Abstract
Rubber [Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg.] plantations are the largest cultivated forest type in tropical China. Returning organic materials to the soil will help to maintain the quality and growth of rubber trees. Although many studies have demonstrated that organic waste materials can be used to improve soil fertility and structure to promote root growth, few studies have studied the effects of organic amendments on soil fertility and root growth in rubber tree plantations. Here, bagasse, coconut husk or biochar were applied with a chemical fertilizer to test their effects on soil properties after 6 months and compared with the effects of only the chemical fertilizer. Results showed that the soil organic matter content, total nitrogen, available phosphorus and available potassium after the chemical fertilizer (F) treatment were all significantly lower than after the chemical fertilizer + bagasse (Fba), chemical fertilizer + coconut husk (Fco) or chemical fertilizer + biochar (Fbi) (p < 0.05). Soil pH in all organic amendments was higher than in the F treatment, but was only significantly higher in the Fbi treatment. In contrast, soil bulk density in the F treatment was significantly higher than in treatments with the organic amendments (p < 0.05). When compared with the F treatment, soil root dry mass increased significantly by 190%, 176% and 33% in Fba, Fco and Fbi treatments, respectively (p < 0.05). Similar results were found for root activity, number of root tips, root length, root surface area and root volume. Conclusively, the application of bagasse, coconut husk and biochar increased soil fertility and promoted root growth of rubber trees in the short term. However, bagasse and coconut husk were more effective than biochar in improving root growth of rubber trees.
Highlights
Tree root systems are vitally important for the proper functioning of forest ecosystems because of their pivotal roles in the absorption of soil nutrients and water, soil organic matter stock, and for maintaining plant growth, tree stability and stem straightness (Lindström and Rune 1999; Collins and Bras 2007; Xi et al 2011; Pransiska et al 2016; Bo et al 2018; Wang and Xie 2018)
soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) and AK content increased by 63–362% in treatments with organic amendments when compared with the F treatment (Fig. 2)
These results are consistent with many studies that have shown that organic amendments increase soil fertility such as SOM, TN, nitrate–N, AP and AK content
Summary
Tree root systems are vitally important for the proper functioning of forest ecosystems because of their pivotal roles in the absorption of soil nutrients and water, soil organic matter stock, and for maintaining plant growth, tree stability and stem straightness (Lindström and Rune 1999; Collins and Bras 2007; Xi et al 2011; Pransiska et al 2016; Bo et al 2018; Wang and Xie 2018). Soil nutrient levels may influence the growth and turnover rates of fine roots and cause plant roots to grow deeper (McConnaughay and Coleman 1999). The variety of rubber trees that have been widely planted on Hainan Island and in Yunnan and Guangdong Provinces cover approximately 1.07 million ha and provide high economic value (Zhang et al 2007a, b; Qi et al 2013). Fertilization is one of the most important practices to maintain tree growth and rubber yield because root morphology depends significantly on nutrient availability (Fransen et al 1998). Trees increase their number of fine roots to absorb more soil nutrients (Bo et al 2018). The fine root biomass of rubber in these fertilization caves accounts for 94.7% of the total fine root biomass (Liu et al 2006)
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