| dc.description.abstract | Nitrogen (N) management is critical for producing high yielding grain sorghum in Texas. Many producers utilize planter options for starter fertilizer application, including in furrow or 2x2 placements of N and phosphorus (P). N and P applied as starter fertilizers could affect optimum rate, timing and nitrogen use efficiency (NUE) of N fertilizer in grain sorghum. Advances in technology for remote sensing enable rapid acquisition of crop canopy spectral measurements. Analysis of spatial variability of crop canopy reflectance may enable site-specific nitrogen (N) management in grain sorghum.
Two field studies were established in Burleson County, Texas during 2016 and 2017 to impose contrasting N status in grain sorghum. The first study employed a single side-dress application of increasing N fertilizer rates (0, 112,168,224, 280 kg ha^-1) for grain sorghum using three starter fertilizer applications. For the second study, timing (20, 42, 56, 65, 81 (2016) 32, 49, 66, 75, control (2017) days after planting) of side-dress N fertilizer application (168 kg N ha^-1) was evaluated for grain sorghum under three starter fertilizer applications. Starter fertilizer treatments (sub-plots) included ammonium polyphosphate (11-37-0) applied at 0, 56 (in-furrow) or 168 (2x2) L ha^-1. Spectral measurements (visible and NIR) of the sorghum canopy were made using ground-based at multiple dates during the growing season. Handheld sensors were also used to monitor N status throughout the season. Spectral indices and the handheld sensor values were used to evaluate and relate to crop biomass, grain yield and N content.
The optimal N rate in 2016 was 168 kg ha^ -1, there was no significance across increasing rates in 2017. Starter fertilizers did not affect the increasing rates. The optimal timing of N in 2016 was <56 days after planting in 2016, in 2017 there was not a significant difference with
delayed N application. Spectral measurements (visible and NIR) of the sorghum canopy were made using ground-based at multiple dates during the growing season. Handheld sensors were also used to monitor N status throughout the season. Spectral indices and the handheld sensor values were used to evaluate and relate to crop biomass, grain yield and N content. | en |
