Mechanisms of environmental factors affecting uptake and utilization of N and P by vegetable crops
IPNI-2010-CHN-ZJ25
04 Mar 2010
2009 Annual Interpretive Summary
Mechanisms of Environmental Factors Affecting Uptake and Utilization of Nitrogen and Phosphorus by Vegetables, 2009
The results from 2009 showed that contents of ammonium (NH4+-N), nitrate (NO3--N), and total inorganic N increased first and then decreased in the incubation soils amended with manure and urea. Temperature and moisture regime had a significant effect on N mineralization rate and nitrification rate of the soils. Soil inorganic N content at 30 ºC was 20% higher than at 5 ºC in non-fertilized soil, and soil inorganic N content under dry-rewetting (DW) was 28% higher than under continuously wet conditions (CWC) in urea-amended soil. The average amounts of N mineralization and nitrification in urea-amended soils were 157 and 165 mg/kg, which were 10 and 8 times those in non-fertilized soils. Meanwhile, the average amounts of soil N mineralization and nitrification in manure-amended soils were 37 and 46 mg/kg, which was 2.3 and 2.1 times those in non-fertilized soils. Soil urease activity at 30 ºC was 22% higher than that observed at 5 ºC, while the urease activity under DW was 10% higher than under CWC. A hydroponic experiment studied the effects of elevated atmospheric carbon dioxide (CO2) concentrations from 350 to 800 µL/L on root exudation of organic C and organic acids, and their activation of insoluble P in the rhizosphere of tomato grown in nutrient solutions with sufficient (2 mmol/L) and deficient (2 µmol/L) P supply. Results showed that elevated CO2 concentration decreased P concentrations, but increased the P contents in roots and shoots of tomato plants. The total C secretion from plants under elevated CO2 treatment was 0.16 mg C/h, which was 2 times that observed under 350 µL/L CO2.
Two hydroponic experiments studied the effects of N levels and forms on biomass and photosynthesis on Chinese cabbage grown with different light (full light, 30% full light) and moisture conditions. Nitrogen was supplied at five levels in Experiment 1, and Experiment 2 used four ratios of NH4+ to NO3- at a total N rate of 15 mM. Results found insignificant changes in biomass and photosynthetic rate when N level decreased from 15 to 12mM, and 9 mM in the nutrient solution, whereas NO3 accumulation was decreased by 38% and 40%. Under conditions of low light and water stress, increased pigment contents, photosynthetic rate, chlorophyll fluorescence parameters, and biomass were found when N form was supplied at a 5/10 (NH4+/NO3-) ratio. Zheijiang-25