Effects of litter on soil water in the steppe of northern Mongolia
The effects of litter on ecosystem functions have been documented by a number of studies worldwide. One of the commonly reported influences of litter is on soil water content by reducing evaporation from soil, which in turn can alter soil moisture and temperature. However, there is uncertainty at which level the litter amount prevents evaporation from soil. Over two growing seasons in 2011 and 2012, we experimentally tested the effects of different amount of litter on soil moisture and temperature in the steppe of northern Mongolia. Using a field experiment manipulating litter amounts (64 g/m2, 32 g/m2, 16 g/m2, 0 g/m2) and rainfall inputs (heavy rain: 20 mm water per two weeks; light rain: 5 mm water per week; control: no water) and volumetric soil water content and soil temperature from 0–6 cm was measured between 2:00 p.m. and 3:00 p.m. on every day. And ecosystem water simulations parameterized by the field data, we set two objectives: (i) which level of litter amount negatively and/or positively affects on soil moisture and temperature, and (ii) is there any threshold level in litter amount to preserve soil moisture? Soil water model (SOILWAT) was used to determine the infiltration rate of rainfall into soil and evaporation from soil.
Results of our experiment showed that litter significantly affected on soil moisture with light rainfall (5 mm), while this effect was not observed with heavy rainfall (20 mm). Simulation experiments on litter interception also indicate that the percentage of total water intercepted by litter decreases with increasing rainfall size (heavy rains). Our field and simulation experiment results showed that litter can affect soil moisture in two different ways; it can either cause increases by reducing evaporation, or decreases by intercepting rainfall. In other words, 32 g/m2 litter reduced evaporation from soil by reducing maximum soil temperature, which in turn could affect on soil moisture positively, whereas 64 g/m2 of litter negatively affected soil moisture by intercepting rainfall. Our results also showed that plots with 32 g/m2 had higher soil moisture content as compared to other litter manipulated plots, which suggested that 32 g/m2 of litter mass would be the optimum litter amount to protect soil moisture in our research site. Moreover, results of our research can be used to improve rangeland management in Mongolia, thus further studies to investigate the effects of litter in other ecosystems of Mongolia are required.