Publications Published in Nutrient Cycling in Agroecosystems

1. Comparing a process-based agro-ecosystem model to the IPCC methodology for developing a national inventory of N2O emissions from arable lands in China. Li, C. S.; Zhuang, Y. H.; Cao, M. Q.; Crill, P.; Dai, Z. H.; Frolking, S.; Moore, B., III; Salas, W.; Song, W. Z.; Wang, X. K..
   Nutrient Cycling in Agroecosystems: 2001
   Notes
   Nations are now obligated to assess their greenhouse gas emissions under the protocols of Article 4 of the United Nations Framework Convention on Climate Change. The IPCC has developed `spreadsheet-format' methodologies for countries to estimate national greenhouse gas emissions by economic sector. Each activity has a magnitude and emission rate and their product is summed over all included activities to generate a national total (IPCC, 1997). For N2O emissions from cropland soils, field studies have shown that there are important factors that influence N2O emissions at specific field sites that are not considered in the IPCC methodology. We used DNDC, a process-oriented agroecosystem model, to develop an unofficial national inventory of direct N2O emissions from cropland in China.
   
   
   
2. Effect of rice cultivars and fertilizer management on methane emission in a rice paddy in Beijing. Kesheng, Shao; Li, Zhen.
   Nutrient Cycling in Agroecosystems: 1997
   Notes
   Experiments were conducted during April-Oct. 1994 in a Beijing rice field. Four types of rice varieties have been tested. Large cultivar differences in methane emission flux have been found. Variety 93812 emitted about fivefold more CH4 than did the Qiuguang variety. An organic amendment plus (NH4)2SO4as the base fertilizer and (NH4)2SO4as the topdressing applied in different amounts and growth stages, compared with no topdressing, reduced methane emission about 58% and increased rice yield about 31.7%. Emission peaks of CH4 in the tillering stage and reproductive stage were suppressed. A comprehensive strategy could meet both the goal for sustainable rice productivity and methane reduction. Such a strategy includes: 1. Selection of cultivars which have reduced root exudate and litter but increased root mass most of which growing in the oxidized soil layer, cultivars also need an effective number of tillers for optimum yield but with less CH4transportation ability; 2. Application of organic manure combined with chemical fertilizers, that reduce CH4 emissions. Fertilizers such as SO4 2 -or other inhibitors can be maintained for a long period in soil; 3. Adoption of scientific irrigation mode such as flooding-drainage- intermittent irrigation ,that can both increase the rice yield and decrease the CH4 emission, etc..
   
   
   
3. Modeling trace gas emissions from agricultural ecosystems. Li, C S.
   Nutrient Cycling in Agroecosystems: 2000
   Notes
   A computer simulation model was developed for predicting trace gas emissions from agricultural ecosystems. The denitrification-decomposition (DNDC) model consists of two components. The first component, consisting of the soil climate, crop growth, and decomposition submodels, predicts soil temperature, moisture, pH, Eh, and substrate concentration profiles based on ecological drivers (e.g., climate, soil, vegetation, and anthropogenic activity). The second component, consisting of the nitrification, denitrification, and fermentation submodels, predicts NH3, NO, N2O, and CH4 fluxes based on the soil environmental variables. Classical laws of physics, chemistry, or biology or empirical equations generated from laboratory observations were used in the model to parameterize each specific reaction. The entire model links trace gas emissions to basic ecological drivers. Through validation against data sets of NO, N2O, CH4, and NH3 emissions measured at four agricultural sites, the model showed its ability to capture patterns and magnitudes of trace gas emissions.
   
   
   
4. Nitrogen leaching and soil nitrate, nitrite, and ammonium levels under irrigated wheat in Northern Mexico. Riley, W.J..
   Nutrient Cycling in Agroecosystems: 2001
   Notes
   Nitrate (NO−1 3) leaching from agricultural soils can represent a substantial loss of fertilizer nitrogen (N), but a large variation in losses has been reported. We report N leaching losses under four N fertilizer treatments and two farmer's fields in the Yaqui Valley, Mexico. In these irrigated wheat systems, farmers typically apply 250 kg N ha−1 as anhydrous ammonia (knifed in) or urea(broadcast), with 75% applied directly before planting and 25% at the time of the first post-planting irrigation. Over two wheat seasons, we compared typical farmer's practices to alternatives that applied less N and more closely timed fertilizer application to plant demand. Field lysimeter measurements and predictions from a water transport simulation model (called NLOSS) were used to estimate the amount of N leached over the season. Approximately 5 and 2% of the applied N leached below the root zone with the typical farmer's practice in 1995–96 and 1997–98,respectively. The alternative treatments reduced N leaching losses by 60 to95% while producing comparable economic returns to the farmer. Leaching losses from the two farmer's fields were substantially higher (about 14and26% of the applied N). Our results indicate that the typical farmer's practice leads to relatively high N leaching losses, and that alternative practices synchronizing fertilizer application with crop demand can substantially reduce these losses.