Traditional yam-based cropping systems (shifting cultivation, slash-and-burn, and short fallow) often result in deforestation and soil nutrient depletion. The objective of this study was to determine the impact of yam-based systems with herbaceous legumes on dry matter (DM) production (tubers, shoots), nutrients removed and recycled, and the soil fertility changes. We compared smallholders’ traditional systems (1-year fallow of
One of the most serious problems of farming system is the excessive reductions of agricultural productivity resulting from major degradation of soil fertility. In 1990 Edouard Saouma wrote that the most serious problem of African countries in the future can be that of land degradation [
Current yam-based cropping systems, which involve shifting cultivation, slash-and-burn, or short fallow, often result in deforestation and soil nutrient depletion [
Yam (
Yam cultivation in West Africa is now confronted with the scarcity of fertile soil available for clearing [
The decline in yam yields under continuous cultivation has led to the largely accepted conclusion that yam requires a high level of natural soil fertility (organic matter and nutrient) [
Studies on improved fallow practices are generally grain-oriented (cereals, such as maize), whereas very little has been done on root and tuber crops, especially yam. Comparative studies are lacking that assess the effects of yam-based technologies with herbaceous legumes intercrops and short fallows on yam production and soil properties in the savannah transition agroecological zone of Benin. We compared in a perennial experiment for 4 years, with 2-year rotations, smallholder farmers’ traditional rotations maize-yam or 1-year
The study was carried out in the Guinea-Sudan transition zone of Benin (centre of Benin) in four sites: Miniffi (District of Dassa-Zoumè), Gomè (Glazoué), Akpéro, and Gbanlin (Ouessè) with latitudes 7°45′ and 8°40′ north and longitudes 2°20′ and 2°35′ east (Figure
Study area location in the savannah transitional agroecological zone of Benin.
The climate is tropical transitional Guinea-Sudan with a rainfall distribution gradient from bimodal (Southern Benin) to monomodal (Northern Benin). The average annual rainfall during the study period was 1052 mm (2002), 1386 mm (2003), 983 mm (2004), and 797 mm (2005). The rainfall regime in the study area is variable and unequal distribution (i.e., number of rainy days per month) varies from one site to another. The 2002 and 2003 cropping seasons were wet and had better rainfall distribution with an average annual precipitation of 1200 mm, whereas 2004 and 2005 were dry (890 mm) with relatively low rainfall distribution.
Most of the soils are tropical ferruginous soils [
Cropping calendar of yam-based cropping systems with herbaceous legumes and short fallow in the 2002-2003 and 2004-2005 cropping seasons.
Dec. |
Feb. | March | April | May | June | July | Aug. | Sept. | Oct. | Nov. | Dec. | |
---|---|---|---|---|---|---|---|---|---|---|---|---|
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T0 | Natural fallow of |
Slashing and biomass incorporation (ridging) | ||||||||||
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TM | Land slashing and ploughing | Maize planting, NPK application, and weeding | Weeding and urea application | Maize harvesting | Slashing and biomass incorporation (ridging) in furrow | |||||||
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TMA | Land slashing and ploughing | Maize planting, NPK application, |
Weeding and urea application | Maize harvesting | Slashing and biomass incorporation (ridging) in furrow | |||||||
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TMM | Land slashing and ploughing | Maize planting, NPK application, and weeding |
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Weeding and urea application | Maize harvesting | Slashing and biomass incorporation (ridging) in furrow | ||||||
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T0 | Seed yam planting, mounds capping with mulch material |
Weeding | Weeding | Yam harvesting | ||||||||
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TM | Seed yam planting, mounds capping with mulch material |
Weeding | Weeding | Yam harvesting | ||||||||
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TMA | Seed yam planting, mounds capping with mulch material |
Weeding | Weeding | Yam harvesting | ||||||||
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TMM | Seed yam planting, mounds capping with mulch material |
Weeding | Weeding | Yam harvesting |
T0: one-year fallow-yam rotation; TM: maize-yam rotation; TMA:
The concept of the experiment was to produce residue biomass followed by planting yam in rotation cropping systems. A previous cover crop (fallows or intercropped maize/legume) was designed to provide organic matter for the following main crop (yam) (Table
Smallholders carried out two-year rotations experiment of yam-based cropping systems repeated twice (2002–2005) on-farm with single-harvest late maturing variety of yam “Kokoro” (
With recurring drought stress exacerbated by highly variable and unpredictable rains in the study area, some farmers grow a second crop, which often fails. This corroborates the great interest of the maize/leguminous crop when no second crop is planned.
