Introduction

1. Yield, Protein, and Quality Response to Planting Date, Variety, and Late N. B.D. Brown. University of Idaho. Introduction Higher market prices for the hard red spring class relative to the soft white class have increased grower interest in the production of hard red spring (HRS). There is also potential for hard white spring. Less HRS wheat is currently grown in SW Idaho in part because of concerns about the management required for producing wheat with acceptable protein. Planting dates have significant impact on wheat production and quality. Delayed spring plantings typically reduce wheat yield. In contrast, yields of late fall (dormant) seedings of spring wheat have exceeded those of early spring planted spring wheat in southern Idaho. Varieties also differ in yield and protein. Discounts for low protein need to be avoided or minimized to maximize the returns for the HRS class. Increasing late season available N is frequently used to enhance grain protein of irrigated hard red spring and winter wheat. The protein response to late season applied N is not uniform in all production areas. The higher the yield the more difficult it may be to raise protein at harvest to levels that enable growers to avoid low protein discounts. This could be particularly true for late fall planted spring wheat that is more productive than the same spring wheat traditionally planted in early or late spring. Protein enhanced with late season N has been questioned for its quality. Specifically, there apparently is concern that NIR measured protein increases from late season N are not associated with baking quality improvements. Information is needed on the hard spring wheat protein and quality response to late season N as affected by planting date and variety in order to guide SW Idaho growers on late season N management decisions. Objective The objective was to evaluate the effects of wide ranging planting dates and varieties on the yield, protein, and quality response to late season applied N. Methods A three year field study was conducted on a Greenleaf silt loam (fine-silty, mixed, superactive, mesic, xeric calciargids) at the University of Idaho Parma Research and Extension Center to measure the yield, protein, and quality response of three hard spring varieties (Vandal and WPB 936 hard reds, and ID377S hard white) grown under wide ranging planting dates (late fall, early spring, and late spring), with four late season urea N rates (0, 28, 56, and 84 kg ha-1) applied dry at heading and incorporated with about 25mm of sprinkler irrigation. Factorial treatments were arranged in a randomized complete block with four replications. Planting dates ranged from 11-23 Nov for the late fall planting, 7-15 March for the early spring planting, and 10-14 April for the late spring planting. Fertilizer N as urea was applied uniformly over the entire experiment to support yields of 8.1 Mg ha-1 according to the UI Fertilizer Guide for Spring Wheat. This urea N (177, 190, and 106 kg N ha-1 for 1999, 2000, and 2001 seasons respectively) was topdressed each year to the entire experiment when the early spring planting was emerging (dates ranged from 23-30 March). Timing corresponded to the tillering stage for the late fall planting and preceded the late spring planting by 15 to 19 days. This N was dependent on rainfall for incorporation and significant rain in one event in any year exceeding 5mm did not occur prior to the first irrigation on 23 April (1999), 24 April (2000), or 19 April (2001). The trial was irrigated each year with sprinklers. Nitrogen was the only limiting nutrient based on fall soil tests. Yield was measured with a small plot combine from 9.3m2. NIR protein (12% moisture corrected) was measured on subsamples of harvested grain. Baking quality measures included flour protein (Fpro), flour yield (Fyd), Mixograph peak time (Mpk), height (Mht), tolerance (Mto), absorbance (Mab), bake or loaf volume (Bvo), and Bvo/Fpro ratio (R). Baking quality results were available for only the first two seasons. Baking quality was determined using AACC method No. 10-10B at the University of Idaho Aberdeen Wheat Quality Laboratory. Bake volume was determined using rape seed displacement. Protein and baking quality was determined at the University of Idaho Aberdeen Wheat Quality Laboratory. Treatment effects were evaluated with ANOVA options in SAS 8.0. Results Yields in excess of the 8.1 Mg ha-1 target were achieved in each year for the late fall planting. The 2000 season was especially productive (Fig. 1). Late fall planting dates were the highest yielding in two of three years and late spring plantings were invariably the lowest. Variety performance depended on the planting date (Fig.1.) Vandal was as high yielding as WPB 936 in two of three years when late fall planted but Vandal was less well adapted to either early spring or late spring plantings as compared to the others. Vandal is relatively late maturing compared to the others. WPB 936 was the highest yielding spring planted variety in two of three