In-Season Prediction of Corn Grain Yield Potential Using Normalized Difference Vegetation Index

Drastic increases in the cost of N fertilizer and increased public scrutiny have encouraged development and implementation of improved N management practices. This study evaluated the relationship between corn (Zea mays L.) grain yield and early season normalized difference vegetation index (NDVI) sensor readings using the GreenSeeker sensor. The relationships between grain yield and several predictor variables were determined using linear and nonlinear regression analysis. Categorizing NDVI measurement by leaf stage indicated that growth stage was critical for predicting grain yield potential. Poor exponential relationships existed between NDVI from early sensor measurements (V6–V7 leaf stage) and grain yield. By the V8 stage, a strong relationship (R 5 0.77) was achieved between NDVI and grain yield. Later sensor measurements (V9 and later) failed to distinguish variation in green biomass as a result of canopy closure. Normalizing the NDVI with GDD (growing degree days) did not significantly improve yield potential prediction (R 5 0.73), but broadened the yield potential prediction equation to include temperature and allowed for adaptation into various climates. Sensor measurements at the range of 800 to 1000 GDD resulted in a significant exponential relationship between grain yield and NDVI (R 5 0.76) similar to the V8 leaf stage categorization. Categorizing NDVI by GDD (800–1000 GDD) extended the sensing time by two additional leaf stages (V7–V9) to allow a practical window of opportunity for sidedress N applications. This study showed that yield potential in corn could be accurately predicted in season with NDVI measured with the GreenSeeker sensor. NITROGEN is well documented as a limiting nutrient in crop production and is considered one of the best producer inputs to increase profitability under an appropriate management system. In 2003, about 11.5 million t of N fertilizer were applied to 96% of the total corn acreage in the Great Plains (National Agricultural Statistics Service, 2005). With the present 33% average NUE (N use efficiency) in world cereal crop production (Raun and Johnson, 1999), .6.7 million t of N fertilizer would have been expected to be lost to the environment in the Great Plains for the 2003 crop year at a cost of US$2.3 billion. Improved N management is essential to maintain producers’ income and diminish environmental degradation. Traditionally, N application rates have been made based on grain yield goals determined from a recent 5-yr crop yield average increased typically by 10 to 30% to assure adequate N for above-average growing conditions (Johnson, 1991; Dahnke et al., 1988). Dahnke et al. (1988) defined yield goal as the “yield per acre you hope to grow”. Setting unrealistic yield goals and not accounting for yield variation between fields and within a field, however, has led to consistent, excessive N application. As a result, some fields have enough inorganic N in the soil in semiarid regions to supply adequate N for multiple years of cereal crop production. Given the fluctuation of growing conditions annually, the yield goal may vary from past average yield to potential yield (Dahnke et al., 1988). Several studies improved the use of yield goal in N decision management by taking into account the soil NO3 level (Johnson et al., 1997). Recommendation guidelines are to apply 33 kg N ha for every 1 Mg of wheat (Triticum aestivum L., Johnson et al., 1997) and 20 kg N ha for every 1Mg of corn (Schmitt et al., 1998), subtracting the soil NO3 level. Further research showed that the percentage increase in grain yield goal above the 5-yr average should be based on either the available soil moisture at planting (Rehm and Schmitt, 1989) or the sum of this soil moisture plus the anticipated growing season precipitation (Black and Bauer, 1988) determined at planting. The environment, however, is not controlled by a single growth factor but rather compounded effects of soil fertility, climate, and inputs. Additional research has focused on determining inseason N need by adjusting either yield goal or N availability. Other research has used PSNT (presidedress soil NO3 tests) as an indication of available mineralized N and setting N application limits based on NO3 levels in the soil (Magdoff et al., 1984; Durieux et al., 1995; Spellman et al., 1996). While the PSNT method increased NUE, consistent results were not obtained since sidedress N applications were not adjusted for fluctuating environmental conditions affecting yield goals. In-season N management was developed using chlorophyll meters (SPAD meters) to determine N need based on an N sufficiency index [(as-needed treatment/wellfertilized treatment)100], where N application was recommended when the index value dropped under 95% (Blackmer and Schepers, 1995; Varvel et al., 1997). Indirect in-season chlorophyll content measurement has been successful in determining N need due to the high correlation between chlorophyll content and leaf N concentration (Wolfe et al., 1988; Schepers et al., 1992). A drawback of chlorophyll meter sampling for determining N need is that plant-to-plant variation can range up to 15% (Peterson et al., 1993), requiring many measurements to obtain a representative average. Such N recommendations are similar in principle to the PSNT Department of Plant and Soil Sciences, Oklahoma State Univ., 368 Agricultural Hall, Stillwater, OK, 74078. Contribution from the Oklahoma Agricultural Experiment Station. Received 4 Apr. 2006. *Corresponding author ([email protected]). Published in Agron. J. 98:1488–1494 (2006). Nitrogen Management doi:10.2134/agronj2006.0103 a American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: DFP, days from planting; GDD, growing degree days; INSEY, in-season estimated yield; NDVI, normalized difference vegetation index; NUE, nitrogen use efficiency. R e p ro d u c e d fr o m A g ro n o m y J o u rn a l. P u b lis h e d b y A m e ri c a n S o c ie ty o f A g ro n o m y . A ll c o p y ri g h ts re s e rv e d . 1488 Published online October 3, 2006