| Vegetable is the indispensable and important foodstuff in our daily life because of its abundant vitamin, minerals, carbohydrate, protein, and so on. With the development of our society and rising of living standard, there is an increasing concern about the nutritive and safety quality of vegetables for researchers, producers and consumers. At present the imbalanced fertilization, typically the excessive application of nitrogen over phosphorus and potassium and organic manure, is becoming a serious problem for vegetable production in Chongqing suburb because of the more remarkable acidity and the inferior characteristics of the soil and the reducing of the yield and quality of vegetable. This has also caused a series of environmental problem. So it was helpful to use fertilizers properly aiming at the soil nutrient status in order to increase the yield and quality of vegetable and protect people health.Lettuce with rich nutrients is broadly cultivated around the whole years in both north and south of China. Among the three nutrient factors (N, P, K), the most amount absorbed for lettuce was K, then N and the least P. The nutrient limiting factors for lettuce growth was N and K. The proper use of them was beneficial to promote its growth, yield and quality, though little information was available on this aspect, especially the effect of nitrogen and potassium on yield and quality of different lettuce varieties and its mechanism. There is more fog and less light in the winter and spring in Chongqing region and the imbalanced light seriously affected the growth and quality of vegetable for the four seasons. It is vital for light to yield and quality of vegetable. Hoverer, there was little research about the effect of light on the quality of lettuce, especially a systemic information about the interaction of light and nutrient on the growth, yield and quality of vegetable.Five varieties of lettuce and a series of research methods including fieldexperiment, pot experiments, incubated experiment in manpower climate house and chemical analysis were adopted in this paper to study the effect of nitrogen, phosphors and potassium combination on the quality of lettuce grown in three acid garden soils, the response of five varieties of lettuce to nitrogen and potassium, and the interaction of nitrogen, potassium and light on lettuce quality and its mechanism. The objectives of this work were to probe the response of lettuces to nitrogen and potassium, to proclaim the interaction of nitrogen, potassium and light on the quality of lettuce and its mechanism and to seek suitable nutrient management measures for lettuce production with high yield and fine quality in acid garden soils. The main results were as follows:1 Effect of nitrogen, phosphors and potassium combination on quality of lettuce(1) There was a significant difference of yield among five treatments, which was in the order of N3P2Kl >N3P1K2 >N2P2K2>N2P3K1 >N2P1K3. When nitrogen was at the middle level (N2), there was a reducing of yield both for higher level of phosphor (P3) and potassium (K3).(2) The highest concentration of nitrate in lettuce leaf was found in treatment N2P3K1, and the lowest was in N3P1K2 and N3P2K.1. In stem the nitrate concentration was in the order of N2PiK3>N3PiK2>N2P2K2>N2P3Kl>N3P2Kl. Among the three nutrient factors, it was the potassium (K) and the phosphors (P) that could decrease the nitrate concentration in lettuce leaf and decrease the nitrate accumulation in lettuce stem, respectively.(3) It was higher concentration of Vc in leaf of lettuce than stem, but the concentration of reductive sugar and amino acid was higher for the latter than the former. It was an obvious effect of nitrogen, phosphors and potassium combination on the nutrient quality (Vc, reductive sugar and amino acid) in leaf and stem of lettuce. There was a better effect of nutrient combination on the nutrient quality of lettuce in N3P2K1, N3P1K2 and N2P2K2, for the best was in N3P1K2 and N3P2K1 in leaf and stem, respectively.(4) Among five treatments of the combination, the higher yield and better quality for lettuce were obtained in N3P2K1, N3P1K2 and N2P2K2, which needed to be demonstrated in field experiment.2 Effects of nitrogen, phosphors and potassium on quality of lettuce in three acid garden soils(1) There was a significant difference of yield for lettuce in three acid garden soils.The highest yield in strong acid soil, acid soil and slight acid soil was acquired in Hnp, Bnpk and Hnk, respectively. The yield of lettuce for the same treatment was in the order of slight acid soil > acid soil > strong acid soil, and the ratio of yields in three acid soilsWas in the Order of Y sijght acid soil /Y strong acid soil > Y acid soil /Y strong acid soil > Y slight acid soil /Yacid soil- So it was of importance of soil pH to affect the fertilizer utilization and the lettuce yield. It is significant to adjust pH value by properly using fertilizer and to improve the fertilizer efficiency and to get higher yield and better quality of vegetable.