crown rot (caused by Fusarium pseudograminearum) in wheat. The experiment was established in 2000 by sowing F. pseudograminearum-colonized ryegrass seed with wheat cv. Janz into plots. In 2001, rape, chickpea, faba bean, sorghum or wheat cv. Janz were grown under a no-till system. In 2002, wheat cv. Sunstate was planted across the winter break crop plots. All four rotation crops proved effective breaks for crown rot. They encouraged breakdown of the 2000 Janz residue. Stubble ground cover in May 2002 was 15% for sorghum, 28% for faba beans, 30% for rape, and 41% for chickpea compared with 88% for continuous no-till wheat (and 60% long fallow). The rotation crops also reduced survival of the pathogen with recovery of F. pseudograminearum ranging from 7-13% in crowns to 10-15% in stubble following break crops compared with 33% in crowns and 49% in stubble for continuous no-till wheat. These effects carried through to the 2002 wheat crop where infection of Sunstate plants at tillering ranged from 25% for wheat after rape to 39% for continuous wheat.