Nitrogen Uptake and Use Efficiency in Sweet Basil Production under Low Tunnels

Low tunnels (LTs) enhance vegetative growth and production in comparison with open field, but it is not known whether nitrogen (N) requirements and use efficiency increase or decrease for optimal crop performance. Therefore, the purpose of this study was to determine differences in N requirement, uptake, and use efficiency in basil grown under LTs compared with open field. The experimental design each year was a split plot with four replications. The main effect (plots) was N fertilizer application rate (0, 37, 74, 111, 148, and 185 kg.ha(-1)) and the secondary effect (subplots) was production system (LTs covered with spun-bonded rowcover vs. open field). Plant height and stem diameter were greater under LT than open field; however, they were unaffected by N fertilizer rate. Total fresh and dry weight increased with LT by 61% and 58% and by 50% and 48% in 2017 and 2018, respectively. Optimum N rates for fresh weight (98% of peak yield) were 124 and 104 kg.ha(-1) N under LT and open field, respectively. Leaf N concentration decreased under LT, but total plant N uptake increased because of increased dry weight. Without fertilization, soil available N use efficiency (SNUE) for dry weight increased by 45% and 66% in 2017 and 2018, respectively. Mixed results were obtained for N fertilizer use efficiency (NFUE) in response to N rate. In conclusion, LT increased summer production of sweet basil, total plant N uptake, and SNUE.