Modeling the regional grazing impact on vegetation carbon sequestration ability in Temperate Eurasian Steppe

Anthropogenic activities profoundly influence carbon sequestration in the Eurasian Steppe. In particular, grazing has been identified as having a major effect on carbon sequestration. However, the extent to which grazing affects regional patterns or carbon sequestration is unknown. In this study, we evaluated the impact of regional grazing on grassland carbon seques- tration using the Boreal Ecosystem Productivity Simulator （BEPS） and the Shiyomi grazing model. Model performances were validated against the results from field measurements and eddy covariance （EC） sites. Model outputs showed that in 2008, the regional net primary productivity （NPP） was 79.5 g C m-2, and the net ecosystem productivity （NEP） was -6.5 g C m-2, characterizing the region as a Weak carbon source. The Mongol Steppe （MS） was identified as a carbon sink, whereas the Kazakh Steppe （KS） was either carbon neutral or a weak carbon source. The spatial patterns of grazing density are divergent between the MS and the KS. in the MS, livestock was mainly distributed in China with relatively good management, while in the KS livestock was mainly concentrated in the southern countries （especially Uzbekistan and Turkmenistan） with harsh environments and poor management. The consumption percentages of NPP in Turkmenistan, Tajikistan and Uzbekistan were 5.3, 3.3 and 1.2%, respectively, whereas the percentages in other countries were lower than 1%. Correspondingly, grazing consumption contributed to the carbon sources of Turkmenistan, Tajikistan and Uzbekistan by 11.6, 6.3 and 4.3%, respectively, while it weakened the carbon sink in Inner Mongolia, China and Mongolia by 1.6 and 0.5%. This regional pattern should be affected by different sub-regional characteristics, e.g., the continuous degradation of grassland in the southern part of the KS and the restoration of grassland in Inner Mongolia, China.

An index method to evaluate growers' pesticide use for identifying on-farm innovations and effective alternative pest management strategies:a case study of winegrape in Madera County,California

Winegrape is an important perennial crop in California,USA.Each year California winegrape farming consumes about 20 million kilograms of pesticides that have been a pollutant source to the fresh water systems of the state.The variation of pesticide use among winegrape growers has been significant.It has been observed that some growers have developed effective ways to reduce pesticide use,yet control pests efficiently to ensure harvest.Iden-tification of the growers with low and high pesticide use is very helpful to extension programs that aim on reducing pesticide environmental risk.In this study,an index approach is proposed to quantitatively measure pesticide use intensity at grower level.An integrated pesticide use index is developed by taking pesticide quantity and toxicity into account.An additive formula and a multiplying formula were used to calculate the pesticide use index,i.e.,PUI and PUIM.It was found that both PUI and PUIM were capable of identifying the low and high pesticide users while PUI was slightly more conservative than PUIM.All pesticides used in California winegrape farming were taken into account for calculating the indices.Madera County,one of the largest winegrape producers in California,was taken as an example to test the proposed approach.In year 2000,among the total 208 winegrape growers,28 with PUI≤10 and 34 with 10<PUI≤20 were identified as low pesticide users who were characterized with both low quantity and low toxicity of pesticide use.Most of the growers had small-sized vineyards,i.e.,one field and small planted areas.Furthermore,they had very low pesticide use intensity,used only 1-2 types of pesticides(mainly fungicides) ,applied few pesticides(1-3 only) ,and emphasized the use of low toxicity compounds.Meanwhile,19 growers with PUI>60,identified as high pesticide users,had large-sized vineyards,i.e.,more fields and large planted areas.They used all types of pesticides and many compounds,which indicated that their pest controls heavily depended on pesticides rather than on-farm management.Through the case study,the proposed approach proved to be useful for analyzing the growers'pesticide use intensities and interpreting their pesticide use behaviors,which led to a new start point for further investigation of searching ways to reduce pesticide environmental risk.