Corn Response to Nitrogen Timing and Rate under Strip Tillage and Low-Yield Environment in Southeastern Coastal Plains

Problem statement: Insufficient rainfall under low yield environment may affect nitrogen management, plant growth indices and grain yields of corn (Zea mays L.). Approach: The objective of this study was to determine the effects of two N application timings (all at planting and as split application with N applied at planting and V6 stage) and five N fertilizer rates (0, 45, 90, 135 and 180 kg N ha⁻¹) on strip-tilled, dryland corn growth and yields under low-yield environmental conditions near Blackville SC, from 2007-2009. Plant growth measurements included plant height, ear height, relative chlorophyll content (SPAD), Leaf Area Index (LAI) and normalized difference vegetation index (NDVI). Results: Plant LAI at V8, NDVI at V8 and R1, SPAD at R1, plant height at V8 and grain yield generally increased with increasing N application rates. Due to most likely insufficient precipitation, the N application timing did not affect corn growth or yield. Despite relatively low grain yields, corn yield was increased by 1.6 Mg ha⁻¹ with increasing N application rate of 100 kg ha⁻¹. Grain yield was positively correlated with plant leaf area index (LAI) at R1 (r = 0.27, p≤0.05) and Normalized Difference Vegetation Index (NDVI) at V8 and R1 (r = 0.33 and 0.29, p≤0.01, respectively) and plant height at V8 stage (r = 0.42, p≤0.001). With N applied at planting, there was a 0.55 and 0.49 Mg ha⁻¹ yield increase with 0.1 increases in plant NDVI at V8 and R1, respectively. Conclusion: Under strip tillage and low yield environment conditions, plant growth and yields may not be affected by timing of N application mainly due to insufficient rainfall. Plant NDVI (for treatments with all N applied at planting) at V8 and R1 can help to estimate potential of corn grain yield, which may be reduced due to low nitrogen use efficiency.