years. Late season N at the 84 kg ha-1 rate increased lodging in 1999 and reduced yield. There was a similar reduced yield trend with high late season N in other years but the effect was non-significant. Protein was invariably affected by planting dates (Fig. 2). Protein was highest with late fall plantings in the first two years and lowest in the late spring planting. In contrast, the late fall planting was lowest in protein in the 2001 season and protein for the late spring planting was highest. It is not clear why planting date effects on protein were inconsistent between years. It also is not clear why the more productive late fall plantings were highest in protein in two of the three years. Vandal in all seasons was the highest in protein and the hard white ID377s was lowest. There were no planting date by variety interactions for protein. Late season N increased protein in all years (Fig. 2). The increase with late N was linear in 1999 and quadratic in 2000 and 2001. The protein increase with the highest late N rate averaged 1.1% in 1999, 1.2% in 2000 and 1.6% in 2001 when averaged across planting dates and varieties. Although planting dates and varieties significantly affected protein they did not affect the protein increase with late season N. Averaged across planting dates, Vandal was the only variety that consistently produced 14% or higher protein with the highest late season N rate. Although late season N was essential in this study for increasing protein to 14%, variety selection was also critical. Not all varieties were capable of producing 14%protein wheat despite high rates of late season N. WPB 936 is the most popular HRS variety grown in the western Idaho and far eastern Oregon production area. Frustration with low protein discounts may in part be due to the use of this and similar varieties. Baking quality as represented by bake volume was influenced by both varieties and planting dates. Bake volume was always lowest with the hard white spring ID377s (Fig. 3). Vandal and WPB 936 were comparable in bake volume although Vandal averaged somewhat higher at some N levels. Planting dates also affected bake volume. Bake volume for the late fall planting was higher than the bake volume for the late spring planting in both 1999 and 2000. The early spring bake volume was comparable to the late fall bake volume in 1999 but lower than late fall bake volume in 2000. Despite significant variety and planting date effects on bake volume, there was no significant interaction of planting dates or varieties in the bake volume response to late season N. Bake volume increased with late season N in both 1999 and 2000. The bake volume response to late season N was linear in 1999 and either linear or quadratic in 2000. Bake volume was greater in 2000 than in 1999. The bake volume to protein ratio provides a rough indication of protein quality in the two years. Despite reports and concerns that late season N enhanced protein may not result in increased protein quality, the calculated ratios here suggest otherwise. We found the bake volume to protein ratio to be stable over a considerable range of late season applied N (Fig. 4), applications that resulted in protein increases ranging from 1.1 to 1.2%protein when averaged across planting dates and varieties. Varieties affected all baking quality parameters as expected given the mix of hard white and reds. Within the hard reds, Vandal had higher Fpro, Mpk, and Bvo than WPB 936. Late fall plantings resulted in higher Fyd, Mht, Mab, and Bvo than early or late spring plantings. Late season N increased Fpro, Mpk, Mht, Mab, Bvo, and reduced Mto in both years (Fig. 5).Baking quality was better in 2000 than 1999. Figure 1. Irrigated hard spring wheat yield as affected by variety and planting date. Parma 1999-01. Figure 3. Hard spring wheat bake volume response to late season N as affected by planting dates and varieties in 1999 and 2000. Figure 2. Irrigated hard spring wheat protein response to late season N as affected by planting dates and varieties in each year of the study. Parma, 1999-01. Figure 4. Bake Volume to protein ratio for the 1999 and 2000 seasons as affected by late season applied N. Summary This study demonstrates the challenge of producing both high yields and high protein hard red spring wheat under irrigation. Relatively high rates of late N were essential for achieving 14% protein or avoiding low protein discounts. Protein was consistently enhanced with late season N. Both varieties and planting dates affected yield and protein, but neither affected the protein response to late season N. Despite previous reports or concerns about limited baking quality improvements with late N enhanced NIR protein, this study suggests that late season N increased not only NIR protein but was also responsible for associated improvements in baking quality as reflected by greater Fpro, Mpk, Mht, Mab, and ultimately Bvo. Figure5. Flour protein, and mixograph peak, height, tolerance and absorption as affected by late season N in the 1999 and 2000 seasons.