Effects of soil-incorporated plant litter morphological characteristics on the soil detachment process in grassland on the Loess Plateau of China

Authors: LIU, JIA-XIN - Northwest A&f University; LIU, GUO-BIN - Northwest A&f University; Flanagan, Dennis; WANG, GING - Northwest A&f University; WANG, ZHONG-YU - Northwest A&f University; XIAO, JING - Chinese Academy Of Sciences

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2019
Publication Date: 11/22/2019
Citation: Liu, J., Liu, G., Flanagan, D.C., Wang, G., Wang, Z., Xiao, J. 2019. Effects of soil-incorporated plant litter morphological characteristics on the soil detachment process in grassland on the Loess Plateau of China. Science of the Total Environment. 705:134651. https://doi.org/10.1016/j.scitotenv.2019.134651.
DOI: https://doi.org/10.1016/j.scitotenv.2019.134651

Interpretive Summary: Soil erosion is a serious problem throughout the world. Some of the most extreme amounts of soil loss have occurred in the silty Loess Plateau of China, that produces sediment in runoff to the Yellow River. Over the past 40 years, efforts in China to control soil loss there have converted much of the Loess Plateau from farmland into forests or grasslands. Some of the plant residues from the grasslands fall to the ground and become incorporated into the soil, which makes it stronger and more resistant to further erosion. In this study, we examined 4 different types of plants and 5 different sizes of residues, and incorporated them at the same mass burial rate into silt loam soil plots. After about two months, soil samples were removed from the different treatments, and tested in a laboratory flume experiment. We found that the smallest pieces of litter were much more effective at reducing soil loss compared to a bare soil control. Also some of the 4 plant types were more effective at reducing soil loss compared to others. The litter surface area density (LSAD) was the best index to use to capture the effectiveness of the different litters at reducing soil detachment (LSAD is calculated by dividing the measured surface areas (m2) of the litter pieces by their volumes (m3)). This research impacts scientists, university faculty, students, and others involved in erosion model development and applications. Equations developed in this study may be useful in improving USDA erosion prediction technologies for locations where grassland plant residues are incorporated into soils and may also be helpful for other buried residue effect estimation.

Technical Abstract: The Loess Plateau of China is one of the most eroded areas in the world. In the past 20 years, effective vegetation restoration measures have significantly changed the near-surface characteristics of soil. In natural conditions, plant litter is widespread in the topsoil. The effects of litter incorporated into soil on the process of soil detachment, which is closely related to plant litter morphology, are still not well known. This study aimed to detect the variation of litter morphological characteristics and quantify their effects on soil detachment capacity and rill erodibility when litter is incorporated into the soil. Four plant litters (Bothriochloa ischaemum (L.) Keng., Artemisia sacrorum Ledeb., Setaria viridis (L.) Beauv., and Artemisia capillaris Thunb.) with five length levels (<0.5, 0.5-2, 2-4, 4-6, and 6-8 cm) were incorporated into soil (idle for 50 days) at the same litter biomass rate (0.7 kg m-2). Then the soil was sampled and cores were subjected to overland flow under six flow shear stress levels (5.66, 8.31, 12.21, 15.55, 19.15 and, 22.11 Pa) using a hydraulic flume (4.0 m×0.35 m). The results showed that the litter morphological characteristics of litter length density (LLD), litter surface area density (LSAD) and litter volume ratio (LVR) differed in plant species at the same litter biomass rate. Correspondingly, soil detachment capacity (ranging from 0.414 to 2.179 kg m-2 s-1) and rill erodibility (ranging from 0.037 to 0.177 s m-1) varied significantly and mean values from the Bothriochloa ischaemum (L.) Keng. treatments were the minimums, which were 28% to 37% and 23% to 35% less than that of the other treatments, respectively. The soil detachment capacity and rill erodibility were significantly correlated with the litter morphological characteristics of LLD, LSAD and LVR (p < 0.01). The contact area between litter and soil was the most critical factor affecting soil detachment. Incorporated plant litter residue litter effect on rill erodibility could be well estimated by LSAD.