• Authors:
    • Dalal, R. C.
  • Source: Soil Science Society of America Journal
  • Volume: 53
  • Issue: 5
  • Year: 1989
  • Summary: There is a paucity of information on the long-term effects of crop residue management under no-tillage culture on properties of clay soils in tropical and subtropical regions. The objective of this study was to compare the effects of 13 yr of conventional tillage vs. no tillage, crop residue retained vs. burned, and no fertilizer N vs. application of 23 and 69 kg N ha-1 yr-1 on organic C content, total N, mineralizable N, pH, electrical conductivity, chloride, exchangeable sodium percentage (ESP), and aggregation index (undispersed fraction <20 fim silt + clay) in a fine-textured Vertisol (650 g clay kg-1 soil). Highest concentrations of organic C and total N were found in the surface soil (0-0.1 m) with a combination of no-tillage, crop residue retained, and fertilizer N. Mineralizable N followed similar trends. Soil pH to 0.3-m depth and electrical conductivity to 1.2-m depth were significantly lower under no-tillage than under conventional tillage. Aggregation index of the surface soil (0-0.1 m), was higher under no-tillage. The ESP was lowest in the surface soil (0- 0.04 m) under no-tillage with crop residues retained; the soil profile (0-1.2 m) under this treatment also contained far less NaCl-equivalent salts (0.8 Mg ha-1) than under conventional tillage with crop residue burned (7.3 Mg ha-1). Available water and nitrate were lower in the surface soil but greater at depths (0.6-1.2 m) under no-tillage than in tilled soil. Thus tillage and crop residue management can substantially affect soil organic matter and microbial activity in the surface layers, and water relations and salt movement to at least 1.2-m depth, even in a fine-textured Vertisol.
  • Authors:
    • Consultative Group on International Agricultural Development (CGIAR)
  • Authors:
    • Partoharjono, S.
    • Hairiah, K.
    • Van Noordwijk, M.
    • Labios, R. V.
    • Garrity, D. P.
  • Source: Agroforestry Systems
  • Volume: 36
  • Issue: 1-3
  • Summary: Purely annual crop-based production systems have limited scope to be sustainable under upland conditions prone to infestation by Imperata cylindrica if animal or mechanical tillage is not available. Farmers who must rely on manual cultivation of grassland soils can achieve some success in suppressing Imperata for a number of years using intensive relay and intercropping systems that maintain a dense soil cover throughout the year, especially where leguminous cover crops are included in the crop cycle. However, tabour investment increases and returns to tabour tend to decrease in successive years as weed pressure intensifies and soil quality declines. Continuous crop production has been sustained in many Imperata-infested areas where farmers have access to animal or tractor draft power. Imperata control is not a major problem in such situations. Draft power drastically reduces the tabour requirements in weed control. Sustained crop production is then dependent more solely upon soil fertility management. Mixed farming systems that include cattle may also benefit from manure application to the cropped area, and the use of non-cropped fallow areas for grazing. In extensive systems where Imperata infestation is tolerated, cassava or sugarcane are often the crops with the longest period of viable production as the land degrades. On sloping Imperata lands, conservation farming practices are necessary to sustain annual cropping. Pruned tree hedgerows have often been recommended for these situations. On soils that are not strongly acidic they may consistently improve yields. But tabour is the scarcest resource on small farms and tree-pruning is usually too tabour-intensive to be practical. Buffer strip systems that provide excellent soil conservation but minimize tabour have proven much more popular with farmers. Prominent among these are natural vegetative strips, or strips of introduced fodder grasses. The value of Imperata to restore soil fertility is low, particularly compared with woody secondary growth or Compositae species such as Chromolaena odorata or Tithonia diversifolia. Therefore, fallow-rotation systems where farmers can intervene to shift the fallow vegetation toward such naturally-occurring species, or can manage introduced cover crop species such as Mucuna utilis cv. cochinchinensis, enable substantial gains in yields and sustainability. Tree fallows are used successfully to achieve sustained cropping by some upland communities. A variation of this is rotational hedgerow intercropping, where a period of cropping is followed by one or more years of tree growth to generate nutrient-rich biomass, rehabilitate the soil, and suppress Imperata. These options, which suit farmers in quite resource-poor situations, should receive more attention.