Planting date and phosphorus fertilizer placement effects on winter wheat

Two banding methods of applying P to winter wheat (Triticum aestivum L.), s eed and knife (dual placement), have generally performed similarly when ave raged over years and locations, However, performance can vary considerably from year to gear, or even between locations, This study was conducted to d etermine the effect of optimal and delayed date of wheat planting on the pe rformance of seed-applied and knifed P on grain yield, P uptake, and yield components. Four rates of P (0, 11.2, 22.4, and 33.6 kg P ha(-1)) were seed - and knife-applied on a Sharpsburg soil (fine, smectitic, mesic Typic Arig udoll) and Crete soil (fine, smectitic, mesic Pachic Argiustoll) in 1986 an d tao Crete soils and one Wymore soil(fine, smectitic, mesic Aquertic Argiu doll) in 1987, There were two planting dates in 1986 and three in 1987, All five soils had soil P test levels of low to very low (Brag and Kurtz P1 of 5 to 7 mg kg(-1)). While seed and knife application performed similarly wi th an optimum planting date, seed application was a superior P application method in terms of grain yield and P uptake when planting was delayed, The primary reason for the superiority of seed P application was its ability to stimulate tillering and head formation at the later planting dates. The di fference in performance between the two methods of P application was probab ly related to quicker root access to the fertilizer P in the fall soon afte r planting. Root access to fertilizer P in the fall influences the number o f tillers developed, which determines head number at harvest and final grai n yield. Results of this research suggest that, when wheat planting date is delayed, fertilizer P should be applied with the seed for maximum effectiv eness.