An algorithm for corn nitrogen recommendations using a chlorophyll meter based sufficiency index

Authors: Varvel, Gary; Wilhelm, Wallace; Shanahan, John; Schepers, James

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2007
Publication Date: 5/15/2007
Citation: Varvel, G.E., Wilhelm, W.W., Shanahan, J.F., Schepers, J.S. 2007. An algorithm for corn nitrogen recommendations using a chlorophyll meter based sufficiency index. Agronomy Journal 99:701-706.

Interpretive Summary: The major input influencing corn yield in the Midwest continues to be nitrogen fertilizer. Higher energy costs associated with both its production and application increase the need for management practices that increase nitrogen use efficiency and producer profit while reducing surface and groundwater contamination. Our objective was to develop a plant-based technique to detect and correct nitrogen deficiencies during the growing season. Chlorophyll meter readings and grain yield were collected from corn in irrigated monoculture corn and soybean-corn cropping systems with four hybrids and five nitrogen fertilizer application rates in the Platte Valley near Shelton NE. Normalized chlorophyll meter readings were used to calculate a sufficiency index from data collected at three growth stages (V8, V10, & V12), during each of the ten years of study (1995-2004). Both sufficiency index and relative yield responded significantly to N fertilizer application. A quadratic model was developed to describe the relationship between N rate and sufficiency index at each of the three vegetative stages. All values were similar, which led to the development of a combined model or algorithms that could be used to compute nitrogen needed to achieve maximum yield. Using this procedure, producers can determine if nitrogen is needed, and if so, the amount of nitrogen needed for maximum yield. In addition if SI is computed for specific areas of the field, nitrogen applications can be tailored to those areas, thereby reducing the potential of introducing more nitrogen into the system than needed to achieve maximum yield, within the constraints of the hybrid, site, and season.

Technical Abstract: Nitrogen fertilizer continues to be the major input influencing corn yield in the Midwest. Improved N recommendations should result in greater N use efficiency and producer profit while reducing surface and groundwater contamination. This study was conducted to develop a plant-based technique to detect and correct N deficiencies during the growing season. Chlorophyll meter readings and grain yield were collected from corn in irrigated monoculture corn and soybean-corn cropping systems with four hybrids and five N fertilizer application rates in the Platte Valley near Shelton NE. Normalized chlorophyll meter readings (sufficiency index, SI) were calculated from data collected at three vegetative stages, defined by thermal time accumulation after planting, during each of the ten years of study (1995-2004). Highly significant linear correlations between SI and relative yield indicated both responded similarly to N fertilizer application. Relationships between N rate and SI (at each of the three vegetative stages and combined over stages) were described by quadratic models. The combined model (SI = 0.8073 + 0.002(N rate) – 0.0000056(N rate)2, R2 = 0.70) can be used to compute N needed to achieve maximum yield. This procedure gives producers the tools to determine if N is needed, and if so, the amount of N needed for maximum yield. In addition if SI is computed for specific areas of the field, N applications can be tailored to those areas, thereby reducing the potential of introducing more N into the system than needed to achieve maximum yield, within the constraints of the hybrid, site, and season.