On treatments TM, TMA, and TMM, 100 kg ha−1 NPK fertilizer (14% N, 10% P, and 11.7% K) was applied to maize in April and 50 kg ha−1 urea (46% N) in June. The maize was harvested in July. The grainless
Composite soil samples were collected in each field before the beginning of the experiment along plot transects at soil depths of 0–10 cm and 10–20 cm (32 farm fields × 2 depths = 64 samples) in order to determine soil characteristics. At the end of 2005 before yam harvesting, composite soil samples were collected at the same depths in the moulds along plot transects (32 farm fields × 4 treatments × 2 depths = 256 samples).
Prior to ridging, in four 1 m2 quadrats within each plot the aboveground biomass of herbaceous legumes and fallow was collected in October 2002 and 2004. The biomass samples were dried at 60°C until constant weight and then dry weight was determined. At maturity, maize grain and stover were harvested per row on each plot and dry matter (DM) determined. DM of yam tubers and shoots was estimated on each plot in December 2003 and 2005 (Tables
Quantity of biomass (t ha−1) dry matter and nutrients contents (% and kg ha−1) applied in each plot in the 2002 cropping seasons, four village sites (Miniffi, Gomè, Gbanlin, and Akpéro), Benin.
Site/treatment | DM | N | P | K | N | P | K |
---|---|---|---|---|---|---|---|
t ha−1 | % | % | % | kg ha−1 | kg ha−1 | kg ha−1 | |
Akpéro | |||||||
T0 | 4.1 | 1.7 | 0.2 | 0.5 | 68.4 | 7.8 | 21.2 |
TM | 3.5 | 1.3 | 0.1 | 0.5 | 45.3 | 5.2 | 17.4 |
TMA | 9.6 | 1.3 | 0.1 | 0.5 | 125.9 | 14.1 | 47.6 |
TMM | 10.2 | 1.7 | 0.2 | 0.5 | 177.8 | 20.2 | 53.9 |
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Gbanlin | |||||||
T0 | 4.0 | 1.0 | 0.2 | 0.5 | 42.2 | 6.0 | 20.7 |
TM | 3.5 | 2.3 | 0.2 | 0.6 | 78.5 | 8.1 | 22.1 |
TMA | 9.1 | 1.5 | 0.1 | 0.6 | 132.3 | 9.3 | 56.6 |
TMM | 9.5 | 1.9 | 0.2 | 0.6 | 180.4 | 14.3 | 61.1 |
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Miniffi | |||||||
T0 | 4.3 | 0.9 | 0.2 | 0.6 | 41.1 | 6.7 | 27.6 |
TM | 3.7 | 1.9 | 0.1 | 0.6 | 70.7 | 4.8 | 22.1 |
TMA | 9.3 | 1.2 | 0.3 | 0.6 | 114.8 | 26.1 | 59.7 |
TMM | 9.9 | 2.4 | 0.1 | 0.6 | 239.6 | 14.9 | 63.2 |
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Gomè | |||||||
T0 | 4.0 | 0.9 | 0.1 | 0.5 | 36.4 | 5.0 | 19.6 |
TM | 3.5 | 2.5 | 0.1 | 0.6 | 86.9 | 2.6 | 22.2 |
TMA | 9.0 | 1.2 | 0.1 | 0.4 | 104.9 | 5.4 | 34.2 |
TMM | 9.8 | 1.6 | 0.1 | 0.6 | 160.1 | 6.7 | 60.1 |
Quantity of biomass (t ha−1) dry matter and nutrients contents (% and kg ha−1) applied in each plot in the 2004 cropping seasons, four village sites (Miniffi, Gomè, Gbanlin, and Akpéro), Benin.
