Predicting sugarcane response to nitrogen using a canopy reflectance-based response index value.

摘要

In Louisiana, sugarcane (Saccharum officinarum L.) N rate recommendations are established based on N response trials and further refined for specific crop age and soil type. Without accounting for current growing conditions and soil N levels, these recommendations can potentially lead to under- or over-application of N fertilizers. The objective of this study was to determine if N response index at harvest (RI_Harvest) can be predicted using normalized difference vegetative index (NDVI) response index value (RI_NDVI). Sensor and yield data were collected from different N field trials from 2008 to 2010 in St. Gabriel and Jeanerette, LA. Nitrogen fertilization treatments ranged between 0 to 201 kg N ha-1. A GreenSeeker Hand Held Optical Active Sensor (Trimble Navigation, Ltd., Sunnyvale, CA) was used to obtain NDVI readings for each of three consecutive weeks beginning 3 wk after fertilization. There was a strong relationship between RI_NDVI and RI_Harvest using the traditional method of determining RI, comparing plots that received high N rates to check plots, with coefficient of determination (r2) values of 0.92 for cane tonnage and 0.81 for sugar yield (P<0.05). When using a modified RI value, which compared all N rates to the check plot, relationships between RI_NDVI and RI_Harvest were comparable, with r2 values of 0.85 and 0.81 for cane tonnage and sugar yields, respectively (P<0.05). Our results suggest that NDVI collected 4 wk after N fertilization can be used to predict sugarcane yield response to fertilizer N using the relationships established by either the traditional or modified RI methods.