Irrigated wheat grazing and tillage effects on subsequent dryland grain sorghum production

Use of conservation tillage has improved sorghum [Sorghum bicolor (L.) Moench] grain yield 10 to 20% in ungrazed wheat (Triticum aestivum L.)-fallow-sorghum production systems. Our objective in this 2-yr field study was to develop tillage guidelines for systems where the wheat was grazed. Grazing duration on winter wheat and tillage during the fallow period preceding dryland grain sorghum were treatments on Pullman clay loam (Torrertic Paleustoll), Grazing increased surface soil compaction and reduced wheat residues, Surface soil (0-5 cm) penetration resistance was 0.36, 0.52, 0.75, and 0.92 Mpa, and wheat residue in 1996 was 6.0, 4.8, 3.5, and 1.2 Mg ha for ungrazed and early, normal, and late cattle removal dates, respectively. As a result, sorghum grain yield in 1996, an exceptionally wet season, was 7.9, 7.5, 7.0, and 3.8 Mg ha(-1), respectively, with no tillage (NT). In 1997, a dry season with low runoff, only the late cattle removal with NT had reduced yield (3.4 Mg ha(-1) compared with 3.9 Mg ha(-1) for ungrazed NT), Use of one-time sweep tillage early in fallow resulted in an increase in sorghum grain yield of 1.9 Mg ha(-1) in 1996 for the late cattle removal treatment compared with NT, but it had no effect on yield with the normal cattle removal treatment. In 1997, one-time sweep tillage increased yield by 0.3 Mg ha(-1) with late removal. When wheat residue was less than or equal to2.4 Mg ha(-1) following grazing, sweep tillage reduced surface compaction, increased soil water at planting an average of 26 mm over 2 Sr, and improved grain yield of sorghum compared with NT, If wheat residues were greater than or equal to3.5 Mg ha(-1) after grazing, NT was as effective as any tillage treatment. Results agree with conservation tillage guidelines del eloped on ungrazed wheat.