PT 2000-13

August 2000

With adequate moisture in the soil at planting to obtain a good stand and/or adequate rainfall in the fall for growth, fall forage produced prior to January 1^st increases as planting date moves from mid-October back into September (see Table 1). In southwest Oklahoma, water stress frequently slows forage growth due to lack of soil water and/or rainfall (Table 2). Under such conditions, forage yields may not differ significantly with planting date as in 1992-93 and 1993-94 (Table 1). Forage yields are determined by clipping to the soil surface and are presented in dry matter per acre.

Grain yields nearly always increase as planting is delayed until an ideal planting date is reached in mid to late October (Table 1). Some years this increase is large (more than 15 bu/a) and other years the grain yield differences are very small as planting date changes from early September into mid-October as seen in 1992-93. Planting as late as mid-November also reduces grain yield as noted in the 1998-99 results. Increasing the seeding rate to 120 lb/a compensated for only about one-half of the yield loss when planting November 18 compared to earlier planting dates( data not shown). Even though grain yields increased by delaying planting until late October, many producers wanting grain only from the wheat crop will plant when they have moisture for stand establishment in early October. This is because of the concern there might not be enough moisture for stand establishment later in October.

Test weight response to planting date has varied. Sometimes test weights increased with later plantings. Sometimes there is no difference.

Root rots and barley yellow dwarf mosaic virus (BYDV) are common diseases that contribute to the lower yield and test weight with earlier than ideal planting dates. The more severe the root rot or BYDV infestations, the greater the increase in test weight and yield with later planting. When barley yellow dwarf mosaic virus infections occur in the fall, which happens more frequently with earlier planting, yield and test weight can be severely reduced.

Except for 1992-93, AgriPro Tomahawk has been planted at 60 lb/a. In 1998 a seeding rate variable was added to the trial which will be summarized after we obtain a couple more years data. Only data from the 60 lb/a treatment are included in the table. Nitrogen fertilization has been enough for a 50 bu/a grain crop and top dressing has been applied to replace nitrogen removed in the forage, assuming 30 lb of nitrogen per 1000 lb of forage.