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Minimum and Delayed Conservation Tillage for Wheat–Fallow Farming

Dep. of Crop and Soil Sciences, Washington State Univ., P.O. Box B, Lind, WA 99341

View larger version (30K): [in a new window]   Fig. 1. Mass of surface soil clods 5 cm in diameter or larger at time sowing in early September for 1994, 1995, 1996, 1998, and the 4-yr mean as affected by conventional, minimum, and delayed minimum tillage during fallow. Within years, means followed by a different letter are significantly different at P < 0.05. NS = nonsignificant.

View larger version (32K): [in a new window]   Fig. 2. Subsurface (0–10 cm depth) soil clods in 1995, 1996, and 1998 as affected by conventional, minimum, and delayed minimum tillage during fallow. Within years, means for each subsurface clod size group followed by a different letter are significantly different at P < 0.05. NS = nonsignificant.

View larger version (62K): [in a new window]   Fig. 3. Soil water content in the 180 cm soil profile during the 6-yr (1993–1999) study period at the beginning of each fallow cycle in early August, in early spring after over-winter soil recharge had occurred, and at the end of the fallow cycle in early September as affected by conventional, minimum, and delayed minimum tillage. Means for each sampling date followed by a different letter are significantly different at P < 0.05. Numbers above bars show storage efficiency (SE), i.e., the percentage of precipitation occurring during the fallow cycle which was stored in the soil. NS = nonsignificant.

View larger version (28K): [in a new window]   Fig. 4. Seed-zone soil water content at time of sowing in September 1994, 1995, and 1996 as affected by conventional, minimum, and delayed minimum tillage during fallow. There were no water differences among treatments at any depth (0–22 cm) in any year.

View larger version (44K): [in a new window]   Fig. 5. Yearly and 5-yr mean grain yield of wheat as affected by conventional, minimum, and delayed minimum tillage during the preceding fallow cycle. NS = nonsignificant.