Studies on the target value of nitrogen supply for greenhouse tomato growth during autumn-winter season

Continuously excessive nitrogen input in greenhouse is one of the major problems in Shouguang, the famous vegetable production base in China, and this led to deteriorated product quality, high risk of nitrate leaching, secondary soil salinization, and low fertilization profit, etc. The main reason for these problems is that there is no effective N recommendation technique for greenhouse vegetable production. The objectives of the present study were to develop a nitrogen topdressing recommendation system and related target values of nitrogen supply at different growth stages for greenhouse tomato grown in autumn-winter season in Shouguang. Two field trials from 2002 to 2003 were conducted to determine the critical target value of nitrogen topdressing for greenhouse tomato at three growth stages in Shouguang, using (real-time) nitrogen control index, i.e. nitrate in petiole sap, fruit expanding rate, marketable yield and quality, and recommending techniques of nitrogen balance method for nitrogen topdressing (Nc), in comparison with farmer's conventional practice (Nt), on the basis of enough basal fertilizer application. Based on the results in 2003 autumn-winter season, with 80% of N supply level determined in the experiment of 2002, it could be concluded that the optimum mineral N supply levels (Nmin content in effective root zone + fertilizer N supply level at topdressing) were N 237, 173 and 153 (kg/hm2) at the first, the second, and the fourth cluster fruit expanding stage, respectively. Besides the N supply from soil mineral N in effective root zone and chemical fertilizer N at topdressing, soil organic N, organic manure, and irrigation water also provided some available N for crop growth in greenhouse. The apparent N mineralization amounts from soil (organic) N pool in effective root zone were N 53, 13 and 21(kg/hm2)at the first, the second, and the fourth cluster fruit (expanding) stage, respectively. Similarly N 41, 8 and -17(kg/hm2) were supplied from apparent organic manure mineralization, and irrigation water provided N 11, 5 and 5(kg/hm2) during the three topdressing stages. Considering the above-mentioned N input components, target values of N supply were N 342, 199 and 162(kg/hm2) at the first, the second, and the forth cluster fruit expanding stage for greenhouse tomato grown in autumn-winter season in Shouguang. Total N target value for the whole growth stage of tomato was N 481(kg/hm2) in order to achieve the target yield of 73(t/hm2) in the (region.) These target values of N supply are useful for N topdressing recommendation of greenhouse tomato grown in (autumn-winter) season.