Changes in Soil Carbon Pools Induced by Substitution of Plantation for Native Forest

Changes in soil carbon pools under Chinese fir (Cunninghamia lanceolata) andbamboo (Phyllostachys pubescens) plantations substituted for a native forest (Quercus acutissima,Cyclobalanopsis glauca, Cas-tanopsis sclerophylla, Platycarya strobilacea, Lithocarpus glaber) werestudied on the hills with acid parent rock and soils classified as red soils (Ferrisols) in Huzhou,Zhejiang Province of east China. It was found that total soil organic carbon (TSOC), easilyoxidisable carbon (EOC) and water-soluble organic carbon (WSOC) under bamboo plantation wereincreased, but microbial biomass carbon (MBC) was decreased. On the contrary, Chinese fir induceddeclines of all fractions of C including TSOC, EOC, WSOC and MBC. The percentages of the activefractions of soil C (EOC and WSOC) were increased in the plantations as compared to the nativebroad-leaved forest, but proportions of soil organic C as MBC were decreased. It could be concludedthat bamboo plantation had a great ability of not only fixing C but also accelerating soil C poolcycle, improving nutrient and microorganism activity; therefore, it is a good ecosystem and could berecommended for wide development. Chinese fir would shrink the soil C pool and deteriorate soilbiological fertility, so it did not benefit CO2 fixing and land sustainable utilization.

Influence of Potassium Fertilization on Yield and Quality of Foliar Vegetable Crops

Over a period of two years , field experiments were conducted on four silty loam soils grown with foliar vegetable crops including Chinese cabbage (Brassica pekinensis Rupr., cv. Lu-Bai 3), autumn greens (B. chinensis L., cv. Piao-Geng-Bai), winter greens (B. var. rosularis Tsen et Lee, cv. You-Dong-Er), and summer greens (B. chinensis L., cv. Zao-Shu 5), respectively. Each experiment included one CK treatment without K, N and P fertilizers applied, and four treatments with from low to high doses, 0-300 kg hm-2 for Chinese cabbage, 0-150 kg hm-2 for autumn and winter greens and 0-180 kg hm-2 for summer greens, of K fertilizers in the form of sulfate of potash (SOP) applied together with N and P fertilizers. One treatment of K fertilizer in the form of muriate of potash (MOP) applied at high levels (150 or 180 kg hm-2) together with N and P fertilizers was included in the experiments of autumn, winter and summer greens , respectively, in order to compare the effects of SOP and MOP. The market yields of the tested crops increased significantly with the increasing rate of K application. The crops supplied with K fertilizers yielded more stably as the CV% of their yields decreased with the rate of K application. K fertilization increased not only K contents but also the amounts of N, P and K absorbed in shoots of autumn, winter and summer greens, which were statistically significantly correlated to their yields. It can also be found that potassium improved the quality of the foliar vegetable crops as their dry mater contents were generally increased and Vc contents obviously increased and nitrate contents markedly decreased. As compared to MOP, SOP was more effective on the yields and quality of autumn, winter and summer greens at the high levels of fertilization.

Differences of cadmium absorption and accumulation in selected vegetable crops

A pot experiment and a sandy culture experiment grown with three vegetable crops of Chinese cabbage ( B. chinensis L., cv. Zao\|Shu 5), winter greens ( B.var.rosularis Tsen et Lee, cv. Shang\|Hai\|Qing) and celery ( A.graveolens L. var. dulce DC., cv. Qing\|Qin) were conducted, respectively. The initial soil and four incubated soils with different extractable Cd (0.15, 0.89, 1.38, 1.84 and 2.30 mg Cd/kg soil) were used for the pot experiment. Five treatments were designed (0, 0.0625, 0.125, 0.250 and 0.500 mg Cd/L) in nutrient solution in the sandy culture experiment. Each treatment in pot and sandy culture experiments was trireplicated. The objectives of the study were to examine Cd accumulation in edible parts of selected vegetable crops, its correlation with Cd concentrations in vegetable garden soil or in nutrient solution, and evaluate the criteria of Cd pollution in vegetable garden soil and in nutrient solution based on the hygienic limit of Cd in vegetables. Cadmium concentrations in edible parts of the three selected vegetable crops were as follows: 0.01—0.15 mg/kg fresh weight for Chinese cabbage, 0.02—0.17 mg/kg fresh weight for winter greens, and 0.02—0.24 mg/kg fresh weight for celery in the pot experiment, and 0.1—0.4 mg/kg fresh weight for Chinese cabbage, 0.1—1.4 mg/kg fresh weight for winter greens, and 0.05—0.5 mg/kg fresh weight for celery in the pot experiment(except no\|Cd treatment). The order of the three test vegetable crops for cadmium accumulation in the edible parts was celery>winter greens>Chinese cabbage in both the pot experiment and the sandy culture experiment. Cadmium accumulation in edible parts or roots of the vegetable crops increased with increasing of cadmium concentration in the medium(soil or nutrient solution). And cadmium concentrations in edible parts of the test vegetable crops were significantly linearly related to the Cd levels in the growth media (soil and nutrient solution). Based on the regression equations established and the limit of cadmium concentration in vegetable products, the thresholds of Cd concentration in the growth medium evaluated was as follows: 0.5 mg/kg soil of extractable Cd for soil and 0.02 mg /L for nutrient solution. The high capacity for cadmium accumulation in the edible parts of different vegetable crops together with the absence of visual symptoms implies a potential danger for humans.

Yield and Quality Responses of Selected Solanaceous Vegetable Crops to Potassium Fertilization

Over a period of two years, field experiments were conducted on two silty loam soils grown with four solanaceous vegetable crops of eggplant (var. serpentinum Bailey), tomato (var. commune Bailey), sweet pepper (var. grossum Bailey) and chilli (var. lengum Bailey), respectively. Each experiment included four treatments with from low to high doses, 0-450 kg ha-l for eggplant, tomato and sweet pepper, and 0-270 kg ha-1 for chilli, of K fertilizers in the form of sulfate of potash (SOP) applied together with N and P fertilizers. One CK treatment without K, N and P fertilizers applied and one treatment of K fertilizer in the form of muriate of potash (MOP) applied at the high level (450 kg ha-1) together with N and P fertilizers were included in the experiments of eggplant, in order to compare the effects of SOP and MOP. The fruit yields of the tested crops increased significantly with the increasing rate of K application. The crops supplied with K fertilizers yielded more stably as the CV% of their yields decreased with the rate of K application. The dry matter and vitamin C contents in fruits of tomato, sweet pepper and chilli, and the sugar content and the titratable acidity level of tomato fruits were increased, and the S/A ratio (ratio of sugar content to titratable acidity) of tomato fruits were decreased by K fertilization, indicating that K fertilization could improve the fruit quality of the solanaseous vegetable crops. However, the high rate of K fertilizer might lower the dry matter and vitamin C contents of tomato fruits and sweet pepper fruits. SOP was more effective than MOP in increasing the yield and quality of eggplant fruits at the high fertilization rate; therefore, the choice of applying SOP may be better for high levels of K fertilization.