Abstract:

As well as being the main natural factor affecting grassland degradation in the eastern desertification area of Ningxia， drought is also the primary limiting factor influencing natural grassland reseeding. Caragana （Caragana intermedia）， which is extensively planted in grasslands in this area， is an abundant source of herbage for mulching for soil water retention. However， little research has been conducted to date on the use of caragana herbage for mulching. In this study， caragana branches were cut and collected from local grasslands， and were then transported and applied as a mulch for water retention on nearby grassland not planted with caragana. Four treatments were applied： control （no mulching， TSM₀）， and caragana mulch applied on the soil surface of degraded grassland to a thickness of 1 cm （TSM₁）， 2 cm （TSM₂）， and 3 cm （TSM₃）. During the experimental period， the soil moisture content and temperature of the 0-40 cm soil layer were monitored， together with the above-ground biomass of reseeded forages. It was found that the mean soil water content was significantly increased by mulched caragana branches， and the thicker the mulch layer， the greater the soil moisture water. However， the soil water contents of the 0-20 cm soil layer did not differ significantly from TSM₀ （P>0.05） in either of two seasons for which data were collected， 2018 and 2019. In contrast， the three mulching treatments increased soil water content in the 20-40 cm soil layer compared with TSM₀， and exhibited a gradation TSM₃>TSM₂>TSM₁>TSM₀. Moreover， mulching with caragana branches decreased soil temperature of the 0-10 cm soil layer during the growing season. The soil temperatures at 8：00， 14：00 and 18：00 were all decreased by mulching， and this effect increased with increasing thickness of caragana branch mulch. In addition， the coefficients of variation for soil temperature in 2019 were 4.6%， 2.3%， 1.7% for treatments TSM₁， TSM₂ and TSM₃， respectively， suggesting that the mulching treatments had a buffering effect on soil temperature fluctuation. We also found that the biomass of reseeded grasses increased as the thickness of caragana-branch mulch increased. Lastly， the biomasses of reseeding grass species Agropyron mongolicum and Astragalus adsurgens， as well as the total biomass of reseeding grasses were positively correlated with the soil water content of the 20-40 cm soil layer （P<0.05）. In conclusion， the application of mulched caragana branches improved soil water content and reduced soil temperature in degraded grassland， and also created a beneficial environment for reseeded forage growth. Therefore， use of mulched caragana branches has the potential to provide a method for enhancement of reseeding and restoration of degraded grassland in this region and other similar environments.

Key words: caragana branch mulching, soil water content, soil temperature, forage biomass, Ningxia desertified grassland