Browsing by Author "Deckers, J. A."

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Effect of conservational tillage on soil loss and plant nutrient status on vegetable yield, Northern slopes of Uluguru Mountains, Morogoro, Tanzania
(2010) Msita, H. B.; Mtakwa, P. W.; Kilasara, M.; Kimaro, D. N.; Msanya, B. M.; Ndyetabula, D. K.; Deckers, J. A.; Poesen, J.
The study was conducted to evaluate effects of conservational tillage on vegetable production on the northeastern part of Uluguru Mountains in Tanzania. Six treatments such as control conservational tillage; conservational tillage with manure; conservational tillage with insitu composting; control traditional tillage; traditional terrace with manure and traditional tillage with in situ composting were examined. Nutrient levels were determined from soil before and after harvest and from plant samples after harvest. Soil losses were assessed by collecting runoff using polyethylene troughs for each treatment. Analysis of variance and Multiple range test (P=0.05) was done to test the effect of the treatments. The differences (P=0.05) on soil loss, plant nutrient status and vegetable yield were observed. All conservational treatments gave high fresh yield (4.3–44.7 ton/ha), high nutrient retention (N% 0.11–0.14, P% 5.17– 16.33, K% 0.33-0.36) and experienced low soil losses (0.49, 0.54 to 0.65 ton/ha/season). While the opposite was true for traditional treatments lower fresh yield (0.9–13.9 ton/ha), low nutrient retention (N% 0.10–0.11, P% 0.91–4.00 and K% 0.29–0.32) and high soil losses (0.54, 0.83 to 1.26 ton/ha/season) at P=0.05. It was concluded from this study that the conservational tillage for vegetable production on sloping land ranging from 20 to 80 percent was the best practice resulting in increased crop yield, nutrient uptake, plant nutrient retention, and reduced soil loss.
Magnitude of soil erosion on the northern slope of the Uluguru Mountains, Tanzania: Interrill and rill erosion
(Elsevier, 2008) Kimaro, D. N.; Poesen, J.; Msanya, B. M.; Deckers, J. A.
The magnitude of interrill and rill erosion was determined on the northern slopes of the Uluguru Mountains, Tanzania which is representative for larger areas of East African Arch Mountains, where population pressure is high and land degradation is severe. The aim of the study was to develop a database to support soil conservation in the area. The study was done on two distinct geomorphic units with respect to altitude and hence rainfall distribution pattern: mountain ridges with an altitude ranging from 1000 to 1500 masl and mean annual rainfall of 2300 mm and mountain foothills whose altitude and mean annual rainfall are 550 to 900 masl and 900 mm, respectively. Total soil loss was measured on 36 individual bounded plots measuring 1.2 m × 20 m using Gerlarch troughs on each day with rain from July 2000 to June 2001. The plots were located on six different geopedologic units, nine on mountain ridges and the rest on the mountain foothills. The slope gradient on the terrain ranged from 30% to 70%. The plots were put under maize cultivation as the main crop. Soil loss through rill erosion was estimated by volumetric measurements of rills on each soil erosion plot. The soil loss due to interrill erosion was obtained by subtracting soil loss through rill erosion from the total soil loss measured in the Gerlarch troughs. The results indicate that soil loss due to both interrill and rill erosion was very high with mean soil loss of 69 and 163 t/ha/year, respectively. Rill erosion accounted for about 58% of the total soil loss while interrill erosion contributed to the remaining 42%. Both interrill and rill erosion were higher in the mountain ridges with mean soil loss of 88 t/ha/year and 210 t/ha/year compared to 49 and 116 t/ha/year in the mountain foothills, respectively. Rill erosion was significantly higher (P ≤ 0.001) in all geopedologic units with slope gradient above 40% (mean soil loss ranged between 91 and 258 t/ha/year) compared to interrill erosion with mean soil loss varying from 41 to 115 t/ha/year. In geopedologic units with slope gradient above 60% both interrill and rill erosion were highly active while in geopedologic units with slope gradient below 40% the two processes were less active. The results demonstrate that rill erosion is more important than interrill erosion in the study area particularly where the slope gradient exceeds 40%. The results further show that the major part of the studied area has moderate interrill erosion (10–50 t/ha/year) and severe to very severe (N 100 t/ha/year) rill erosion. This study clarifies the magnitude of interrill and rill erosion which is important for designing soil conservation on agricultural fields.
Short and medium term assessment of tillage erosion in the Uluguru Mountains, Tanzania
(Elsevier, 2004-05-26) Kimaro, D. N.; Deckers, J. A.; Poesen, J.; Kilasara, M.; Msanya, B. M.
Soil translocation due to shallow tillage by manual hoeing appears to be one of the most important erosion processes in the Uluguru Mountains. In order to quantify erosion rates caused by manual hoeing in the area a tillage experiment was set up and an on-farm survey was conducted during the dry season of the years 2000 and 2001, respectively. Soil flux rates on eight slope gradients (31–67%) were monitored by measuring the tillage step characteristics using Trapezoid-step method and by collecting soil material lost in Gerlarch troughs. Soil flux rates due to medium-term (30 years) manual hoeing along contour bands with grass barrier were also monitored by measuring volumes of tillage step below and colluvium accumulation above the surface of the original slope on six slope gradients (51, 52, 55, 56, 58 and 60%). Average tillage depth for superficial tillage was 5.2 cm. The results obtained by the Trapezoid-step method ranged from 43 to 70 kg m À1 per tillage pass with a mean tillage transport coefficient (k) of 107.5 kg m À1 on the tested slopes. Mean soil flux rates obtained by Gerlarch trough method were slightly lower than those obtained by Trapezoid-step method with values ranging from 14 to 77 kg m À1 per tillage pass and a tillage transport coefficient (k) of 83.9 kg m À1 per tillage pass. The rates measured by both methods showed an increasing soil flux with slope gradient. Results on soil flux rates due to the medium-term tillage operation (step measurements) showed a negative trend with increasing slope gradient. Soil flux ranged from 148 to 42 kg m À1 per year for slopes between 51 and 60%. Soil flux due to colluviation behind grass barriers showed a similar trend with values higher than those obtained by step measurements. The soil flux rates behind grass barriers ranged from 153 kg m À1 per year on slope of 51% to 67 kg m À1 per year on a 60% slope in approximately 30 years of cultivation. A reasonable correspondence between calculated displaced soil (area under original slope) and the accumulated colluvium (area above the original slope) was obtained indicating significant contribution of tillage erosion. Contribution due to water erosion processes ranged from 7 kg m À1 per year on slopes of 51% to 25 kg m À1 per year on a slope of 60%. The study demonstrated that tillage translocation rates due to manual superficial tillage are very high and could partly be held responsible for the development of shallow soils observed on steep slopes and the accumulation of colluvium behind grass barriers along contour bands in the Uluguru Mountains.