Association of host plant growth and weed occurrence with armyworm(Mythimna separata) damage in corn fields

To clarify association between armyworm（Mythimna separata） damage level and the corn growth and weed occurrence, we investigated corn plant height, stem diameter and vigor as well as weed coverage and biomass. The investigations were conducted at three locations of Shaanxi Province, China which were suffered seriously from armyworm. Significant correlations were found between the parameters analyzed. At stunted corn growth and presence of plenty of weeds, the armyworm damage tended to be heavy; oppositely, when corn grew well and weed density were low, armyworm harm was the minimal. Therefore, corn growing status and weed density can significantly affect armyworm damage level. Our results imply that promoting corn growth and timely removal of weeds are conducive to reducing armyworm occurrence.

Comparison between Microwave Coherent and Incoherent Scattering Models in Corn Field

[Objective] The aim was to compare and analyze microwave coherent and incoherent scattering models in a corn field. [Method] In the research, based on a coherent scattering model （Stile）, we proposed a coherent scattering model exclusive for corn, in which, physical optics （PO） and infinite-length dielectric cylinder were used to calculate single-scattering matrices of corn leaves and stalks. In addition, coherent components produced from interaction among the scattering mechanisms were also considered and this coherent model was compared with the Michigan Mi- crowave Canopy Scattering （MIMICS） model. The measured data in a corn filed in Gongzhuling in Jilin Province were used as the input parameters of the coherent and incoherent models. We simulated backscattering coefficients of VV and HH po- larization at L and C bands and made a comparison between the simulation results. [Result] The simulation results at L-band were poor, which indicated that we could not find regularity at early growth stage of vegetation. In addition, comparisons be- tween coherent and incoherent scattering models proved that the coherence triggered by the scattering mechanism was small. [Conclusion] In the research, we analyzed differences between coherent and incoherent scattering models with change of incident angle, and further analysis on the differences with change of vegetation and soil needed to be made in future.

Emergy assessment of three home courtyard agriculture production systems in Tibet Autonomous Region, China

Home courtyard agriculture is an important model of agricultural production on the Tibetan plateau. Be- cause of the sensitive and fragile plateau environment, it needs to have optimal performance characteristics, including high sustainability, low environmental pressure, and high economic benefit. Emergy analysis is a promising tool for evaluation of the environmental-economic performance of these production systems. In this study, emergy analysis was used to evaluate three courtyard agricultural production models： Raising Geese in Corn Fields （RGICF）, Con- ventional Corn Planting （CCP）, and Pea-Wheat Rotation （PWR）. The results showed that the RGICF model produced greater economic benefits, and had higher sustainability, lower environmental pressure, and higher product safety than the CCP and PWR models. The emergy yield ratio （EYR） and emergy self-support ratio （ESR） of RGICF were 0.66 and 0.11, respectively, lower than those of the CCP production model, and 0.99 and 0.08, respectively, lower than those of the PWR production model. The impact of RGICF （1.45） on the environment was lower than that of CCP （2.26） and PWR （2.46）. The emergy sustainable indices （ESIs） of RGICF were 1.07 and 1.02 times higher than those of CCP and PWR, respectively. With regard to the emergy index of product safety （EIPS）, RGICF had a higher safety index than those of CCP and PWR. Overall, our results suggest that the RGICF model is advantageous and provides higher environmental benefits than the CCP and PWR systems.