No abstract

This study examined the influence of biofilmed biofertilizers (BFBFs

Nutrient leaching in RYP soils lowers the fertilizer use efficiency in plantation agriculture of Sri Lanka. The study was conducted to determine nutrient leaching and their availability in a rubber (Hevea brasiliensis Mull Arg.) growing RYP soil supplied with biofilm biofertilizers (BFBF). Microorganisms isolated from rubber roots were formulated as BFBF under in-vitro conditions, and applied with or without 50% and 100% recommended chemical fertilizers into rubber seedlings growing in RYP soils packed in PVC columns. Combine use of inorganic fertilizer with BFBF reduced leaching loss of soil organic carbon throughout the experimental period. The application of BFBF had a marginal influence on leaching losses of K but it significantly reduced Mg losses. The leaching loss of N was not affected in the first two months, but from three months onward a significant reduction was observed with combine use of full recommended inorganic fertilizer with BFBF (100%F+BFBF) compare to inorganic fertilizer alone (100%F). Available nutrients, organic carbon and cations exchange capacity (CEC) in these two treatments were also comparable. Reduced leaching losses of some nutrients in the combine use of inorganic fertilizer with BFBF treatments (50%F+BFBF &100%F+BFBF) were not reflected in the nutrient status of the top soil layer (0-5 cm) but high plant dry matter accumulation was observed in BFBF treated plants. There is a possibility to reduce leaching loss of some nutrients and induce dry matter accumulation of rubber plants by BFBF application into RYP (Hapludults) soils.

Phosphorus (P) fertilizers contain cadmium (Cd) as a contaminant at levels varying from trace amounts to high levels and therefore, can be a major source of Cd to agricultural systems. This study was designed to assess the impact on application of Eppawala rock phosphate (ERP) and triple super phosphate (TSP) as P fertilizers and different soil amendments on P and Cd uptake in maize (Zea mays L.). The field trial was carried out at Field Crop Research and Development Institute at Mahailluppallama, Sri Lanka. A randomized complete block design was employed with three replicates as ERP and TSP separately applied with arbuscular mycorrhizal fungi (AMF) and three types of amendments (biochar, compost and dolomite) and the control without adding P fertilizers. Phosphorus content and Cd content of soil, maize roots and seeds were quantified. Results revealed that available soil Cd and total accumulated root and seed Cd amounts were significantly higher in TSP added treatments with and without amendments compared with ERP added soil. Considering soil available P, root and seed P, there was no significant difference observed in different treatments of TSP and ERP added treatments. A similar phenomenon was also observed in growth and yield parameters with both fertilizers added and with the added amendments. There was no colonization of AMF in maize roots in TSP applied soil while 25-60% of colonization was recorded with ERP. Synthetic fertilizer (TSP) must have inhibited the AMF colonization and thereby increasing the Cd content in maize seeds. AMF colonization increased with comparatively low soil available P in ERP added treatments. The results revealed that TSP could be effectively substituted by ERP as a source of P for maize soils. The addition of AMF, compost and biochar further increased the effect.

Weed control is important during immature stage of rubber plantations particularly, before fertilizer application. Most of the chemicals are being restricted due to health and environmental concerns thus investigations on chemical free weed control methods are important. The effect of different natural and synthetic mulching materials on weed control was studied compared to manual weeding. Oil palm Empty Fruit Bunches (EFB) was used as natural mulch and shade net and polythene were used as synthetic mulch. Labor requirement in each treatment was evaluated. Effect of mulching on soil nitrogen content, pH, organic carbon content and cation exchange capacity was also measured at three months and one year after treatment application. All the mulching treatments showed significant weed control compared to the control. Since, weed regeneration was observed in oil palm EFB treatment from ten weeks of its application, it was applied again in three months intervals. There were no weeds observed in both in shade net and polythene mulch treatments from four weeks of their application up to one year period. All the mulching treatments reduced labor requirement compared to the control. Organic carbon content was significantly improved by mulching while other soil parameters were not affected compared to the control. Shade net and polythene could be effectively used for weed management and they will be beneficial under labor shortage. Oil palm EFB is effective for weed control with labor saving and it has to be applied in three months intervals. However, there will be no environmental pollution with Oil palm EFB mulch as it is a natural waste material.