Studies On Nutrient Uptake And Nitrogen Balance In Protected-field Tomato In Beijing Suburb

Excessive nitrogen inputs and inappropriate irrigation regimes are two major problems in protected vegetable cropping systems, including tomato production, in the suburbs of Beijing.These practices can lead to deterioration in vegetable quality and contamination of groundwater. The objectives of the present study were: 1) to develop N target value for efficient N management of protected tomato, 2) to compare the effects of furrow irrigation and drip irrigation on tomato growth and N utilization, and 3) to compare nutrient uptake and distribution in tomato grown in spring and autumn seasons.Based on tomato yields and N utilization with different N input levels, the nitrogen target value of 535 kg-hm-2N was estimated for the maintenance of protected tomato production in Beijing suburb. Although the recommended N fertilizer application rate calculated by the target value was significantly lower than the traditional fertilizer application rate, there was no significant difference in marketable yield between the two N treatments, indicating that the recommendation method based on the N target value can give substantial savings in N inputs while maintaining crop yields.Irrigation technique is an important factor affecting nutrient movement in soil and nutrient use efficiency in vegetable production. The experiment was conducted to compare the effects of furrow irrigation and drip irrigation on tomato growth and N utilization. The drip irrigation system saved substantial amounts of water in comparision with furrow irrigation and produced the same high yields. Comparison of NO3-N distribution in the soil profile under the two irrigation systems showed that the NO3-N concentrations in the 0-30 cm soil layer of all N treatments were generally higher than 50 mg-kg-1 with both irrigation systems. Although the N fertilizers were applied as several split dressings using drip irrigation, the NO3-N concentration in the 30-60 cm soil layer was not found to be reduced. There was no significant difference between furrow irrigation and drip irrigation in soil Nmin residues at harvest.In practice, tomatoes are grown in both spring and autumn seasons in Beijing region. N, P and K uptake were investigated during the growing seasons to obtain information about nutrient uptake by tomato plants. Most of the N, P and K were taken up by spring-grown tomato plants in the middle and later stages of the growing season. In contrast, most of the N, P and K were taken up by autumn-grown plant during the early and middle stages of growth. Accordingly, different N distribution was generated from the variance in nitrogen uptake. It was found that N fertilizer for spring-grown tomatoes should be applied in four split dressings, with 5% of the total applied at the transplanting stage, 25% at flowering, 50% at fruit development, and 20% before harvest. Four applications times are also recommended forautumn-grown tomatoes, but with 15% of the total recommendation at transplanting, 45% at flowering, 25% at fruit development, and 15% before harvest.