Evaluation and implementation of nitrogen fixing species in hedgerow intercropping in Marianas
Nitrogen fixing trees (NFTs) provide many benefits to tropical island farming system in the western Pacific. Hedgerow intercropping with NFTs, as an example, prevents soil erosion, provides a barrier for disease and pest spread, and suppresses weeds by mulching with leaf litter generated from NFTs. This farming operation would help reduce usage of fertilizers and pesticides which potentially contaminate the island environment.
Our work during this period emphasized the study of adaptability of NFTs to three different soil regimes on Guam. The study result indicated that fresh biomass production was greatly influenced by soil types as well as plant species. Leucaena leucocephala K636 was the most adapted NFT to calcareous soil (Lithic Ustorthents) which is a dominant soil type in northern Guam. In the central part of the island with Udic Haplustalfs soil, most of eight NFT species performed very well. In contrast in Oxic Haplustalfs soil of southern Guam, most NFTs yielded poorly. The 9-month biomass production of eight NFTs was summarized and the result was presented at the 10th Pacific Science Inter-Congress Conference as a poster presentation in June 1-6, 2001. The result was also disseminated as a educational factsheet to local community.
Three new experiments were initiated in the second year of the project. First, selected NFTs were planted at a farmer’s field to find plant adaptability to farm’s soil, and to test the palatability of NFTs as fodder for goats on the farm. The second experiment was erosion control study. Selected NFTs were planted at two sites with southern soil with slopes. The depth of soil accumulation and the loss of soil will be measured periodically to evaluate effects of NFTs on erosion control. Thirdly four germlines of Leucaena spp. were obtained from the University of Hawaii for field evaluation in calcareous soil.
1: Develop a protocol of seed propagation methods of leguminous plants as hedgerows and produce a propagation guidebook.
2: Examine biomass production of leguminous hedgerow plants grown in different soil regimes on Guam.
3: Examine seed production of leguminous hedgerow plants grown in different soil regimes on Guam.
4: Examine susceptibility of leguminous hedgerow plants to arthropod, nematode and disease problems.
5: Produce educational publications on plant management of nitrogen fixing trees (NFTs).
Seed propagation methods of potential NFTs for Guam were reviewed in the literature and tried out in a plant nursery. An outline of a propagation guidebook is under development. Important steps of the propagation method are being photographed for including in the guidebook.
Plant development of eight nitrogen fixing trees (NFTs) as potential hedgerow plants were evaluated on three soil regimes on Guam. Monthly harvest of biomass is being used as an indicator of adaptability of hedgerow accessions to a soil type. Test plants included Acacia angustissima (Mill.) Kluntz, Cajanus cajan (L.) Millsp., Calliandra calothyrsus Meissner, Desmodium rensonii, Flemingia macrophylla (Willd.) Merr., Gliricidia sepium (Jacq.) Kunth ex Walp., Leucaena leucocephala (Lam.) de Wit cv. K636, and Sesbania sesban (L.) Merr. cv. Nubica. From November 2000 to July 2001, NFTs other than F. macrophylla and C. calothyrsus yielded more than 11 t ha-1 of biomass in the soil of Udic Haplustalfs at Barrigada in central Guam. L. leucocephala cv. K636 produced the greatest biomass of 26.1 t ha-1 in the trial, followed by S. sesban cv. Nubica with 19 9 t ha-1 The average biomass of eight NFTs was 3.63 t ha-1 in very shallow Yigo soil classified as Lithic Ustorthents,. L. leucocephala out-yielded with 12.3 t ha-1 that was only promising NFT in this location. In the acidic Oxic Haplustalfs soil in Ija, in southern Guam, F. macrophylla, S. sesban, G. sepium, and D. rensonii produced about the same amount of biomass, ranging from 6.6 to 4.8 t ha-1 while L. leucocephala, A. angustissima, and C. calothyrsus grew very poorly. The result was presented at the 10th Pacific Science Inter-Congress in June, 2001. For our local community, a factsheet was produced to disseminate the findings.
Border plants planted for the biomass production experiment at three sites were studied to investigate development of reproductive stages and seed production. Flowering, seed pod formation and seed development were recorded for each species at each location. Seed pods and seeds were also classified as damaged and undamaged ones. Currently, these data are being compiled and analyzed.
Diseases and pest problems were monitored at each planting site. Samples of each hedgerow plant with diseases and pest damaged were collected and identified by R. Schlub, plant pathologist and R. Miller, entomologist. No serious pathogens were observed, however arthropod pests such as pod borers and mealybugs were commonly found on all plants at all three locales. Those pests could become problems in seed production of NFTs on Guam. Severity of plant damage by the pests is being examined.
Dissemination of our work results was a goal of the second year’s project. The study on biomass production of NFTs was presented as a poster in the session of Agriculture Issues: Sustainable Agriculture in the Pacific and Asian Regions at the 10th Pacific Science Inter-Congress in June, 2001. The paper was also accepted in the Proceedings. The study result was prepared as a factsheet which was reviewed by peers and will be distributed to local community in form of hard copy and in a website of the College of Agriculture and Life Sciences, University of Guam.
An outline of seed propagation guide of NFTs is being created. The final guide will have photographs showing plant propagation mehotds, plant development stages and classification of NFTs. Also a script of a video production on the benefits of NFTs is being created for educational purposes.
Impacts and Contributions/Outcomes
Results of NFT studies generated from this project will contribute to improve farm management using hedgerow plants to increase soil productivity, to provide erosion control, to form wind barriers and to provide animal fodder in agricultural system in the Western region. Leucaena leucocephala was found to be adapted to calcareous soil. There will be a need for further research of other Leucaena spp. to determine their suitability and potential usages on northern Guam’s calcareous soil.
A cooperator accepted and appreciated benefits of the use of NFTs in his farm. NFTs as fodder for goat production was his main interest and the farmer found four NFTs as acceptable plants in his farming system. This is an example for grower’s adoption of using NFTs in farming system.