Biostimulants decreased nitrogen leaching and NH3 volatilization but increased N2O emission from plastic-shed greenhouse vegetable soil

Abstract

Biostimulant application is an effective strategy to enhance soil fertility and plant growth. However, its comprehensive impacts on nitrogen (N) uptake and reactive N (Nr) losses via leaching, ammonia (NH3) volatilization, and nitrous oxide (N2O) emission from plastic-shed greenhouse vegetable system are still little known. Therefore, a field experiment was conducted with cauliflower-tomato growth rotation (from September 6, 2018, to July 17, 2019) receiving three biostimulants, i.e., humic acid (HA), algae extract (AE), and chitosan (CT), as well as a control without stimulant. The cumulative Nr losses over the cauliflower-tomato growth cycle via leaching, NH3 volatilization, and N2O emission were 104-175 kg N ha-1, 2.32-3.85 kg N ha-1, and 0.70-0.85 kg N ha-1, respectively. Biostimulant application significantly (P < 0.05) retarded the total N leaching by 17-44% in tomato season, while suppressed the NH3 volatilization by 18-38% in cauliflower season. Overall, AE showed the best inhibition efficiency on Nr losses by significantly (P < 0.05) decreasing total N leaching and NH3 volatilization by 36-44% and 38-52% in both vegetable seasons, compare to the control. However, all three biostimulants stimulated the N2O emission under both vegetable cycles. Interestingly, all biostimulant-added treatments promote the cauliflower and tomato yield, particularly following the HA and AE amendments, which bring local farmers approximately 4,384-10,035 yuan RMB ha-1 more income. Enhanced yield under biostimulant treatments was due to higher N uptake capacity and enhanced root morphology. In summary, biostimulants have a contrasting influence on three major Nr lost pathways in greenhouse vegetable production. We recommend that AE is the most optimal biostimulant as it increases vegetable yield and decreases total N leaching and NH3 volatilization while not dramatically increase the N2O emission.