Pre-sidedress nitrate test and other crop-based indicators for fresh market and processing sweet corn

Commercial sweet corn (Zea mays L.) production requires significant quantities of fertilizer N, leading to inefficient N use and negative environmental impact. A field experiment was conducted for 4 yr (2001-2004) in Ottawa, Canada, to assess and compare preside-dress soil nitrate test (PSNT) with some crop-based measurements (canopy reflectance, leaf chlorophyll and plant total N) for improved N management. A fresh market sweet corn (FMSC, hybrid 'Temptation') grown from 2001 to 2003, and a processing sweet corn (PSC, hybrid 'Hollywood') from 2002 to 2004, both received five fertilizer N rates (0, 50, 100, 150, and 200 kg N ha(-1)). Soil samples taken from the V4 to V8 growth stages were analyzed for NO3--N. Leaf chlorophyll content (SPAD) and canopy reflectance were also measured for FMSC at the same time. All N treatments affected the number of marketable ears, kernel dry weight and total biomass production. However, in most cases, there was no difference between N treatments from 100 to 200 kg ha(-1). The PSNT NO3--N increased linearly with the fertilizer N rates, and there were significant positive correlations between PSNT at V4 to V6 and the number of marketable ears. It was evident that PSNT, plant N concentration at V6, SPAD and canopy reflectance all differentiated sweet corn N response similarly, and they were highly correlated with one another. We concluded that PSNT at V4 to V6 was effective in predicting sweet corn N requirement in this cool and short-growing region.