Improving desertified soil properties by incorporating and mulching tree branch in Ningxia province

Desertification is one of most serious problems which affect eco-construction and agricultural production in Ningxia and other arid and semiarid areas in China. To study the effects of tree branch application patterns on physicochemical property and microbial activity of desertified soil, pruned tree branches were collected as soil amended materials from local common trees of farmland shelterbelt, and a two-year study was conducted from October 2011 to October 2013 in Yinchuan Belly Desert of Ningxia. Four experimental treatments were set up, including 1) CK (no tree branches applied), 2) CI (5% (w/w) grinded poplar branch chips incorporated into 0-20 cm soil layer), 3) CM (grinded poplar branch chips mulched on soil surface with a thickness of about 3 cm) and 4) CI+BM (5% (w/w) of grinded poplar branch chips incorporated into 0-20 cm soil layer plus ungrinded willow branches crisscross mulched on soil surface with a thickness of 30-40 cm and a coverage of 50%-60%). The 0-20 cm soils were sampled and measured in October 2012 and October 2013 respectively. Results showed as follows: To physical properties, compared with CK, CI and CI+BM decreased bulk density yet increased total porosity and field water holding capacity of desertified soil in 2012 and 2013 (P<0.05), and there was no significant difference between the two on other physical properties except CI+BM had more effect on increasing total porosity than CI in 2013; CM significantly increased total porosity in 2012 (P<0.05), but had no effect on other indicators of physical properties compared with CK in 2012 and 2013. To chemical properties, compared with CK, both CI and CI+BM increased organic carbon, available phosphorus (P) and available potassium (K) in 2012 and then increased total salt, organic carbon, total nitrogen (N), total P, alkaline N, available P and available K in 2013 (P<0.05), yet had no effects on pH value (P>0.05); furthermore, CI+BM had more effect on increasing total N than CI in 2013; compared with CK, CM increased total available P and available K in 2012 and then increased pH value, total N, alkaline N, available P and available K in 2013 (P<0.05), yet had no effect on other chemical properties compared with CK (P>0.05). To biological properties, it showed an order of CI+BM > CI > CM > CK on enhancing microbial activity, CI and CI+BM enhanced soil respiration, microbial number, urease activity and catalase activity compared with CK in 2012 and 2013 (P<0.05), and CI+BM tended to have more effect on enhancing microbial activity than CI; and also compared with CK, CM also increased soil respiration, urease activity and catalase activity in 2012 and 2013 (P<0.05), as well as increased bacteria and fungi number in 2012, yet had no effect on microbial number in 2013. An analysis indicated that soil physical, chemical and biological properties were improved in 2013 than in 2012. Additionally, a correlation analysis indicated that most of measured soil indicators were significantly or highly significantly correlated with organic carbon content (except pH value and total K in 2013), and organic carbon content presented a tendency of CI+BM > CI > CM > CK among treatments in 2012 and 2013; a comprehensive index SQI (soil quality index), which was applied for assessing soil quality, also presented a tendency of CI+BM > CI > CM > CK in 2012 (0.907, 0.678, 0.259 and 0.105 respectively ) and 2013 (0.926, 0.828, 0.258 and 0.136 respectively). In summary, all tree application patterns have positive effects on improving soil properties or quality during experimental period, which presents a tendency of CI+BM > CI > CM > CK among treatments. Above study provides a successful case for ecological management and agricultural production for Ningxia and other arid and semiarid areas of North China; meanwhile it also may be beneficial to tree branch recycling and utilization.