Efficiency of wheat straw mulching in reducing soil and water losses from three typical soils of the Loess Plateau, China

Mulching the soil surface with a layer of plant residue is considered an effective method of conserving water and soil because it increases water infiltration into the soil,reduces surface runoff and the soil erosion,and reduces flow velocity and the sediment carrying capacity of overland flow.However,application of plant residues increases operational costs and so optimal levels of mulch in order to prevent soil and/or water losses should be used according to the soil type and rainfall and slope conditions.In this study,the effect of wheat straw mulch rate on the total runoff and total soil losses from 60-mm simulated rainstorms was assessed for two intensive rainfalls (90 and 180mmh^-1) on three slope gradients typical conditions on the Loess Plateau of China and elsewhere.For short slopes (1 m),the optimal mulch rate to save water for a silt loam and a loam soil was 0.4 kg m^-2.However,for a clay loam soil the mulch rate of 0.4 kg m^-2 would be optimal only under the 90 mm h^-1 rainfall;0.8 kg m^-2 was required for the 180 mm h^-1.In order to save soil,a mulch rate of 0.2 kg m^-2 on the silt loam slopes prevented 60%-80% of the soil losses.For the loam soil,mulch at the rate of 0.4 kg m^-2 was essential in most cases in order to reduce soil losses substantially.For the clay loam,0.4 kg m^-2 may be optimal under the 90 mm h^-1 rain,but 0.8 kg m^-2 may be required for the 180 mm h^-1 rainstorm.These optimal values would also need to be considered alongside other factors since the mulch may have value if used elsewhere.Hence doubling the optimal mulch rate for the silt loam soil from 0.2 kg m^-2 or the clay loam soil under 90 mm h^-1 rainfall from 0.4 kg m^-2 in order to achieve a further 10% reduction in soil loss needs to be assessed in that context.Therefore,Optimal mulch rate can be an effective approach to virtually reduce costs or to maximize the area that can be treated.Meantime,soil conservationist should be aware that levels of mulch for short slopes might not be suitable for long slopes.

Comparison of direct and indirect determinations of dynamic ventilation rate in a modern dairy free stall barn

Reliable estimation of the ventilation rate(VR)in intensive livestock buildings is necessary for studying building environmental control strategies and predicting indoor air quality and air emissions.As direct air exchange measurements are time-consuming and expensive,it is environmentally inefficient to measure livestock building VR continuously in practice.Hence,indirect VR estimation methods have been widely used in modelling environmental control and air emissions,and also to measure airflow in the field.The accuracy of indirect measurement methods needs to be evaluated by comparing with direct measurements.In this study,the direct and indirect methods of determining hourly and daily mean VRs were applied to a mechanically-ventilated dairy free stall barn monitored by the 24-month National Air Emissions Monitoring Study.The direct method was used to continuously monitor fan rotational speeds,and differential static pressures,coupled with periodic in-situ fan performance assessments,to calculate the VR.The indirect method consisted of estimating the VR using CO2 concentration measurements and the CO2 mass balance method.The average daily and hourly means(mean±SD)of directly measured barn ventilation rates for two years were(246±73)m3/s and(245±77)m3/s,respectively.The average daily and hourly means(mean±SD)of barn ventilation rates estimated by the CO2 mass balance method were(287±93.4)m3/s and(287±118)m3/s,respectively.Correlation analyses showed a strong correlation between the indirect CO2 mass balance method and direct measurement methods(r=0.93 for daily means and r=0.85 for hourly means).

Gases emissions estimation and analysis by using carbon dioxide balance method in natural-ventilated dairy cow barns

Contaminated gases emissions from livestock industry are becoming one of the most significant contributors to the increasingly serious environmental pollution.To find a way to reduce gases emissions,it is essential to reveal the factors that can affect the gases emissions.In this study,the concentrations of typical gases(including ammonia(NH_(3)),carbon dioxide(CO_(2)),hydrogen sulfide(H_(2)S),and sulfur dioxide(SO_(2)))generated from naturally-ventilated dairy cow barns were detected through the sample-data method in Tianjin,northern China.Indoor environmental conditions,such as temperature(T)and relative humidity(RH),were measured simultaneously.After applying the carbon dioxide mass balance method,ammonia,hydrogen sulfide and sulfur dioxide emissions were determined.The correlation analysis and regression analysis between the climate condition and gas emissions were conducted to assess the data collected in dairy cow barns during the whole study period.There was a significant relationship between environmental conditions and gas emissions.NH3,H2S and SO_(2) emissions from the building are in the range of 0.98-2.36 g/LU·h,0-0.034 g/LU·h,and 0-0.069 g/LU·h,respectively.The numerical analysis shows that the NH3 emission is highly correlated with the temperature and relative humidity.The ventilation rate shows a positive correlation with all the three gases.