Summary

Dendrimers are a class of hyperbranched polymers with welldefined, nanoscaled structure.

When more than 50 % of the applied N-fertilizer is lost from active root zone of a crop, which is very common in vegetable based cropping systems in Sri Lanka, farmers do not realize the full benefit of money invested on N-fertilizers (both organic and inorganic) but end up contributing to severe taxes on environmental and public health. Improving yield return on N-fertilizers applied (N-fertilizer use efficiency – NUE) by suppressing soil nitrification has not been researched adequately in Sri Lanka. The only techniques implemented to improve NUE are matching fertilization events with crop requirement and the use of slow releasing fertilizers. Although synthetic nitrification inhibitors are in the global market for several decades these products are not economically feasible for our farmers. The overarching goal of the proposed research is to reduce the N- fertilizer wastage in vegetable cropping systems by improving the efficiency and effectiveness of applied N-fertilizer. Through the proposed research we aim to develop botanical nitrification inhibitors to achieve this goal.

We have identified intensive vegetable cropping systems in Kalpitiya and Marassana as the target sites for the proposed study considering their contribution to the vegetable production in Sri Lanka and environmental risks associated with present way of nutrient management. We will identify locally available plant species in these two areas to develop botanical nitrification inhibitors. From preliminary information gathering we have identified Pinus spp., Eucalyptus spp., Brachairia humidicola, Helianthus anuus, Citrullus colocynthis, Lantana camara, and Azadiracta indica to be included in the list of plant species we will be testing. The effectiveness and persistence of the developed botanical nitrification inhibitors will be evaluated by testing against nitrifying communities isolated from soils collected from the two areas as well as from research fields at Horticultural Research and Development Institute (HORDI), Gannoruwa. We will be investigating on the use of pyrogenic carbon produced from a locally available organic material such as poultry manure or paddy-husk to improve the effectiveness of botanical nitrification inhibitors. We will be testing selected products across two different cropping histories (0 and >20 years of continuous cultivation) from each location (Kalpitiya, Marassana and Gannoruwa) to identify widely adaptable botanical nitrification inhibitors. Selected botanical nitrification inhibitors will be tested in a series of greenhouse pot experiments and a field trial at HORDI to determine their effects on NUE of selected crops and to estimate the reduction in N losses from soil. From the results we will estimate the reduction in N-fertilizer losses and yield advantage of applying botanical nitrification inhibitors with N-fertilizers to the selected crops.

As deliverables we expect to develop effective botanical nitrification inhibitors adaptable to a wider range of vegetable cropping systems using locally available materials to the farmers. Further we expect these products would significantly reduce N-fertilizer losses from soil and improve the return of crop yield per unit of N-fertilizer applied. The production techniques of effective botanical nitrification inhibitors will be an output of the project, which we will consider for patenting but not limiting dissemination of knowledge to farmers. Findings will be published in reputed refereed journals and at local and international scientific forums. Two workshops will be conducted to disseminate research findings to the farmers. We envisage the technique and the products we develop from the proposed research would reduce the N-fertilizer wastage from vegetable based cropping systems, and would be applicable to other cropping systems as well.

Objectives

The money spent on importing fertilizers and recovering from damage caused to environment and public health by excessive use of fertilizers is a burden to a country’s economy. However, the management practices we should introduce to reduce fertilizer wastage and fertilizer usage while maintaining or improving crop yield should be economical and practicable to farmers. The overarching goal of the proposed research is to reduce the N- fertilizer wastage in vegetable cropping systems by improving the efficiency and effectiveness of applied N-fertilizer. Through the proposed research we will develop botanical nitrification inhibitors to achieve this goal. Therefore, the specific objectives are aimed to:

1. Identify locally available plant species with biological nitrification inhibition ability.

2. Evaluate the nitrification inhibition potential of different materials/ constituents obtained from selected plants.

3. Identify the effect of mixing botanical nitrification inhibitors with prolyzed carbon on effectiveness in suppressing nitrifiers and the persistence of the material in soil.

4. Evaluate the effectiveness of selected improved and crude botanical nitrification inhibitors across different soil types on retarding nitrification and improving plant performance.

5. Identify the right rate and right frequency of application for selected botanical nitrification inhibitors.

6. Estimate the N leaching from soil treated with different botanical nitrification inhibitors.

7. Estimate the N-fertilizer use efficiency of selected vegetable crops as affected by applying botanical nitrification inhibitors with N-fertilizers.

8. Estimate the yield advantage of applying botanical nitrification inhibitors with N-fertilizers.

9. Disseminate knowledge generated from the study to farmers