Nitrogen topdressing and feedback control in greenhouse tomato

The trial of real-time control for nitrogen topdressing in protected-field tomato was conducted in autumn-winter season in Shouguang,Shangdong province using the technique of nitrate quick-testing under enough organic manure application at preplanting. Farmer's conventional practice in N topdressing was used as control in the trial. Nitrogen recommendation in topdressing was based on the results of nitrate quick-testing in the rooted soil layer and petiole sap before topdressing. The results showed that compared with conventional topdressing practice the amount of applied N in topdressing reduced by N 170 kg/hm2 without any negative effects on shoot height, fruit developing rate, and marketable yield. Based on soil nitrate measurement and applied N rate in topdressing it was suggested at least N recommendation in topdressing of greenhouse tomato production should meet the target values of N 296 kg/hm2, 216 kg/hm2, and 191 kg/hm2 at the first, the second, and the forth cluster fruit expanding stage, respectively. Successful results were also collected from the validating trials in the other three greenhouses using these target values at the same time. It means that no yield reduction using these real-time control for N topdressing was investigated in the validating trials with different nitrate content at preplanting stage, in comparison with conventional N topdressing practice. Although the N target values were not "critical" value, this suggested it was still very useful in N management for sustainable vegetable production.