亚热带湿润地区城市公园重建强度对其土壤酸化和土壤中重金属的影响

Soil quality is a major concern in the management of urban parks. In this study, the soils at 0–3, 3–13, and 13–23 cm depths were sampled from six urban parks, differing in reconstruction intensity(mainly changes made during conversion of natural forests into parklands), in the Pearl River Delta, China to determine how reconstruction intensity influenced the extent of acidification and heavy metal levels in the soils of urban parks in a humid subtropical environment. High reconstruction intensity(HRI) was practiced in three parks and low reconstruction intensity(LRI) in three other parks. The LRI soils were strongly to extremely acidic(with low exchangeable Ca, Mg, and K concentrations) while the HRI soils were much less acidic. Both total and extractable concentrations of soil heavy metals were related to the specific management practices and age of the park, but did not differ significantly between LRI and HRI parks or among soil depths. Soil p H was significantly related to soil exchangeable cation concentrations and base saturation but was weakly related or unrelated to soil heavy metal levels. Our results suggest that high intensity but not low intensity reconstruction significantly reduces the extent of soil acidification in the urban parks in a humid subtropical environment.     

Effects of leguminous plant residues and NPK fertilizer application on the performance of yam (Dioscorea rotundata ‘c.v.’ ewuru) in south-western Nigeria

The effects of cultivating and incorporating residues of previous tropical kudzu (Pueraria phaseoloides) and soybean (Glycine max) with application of NPK fertilizer on yam performance were evaluated at the teaching and research farm, LAUTECH, Nigeria. There were nine treatments: incorporation of legume residues (5 t DM ha^?1), application of recommended fertilizer rate for yam (90–50–75 kg NPK ha^?1) in the zone or 50% of recommended rate (45–25–37.5 kg NPK ha^?1), alone and in combination with residues and a control without residues or fertilizer in a randomized complete block design. Cultivation of previous legumes reduced soil nematode population (>200%) compared with no legumes. For both years, application of Pueraria residues improved tuber yield by an average of 15.8% compared with control. Fertilizer application enhanced arbuscular mycorrhizal (AM) colonization of yam roots but AM colonization was lower (～50%) in plots where Pueraria residues were incorporated compared with other plots. Combined application of plant residues with fertilizer improved soil organic carbon, total N, exchangeable Ca and Mg compared with application of NPK fertilizer. From these results, it is concluded that half of the recommended NPK rate may be adequate and incorporation of residues with reduced NPK fertilizer application may be a sustainable soil fertility management option for continuous yam production.     

Zinc sorption–desorption by sand,silt and clay fractions in calcareous soils of Iran

Zinc sorption–desorption by sand, silt and clay fractions of six representative calcareous soils of Iran were measured. Sand, silt and clay particles were fractionated after dispersion of soils with an ultrasonic probe. Zinc sorption analysis was performed by adding eight rates of Zn from 6 to 120 μmol g^?1. For the desorption experiment, samples retained after the measurement of Zn sorption were resuspended sequentially in 0.01 M NaNO₃ solution and shaken for 24 h. Results indicated that Zn sorption by soil fractions increased in the order clay > silt > sand, and correlated negatively with CaCO₃ content and positively with cation exchange capacity (CEC) and smectite content. Results indicated that for all fractions, the Langmuir equation described the sorption rates fairly well. In contrast to sorption, Zn desorption from soil fractions increased in the order sand > silt > clay, and correlated positively with CaCO₃ content, CEC and smectite content. Results showed that parabolic diffusion and two constant equations adequately described the reaction rates of Zn desorption. In general, for all soils studied, the coarser the particle size, the less Zn sorption and more Zn desorption, and this reflects much higher risk of Zn leaching into groundwater or plant uptake in contaminated soils.