(2) In acid and slight acid soil, the highest nitrate concentration in lettuce leaf and stem was procured in Hnk and the lowest in BnpK- In strong acid soil, the highest nitrate concentration in lettuce leaf was in Hnk and the lowest was in Bnpk, although it was contrast in stem. The highest nitrate concentration in leaf and stem were in acid soil and it was in the order of acid soil>slight acid soil>strong acid soil. The nitrate concentration was higher in lettuce stem than leaf in acid soil, though in the contrast way in slight acid soil.(3) The combination of fertilizer had a more obvious effect on the concentrations of Vc and amino acid than the reductive sugar in three acid garden soils. There was better effect of Hnk and Hnp on nutrient quality of lettuce in leaf and stem respectively in strong acid soil. It was the better effects of Hnp and Hnk on nutrient quality of lettuce (leaf and stem) in acid soil and slight soil, respectively. It was the highest concentration of Vc and amino acid in slight acid soil and the lowest concentration of reductive sugar among three acid garden soils.(4) The optimum treatment was Hnp, Bnpk and Hnk for lettuce with high yield and fine quality in strong acid soil, acid soil and slight acid soil, respectively.3 The response of five varieties of lettuce to nitrogen and potassium(1) There were significant differences between the five varieties of lettuce in height, type, amount, area and chlorophyll of leaf, the concentration of macro-and micro- nutrient elements and the characteristics of nutrition. The maximum height was observed in Dabaijia, the most amount of leaf was in Guasihong, the largest area of leaf was in Runnong, the higher concentration of chlorophyll was in Guasihong and Dabaijia, and the higher concentration of nutrient elements was also in Guasihong.(2) The yields of lettuce were in the order of Guasihong > Tip > Runnong > Doubletip>Dabaijia, which had significant difference between treatments. The yields of five lettuces were remarkably increased by adding nitrogen and potassium fertilizers.The increase efficiency of yield by N fertilizer was the highest for Dabaijia at the middle level of nitrogen, but Doubletip has the highest at the higher nitrogen level. The increase efficiency of yield by K fertilizer was the highest for Dabaijia, and then followed by Doubletip. The yields of five varieties were decreased by adding nitrogen fertilizer in N15K15 treatment and by potassium in N2oKiO treatment.(3) The nitrate concentration in lettuce leaf was in the order of Tip >Runnong> Doubletip > Dabaijia >Guasihong. Application of nitrogen fertilizer increased the nitrate concentration in lettuces and the higher nitrate concentration was acquired in Dabaijia and Guasihong in N20K|0 treatment. The nitrate concentration in lettuces in Ni5K 10 treatment was obviously lower than N|5K5 treatment. The application of high-level nitrogen was the principal cause for the nitrate accumulation in lettuces. It was the effect of potassium fertilizer on nitrate concentration that related to potassium fertilizer rate and the heredity characteristic of vegetable varieties.(4) Runnong, Guasihong and Dabaijia had some higher concentration of Vc. The highest concentration of reductive sugar was got in Tip, then followed by Guasihong, and the lowest was in Runnnong. The highest concentration of amino acid was in Runnnong, and the lowest in Guasihong. The corresponding treatment with the highest Vc concentration was Ni5K10, N20K|0, N2oKiO, Ni5K|5 and Ni0Ki0; for reductive sugar it was N15K5, N10K10, N)5Kio, N2oK|o and N20K|0; and for amino acid it was N|5Ki0, N20Ki0, N15K15, N20K10 and Ni0KIO, in Doubletip, Runnong, Guasihong, Dabaijia and Tip, respectively. These analyses showed that it was different response of lettuce varieties to nitrogen and potassium, which needed be paid more attention to the vegetable with high yield and fine quality.(5) Guasihong had the higher yield and better quality among five varieties. The best treatment was N,5Ki0 for Doubletip, Guasihong, Dabaijia and Tip, and it were N|5Ki5and N20Ki0for the higher yield and better quality in Runnong.4 Coupling effects of nitrogen, potassium and light on quality of lettuce and its mechanism(1) The photosynthetic rate (Pn) of lettuce was increased by adding nitrogen fertilizer and it was also increased with the intensity of light. The higher Pn was observed in Dabajia and Guasihong, and the lowest was in Doubletip. The higher photosynthetic characteristic of Guasihong was obtained in N15K15, N20Ki0 and N20K|0 treatments under lower, middle and higher intensity of light, respectively. The higherpositive photosynthetic characteristic was in N20K|0, Ni5K,5 and N,5K15 under three light intensities for Dabaijia. The contents of Pn, Gs, Ci and Tr for Dabaijia were increased by N20K10+C treatment under lower and higher intensity of light, but there were little effect on the four factors under middle light intensity.