4.3 Strategy for agro-ecological reclamation of post-tin mining areas
Evaluation of soil characteristics showed the current post-tin mining areas have many severe constraints for crop growth and environmental reclamation. Major constraints included sandy soil texture, the absence or limited weatherable minerals (potential native nutrient sources), the dominance of quartz mineral in tailings, the low water holding capacity, the extreme low in soil organic matter and all nutrients, and nutrient susceptible to leaching. Reclamation of soil capability to retain nutrients and water was prerequisite. We proposed the strategic approach in the view of long-term investment in agroecological reclamation as follows: (i) levelling measures of on-site mounds resulted from refused material dumping; (ii) building up soil organic matter content (SOM) of sand tailing using green manure or compost to increase soil organic C, supply various nutrients, promote microbial activities and aggregate formation, reduce soil temperature, and increase soil ability to hold water and nutrients; (iii) establishing a special cultivation technique. Direct planting on soil tailings with sandy texture dominated by quartz minerals is unlikely to allow crop growth as shown in Fig.3a. Hence, the “pot planting point” technique could be introduced to overcome the unfavourable conditions for crop development. The technique is experimentally being tested in the field and is still collecting more data (Fig.3c). Crop performance using pot planting point technique showed rigorous growth of Paspalum grass (Paspalum atratum ) (Fig. 3d) and various legumes, namely Gliricidia (Gliricidia sepium , Jacq.) (Fig.3b, background), Sesbania (Sesbania grandifora (L) (Fig.3b, front), Indigofera (Indigofera zollingeriana ) (Fig. 3e), Stylosanthes (Stylosanthes quianensis ) (Fig. 3f) and Lab lab (Lab lab purpureus ) (Fig.3g). This technique is highly promising to restore soil productivity and ecological recovery in post tin mining areas; and(iv) complete fertilizer application and selection of crops with an ability to fix nutrient from the atmosphere. The suggested adaptive legumes with nodules on roots to fix atmospheric N are Indigofera (Figure S3a) and Lab lab (Figure S3b).