Uptake capacity of several vegetable crops to nitrate and ammonium

Solution culture experiment was conducted in order to investigate the relative uptake capacity or preference to nitrate and ammonium of lettuce, spinach, cabbage and garden sass, as well as the influence of 3 different nitrogen sources on growth and development of these 4 crops. The obtained results showed:(1) When the distilled water was supplied as the growth medium in the nutrient solution, different nitrogen sources affected greatly on the growth and development of lettuce, spinach, cabbage and garden sass. When nitrate was the sole N source, all these vegetable crops growed very well; when the same amount of nitrate and ammonium was supplied in the nutrient solution, the growth amount of 4 crops decreased to some extent; While ammonium was the sole N source, the growth amounts of 4 vegetable crops decreased greatly, when NO3--,NO3--+NH4+(1∶1), NH4+ were the N source for 4 crops, respectively. The ratios among dry matter weight of 4 crops were: lettuce was 1∶0 57∶0 12,spinach was 1∶0 91∶0 37,cabbage was 1∶1 07∶0 36, and garden sass was 1∶1 05∶0 21,respectively.But the mechanism why ammonium inhibited crop growth is worth studying further.(2) During the solution culture, the total nitrogen uptake amount of the tested crops had close relation to the nitrogen source. To lettuce, the nitrogen uptake amount as nitrate supplied was significantly higher than that when the same amount of nitrate and ammonium was supplied, if comparing the same amount of nitrate and ammonium treatment with solely supplying nitrate nitrogen treatment, and the nitrogen uptake amounts of garden sass and spinach were almost same; While supplying the same amount of NO3- and NH4+,the nitrogen uptake amount of cabbage was the largest, when solely supplying nitrate it greatly decreased, and ammonium was supplied,the nitrogen uptake amount was the lowerest. To all of 4 crops, when ammonium was the sole N source, the N uptake amount was the lowerest. (3) The tested crops had apparent preference to uptake of nitrate or ammonium. When the same amount of ammonium and nitrate was supplied, the uptaked nitrate by spinach and cabbage was larger than ammonium, but the lettuce was vice verse(N, 8.911.56, 12.311.24 mg /plant, respectively),and the absorped nitrogen of two forms by garden sass were almost the same. The preference had characteristics of stage, generally speaking, the crop which prefer nitrate to ammonium maybe show property of favours ammonium at certain stage.