Water-budget evaluation of prairie and maize ecosystems

Annual monitoring of water-budget components is useful for comparing the fa te of water inputs among ecosystems. Land-use changes from natural prairies to managed agroecosystems alter water-budget components. Weekly hydrologic al budgets for a restored natural prairie and maize (Zen mays L,) agroecosy stems (no-tillage and chisel-plow) were constructed for 132 consecutive wk between June 1995 and January 1998. Precipitation, drainage, soil water-sto rage changes, and snow-cover changes were measured on Piano silt loam soil (fine-silty, mixed, superactive, mesic Typic Argiudoll) at agricultural and prairie sites. Compared with the maize ecosystems, the prairie maintained greater soil water contents deeper in the soil profile (0.8-1.4 m), somewha t larger evapotranspiration (Et), and significantly less drainage because o f considerable interception of precipitation by a residue layer. Soil water storage in the no-tillage maize setting was more similar to the prairie, w hile Et, net primary productivity, and drainage were more comparable to the chisel-plow agroecosystem. Total drainage measured with equilibrium-tensio n lysimeters was 199 mm of water (coefficient of variation [CV] = 5.7%) for the prairie ecosystem, 563 mm of water (CV = 13.6%) for the no-tillage mai ze ecosystem, and 793 mm of water (CV = 18.5%) for the chisel-plow maize ec osystem. Residue interception for the prairie was 477 mm, compared with 681 mm of precipitation during the growing season of 1997, which contributed t o lower prairie drainage. The combination of similar productivity, higher s oil water contents, and less drainage than the chisel-plow ecosystem sugges ts that a no-tillage ecosystem is more sustainable than the chisel-plow agr oecosystem in terms of reducing potential adverse environmental impacts ass ociated with soil water movement.