Phosphorus Fertilization of Late-Planted Winter Wheat into No-Till Fallow

Winter wheat (L.) is planted in low precipitation areas of north-central Oregon and east-central Washington after 14 mo of tilled fallow. No-till fallow (NTF) is an alternative to the tillage-based method. The disadvantage of NTF is the loss of seed-zone moisture and inability to plant early. Delayed plant growth and reduced grain yield (GY) associated with late planting in NTF may be offset by P fertilization. We conducted a field experiment at three locations for 3 yr to evaluate effects of 0, 5, and 15 kg ha of P fertilizer on plant P concentration (PPC), dry matter accumulation (DMA), P uptake (PU), spikes per unit area (SPU), 1000 kernel weight (KW), kernels per spike (KPS), and GY. Soft white winter wheat was planted into NTF during the third week of October. Phosphorus fertilizer was placed below and beside the seed while planting. Application of 5 and 15 kg ha P increased PPC and/or DMA and enhanced overall PU by 0.6 and 1.7 kg P ha, respectively. Corresponding increases in SPU were equal to 35 and 55 spikes m Phosphorus application had no effect on KW or KPS. The 5 kg ha P treatment increased overall GY by 4.4%. The 15 kg ha P treatment increased overall GY by 7.6%. Significant GY responses to P application, across sites, ranged from 2.2 to 14.5%. Improvement in P nutrition and increases in SPU and GY were observed at sites where initial soil test P (STP) levels were <12 mg kg