Are Modern Wheat Varieties More Responsive to in-Furrow Fertilizer Than Historical Ones?.

Wheat varieties released during different historical eras have shown increased genetic yield gain as a result of direct selection for grain yield, which consequently increases their nutrient requirement. However, current university recommendations have been developed in past decades and limited information exists on the differential responses of modern and historical varieties to fertilizers. Our objective was to determine the agronomic responses of historical and modern winter wheat varieties to two different fertilization programs. Field experiments were established during 2016-17 in two sites characterized by >40 ppm extractable P, namely Ashland Bottoms and Belleville, Kansas. A two-way factorial treatment structure was established in a split-plot design with four replications, with main plots arranged as randomized complete block design and subplots completely randomized within main plots. Seven winter wheat varieties released between 1920 and 2016 constituted the main plots and two fertilizer practices (no fertilizer versus 112 kg ha^-1 in-furrow 12-40-0-10-1) constituted sub-plots. Historical varieties were taller (122 cm) and had thinner stems (2.9 mm) than modern ones (93 cm and 3.1 mm); thus, year of variety release negatively correlated to plant height (0.3 cm yr^-1) and positively correlated to stem diameter (0.0036 mm year^-1). Non-linear regression indicated that in-furrow fertilizer increased the asymptotic maximum canopy cover (+2-4%), led to a quicker achievement of maximum rate of canopy cover (53-564 less GDD), irrespective of era of variety release. Modern varieties increased grain yield due to fertilizer in ~415 kg ha^-1 whereas historical ones showed neutral to negative (~215 kg ha^-1) responses. Genetic yield gain was 34.3 (±5.7) kg ha^-1 yr^-1 without fertilizer and 45.2 (±7.4) kg ha^-1 yr^-1 with in-furrow fertilizer, suggesting the need for re-evaluation of current fertility recommendations for modern wheat varieties to better explore the yield potential and increase on-farm productivity.