Page 2 - January Newsletter

Crop Production By: Jeanne Falk JonesLong –Term Nitrogen and Phosphorus Fertilization in Irrigated CornThis is research from the K-State Experiment Sta- tion in Tribune. The complete research report is avail- able at www.sunflower.ksu.edu/agronomy.Long-term research shows that phosphorus (P) and nitrogen (N) fertilizer must be applied to optimize pro- duction of irrigated corn in western Kansas. In 2017, N applied alone increased yields by 70 bu/a, whereas P applied alone increased yields by less than 10 bu/a. Ni- trogen and P applied together increased yields up to 130 bu/a. This is 10 bu/a less than the 10-year average, where N and P fertilization increased corn yields up to 140 bu/a. Application of 120 lb/a N (with highest P rate) produced 93% of maxi-mum yield in 2017, which is similar to the 10-year average. Application of 80 in- stead of 40 lb P2O5/a increased average yields 10 bu/a. Average grain N content reached a maximum of 0.6 lb/ bu while grain P content reached a maximum of 0.15 lb/bu (0.34 lb P2O5/bu). At the highest N and P rate, apparent fertilizer nitrogen recovery in the grain (AFNRg) was 42% and apparent fertilizer phosphorus recovery in the grain (AFPRg) was 61%.IntroductionThis study was initiated in 1961 to determine re- sponses of continuous corn and grain sorghum grown under flood irrigation to N, P, and potassium (K) fertili- zation. The study is conducted on a Ulysses silt loam soil with an inherently high K content. No yield benefit to corn from K fertilization was observed in 30 years, and soil K levels remained high, so the K treatment was discontinued in 1992 and replaced with a higher P rate.ProceduresThis field study is conducted at the Tribune unit of the Kansas State University Southwest Research- Extension Center. Fertilizer treatments initiated in 1961 are N rates of 0, 40, 80, 120, 160, and 200 lb/a without P and K; with 40 lb/a P2O5 and zero K; and with 40 lb/ a P2O5 and 40 lb/a K2O. The treatments were changed in 1992; the K variable was replaced by a higher rate of P (80 lb/a P2O5). All fertilizers were broadcast by hand in the spring and incorporated before planting. The soil is a Ulysses silt loam. The corn hybrids [Pioneer 34B99 (2008), DeKalb 61-69 (2009), Pioneer 1173H (2010), Pioneer 1151XR (2011), Pioneer 0832 (2012-2013), Pio- neer 1186AM (2014), Pioneer 35F48 AM1 (2015), Pio- neer 1197 (2016), and Pioneer 0801 (2017)] were plant- ed at about 32,000 seeds/a in late April or early May.Hail damaged the 2008, 2010, and 2017 crops. The corn is irrigated to minimize water stress. Sprinkler irrigation has been used since 2001. The center two rows of each plot are machine harvested after physio- logical maturity. Grain yields are adjusted to 15.5% moisture. Grain samples were collected at harvest, dried, ground and analyzed for N and P concentrations. Grain N and P content (lb/bu) and removal (lb/a) were calculated. Apparent fertilizer N recovery in the grain (AFNg) was calculated as N uptake in treatments re- ceiving N fertilizer minus N uptake in the unfertilized control divided by N rate. The same approach was used to calculate apparent fertilizer P recovery in the grain (AFPRg). Pesticide for grasshoppers was applied on July 18 and hail damage occurred on August 18.ResultsCorn yields in 2017 were 25% lower than the 10- year average . Nitrogen alone increased yields 70 bu/a, whereas P alone increased yields less than 10 bu/a. However, N and P applied together increased corn yields up to 130 bu/a. Maximum yield was obtained with 200 lb/a N with 80 lb/a P2O5.Corn yields in 2017 (averaged across all N rates) were 10 bu/a greater with 80 than with 40 lb/a P2O5.The 10-year average grain N concentration (%) in- creased with N rates but tended to decrease when P was also applied, presumably because of higher grain yields diluting N content. Grain N content reached a maxi- mum of 0.6 lb/bu. Maximum N removal (lb/a) was greatest at the highest yield levels, which were attained with 200 lb N and 80 lb P2O5/a. At the highest N and P rate, AFNRg was 42% and AFPRg was 61%.Similar to N, average P concentration increased with increased P rates but decreased with higher N rates. Grain P content (lb/bu) of about 0.15 lb P/bu (0.34 lb P2O5/bu) was greater at the highest P rate with low N rates. Grain P removal averaged 29 lb P/a at the highest yields.Data tables, with corn yields and grain removal of N and P from 2008 to 2017 are available online or at the Extension Office. These tables contain yields and removal for each treatment (combination of N and P205 rates). They are available online at www.sunflower.ksu.edu/agronomyK-State Research and Extension is an equal opportunity provider and employer.