Site/treatment | DM | N | P | K | N | P | K |
---|---|---|---|---|---|---|---|
t ha−1 | % | % | % | kg ha−1 | kg ha−1 | kg ha−1 | |
Akpéro | |||||||
T0 | 4.3 | 1.7 | 0.2 | 0.5 | 72.7 | 8.3 | 22.4 |
TM | 3.7 | 1.3 | 0.1 | 0.5 | 47.2 | 5.4 | 18.1 |
TMA | 9.3 | 1.3 | 0.1 | 0.5 | 121.5 | 13.7 | 46.0 |
TMM | 10.2 | 1.7 | 0.2 | 0.5 | 179.7 | 20.4 | 54.4 |
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Gbanlin | |||||||
T0 | 4.1 | 1.0 | 0.2 | 0.5 | 42.7 | 6.1 | 21.0 |
TM | 3.5 | 2.3 | 0.2 | 0.6 | 78.7 | 8.1 | 22.2 |
TMA | 9.0 | 1.5 | 0.1 | 0.6 | 131.0 | 9.2 | 56.1 |
TMM | 9.6 | 1.9 | 0.2 | 0.6 | 182.0 | 14.4 | 61.6 |
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Miniffi | |||||||
T0 | 4.0 | 0.9 | 0.2 | 0.6 | 38.2 | 6.2 | 25.5 |
TM | 3.4 | 1.9 | 0.1 | 0.6 | 65.0 | 4.4 | 20.3 |
TMA | 9.4 | 1.2 | 0.3 | 0.6 | 115.4 | 26.3 | 60.1 |
TMM | 10.0 | 2.4 | 0.1 | 0.6 | 240.2 | 14.9 | 63.3 |
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Gomè | |||||||
T0 | 4.0 | 0.9 | 0.1 | 0.5 | 36.3 | 5.0 | 19.5 |
TM | 3.5 | 2.5 | 0.1 | 0.6 | 86.5 | 2.6 | 22.2 |
TMA | 9.3 | 1.2 | 0.1 | 0.4 | 107.9 | 5.6 | 35.2 |
TMM | 9.6 | 1.6 | 0.1 | 0.6 | 157.3 | 6.6 | 59.1 |
The nutrients contents of the soil samples were performed in the Laboratory of Soil Sciences, Water and Environment (LSSEE) of INRAB (Benin National Research Institute). The plant nutrient content was estimated according to the biomass amount.
Soil and plant macronutrients content (N, P, and K) were analyzed. Nitrogen (N) content was analyzed using the Kjeldahl method [
Analysis of variance (ANOVA) using the general linear model (GLM) procedure [
The relevant general soil physical and chemical characteristics before are presented in Table
Initial soil characteristics at the beginning of the experiment at 0–10 and 10–20 cm layers in four village sites (Miniffi, Gomè, Gbanlin, and Akpéro) with 32 farmers, Benin.
Akpéro | Gbanlin | Miniffi | Gomè | |||||
---|---|---|---|---|---|---|---|---|
Depth (cm) | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 |
“Plinthosols” | “Plinthosols” | “Luvisols ferriques” | “Luvisols ferriques” | |||||
Clay% | 6.58 | 7.281 | 5.788 | 5.66 | 6.758 | 6.51 | 6.828 | 7.861 |
Silt% | 11.66 | 11.798 | 5.808 | 5.55 | 6.828 | 7.081 | 16.071 | 17.36 |
Sand% | 81.76 | 80.920 | 88.402 | 88.79 | 86.412 | 86.408 | 77.10 | 74.778 |
C% | 1.31 | 1.050 | 0.69 | 0.788 | 0.80 | 0.64 | 0.65 | 0.54 |
N% | 0.112 | 0.092 | 0.059 | 0.081 | 0.081 | 0.056 | 0.073 | 0.062 |
C/N | 11.70 | 11.43 | 11.70 | 9.68 | 9.83 | 11.43 | 8.90 | 8.69 |
OM% | 2.25 | 1.81 | 1.19 | 1.36 | 1.37 | 1.10 | 1.12 | 0.93 |
PH | 6.7 | 6.7 | 6.6 | 6.3 | 6.7 | 6.8 | 6.6 | 6.6 |
Bray P | 20.125 | 14.875 | 7.00 | 4.00 | 11.00 | 3.012 | 7.987 | 4.00 |
C%: soil carbon concentration; N%: soil nitrogen concentration; OM% (=1.72 × C%): soil organic matter content; C/N: index of biodegradability or ratio of soil carbon to nitrogen; Bray P (mg kg−1): soil phosphorus.
