There are several areas in the interface between theoretical and applied ecology where our knowledge of soil physics, chemistry, and biology can, and should, be put to good use. One of these is in the area of agroecosystem studies. The essentials of decomposition and nutrient dynamics in temperate agroecosystems were reviewed by Andren et al. (1990), Hendrix et al. (1992), Coleman et al. (1993), and in Africa by Vanlauwe et al. (2002).
It is generally acknowledged that zero, or reduced, tillage has several effects on abiotic and biotic regimes in agroecosystems. Retention of litter keeps the surface of the soil cooler and moister than in a conventionally tilled plot (Fenster and Peterson, 1979; Phillips and Phillips, 1984), and also leaves more substrate available in the 0-7.5 cm depths for nitrifiers and denitrifiers (Doran, 1980a, b). This abiotic buffering seems to promote a slower nitrogen cycle, one that continues over a longer time span but at a lower rate per unit time (House et al., 1984; Elliott et al., 1984). Soil invertebrate populations, particularly microarthropods (Stinner and Crossley, 1980; House et al., 1984), and earthworms (Parmelee et al., 1990) are enhanced as well (Table 5.5) (Coleman and Hendrix, 1986). The microarthropods are undoubtedly responding to increased populations of litter-decomposing fungi, which tend to concentrate nitrogen by hyphal translocation (Holland and Coleman, 1987). In fact, dominant families of fungivorous mites responded by markedly decreasing in numbers in field mesocosm plots treated with captan, which brought fungal populations down to about 40% of normal levels (Mueller et al., 1990).
A total of 22 agroecosystem components and processes were compared in no-till and conventional tillage in Georgia. In many instances, there was greater resilience in the no-till system, as shown by greater invertebrate species richness, greater soil organic matter, and ecosystem nitrogen turnover time (Table 5.6) (House et al., 1984).
These findings were confirmed and extended by Elliott et al. (1984), who examined dynamics in long-term stubble-mulch and no-till plots on a silty-loam soil in eastern Colorado that underwent alternate crop and fallow regimes. These plots had been under cultivation for more than 75 years, and no-till had been an experimental treatment for nearly 20 years. Nitrate accumulated to a greater extent in the fallow than in the cropped rotation (Table 5.7). Ammonium-N was usually at very low levels (about 1.0 |ig NH4-N per g-1 soil), but on one date the concentration reached 4.6 |g NH4-N per g-1 soil in the top 2.5 cm of the no-till plots just
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