The effect of nitrogen fertility rate and seeding rate on yield, nutritive value and economics of forage corn in a low corn heat unit region of Western Canada

Abstract

Grazing whole plant forage corn ( Zea mays L.) during winter by gestating beef cows ( Bos taurus ) is an alterative feeding strategy in Saskatchewan, Canada. Seeding rate for target plant population and N fertility rates for grazing corn have been based on grain corn research results. The objectives of this study were to determine seeding rate and N fertility rate effects and interaction on forage corn yield and nutritive value. Trials were conducted over three growing seasons (2016, 2017, and 2018) at six sites: Scott, Lanigan, Melfort, Yorkton, Outlook, and Redvers Saskatchewan, that ranged from 2100 to 2450 corn heat unit (CHU) rating. Three N fertility rates, 112, 168 and 225 kg ha −1 , and 3 seeding rates, 75,000, 100,000 and 125,000 seeds ha −1 , were evaluated with corn hybrids that were adapted to each site. Dry matter (DM) forage yield at the half-milk line stage was determined and samples analyzed by NIRS at a commercial lab for nutritive value. Increased seeding rate from 75,000 to 125,000 seeds ha −1 resulted in increased DM yield by 1.0 ± 0.1 Mg ha −1 and increased total digestible nutrients (TDN) yield while crude protein (CP) and P concentrations decreased. Fiber, TDN, and carbohydrate concentrations were not affected by seeding rate. Increased N fertility from 112 to 225 kg ha −1 resulted in increased DM yield by 0.6 ± 0.1 Mg ha −1 , and increased CP yield, and TDN yield. CP and soluble protein concentrations increased while neutral detergent fiber digestibility (NDF- dig ) concentration decreased with increased N fertility. Mineral concentrations also increased with increasing N fertility. There were no seeding rate x N rate interactions for yield or nutritive value. Site-years varied in most yield and nutritive value variables. N rate x site-year interactions were significant for DM yield, CP yield and TDN yield because the effect of N fertility was significant at only one third to one half of the site-years. Cost of production per tonne of DM or TDN increased with increased seeding rate but neither was affected by N fertility rate. Net revenue was reduced from $522 ha −1 to $462 ha −1 by increased seeding rate while there was no effect of N fertility rate on net revenue. Current seeding rate and N fertilizer rates for grazing corn in Saskatchewan will provide producers with the highest net return. • Grazing corn yield increased by 1.0 Mg ha −1 when seeding rate increased. • Increased N fertilizer rate increased yield by 0.6 0 Mg ha −1 . • Seeding rate and N fertility rate affected nutritive value of grazing corn. • Highest net returns of grazing corn occurred at recommended seeding and N rates. • Variation in nutritive value among site-years means feed testing is essential.