Concentrations of 15 mineral elements -S, K, Al, Ca, Mg, Cl, Si, Na, B, Cu, Fe, Mn, P, Sr, and Zn -appearing in 457 bark samples of trees in a 1 ha observation plot in West Sumatra, Indonesia, were analyzed. Based on the analytical results, an elemental non-accumulating tree was defined for each element as a tree with its concentration of the element in question within the bottom 5% (in this case 23 trees) of the 457 samples, irrespective of tree species. The relationships between the spatial distribution of the non-accumulating trees and the soil edaphic status at two depths (0-5 cm and 5-15 cm) were studied.The non-accumulating trees of K, Al, Ca, Na, B, Cu, Mn, Sr and Zn tended to be distributed in areas where the concentration of those extractable elements in the soil was low. This indicates that a positive association between the soil edaphic status and the nutritional characteristics of the tree bark existed, as demonstrated by the distribution pattern of these non-accumulating trees. On the other hand, the distribution of the non-accumulating trees of S, Mg, Si, Fe and P was rather independent of the soil edaphic status of those elements, suggesting that the distribution of these non-accumulating trees was affected more by genetic factors or by environmental factors other than the soil edaphic status of those elements.The relationship between the elemental concentrations in the bark and in the soil was also studied.A significant positive correlation was observed for K, Mg, Na and Sr, and a significant negative correlation was observed for B, Mn and P among the 457 trees, suggesting that those elemental concentrations in the bark were strongly related to the soil edaphic status. The non-accumulating trees of K, Na and Sr were distributed in the areas with the low and narrow elemental concentration range in soil, suggesting that the low edaphic levels seemed to strongly contribute to the low concentration level in the bark. However, in terms of the other accumulating trees and non-accumulating trees, the concentration levels in the bark were considered to be regulated not only by the soil edaphic status, but also by the tree genetic characteristics.Key words: non-accumulating tree / bark / mineral nutrients / spatial distribution / soil edaphic status / tropical rain forestIn a previous paper (Masunaga et at., 1998), the relationships between the distribution of accumulating trees and the soil edaphic status at the depth of 0-5 c m and 5-15 c m were studied. The results

The contribution of the sawah system (bunding, leveling, and puddled fields to irrigated rice cultivation) was studied alongside the traditional slash-and-burn, rain-fed lowland rice farming system in the inland valley bottom of the Ashanti region, a semi-deciduous forest zone in Ghana. Different organic and inorganic fertilizers were tested under the different systems. The results revealed that the sawah system resulted in a greater number of productive tillers, higher straw production, and higher grain yield compared to the farmers' rain-fed lowland practice.Among the fertilizer treatments, the poultry manure, relatively rich in both N (nitrogen and P (phosphorous), and the use of the inorganic fertilizers N 90, P205 60, and K2O 60 kg ha-I at the recommended rate for rice exerted similar effects on grain yield under both systems This means the soils were relatively deficient in available N and P. The sawah system had a remarkable effect on N uptake by rice grain and straw in the inland valley bottom. Agronomic uptake N efficiencies and agronomic N efficiencies of fertilized N in both mineral and organic forms were considerably higher under the sawah system in the valley bottom. The present rain-fed lowland condition of local farms in the inland valley bottoms of the Ashanti region of Ghana showed very poor efficiency in the use of fertilized N in both the mineral and organic forms. Our study results indicate that use of the sawah system is a prerequisite for the efficient use of fertilizer to increase rice yield in the inland valley bottom.Key words: agronomic efficiency / Ghana & West Africa / inland valley bottom / inorganic fertilizers 1 rain-fed lowland condition / organic manures / phosphorous deficiency / sawah systemThe agricultural productivity index in Ghana and other countries in West Africa fluctuates mainly because the country's agriculture is rain-fed and subsistence farmers relying on the rain are the main backbone of farming in the country. The majority of farmers still practice the traditional shifting cultivation method of farming. Under this system, farmers clear the native vegetation by the slashand-bum method and then grow crops. The efficiency of shifting cultivation depends mostly on the duration of the fallow period and the nature and density of the fallow vegetation. Rapid increases in human population and the associated increases in demand for farmland and wood products have overburdened this traditional cultivation method. Long fallow periods, which in the past lasted 10 to 25 years, have been shortened drastically (to one or two years) or disappeared in areas like the valley bottom sites in Ashanti where rice is cultivated yearly. This has resulted in increasing degradation of farmland increasing infestation of problem weeds, and declining yields and production of food crops