Soil erosion is among the critical environmental constraint for crop production in southern Mali. Contour ridge tillage (CRT), a water conservation technique had been locally applied since 1990. The objective of this study was to determine the effects of CRT compared with farmer conventional agriculture practice (NoCRT) on runoff, soil loss, nutrient loss, moisture conservation and cereals yields under rainfed conditions in two Southern Mali sites, in 2016 and 2017 in farmer fields. Measurements were performed on erosion plots composed of CRT and NoCRT plots from which water samples were collected to determine sedimentation levels, concentration and nutrients losses using pairwise comparison. Average runoff coefficient in NoCRT plots was 35.62% compared to 19.25% for the CRT plots explaining a runoff reduction of 46%. Mean soil losses of 12,095 t·ha -1 and 4970 t·ha -1 were respectively measured in NoCRT and CRT plots. Losses in calcium, magnesium and potassium nutrients in the NoCRT plots were 80%, 66%, 75% higher compared to CRT ones, respectively. Sorghum grain yield was at least two folds higher in CRT plots compared to the NoCRT plots. Maize average grain yield was 87% higher in CRT plots than in the NoCRT. For sustained soil productivity, CRT is advocated as a better soil and water management technique than the NoCRT one.
Mali’s economy is essentially based on the primary sector where agriculture accounts for more than 35 percent of gross domestic product (GDP) and 80 percent of livelihoods [
Runoff is harmful to agricultural production. In one hand, it reduces water availability for crops and parkland trees, and on the other hand, it can lead to soil degradation by erosion of the upper soil layer [
Losses were estimated in cultivated soils of southern Mali [
In southern Mali, erosion was emphasized by inadequate soil and crop management which could even jeopardize national food security goals, since impacting negatively directly on crop productivity [
In Mali, contour ridge tillage (CRT), which is also referred to as “Aménagement en courbes de niveau” [
In the semi-arid zones of southern Mali where low inputs and low yields agriculture systems dominate, the development of soil and water conservation techniques such as CRT, is essential to ensure sustainable farming systems [
In the Soudanian area of southern Mali, although the effects of CRT on crop yield and infiltration were widely studied [
The experiment was conducted in two sites of southern Mali belonging to Soudanian Agro-ecological zone. The first one is located at a technology park in Flola village, district of Bougouni. The second site is at a technology park in Mpessoba village, district of Koutiala. The technology park of Flola is at 11˚42'N latitude, 7˚64'W longitude and 350 m altitude and the technology park of Mpessoba is at 12˚67'N latitude, 5˚71'W longitude and 346 m altitude. The two experimental sites are represented in
The average annual rainfall over the last 46 years (1971-2017), was 857 mm in Koutiala (40 km from Mpessoba village toward north) and 1095 mm for Bougouni (15 km from Flola village toward south) and has an irregular spatio-temporal distribution. Over 37 years (1971-2008), low temperatures occurred between December and February with monthly averages of 16.8˚C and 16˚C, and high temperatures between April and May, with monthly averages of 38˚C and 37˚C, respectively for Koutiala and Bougouni (
Rainfall follows a uni-modal pattern with maximum events occurring in July and August. Enough rain for crop planting without prolonged dry spells that could hurt seedlings after sowing occurs in May and ends of rainy season in October [
Dominant soil types in the study areas are classified as leached tropical ferruginous soils with spots and concretions [
The main farming system in Bougouni and Koutiala is a crop-livestock based rotation system of Cotton (Gossypium hirsutum, L.), Maize (Zea mais), and Sorghum (Sorghum bicolor).
Tested varieties were Sotubaka (improved maize variety) and Pablo (sorghum hybrid).
