Predicting Rice Response to Midseason N Using the Greenseeker Handheld Unit.

Traditionally most rice producers in Arkansas have applied nitrogen (N) fertilizer using a two-way split application with majority of the N fertilizer applied pre-flood and the remaining 50.4 or 33.6 kg N/ha applied at midseason or boot.  Many farmers striving to increase their N management efficiency are interested in implementing a single preflood N application.  However, many producers are reluctant to move towards a single preflood-N application due to the inability to determine if the N rate was sufficient to produce maximal yields or if their preflood-N was managed properly. While hybrid cultivars continue to benefit from 33.6 kg N/ha at boot, most of Arkansas semi-dwarf, stiff-strawed cultivars do not consistently exhibit an increased yield response to the 50.4 kg N/ha midseason-N application.  Soil testing drives fertilization decisions early in the season, yet farmers rely heavily on visual guesswork. At six of the Rice Research Verification (RRVP) fields from 2015, two N-rich strips were established in each field using the current standard N rate determined by N-STaR plus 224 kg N/ha applied a single pre-flood.  Normalized Difference Vegetative Index (NDVI), was measured at 10 random 15.24- 30.48 meter strips across the field at three weeks post-flood using the Trimble GreenSeeker Handheld and compared to the N-rich strip to determine a response index defined as the NDVI of the reference strip divided by the NDVI of the field.  An average response index less than 1.2 indicates relative grain yield would not benefit from additional midseason-N application.  Only one of the six fields evaluated called for additional midseason-N on only half of the field.  The Trimble GreenSeeker Handheld offers producers and consultants an easy to use, in-season assessment tool to aid in N management decisions and to answer the question- will I benefit from a midseason-N application?