Shi Wei-ming

Short-Term Responses of Nitrous Oxide Emissions and Concentration Profiles to Fertilization and Irrigation in Greenhouse Vegetable Cultivation

Abstract In vegetable cultivation, the majority of N2O emissions occur after fertilization; it is therefore important to understand any factors contributing to this process. An experiment was conducted to investigate short-term N2O dynamics following topdressing in a greenhouse vegetable field in South China. During two topdressing processes, three different urea-N treatments with irrigation were conducted in May and June in a tomato (Lycopersicum esculentum) cultivation. The N2O fluxes, soil concentration profiles and soil environments at the 0–60 cm depths at 10 cm intervals were measured both immediately prior to and 5 days after topdressing. The N2O fluxes before topdressing ranged from 6.7±2.1 to 55.0±28.8 μg N m−2 h−1; even higher numbers were recorded in highly fertilized plots. The NO−3-N accumulation in the soil caused by vegetable cultivation during the 5 years prior to the start of the experiment, resulted in high background N2O fluxes. One day after topdressing (1 DAT) in May and June, N2O fluxes increased, which coincided with sharp increases in soil N2O concentrations at depths of 2.5 and 15 cm and in NO−3-N and NH+4-N contents at depths of 0–20 cm. From 1 to 5 DAT, fluctuations in the N2O fluxes did not harmonize with the N2O concentrations at a depth of 2.5 cm, which was attributed to different gas diffusion rates at depths of 0–10 cm. These results suggested that surface soil N and environmental conditions were crucial for determining the short-term N2O ebullitions during topdressing in greenhouse vegetable cultivation.

Genotypic variation of rape in phosphorus uptake from sparingly soluble phosphate and its active mechanism

Phosphorus deficiency is one of the most growth-limiting factors in soils in various parts of the world. Two rape cultivars, which differed in Phosphorus (P) uptake from Fe-P (FePO 4 ·4H 2 O) and Al-P (AlPO 4 ), were investigated to elucidate the contributions of root morphology and organic acids exudation to P uptake by rape from iron phosphate and aluminum phosphate. By solution culture and sand culture experiments, the activation capacity of insoluble Fe-P and Al-P of organic acids secreted by different rape genotypes roots was studied. The results show that two rape cultivars has significant genotypic variations in both plant dry weight and P uptake per plant when supplied with Fe-P and Al-P as the P source. When supplied with sparingly soluble phosphate (Fe-P and Al-P), the root length, surface area and number of roots tips of genotype HG (phosphorus efficient rape) were significantly higher than genotype LG (phosphorus inefficient rape). The rape grew better in Al-P treatment than Fe-P treatment. Root exudates of rape has certain ability to activate insoluble P and it had better activation capacity of insoluble Fe-P under the condition of P stress than normal supply of P. Hence, the large differences show traits for more phosphorus efficient plants between in the tested rape genotypes. The genotype HG showed increased P acquisition from the Al-P and Fe-P than the genotype LG. This opens the possibility to breed for more P uptake-efficient varieties as a way to bring more sparingly soluble soil P into cycling in crop production. Key words: Sparingly soluble phosphate, phosphorus efficiency, genotypic differences, rape.

The mechanism on rhizosphere phosphorus activation of two wheat genotypes with different phosphorus efficiency

A short-term greenhouse experiment was carried out with two phosphorus (P) levels of purple soil to investigate P availability and associated processes in the rhizosphere of two different P-efficiency wheat genotypes using a thin slicing technique. Two genotypes with different P efficiencies were grown in a root-compartment experiment under low P (P 10: 10 P mg/kg) and high P (P 100: 100 P mg/kg) treatments. Results show that readily extracted forms of soil inorganic P were depleted by the two wheat genotypes, depletion zones extended further adjacent to 4 to 6 mm. Enhanced depletion of sodium hydroxide extractable organic P apparent in the rhizosphere of high P-efficient wheat cultivar 10098 compared with low P inefficient wheat cultivar 10026 was related to the presence of greater concentrations of microbial biomass and higher soil acid phosphatase and phosphodiesterase enzyme activities. These results confirm that microorganisms and soil enzymic activities played important roles in the mineralization of soil organic P, particularly under high P-efficient wheat cultivar 10098. These results suggest that improving P efficiency based on the character of P efficiency acquisition in Pefficient genotype would be a potential approach for maintaining wheat yield potential in soils with low P bioavailability.