• Authors:
    • Doran, J. W.
  • Source: Soil Science Society of America Journal
  • Volume: 44
  • Issue: 4
  • Year: 1980
  • Summary: The physical, chemical, and biological soil environment for reduced or no-till farming differs greatly from that for conventional tillage. Evaluation of the soil microbial and biochemical environment greatly aids predictions of N availability to crop plants and in optimizing management practices for reduced and no-till soils. Surface soils from long-term no-till and conventional tillage plots at seven U.S. locations were characterized for microbial and biochemical components. The counts of aerobic micro-organisms, facultative anaerobes, and denitrifiers in the surface (0-7.5 cm) of no-till soils were 1.14 to 1.58, 1.57, and 7.31 times higher, respectively, than in the surface of plowed soil. Phosphatase and dehydrogenase enzyme activities and contents of water and organic C and N in the surface of no-till soil were also significantly higher than those for conventional tillage. However, at the 7.5- to 15-cm and 15- to 30-cm depths these trends were reversed and microbial populations, enzyme activities, and water and organic C and N contents were the same or higher for conventional tillage than for no-till. The trends in microbial populations with both tillage treatments were closely paralleled by soil enzyme activities and were also regulated by soil pH and levels of organic C and N. The surface 0- to 7.5-cm of no-till soil contained more potentially mineralizable N--20 to 101 kg/ha--than did that of plowed soils. This increased labile N reserve is apparently related to the higher microbial biomass present under no-till soils. Maximum aerobic microbial activity with conventional tillage extends to a greater depth than with no-till. Microbial populations under no-till decrease rapidly below the 7.5-cm depth. At the 7.5- to 15-cm depth counts of aerobic microor-ganisms and nitrifiers were 1.32 to 1.82 times higher on the conventionally tilled soils. However, counts for facultative anaerobes and denitrifiers were 1.23 to 1.77 times higher for no-till soil. Also, the proportion of the total aerobic population represented by facultative anaerobes and denitrifiers for no-till was twice that for conventional tillage. Consequently the potential rate of mineralization and nitrification is higher with conventional tillage while that for denitrification is higher with no-till. Microbial population counts and the relative abundance of various microbial types suggests that the bochemical environment of no-till soils is less oxidative than that under conventional tillage. Changes in tillage and fertilizer management practices required for no-till soils should reflect the increased potential for immobilization of surface applied N and the lower levels of plant available NO3- as compared with those under conventional tillage.
  • 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.