Evaluation of a Reduced Cost Active NDVI Sensor for Crop Nutrient Management

Table 7

Changes in nitrogen recommendations from varying NDVI values. Nitrogen recommendations were made from the sensor-based nitrogen rate calculator (http://www.soiltesting.okstate.edu/SBNRC/SBNRC.php) accessed March 10, 2011.

Crop	Farmer practice	𝑁; rich strip	𝑁; recommendations	+0.025 NDVI	Δ𝑁	−0.025 NDVI	Δ𝑁	+0.05 NDVI	Δ𝑁	−0.05 NDVI	Δ𝑁
Wheat*	0.8	0.83	7.6	0	−7.6	14.8	7.2	0	−7.6	21.8	14.2
Wheat*	0.625	0.83	54.2	47.9	−6.3	60.3	6.1	41.6	−12.6	66.5	12.3
Wheat*	0.45	0.83	59	54.9	−4.1	63.3	4.3	85.5	26.5	67.9	8.9
Wheat*	0.6	0.65	12.4	5.7	−6.7	18.9	6.5	0	−12.4	25.4	13
Wheat*	0.5	0.65	38.4	31.9	−6.5	45	6.6	25.4	−13	51.8	13.4
Average recommended difference					−6.24		6.14		−3.82		12.36
Maize**	0.8	0.83	25.9	19.1	−6.8	32.3	6.4	12.1	−13.8	38.5	12.6
Maize**	0.625	0.83	66.8	61.3	−5.5	72.1	5.3	55.8	−11	77.5	10.7
Maize**	0.45	0.83	70.6	74.5	3.9	66.9	−3.7	78.6	8	63.4	−7.2
Maize**	0.6	0.65	24.2	18.2	−6	30	5.8	12.1	−12.1	35.8	11.6
Maize**	0.5	0.65	47.4	41.6	−5.8	53.3	5.9	35.8	−11.6	59.3	11.9
Average recommended difference					−4.04		3.94		−8.1		7.92

Δ𝑁: difference in nitrogen recommendation based on change in NDVI value.
* 𝑁 recommendations determined for wheat at normal planting time sensed at the 1st week of March. 𝑁 rich strip and farmer values are a range of what would normally be encountered in the field.
** 𝑁 recommendations determined for corn with a normal planting date sensed during the 2nd week of June. 𝑁 rich strip and farmer values show both representative and extreme values found in the field.