Effectiveness of Selected Soil Conservation Practices on Soil Erosion Control and Crop Yields in the Usambara Mountains, Tanzania

Indigenous soil conservation measures such as miraba have been widely used in Usambara Mountains for controlling soil erosion but with little success. On-farm runoff experiments were set from 2011–2014 on Acrisols in Majulai and Migambo villages with contrasting agro-ecological conditions in the Usambara Mountains, Tanzania. The aim was to investigate the effectiveness of miraba and miraba with various mulching materials in reducing runoff, soil and nutrient losses and improving productivity of maize (Zea mays) and beans (Phaseolus vulgaris). Results show that mean annual runoff coefficients (mm mm-1) ranged from 0.72 for cropland with no soil conservation measure (control) to 0.15 for cropland with miraba and Tithonia (Tithonia diversifolia) mulching in Majulai village and respectively from 0.68 to 0.13 in Migambo village. Soil loss was significantly (P = .05) higher under control than under miraba with either Tughutu (Vernonia myriantha) or Tithonia mulching e. g. 184 vs. 20 in Majulai and 124 vs. 8 Mg ha-1 year-1 in Migambo village in 2012. The Pfactors were significantly (P = .05) higher under miraba sole than under miraba with mulching in Majulai village (0.18 vs. 0.11) and in Migambo village (0.10 vs. 0.05).The annual nutrient losses in kg ha-1yr-1 were significantly (P = .05) higher under control than under miraba with mulching 367 vs. 37 total N, 0.8 vs. 0.1 P and 14 vs. 4 K for Majulai village; 474 vs. 26 total N, 0.7 vs. 0.1 P and 20 vs. 1.2 K for Migambo village in 2012. Maize and bean yields were significantly (P = .05) higher under miraba with Tughutu mulching than under control (e.g. 2.0 vs. 0.7 Mg ha-1 for maize in Majulai in 2012). Thus miraba with Tughutu mulching is more effective in improving crop yields than miraba with Tithonia and miraba sole.status: publishe

Root Properties of Plants used for Soil Erosion Control in the Usambara Mountains, Tanzania

Plant roots may have a strong erosion-reducing effect. However, little is known about root characteristics of tropical plants used for erosion control. A study was thus conducted in the Western Usambara Mountains, Tanzania to investigate rooting characteristics of Guatemala grass (Tripsacum andersonii), Napier grass (Pennisetum purpureum) and Tithonia shrub (Tithonia diversifolia), also referred to as wild sunflower, and to evaluate their potential for erosion control. For each plant species, mean root diameter (D), root density (RD), root length density (RLD) and root area ratio (RAR) were assessed for six plants in each species and relative soil detachment rate (RSD) predicted. Mean RD values in the 0 - 0.4 m soil depth for Majulai village and Migambo village respectively were 50.9 and 58.6 kg/m3 for Guatemala grass, 30.4 and 31.3 kg/m3 for Napier grass and 22.1 and 23.0 kg/m3 for Tithonia shrub. RLD values were 35.9 and 45.0 km/m3 for Guatemala grass, 31.3 and 150.0 km/m3 for Napier grass and 10.5 and 6.4 km/m3 for Tithonia shrub. Predicted RSD values were 4.43*10-12 and 1.20*10-14 for Guatemala grass, 6.10*10-5 and 2.74*10-4 for Napier grass and 4.43*10-3 and 2.24*10-4 for Tithonia shrub in the 0 - 0.4 m soil depth. The results indicate that Guatemala grass has a higher potential to reduce soil erosion rates by concentrated flow as compared to Napier grass or Tithonia shrub in the 0 - 0.4 m soil depth. These findings have implications on the selection and use of appropriate plants for soil erosion control.status: publishe

The Influence of Selected Soil Conservation Practices on Soil Properties and Crop Yieldsin the Usambara Mountains, Tanzania

The Usambara Mountains in Tanzania are severely affected by soil erosion which has led to deterioration of soil properties and reduced crop productivity. Indigenous soil erosion control measures such as miraba which are widely practised in the area have yielded little success. Field plot experiments were laid down in Majulai and Migambo villages from 2011 – 2014 on typical soils of the area (Acrisols). The aim was to single out soil properties developed under the studied soil conservation practices and their impact on crop productivity with reference to maize (Zea mays) and beans (Phaseolus vulgaris). Results showed that total N, OC, available P, Ca2+, Mg2+, K+ and Ph were powerful (P = .05) attributes that discriminated conservation measures. Magnitudes of the discriminating attributes followed the trend: miraba with Tughutu (Vernonia myriantha) mulching >miraba with Tithonia (Tithonia diversifolia) mulching > miraba sole > cropl and with no ‘Soil and Water Conservation’ (SWC) measures (control). Contents ofmicro-nutrients did not differ significantly with SWC measures except for Zn which was significantly (P = .05) lowin the control. Bulk density and available moisture content (AMC) were also strong discriminators of conservation measures. Maize and bean grain yields differed significantly (P = .05)with the trend: miraba with Tughutu > miraba with Tithonia > miraba sole > control in both villages. Crop yields under miraba were a function of AMC and pH (R2= 0.71); AMC, available P, Ca2+ and K+ (R2= 0.89) under miraba with Tithonia mulching; AMC, available P, Ca2+ and K+ (R2= 0.90) under miraba with Tughutu mulching. These findings imply that miraba with Tughutu mulching had greater potential in improving soil properties and crop yields than miraba with Tithonia mulching and miraba sole.status: publishe

Soil Fertility and Crop Yield Variability under Major Soil and Water Conservation Technologies in the Usambara Mountains, Tanzania

Indigenous soil and water conservation (SWC) technologies such as miraba (rectangular grass strip bounds that do not necessarily follow contours) and micro ridges have been used widely in the Usambara Mountains, Tanzania. However, their strengths and limitations to crop productivity have not been investigated. This study aimed to determine soil fertility and crop yield variability under miraba, micro ridges and bench terraces as a way to explore and compare these SWC technologies. A survey was carried out in Majulai watershed (with Acrisols as dominant soils) which is highly affected by soil degradation due to water erosion. Composite soil samples were collected from 0 - 30 cm depth in upper, middle and lower segments within bench terraces, micro ridges and miraba at the upper, mid and lower slopes of the watershed. Contents of most soil nutrients (e.g. available P, K+, Ca2+ and Mg2+) and maize grain yields varied significantly (P=.05) between SWC technologies, with the trend: bench terraces > micro ridges >miraba>control (fields with no SWC measures). Similarly under all SWC technologies soil fertility and maize grain yields varied significantly (P=.05) with slope position, showing the trend: lower slopes > mid slopes > upper slopes. Moreover, soil fertility and maize grain yields varied significantly (P=.05) between segments of the studied SWC technologies except for bench terraces. The trends for both soil fertility and maize grain yields were as follows: lower segments > middle segments > upper segments under micro ridges; lower segments > upper segments > middle segments under miraba. These observations call for management strategies and technological adjustments that would reduce pattern and magnitude of spatial variations of soil nutrients and crop yields under miraba and micro ridges for improved crop production in the Usambara Mountains.status: publishe