Abstract
Recent increases in irrigated hectares in the Southeastern US have enabled growers to obtain higher yields through applying nutrients through irrigation water. Therefore, many growers apply nutrients through irrigation systems, known as fertigation. Currently, there are no practical decision-making tools available for variable-rate application of nitrogen (N) through overhead sprinkler irrigation systems. Therefore, field tests were conducted on cotton (Gossypium hirsutum L.) during the 2016 and 2017 growing seasons to 1) adapt the Clemson sensor-based N recommendation algorithms from a single side-dress application to multiple applications through an overhead irrigation system; and 2) to compare sensor-based VRFS with conventional nutrient management methods in terms of N use efficiency (NUE) and crop responses on three soil types. Two seasons of testing Clemson N prediction algorithms to apply multiple applications of N were very promising. The multiple applications of N compared to the grower’s conventional methods (even though less N was applied) had no impact on yields in either growing season. There was no difference in cotton yields between 101 and 135 kg/ha N applications in either management zone. Also, there were no differences in yield between sensor-based, multiple N applications and conventional N management techniques. In relation to comparisons of the sensor methods only applying N in three or four applications, statistically increased yields compared to single or split applications in 2016. Applying N in four applications, statistically increased yields compared to single, split or triple applications in 2017. When the sensor-based methods were compared to the grower’s conventional methods averaged over four treatments, the sensor-based N applications reduced fertilizer requirement by 69% in 2016 and 57% in 2017 compared to grower’s conventional methods. When comparing N rates among the four sensor-based methods (three or four) applications, increased N rates by 22 kg/ha in 2016 and 26 kg/ha in 2017 compared to single or split applications but increased the cotton lint yields by 272 and 139 kg/ha, for 2016 and 2017, respectively.
Highlights
Irrigation can significantly increase crop yields and provide monetary savings compared to dryland production [1] [2]
There was no difference in cotton yields between 101 and 135 kg/ha N applications in either management zone
There were no differences in yield between sensor-based, multiple N applications and conventional N management techniques
Summary
Irrigation can significantly increase crop yields and provide monetary savings compared to dryland production [1] [2]. Irrigated hectares have doubled from to 2011, and the adoption of irrigation has accelerated considerably since. 2002, increasing at a rate of over 4000 hectares per year [3]. With the increases in irrigation across the Southeastern US, many growers apply nutrients through irrigation systems, known as fertigation, which has become a common practice for cotton growers in this region. Results of field research demonstrated the uptake of foliar applied 15N urea by cotton leaves and translocation to the developing bolls [4]. Once the nitrogen (N) was applied, it was rapidly absorbed by the leaf at a rate of 30% within one hour and translocated to the closest boll within 6 to 48 hrs., after application. The remaining N is moved progressively into adjoining bolls for the few days with no translocation to other leaves [4]
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