Rotation head is cotton followed by maize and sorghum allowing cereals to benefit from the cotton residual fertilizer effects. Annual staple crops, sorghum and maize, were planted in the middle and bottom of the catena. Cotton was also planted in the bottom while grazing area was in the top of the catena. Smallholder farmers used extensively animal manure collected in farmyard or sometime compost to improve crop productivity for food (grain) and straw for feed. The rainy season covers May to November for the main cropping period. Income from cash crops and livestock sales was partially used to cover farm inputs and other household needs [
For both sites, maize and sorghum were planted from 15-25 June in 2016 and from 18-30 June in 2017 respectively in CRT and NoCRT plots. Planting density was 0.40 m within hills on the row and 0.75 m between rows for maize. For sorghum, density was 0.5 m within hills on the row and 0.75 m between rows. Elementary plot sizes were 34 m length and 7.5 m width for 255 m2. One row at each border of the plot was discarded to determine the net plot sizes leading to 34 m length and 6 m width i.e. 204 m2. Seedlings were thinned to two plants per hill 15 days after emergence for targeted populations of 66,666 (Maize) and 53,333 (Sorghum) plants·ha−1 which are the density advised by extension services for the area. Thinning was done two weeks after emergence. Base fertilizer was uniformly applied to each treatment (CRT and NoCRT plots) at the rate of 100 kg·ha−1 of NPK (15–15–15) at planting time for both crops. Thirty days after germination, 75 kg·ha−1 of urea for Maize and 50 kg·ha−1 of urea (46% of nitrogen) for sorghum were applied followed by hand hoeing. A second dose of 75 kg·ha−1 of urea was applied 45 days after germination on maize. Fertilizer was buried 5 cm below and 5 cm away from plants on the row banks.
In CRT and NoCRT plots, harvest was done from 2-30 October and from 7-27 October in 2016 and 2017, respectively for maize and sorghum, followed by 20 days of sun drying.
The erosion study was conducted in 2016 and 2017 in the technology park of Flola and Mpessoba, in Mali. Experiment plot was divided in two parts: the first one was under contour ridge tillage (CRT) and the second one with farmer’s practice (NoCRT) as a control. There were 4 experimental plots with 0.75 m width and 34 m length surrounded by an oblique galvanized iron sheets of 55 cm height inserted to a depth of 15 cm to prevent runoff to seep in or out from the plot, corresponding to four replicates for both in CRT and NoCRT plots.
In the paired CRT and NoCRT erosion plots, the surface runoff from each experimental plot was 1/10 diverted by a channel into a collection barrel of 200 liters capacity and an additional barrel for collecting another 1/10 of total runoff water. These barrels were placed in a pit of 1.5 m × 0.7 m × 1.3 m, covered by a metal sheet of 1.8 m × 1.0 m.
Runoff coefficient (Rco) was used to compare the influence of CRT and NoCRT and expressed as follow:
Rco = Rw ( mm ) Ra ( mm ) (1)
where Rw = Runoff water; Ra = Rainfall received;
Rw = Vw ( m 3 ) S ( m 2 ) (2)
where Vw = Volume of water generated; S = Water measurement area.
To measure the average sediment concentration in the runoff water and estimate soil loss in each of the four replicates of the CRT and NoCRT plots. Three water samples of one-liter each were taken in each collecting barrel to maximize accuracy of the operation. These samples were taken after runoff water has been stirred vigorously to better capture sediments in the barrel. Sediments and nutrients concentrations were measured by oven drying at 40˚C for 7 days to constant weight and chemical analysis (organic carbon, N, P, K) whereas concentrations were determined in the Soil Plant and Water Laboratory of Institut d’Economie Rurale (IER). Runoff, soil loss by erosion, and nutrients contents were compared between CRT and NoCRT plots using pairwise t test at 0.05 significant levels. Two rain gauges were installed in each research site. Time-domain refractometry probes were installed, 100 cm deep below soil surface at the middle of CRT and NoCRT plots to measure soil moisture during the whole cropping season. Before rain onset, dry soil moisture content was recorded immediately after trials installation. In order to characterize soil moisture during the cropping season, CRT and NoCRT plots were represented by soil moisture daily measured, at the months of July (beginning of the rainy season), August (at the middle of the rainy season) and September (at the end of the rainy season) in 2016 and 2017.
In each site (CRT and NoCRT) plots were treated the same way in sowing dates, crop species and other cropping operations, except ridging mode.
Soil Water Storage calculation was performed to quantify the water stored in each soil profile,
In each profile it was calculated as the sum of the soil water per depth interval through the profile.
