As a globally important sugarcane-producing region, Southern China (SC) is severely affected by various agrometeorological disasters. This study aimed to comprehensively assess multiple sugarcane agrometeorological disasters with regards to sugarcane yield in SC. The standardized precipitation evapotranspiration index and the heat degree-days were employed to characterize drought, flood, and high temperature (HT) during sugarcane growth stages in three provinces in SC in the period 1970–2020. Moreover, the relationships between sugarcane climatic yield and disaster intensities were investigated. The results indicated that the most recent decade witnessed the most intensive sugarcane agrometeorological disasters; sugarcane drought and HT intensities significantly (p < 0.05) increased in one and two provinces, respectively. Central and western SC was most drought-prone, while eastern SC was most flood-prone; sugarcane HT was concentrated in southwestern SC. The mature stage exhibited the greatest monthly intensities of drought and flood; the most HT-prone growth stage varied with provinces. The relationships between drought/flood intensity and sugarcane climatic yield were significant in seven districts; the yield-reducing effect of sugarcane flood was more obvious than that of drought. In conclusion, this study provides references for agrometeorological disaster risk reduction for sugarcane in SC.

Soil respiration is controlled by land‐use changes associated with cropland vegetation restoration, and this can vary with topography, although the magnitude of this effect and the underlying mechanisms are still unclear. We synthesized 69 recently published papers from China to explore the influence of topography‐related changes in land use on soil respiration where croplands were converted into orchards (abbreviated as C‐O), grasslands (abbreviated as C‐G), or woodlands (abbreviated as C‐W). Our results showed that not only did land‐use change have a significant influence on soil respiration, but this varied with topography. While C‐O resulted in a decrease in soil respiration by, on average, 3.1%, both the magnitude and sign of the change varied with topography, with an 8.2% increase for flat areas and a 14.7% decrease for slopes. For the C‐G conversions, soil respiration increased, on average, by 21.4%, with a 19.5% and a 24.3% increase for flat and slope topography, respectively. For C‐W, soil respiration increased, on average, by 28.0%, with only a 1.6% increase for flat areas, but a 39.9% increase for slopes. Soil temperature, soil moisture, root biomass, soil organic carbon (SOC), soil microbial biomass carbon (MBC), soil carbon‐to‐nitrogen ratio (C:N ratio), and soil density also varied with topography, with larger changes for slopes than for flat topography. Increases in soil respiration associated with different topography were closely related to changes in soil temperature, SOC, MBC, and root biomass (P < 0.05), but were not correlated with changes in soil moisture, C:N ratio, or soil density (P > 0.05). The contribution of different drivers to the change in soil respiration under different topographical conditions showed a trend of SOC > root biomass > MBC > soil temperature. Based on these results, topography‐related variations in soil respiration need to be accounted for when quantifying the impact of land‐use change on C budgets.

Aim of study: To investigate how the cross section of a drip-irrigation tape affects local head loss.Area of study: The work was carried out in the laboratory of Irrigation hydraulics, College of Water Conservancy and Environment, Three Gorges University, Yichang, Hubei province.Material and methods: Tapes with six different wall thicknesses were studied experimentally to determine the relationship between cross-section deformation, wall thickness, and pressure. Based on the experimental results, we determined the factors that influence local head loss in drip-irrigation tapes by numerical simulation and dimensional analysis.Main results: The cross-sectional shape of the drip-irrigation tape varied with pressure: under low pressure, the cross section was nearly elliptical. The cross-sectional shape of the tape strongly influenced the local head loss, which was inversely proportional to the 0.867th power of the flattening coefficient of the drip irrigation tape. We expressed the local head loss of a drip-irrigation tape equipped with integrated in-line emitters by considering the deformation of the cross section. Under the conditions used in this study, when the cross section is circular, the ratio of local head loss to frictional head loss was about 10% but, when the cross section is elliptical, this ratio increased to 15%.Research highlights: The shape of the cross section of a drip-irrigation tape is nearly elliptical under low pressure. Local head loss is inversely proportional to the 0.867th power of that is the flatting coefficient of the drip-irrigation tape. Local head loss is about 1.5 times for elliptical tape than circular tape.