Agroforestry systems in Nothern Vietnam with Tephrosia candidaas an alternative to short-fallow crop rotation

Abstract

Hoang Fagerstrom, M.H. 2000. Agroforestry systems in northern Vietnam with Tephrosia candida as an alternative to short-fallow crop rotations. Doctoral thesis. ISSN 1401-6249, ISBN 91-576-5737-8. Tephrosia candida was experimentally tested on-farm as an improved fallow species (TepFa), in hedgerows (TepAI) and in a mulch transfer system (TepMu) in an upland rice (Oryza sativa) system on sloping land in northern Vietnam during the period 1996-1999. The objectives of this study were: (1) to investigate whether the existing monocropping (Mono) and short-fallow crop rotations (NaFa) are sustainable systems with respect to soil erosion and concomitant nutrient losses; (2) to determine whether agroforestry systems with Tephrosia (TepFa, TepAl, TepMu) can improve nutrient cycling and nutrient balances, for instance by preventing nutrient losses through erosion, as well as sustaining upland rice yields, A criteria system, including soil and nutrient losses, nutrient balances, changes of P-available pools, returns on tabour and farmers' response, was used for comparing the systems tested. Only TepFa gave a positive input-output balance for both P and N. TepFa increased soil N and seemed to positively affect the release of soil labile P. However, the cost of Tephrosia seeds made the Net Present Value (NPV) of the Tephrosia fallow crop rotation system negative. TepMu increased upland rice yield by 50% compared to Mono. As a result, NPV was positive and sufficient rice for one more person could be produced per ha and year. However, the yield increase could cause a depletion of plant-available P, and the timing for pruning and mulching activities coincided with the fanning activities in paddy fields. TepAl increased soil N, gave a neutral overall effect on crop yield but a negative NPV. NaFa gave a positive and highest NPV. In general, TepFa and TepMu were shown to increase crop yield per hectare with acceptable returns on tabour and also to do better than Mono and NaFa with respect to preventing soil and nutrient losses through erosion. Recommendations are made for further research to focus on alternatives to maintain soil P, mechanisms of P pool reallocation and adoption potentials of the Tephrosia systems tested