Models To Estimate Growth And Development Of Hydroponic Lettuce

Lettuce (Lactvca sativa L.) is a typical leaf vegetable, and there were few reports about the effect of seedtime, harvest time and growth and development models on lettuce. In this study, the effects of different seedtime and harvest time on the growth, quality, yield of lettuce (cv. Lvling and Hongnong) were investigated. This study was made up of three parts: different seedtime treatments, different harvest time treatments, and research of growth modeling, including simulation on development stage model: dry matter accumulation, leaf growth speed, rate of leaf emergence and yield formation model of hydroponic lettuce.1. In this part, we combined the six different seedtime experiments with the weather data in 2007 and 2008. Models to estimate development stages was set up with different temperature response mechanism during vegetative growth and reproductive growth, the methods could accurately simulate the changes of the growth period of the lettuce's. The product of thermal effectiveness and PAR as variables, a modified Logistic function dry matter production model was developed. The relationship between leaf growth and accumulated teperature, the single leaf area and rate of leaf emergence models was estimated. We also set up a simple model to estimate yield, it could be accurately estimated by these regression equations.2.The effects of different seedtime(six seed time were March 1st, March 9th, March 17th, March 26th, April 2th, and April 10th respectively)on the growth and quality of lettuce were investigated. 30 days after planting were harvest time, The results showed that the third seedtime (March 17th) is the best. The yield is 85 % and 104.68 % higer than that of the first seedtime, and the vitamin C content is also the highest under this seedtime, but nitrate content is low, additionally, leaf number, shoot fresh and dry weight, root fresh and dry weight, and leaf area are significantly better than those in the other. Taking the quantity and quality into consideration, seeding at middle of March was the proper seedtime for lettuce production.3. The effects of harvest time on the growth and quality of lettuce were investigated. There were four harvest time, The results showed that the shoot fresh and dry weight, root fresh and dry weight, and water content increased significantly with the harvest time. The vitamin C content of lettuce increased during the first three harvest time whereas the nitrate decreased at the meantime, and then vitamin C began to decrease while the nitrate increase. Taking the quantity and quality into consideration, the third harvest time is the best time for the lettuce production. The yield and quality of lettuce can be improved under proper seedtime and harvest time.