Ammonia (NH 3 ) volatilization was measured with the continuous airflow enclosure chamber method under different urea application amounts using pots in paddy fields in Erhai Lake Watershed, China. Several factors, such as the urea nitrogen application amount, days after fertilization, NH 4 ? -N concentration and pH of surface water, and climate, that could affect ammonia volatilization were also studied. The results indicated that ammonia volatilization loss increased linearly with increasing amounts of applied urea. The ratios of the ammonia volatilization loss to the applied nitrogen ranged from 16.59 to 18.43 % with different nitrogen application amounts. The ammonia volatilization loss peaked within the first 3 days after fertilization, which accounted for 65-82 % of the total ammonia loss in each period. We observed the following degree of the effects of various factors on ammonia volatilization: NH 4 ? -N concentration of surface water [ urea application amount [ pH of surface water [ days after fertilization [ water temperature of surface water. The wind velocity and rainfall were the key factors affecting ammonia volatilization. The model of ammonia volatilization flux was established by using the measured dates from 2013 and was represented as Y = 0.008(x 1 ? x 2 ? x 3 ) ? e 0.056x4-0.068x5 -0.623 (R 2 = 0.81, P \ 0.0001). The model was verified by using the measured dates from 2012. The calculated values fitted well with the field observations. However, the model parameters need to be amended using the model to predict the ammonia volatilization flux in the rice season from other regions.
Utilization and transfer of nitrogen (N) in a strip intercropping system of garlic (Allium sativum L.) and broad bean (Vicia faba L.) have been investigated rarely. The objectives of this study were to quantify N uptake and utilization by intercropped broad bean and garlic and determine the magnitude of N transfer from broad bean to garlic. Field and pot trials were carried out in the Erhai Lake Basin in China using 15 N tracer applied to the soil or injected into broad bean plants. Strip intercropping of garlic and broad bean increased N absorption (47.2%) compared with sole crop broad bean (31.9%) or sole crop garlic (40.7%) and reduced soil residual N. Nearly 15% of 15 N injected into petioles of broad bean intercropped with garlic was recovered in garlic at harvest, suggesting that N could be transferred from broad bean to strip intercropped garlic. The findings provide a basis for evaluating legumes' role in optimizing N fertilization when intercropped with non-legumes.
We investigated the effects of land use conversion from cereal grain fields (GF) to greenhouse vegetable fields (VF) on total soil organic C (SOC) and total N (TN) and the labile soil organic matter pools dissolved organic C (DOC), permanganate‐oxidizable C (POC), dissolved organic N (DON), mineral N, and microbial biomass C (MBC) in the top 30 cm of the soil profile. The soil samples were collected in 20 sets of paired soils (greenhouse vegetable vs. wheat [Triticum aestivum L.]–maize [Zea mays L.] rotation fields) in northeast China. Compared with those in GF, the SOC and TN concentrations in VF increased by 28 and 58%, respectively. The accumulation rate of TN vs. SOC, however, led to a significant decrease in soil C/N ratio in VF compared with GF systems. The greatest difference in C/N ratios between GF and VF was observed in the large macroaggregates (>2000 μm). Conversion to VF led to increased DOC, POC, and DON concentrations and an increase in the percentage of SOC as DOC and POC. The pH, MBC, and percentage of SOC as MBC, however, were lower in the VF than GF systems. Furthermore, a significant positive relationship was found between pH and MBC in the VF systems, while MBC was positively related to total SOC and POC in the GF systems. In conclusion, the results show tradeoffs between increasing SOC sequestration when agricultural land is converted from wheat–maize to vegetable systems and decreased C/N ratios and soil acidification. Improvements in soil and crop management for vegetable production systems in China, particularly the avoidance of excess N fertilizer and manure applications, are recommended.
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