Erhaltung der Bodenfruchtbarkeit unter Anwendung angepasster Anbausysteme in Bergregionen Vietnams

Abstract

In sloping lands in Vietnam, the influence of topography, geology, morphology, climate, etc., and of human activities has resulted in serious environmental degradation, particularly of soil and water. Consequently reducing crop yields and deteriorating living standard as well as food security for people lives there. Therefore, in order to improve living standard and food security situation for the farmers in the mountainous areas, a shift toward sustainable land use systems is required. The socio-economic analysis show that family income was found to have close relationship with land size. The higher the available of land the higher the income. Crop yields on the sloping areas decreasing overtime due to increasing of land degradation. However, it should be noted that there are some farmers (34%) who do not know the causes leading to soil erosion, and the higher percentage (62%) of farmers in the area didn t care about the dangers and consequences of soil degradation. To overcome the increasing food deficit problems due to the rapid population, the natural fallow period was reduced to 2 - 3 years currently. In addition, agricultural land expanding to the forests cause for increasing degradation land process in the region. The results of the experiment show that during the rainy season (April to Septembers) soil erosion level increasing from the plots of first year (43 tons/ha) to the plot at fourth year after slash and burn (58,3 tons/ha). While in the plots of Agro forest with mulch only 3.7 tons of soil loss/ha was recorded during this period. The highest amount of soil loss is equivalent to lose of 1234 kg org. substance, 82 kg N, 1468 kg K, 82 kg P, per ha per year and approximately with 9,000,000 VND to spend for buying fertilizer to replace or purchase the amount of nutrient elements lost by erosion per year. This expense seem will increase year after year if current use of land with the traditional shifting cultivation method continues. Consequently, reducing the yield of maize cultivated on the plot in the fourth year is only 1/3 of the yield of maize on the plot of first year after slash and burn. The examination of soil samples shows that due to the different level of soil erosion in different plots, pH value and alkalinity saturation in the area clearly decreased from 6.5 in the plots of the first year to 4.4 in the plot cultivated of fourth year cultivatated land due to the V-wert decreased from 99.6% to 28.9% respectively. The degradation of soil during period of use shown clearly by the decrease of basic elements (organic substance, total nitrogen content and the cations exchange capacity) between forestland, the first year and the fourth years after slash and burn. The availability of P content after Bray analysis were very low especially in the plots that was used for long time and tended to decrease fast from the first year to the fourth years after cultivation due to the fact that partly available P is lost through erosion process and also due to iron and aluminum enrichment at low pH values leading to reduce phosphorus availability through the irreversible phosphate fixation. Therefore, long time use of land without any soil conservation measures may lead to degradation and unusable land. The Agro-forestry with mulch indicates the high improved soil erosion control and available rehabilitating measures for the sloping lands. Since it reduces soil erosion during the cultivated periods in addition to increasing soil fertility when compared with the degraded plots at Alang-alang. The Agro-forestry with mulch have a high potential to substitute the traditional shifting cultivation method because this system increases land use rate (R). Therefore, this model should be extended and developed for the whole region. Further more, the result of the research also contributed to overall food and poverty reduction effort by quantifying what would be gained in term of yield gain if these measures are probably implemented in the mountainous areas, where mainly ethnics and poor people live. Therefore, the study result did not only establish the sustainable of land resources use but also contributed to the equal development between the mountainous and the lowland areas.