(2) The activities of CAT, POD, NR and GS in three lettuces was remarkably affected by nitrogen and potassium fertilizer under three intensity of light, but the effect was related to the light intensity, lettuce varieties and fertilizer rate. There was a coupling effect between the light intensity and nutrients (nitrogen and potassium). With application of potassium fertilizer, the CAT activity of Dabaijia and Doubletip were enhanced under middle and higher intensity of light, and the CAT activity of Guasihong was reduced under lower intensity of light. The activities of POD were obviously increased by nitrogen fertilizer under middle intensity of light and the N20K10+C treatment under higher intensity of light. The activities of NR and GS of were also increased by nitrogen and potassium fertilizer and it was boosted for the two enzymes with enhance of light intensity, too.(3) The yield of lettuce was in the order of Guasihong >Dabaijia>Doubletip. Under higher intensity of light, the highest and lowest yield increase efficiency of N and K was acquired in Doubletip and Dabaijia, respectively. It was in Dabaijia for the highest efficiency under middle intensity of light, and in Guasihong for the lowest under lower intensity of light. The yield increase efficiency of N was higher than K under lower intensity of light, but the latter was higher than the former in Dabaijia and Guasihong, and the former was higher than the latter in Doubletip under middle and higher intensity of light. The yields were obviously reduced in the N20Ki0+C treatment comparing with N20K|0 (except for Doubletip under lower intensity of light and Guasihong under higher intensity of light).(4) The concentration of nitrate in lettuces was in the order of light intensity lower > middle > higher. At the level of N15K10, the nitrate concentrations in lettuces were increased by nitrogen fertilizer and decreased by potassium under three light intensity. Compared with the N2oKiO,the nitrate concentration of lettuces was reduced in N20K|0+C treatment (except Guasihong under lower and higher light intensity).(5) The effect of nitrogen and potassium fertilizer on Vc, reductive sugar, amino acid and soluble protein varied with the varieties and light intensity. The highest concentration of Vc was obtained under higher intensity of light and the higher Vc was in N20K10 and N2oK|0+C treatments under three light intensity. The concentration ofreductive sugar was decreased in Ni5K15 under higher intensity of light. It was in N15K15 and N20K10 treatments for the higher concentration of soluble protein and amino acid, respectively.(6) The main form of nitrogen in lettuce leaf was protein-N (PN). It was the lower ratio of protein-N to total nitrogen (TN) under middle light intensity, and the higher under lower and higher intensity of light. It was the higher concentration of TN in Doubletip. The concentration of TN and PN in three lettuces was increased with the application of nitrogen and potassium fertilizers, but it was different for the effect on non-protein N (NPN). There was little effect on the concentrations of TN and PN in lettuces in N2oKiO+C treatment under three lights (except for the concentration of PN in Guasihong under lower light intensity), but the concentrations of NPN were increased under higher light intensity, although it was different effect on NPN concentration under lower and middle intensity of light.(7) It was different combination of nitrogen and potassium for the higher yield and better quality of lettuces under three intensity of light. The optimum treatment was N15K15 under three lights for Dabajia, and N15K15 under lower and higher light intensity and N20K10 under middle light intensity for Doubletip. It was N20Ki0+C under lower intensity of light, but N20K10 under middle and higher intensity of light for Guasihong.(8)There was obvious co-relationship between photosynthetic characteristic, enzymes activity and quality of lettuce, and between nitrogen metabolism and photosynthetic characteristic, enzymes activity and quality of lettuce. The interaction of nitrogen, potassium and light affected the photosynthetic characteristic, enzymes activity and nitrogen metabolism, and then leading to the formation of yield and quality of lettuces.5 Effect of nitrogen and potassium on quality of lettuce(1) The photosynthetic characteristic of Doubletip was more affected by different treatments. The better effect on photosynthetic characteristic was in SRF (L) and SRF (H) treatments for Dabaijia and Doubletip, respectively. It was in N20K.,0 with the better effect on photosynthetic characteristic for two varieties.(2) The yields of leaf and stem in Dabaijia were increased in all treatments (except for stem in N20Ki0). The N|5Ki5, N20Ki0+C and SRF (H) treatments remarkably increased the yield of Doubletip. It was reduced in N2oKiOand SRF (L). The yield was higher for Dabaijia than Doubletip. There were higher yield of two lettuces in N15K15 and SRF (H). |
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