Soil Science

Yao, Jingjing; Cheng, Jinhua; Sun, Long; Zhang, Xin; Zhang, Hongjiang

doi: 10.1097/SS.0000000000000198pmid: N/A

ABSTRACT Antecedent soil water exerts considerable influence on the infiltration rate and distribution of preferential flow. Effects of antecedent soil water on preferential flow were investigated through dye experiments with Brilliant Blue FCF (C.I. Food Blue 2) in four soybean plots with low (LWC) and high (HWC) antecedent soil water levels. Changes in soil water were measured during the dye experiments. Horizontal and vertical soil slices were exposed every 10 cm approximately 24 h after the dye tracer application, and staining ratios (stained area to total area) were calculated from photographs. This study demonstrated that the dye tracer infiltrated to a mean depth of 56 cm at an average rate of 1,455 mm h−1 in the LWC plots and to a mean depth of 34 cm and at an average rate of 523 mm h−1 in the HWC plots. Finger flow occurred in Layer B of the LWC plots, possibly resulting in their deeper infiltration depth. The staining ratio in each layer of the LWC plots was generally larger than the corresponding one of the HWC plots. In both the LWC and HWC plots, the average staining ratios decreased with soil depth and exhibited a sharp decrease from Horizon A to B. The largest effect of antecedent soil water on dye tracer movement was found in Layer B. The results indicated that preferential flow was substantial under conditions of low antecedent soil water content in the conditions found in southwestern China. These results could be helpful in improving crop yields and reducing pollution of shallow groundwater by leading farmers to irrigate and till the soil surface with the appropriate frequency.

Bahadori, Mohammad; Tofighi, Hasan

doi: 10.1097/SS.0000000000000201pmid: N/A

ABSTRACT The Walkley-Black (WB) method has been widely used during the past 50 years because of its simplicity and rapidity. The main problem with this method is its incomplete oxidation of soil organic carbon (OC) and inconstancy in efficiency of oxidation in different soils. A practical way to improve the accuracy of this method is by applying a correction factor. However, correction factors can be affected by environmental conditions, vegetation, soil characteristics, and systems of cultivation. The objectives of this study were to evaluate the efficiency of the WB method in soils under four diverse vegetation systems and to introduce appropriate correction factors for each vegetation system. In this study, 94 composite soil samples were collected from soils under pastures, a forest, and from rice and annual crop fields. In addition, 16 samples from saline soils were analyzed to find the possible effect of salinity on the efficiency of the WB method. The OC contents of the samples were measured by the WB method and by a total carbon analyzer, and the obtained data were statistically analyzed with the Duncan method. The results demonstrated that there is a significant difference between soil OC recovery by the WB method under diverse vegetation systems and also in soils with different contents of OC and salinity, with correction factors ranging from 1.21 (annual crops in soils with OC >1%) to 2.26 (pastures in soils with OC <1%). Differences in the efficiency of the WB method were attributed to changes in the residue fragmentation and quality as a result of the cultivation or vegetation system, as well as the presence of chloride ions in saline soils.