On each site, 40 samples from horizon 0 - 20 cm were randomly collected in May 2016, on 1ha, using an Edelman Combination Auger (4 cm core) of 1.2 m length, mixed to form composite soil samples. Samples were air dried by spreading them on a plastic sheet at room temperature. Composite samples were made from the ones taken in an asterisk shape pattern in each site. Samples were analyzed for both physical and chemical properties. Particle size (soil texture) analysis was performed by the hydrometer method [
Crop yields were measured in central rows while discarding the two border rows on each side of the plot. At harvest, total panicles and cobs, grain and stems dry weights were recorded in the central rows and data extrapolated from the subplot size to hectare. Paired CRT and NoCRT plots data were analyzed as a simple trial in a four-block experimental design to determine the global significance of runoff volume, soil erosion, nutrient losses and crops yields using STATBOX 7.4.4. Newman-Keuls test was used to separate means for significant differences between treatments. Treatments effects were considered significant at P < 0.05.
Total cropping season rainfalls were 730 and 954 mm in 2016 and 635 and 945 mm in 2017 for Koutiala and Bougouni, respectively. Maximum rainfalls of 264 and 391 mm were received in July in 2017, while 260 and 269 mm were observed in August 2016, for Koutiala and Bougouni, respectively. July 2017 accounted for 42% and 41% of the total amount of rainfall in Koutiala and Bougouni, respectively. In August 2016, rain amount was +79 and +65% higher than those of 2017 for the same month, for Koutiala and Bougouni respectively. These increases represented 36% for Koutiala and 28% for Bougouni. In May, at the beginning of the rainy season, on both sites, rainfall was less than 85 mm (
The mean annual minimum temperature was 16˚C and 15.5˚C and maximum temperature was 38.8˚C and 39.5˚C, for Koutiala and Bougouni, respectively.
Lowest mean annual potential evapotranspiration (PET) of 3.65 and 3.20 was recorded from June to September for Koutiala and Bougouni, respectively, while the other months of the year showed values varying from 5 to 6 mm.
Monthly rainfall distribution, runoff and soil loss in 2016 and 2017 is given in
For the two years experiments, a mean of 12,095 t·ha−1 of soil was lost from the NoCRT plots, compared to a mean of 4970 t·ha−1 from the CRT plots. It appeared clearly that the use of CRT contributed to a significant decline in soil loss from cultivated lands. Thus, erosion was 2.4 times greater in NoCRT plots than those of CRT ones and the difference was statistically significant (p = 0.02). Erosion varied greatly among sites (p = 0.04) and was 97% greater in Bougouni, where average rainfall on the two years was also 39% higher than in Koutiala. Erosion varied among years (p = 0.04) with the highest values in 2016 (+92%) which was also the rainiest year.
Sites | Koutiala (Mpessoba) | Bougouni (Flola) |
---|---|---|
pH (water) | 5.7 | 6.3 |
pH (KCl) | 4.9 | 5.5 |
OC (g·kg−1) | 4.1 | 5 |
Azote total (g·kg−1) | 0.33 | 0.42 |
P Available (mg·kg−1) | 5.71 | 6.12 |
CEC cmol·kg−1 | 3.69 | 5.18 |
Ca cmol·kg−1 | 2.63 | 3.85 |
Mg cmol·kg−1 | 0.81 | 0.98 |
K cmol·kg−1 | 0.22 | 0.31 |
Na cmol·kg−1 | 0.03 | 0.03 |
Sand% > 0.05 mm | 76 | 70 |
Silt% 0.05 - 0.002 mm | 19 | 23 |
Clay% < 0.002 mm | 5 | 8 |
Runoff coefficient (%) | Soil loss kg·ha−1·year−1 | ||
---|---|---|---|
Technique | CRT | 19.25 b | 4970 b |
NoCRT | 35.62 a | 12,095 a | |
P value | 0.004 | 0.02 | |
Sites | Mpessoba | 23.75 b | 5733 b |
Flola | 31.12 a | 11,332 a | |
P value | 0.03 | 0.04 | |
Year | 2016 | 30.87 a | 11,228 a |
2017 | 24.00 b | 5837 b | |
P value | 0.05 | 0.04 |
Values with different letters are statistically different at P = 0.05. Column means represent runoff coefficient and soil loss; row means are for techniques, sites and years.
