Establishment practices for prerice green manures

Wider farm-level use of green manures (GMs) depends on the availability of effective crop establishment practices with minimum investment in seed, tillage, and labor. This chapter reviews recent research on the interactions among the techniques and levels of these production factors in determining low-risk, low-cost GM production. In the dry-to-wet transition in fallow ricefields, surface soil may either be dry or saturated, and crop establishment methods suitable for the two situations differ considerably. Although there are a number of suitable techniques for crop establishment with reduced tillage in dry soils, these techniques somewhat lower the percentage emergence, which tend to favor higher seeding rates. Weed pressures may also be severe with reduced tillage. Zero or minimum tillage practices need to take these agronomic conditions and germination risks into consideration. Alternative methods may also be used, such as animal-drawn seeders specifically adapted to these peculiar soil conditions, or simple broadcast and harrow methods, which are presumably more sensitive to soil moisture conditions after seeding, but may be quite successful. Low seeding rates are feasible when the window of time available for the GM crop in the field exceeds 50 d. This allows the lower plant density to be compensated for by higher biomass and N accumulation per plant. High plant densities are, in fact, unnecessary in such situations, as they would only lead to greater

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