The impact of weather and increased atmospheric CO2 from 1892 to 2016 on simulated yields of UK wheat

Climate change effects on UK winter wheat grain yield are complex: warmer temperature, negative; greater carbon dioxide (CO2) concentration, positive; but other environmental variables and their timing also affect yield. In the absence of long-term experiments where temperature and CO2 concentration were manipulated separately, we applied the crop simulation model Sirius with long-term daily meteorological data (1892-2016) for Rothamsted, Hertfordshire, UK (2007-2016 mean growing season temperature 1.03°C warmer than 1892-1991), and CO2 concentration over this period, to investigate the separate effects of historic CO2 and weather on simulated grain yield in three wheat cultivars of the modern era. We show a slight decline in simulated yield over the period 1892-2016 from the effect of weather (daily temperature, rainfall and sunshine hours) at fixed CO2 (294.50 ppm, 1892 reference value), but a maximum 9.4% increase when accounting for increasing atmospheric CO2 (from 294.50 to 404.21 ppm), differing slightly among cultivars. Notwithstanding considerable inter-annual variation, the slight yield decline at 294.50 ppm CO2 over this 125-year period from the historic weather simulations for Rothamsted agrees with the expected decline from temperature increase alone, but the positive yield trend with actual CO2 values does not match the recent stagnation in UK wheat yield.

[Changes in Physical Fractions within Soil Aggregates Under Nitrogen Reduction and Film Mulching Measures in Dryland Wheat Field]

We studied the changes in various physical fractions within aggregates in the arid plateau of southern Shanxi Province, which has great significance for synergistically improving soil fertility and crop productivity in this region. Bulk soil samples were collected from 0-20 cm layers during a 7-year long-term experiment in Hongtong County, Shanxi Province. Wheat grain yields, SOC concentrations, proportions, and OC contents within soil aggregates were analyzed. OC contents included： unprotected coarse particulate organic carbon within macroaggregate （M-cPOC） and fine particulate organic carbon within macroaggregate （M-fPOC）, physically protected intra-aggregate particulate organic carbon within macroaggregate （M-iPOC）, chemically/biochemically protected mineral organic carbon within macroaggregate （M-MOC）, unprotected fine particulate organic carbon within microaggregate （m-fPOC）, physically protected intra-aggregate particulate organic carbon within microaggregate （m-iPOC）, and chemically/biochemically protected mineral organic carbon within microaggregate （m-MOC）. The treatments were ① farmer fertilization （FP）, ② nitrogen reduction monitoring and control fertilization （MF）, ③ nitrogen reduction monitoring and control fertilization plus ridge film and furrow sowing （RF）, and ④ nitrogen reduction monitoring and control fertilization plus flat film hole sowing （RF）. The results showed that compared with that in the FP treatment, MF reduced SOC concentration while maintaining wheat grain yield, RF and FH synergistically improved soil fertility and crop yield, especially for the FH with SOC concentration, and wheat grain yield increased by 8.44% and 48.86%, respectively. MF significantly reduced the content of M-cPOC, RF significantly increased the content of M-iPOC, and FH significantly increased the contents of M-fPOC, M-iPOC, M-MOC, and m-iPOC by 64.00%, 98.39%, 6.16%, and 17.48%, respectively. In addition, combined with redundancy analysis, we found that the M-iPOC fraction played a major role in increasing SOC concentration and wheat grain yield, with a contribution rate of 61.5%. Therefore, the contribution of macroaggregates to soil fertility and crop productivity was higher than that of microaggregates in the arid plateau area of southern Shanxi, and flat film hole sowing could increase the content of M-iPOC, thereby synergistically increasing SOC sequestration and wheat grain yield, which could promote this cultivation technology in the region and even in the country's arid agricultural areas.