Except for phosphorous (p = 0.12), nutrient loss was significantly higher in 2016 than 2017 (P values varying from 0.003 to 0.02). Carbon, nitrogen, phosphorous, calcium, magnesium and potassium losses in total nutrients eroded from the fields were 74%, 6.6%, 5.0%, 6.6%, 3.3% and 5.0% in 2016 compared to 66%, 8.0%, 7%, 8.0%, 5.0% and 5.0% in 2017, respectively.
At the beginning of the rainy season (June), in the 10 cm of soil surface layer, differences of soil water content between CRT plots in 2016 and 2017 and NoCRT plots were +33% and +37% respectively for Flola and Mpessoba. Also, in all cases, a global moisture decrease was observed in the 10 - 20 cm depth. Soils moisture mean differences of 21% and 27% were observed at 100 cm depth, respectively at Mpessoba and Flola. In the upper 60 cm soil layer, soil moisture was not greater than 20% in both sites.
August, the middle of the growing season, had frequent rainfalls with deep drainage, where mean soil moisture content along the profile was about 30% in Flola while this value was rather observed in the 60 - 100 cm soil layers in Mpessoba. Here also, soil water content was always higher in CRT plots compared to the NoCRT plots. The difference between CRT and NoCRT was visible along the profile where, at the deepest 100 cm soil layer, mean soil moisture was +40 and +31% greater in the CRT plots (32.68 and 23.27) compared to the NoCRT plots (32.57 and 24.80), respectively for Flola and Koutiala.
At the end of the growing season (October), the drainage was deep with less water, but at 100 cm, mean soil moisture in CRT plots was 31% in both sites. Soil moisture remained always greater in CRT plots than the NoCRT ones. Also, mean differences of 24% and 33% were observed between CRT and NoCRT plots at 100 cm depth, respectively in Flola and Mpessoba.
C | N | P | Ca | Mg | K | ||
---|---|---|---|---|---|---|---|
Technique | CRT | 45b | 5b | 4b | 5b | 3b | 4b |
NoCRT | 106a | 11a | 8a | 9a | 5a | 7a | |
P value | 0.04 | 0.006 | 0.02 | 0.01 | 0.01 | 0.02 | |
Sites | Mpessoba | 75 | 7 | 4 | 8 | 4 | 5 |
Flola | 76 | 8 | 6 | 7 | 4 | 6 | |
P value | 0.97 | 0.98 | 0.06 | 0.6 | 0.62 | 0.76 | |
Year | 2016 | 112a | 10a | 7 | 10a | 5a | 7a |
2017 | 39b | 5b | 4 | 5b | 3b | 3b | |
P value | 0.02 | 0.01 | 0.12 | 0.008 | 0.003 | 0.01 |
Values with different letters are statistically different at P = 0.05.
Water storage in CRT plots reached a maximum of 218 mm end of July 2017 and 200 mm end of August 2016 in Mpessoba (
Average maize grain yields in Mpessoba were 2296 kg·ha−1 and 1729 kg·ha−1 in 2016 and 2017, respectively (
Sites | Year | Technique | Maize Grain | Maize Straw | Sorghum Grain | Sorghum Straw |
---|---|---|---|---|---|---|
Mpessoba | 2016 | CRT | 3017 a | 6567 a | 2350 a | 12,150 a |
NoCRT | 1575 b | 3800 b | 1068 b | 8163 b | ||
Mean | 2296 | 5184 | 1709 | 10,156 | ||
Probability | 0.007 | 0.002 | 0.008 | 0.01 | ||
MSD | 428 | 577 | 359 | 1432 | ||
CV (%) | 17.8 | 9.9 | 17.8 | 14.1 | ||
2017 | CRT | 2233 a | 4167 a | 3267 a | 19,768 a | |
NoCRT | 1225 b | 2500 b | 1358 b | 7563 b | ||
Mena | 1729 | 3334 | 2312 | 13,665 | ||
Probability | 0.0002 | 0.003 | 0.004 | 0.005 | ||
MSD | 139 | 414 | 483 | 3476 | ||
CV (%) | 8.5 | 12.7 | 19.8 | 27.5 | ||
Flola | 2016 | CRT | 3823 a | 8384 a | 2836 a | 11,329 a |
NoCRT | 1641 b | 4961 b | 922 b | 4267 b | ||
Mena | 2732 | 6673 | 1879 | 7798 | ||
Probability | <0.0001 | <0.0001 | <0.0001 | <0.0001 | ||
MSD | 368 | 670 | 480 | 1569 | ||
CV (%) | 15.3 | 11.7 | 27.8 | 22.9 | ||
2017 | CRT | 2950 a | 6500 a | 1825 a | 9100 a | |
NoCRT | 2000 b | 3800 b | 842 b | 4200 b | ||
Mean | 2475 | 5150 | 1334 | 6650 | ||
Probability | 0.01 | 0.01 | 0.005 | 0.01 | ||
MSD | 206 | 562 | 144 | 917 | ||
CV (%) | 8.5 | 12.4 | 9.1 | 16.3 |
MSD = mean standard deviation; CV = coefficient of variation; CV ( % ) = MSD M × 100 .
The use of CRT significantly improved maize grain and straw yields in both sites. Maize grain yield in Mpessoba was 92% and 82% higher in the CRT compared to the NoCRT plots, respectively for 2016 and 2017. In Flola, maize average grain yield in CRT plots was more than two folds compared to that of NoCRT plots in 2016 and 48% in 2017 (
Maize average straw yields in CRT plots were 73%, 67%, 67%, 71% higher in 2016 and 2017 than the ones of NoCRT plots, respectively for Mpessoba and Flola sites.
Sorghum average grain yield was at least two folds higher in CRT plots than in the NoCRT plots for both years in both sites. The same trend was observed for sorghum straw, except in Mpessoba, in 2016, where average CRT plot was only 49% higher than the NoCRT (
Rainfall analysis revealed not only inter-annual rainfall variabilities (635 - 1437 mm) but also intra-annual rainfall distributions. This situation is likely to negatively impact crop production as reported by [
Soils were predominately loamy and sandy (
For all rainfall events measured, runoff was always greater in the NoCRT plots than the CRT ones. The greater rainwater loss was probably due to high runoff and low infiltration rates during intensive rainfall peaks (
Mean runoff coefficient was significantly higher in the NoCRT plots cultivated up and down the slope which was farmer’s practice compared to the CRT plots where ridges followed the contour line. This practice of up and down ridging does not create any kind of resistance to runoff flow, facilitating faster flow of excess water leading to high runoff amounts. This water loss is detrimental to agricultural production because, it reduces availability for crops and can result in severe moisture shortage during dry spells occurrences which are the cropping season characteristic in the area. These results agreed with other findings [
Mean runoff coefficient was higher in 2016 than 2017 for both sites. This situation can be attributed to rainfall difference between year and rain erosivity, in agreement with those reported by [
Mean soil loss was two folds greater in NoCRT plots than CRT ones where the difference was statistically significant (p = 0.02). Similar observations were reported [
In NoCRT plots, a large amount of organic carbon, nitrogen, phosphorous and exchangeable bases, vital plant nutrients, were annually lost through eroded sediments, compared to the CRT ones. This situation can be explained by the serial disposal of narrowly spaced ridges (0.6 - 0.70 m) and furrow between ridges, which allow rainwater to be retained where it falls, resulting in better infiltration and remarkable slowing down or stopping runoff, erosion and nutrients losses. Higher nutrient loss in farmer’s practice (NoCRT) and reduced nutrient loss in CRT plots in the fields on gentle slope (1% - 3%) is in line with earlier similar studies on CRT [
It was observed that higher quantities of carbon, nitrogen, calcium, potassium, phosphorus and magnesium were lost in eroded soil in 2016 compared to 2017. This could be attributed to higher and severe rainfall events in 2016, where, for instance, in Flola, 31 July and 07 August rains produced 60 mm and 70 mm corresponding to I30 of 67- and 75-mm·h−1, respectively. For Mpessoba, in 2016, 21 July and 07 August rains produced 76 and 65 mm corresponding to I30 of 80 and 72 mm·h−1, respectively. Additionally, in Flola, 32 rain events producing runoff were recorded in 2016 against 19 in 2017. For Mpessoba, the number of rain events was almost the same (21 in 2016 and 22 in 2017) but rain intensity and quantity were greater in 2016.
In Mpessoba and Flola, soil moisture was always higher in the CRT plots compared to the NoCRT ones. CRT technology is applied to reduce runoff, which therefore increases infiltration and soil moisture as demonstrated by the work of [
Water storage was always higher in CRT plots than the NoCRT ones in both sites. These observations were supported by [
Significantly lower maize and sorghum grain and straw yields were obtained under NoCRT plots, a traditional cropping system [
Higher grain and straw biomass sorghum yields compared to the national average yield of 1000 kg·ha−1 of grains, could be attributed to growth and genetic characteristics of hybrid crop. In fact, improved varieties have a greater ability to convert assimilates to grain and biomass as reported by [
The average maize grain yield of 2600 kg·ha−1 for the same variety reported by [
This study, besides what has been mainly reported in Mali, combines determination of runoff, erosion, nutrient losses and crop yields at the same time. These data on soil and yield are strong decision-making tools for agricultural policies under rainfall conditions in Sub-Saharan Africa. Thus, farmers can increase crops grain yield by 50% and up to 87% for maize grain. For draught and fattening animals, there are gains of 116% and 70% for sorghum and maize straw yields, respectively. All these advantages were obtained when CRT was applied. Consequently, this study pleads for training of farmers, NGOs and extension agents on the contour ridge tillage technique for wide up scaling, targeting sustainable crop production through more water and nutrient conservation to mitigate recurrent drought.
This research results updated erosion and runoff data performed since the 1990s in Mali. The study highlighted threats related to nutrient and crop yield losses. Scientists can use these current data to advocate policy and lawmakers in reorienting strategies and efforts for food security. Current findings clearly showed that NoCRT, a farmer traditional practice, does not only increase water, soil and nutrient losses from farm fields, but also results in low maize and sorghum yields subsequent to its higher erosion, runoff and soil nutrients depletion. CRT, a soil and water conservation technology, provides lower water and nutrients losses, thus increases crops yield. Therefore, it became very important to undertake awareness and proactive CRT training of stakeholders, mainly farmers, NGOs and extension agents of Malian Agricultural Ministry to change its traditional practice in order to reduce farm runoff, erosion, nutrient and crop yield losses from agricultural lands. The CRT technology could be a good option in similar ecologies in other West African countries. This could be a motivation source for CRT adoption for food security with a great advantage for draught and fattening animals in Mali and beyond; allowing a better integration between crop and livestock production, a key strategy to sustain agricultural production in a climatically volatile environment.
This work was funded by Africa RISING Project in West Africa and the Water Land and Ecosystem (WLE) CRP (CGIAR Research Program) Programs based in ICRISAT-Mali which coordinated all the activities. The funding source is USAID through IITA. Agreement No. AID-BFS-G-11-00002 to the International Institute of Tropical Agriculture (IITA). IITA has entered into sub-award Agreement with ICRISAT for participation and implementation of research activities under the project’s approved work plan. Additional funding from the Institute of Rural Economy of Mali is also gratefully acknowledged.
Dr. Niaba TEME, senior scientist of the Institute of Rural Economy is acknowledged for his support for corrections on the earlier version of this article.
We are grateful to Cheick oumar Dembele and Oumar Samake M.Sc. Soil Sciences, Institute of Rural Economy (IER) for helping data collection.
Dicko Mahamadou Moctar. M.Sc. Climate Change and Human Security site coordinator at the technology park of Flola and Karamoko Traore. M.Phl. Extension; site coordinator at the technology park of Mpessoba for their support on data collection.
AMEDD and FENABE NGOs for facilitating contact with collaborative farmers.
The authors declare no conflicts of interest regarding the publication of this paper.
Traore, K. and Birhanu, B.Z. (2019) Soil Erosion Control and Moisture Conservation Using Contour Ridge Tillage in Bougouni and Koutiala, Southern Mali. Journal of Environmental Protection, 10, 1333-1360. https://doi.org/10.4236/jep.2019.1010079