Site physical characteristics such as soil texture (sand) were relatively high (74.778%–88.79%) followed by silt (5.55%–17.36%) and clay (5.66%–7.861%) with the lowest content. The soils had a neutral reaction, with pH (H2O) ranging from 6.3 to 6.8.
The initial soil fertility status of different sites was low. Soil organic matter (SOM) contents were low in all fields, ranging from 0.93% to 2.258%, and the C : N ratio ranged from 8.69 to 11.70. Available P levels were very low and varied from 3.012 to 20.125 mg/kg-soil. Soil N concentration ranged from 0.056% to 0.112%. N, P, and SOM contents were significantly higher in 0–10 cm than in 10–20 cm depth, except at Gbanlin site for N and SOM. Gomè site showed, for both soil depths, the lowest values of carbon (C%), N%, P (mg/kg-soil), and organic matter (%), whereas Akpéro had the highest values.
In the 2002 and 2004 cropping seasons, the highest biomass dry matter (DM) amount recycled was recorded on TMM (Table
Dry matter (t ha−1) of plant parts returned to the soil significantly increased according to four cropping systems (
Cropping system | Cropping season 2002 | Cropping season 2004 |
---|---|---|
DM (t ha−1) | DM (t ha−1) | |
T0 | 4.1 |
3.9 |
TM | 3.5 |
3.2 |
TMA | 9.2 |
8.3 |
TMM | 9.7 |
8.8 |
Means with the same letter within row are not significantly different (
T0 (control 1): one-year fallow-yam rotation; TM (control 2): maize-yam rotation; TMA:
The ANOVA partial nested model shows that yam yield DM differed significantly depending on the factor Treatment (
ANOVA, partial nested model of the effect of the four treatments on logarithmic transformed values of dry matter yields of “Kokoro” yam (
Source | DF | Adj. SS | Adj. MS |
|
|
---|---|---|---|---|---|
Site | 3 | 0.4258 | 0.1419 | |
|
Farmer (Site) | 28 | 3.4833 | 0.1244 | 0.18 | 1.000 |
Replicate (Site) | 96 | 42.3111 | 3.5259 | 27 | 0.000 |
Year | 1 | 0.0002 | 0.0002 | 0.01 | 0.943 |
Treatment | 3 | 224.0376 | 74.6792 | 5344.06 | 0.000 |
Site × Treatment | 9 | 0.0291 | 0.0032 | 0.11 | 0.999 |
Treatment × Farmer (Site far) | 84 | 2.2389 | 0.0267 | 1.62 | 0.001 |
Year × Farmer (Site) | 28 | 6.933 | 0.2476 | 15.02 | 0.000 |
Year × Treatment | 3 | 0.0114 | 0.0038 | 0.2 | 0.892 |
Year × Site | 3 | 0.141 | 0.047 | 0.19 | 0.904 |
Year × Site × Treatment | 9 | 0.1685 | 0.0187 | 1.14 | 0.334 |
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Error | 756 | 12.4598 | 0.0165 | ||
Adjusted |
94.24 |
DF: degree of freedom; Adj. SS: adjusted sums of squares; Adj. MS: adjusted mean squares;
Dry matter (t ha−1) of yam tubers removed and yam shoots recycled, N, P, and K content (kg ha−1) dry matter of plant parts removed in the crop harvest, and those returned to the soil in yam-based cropping systems were significantly higher in TMA and TMM than in T0 and TM during both cropping seasons (Tables
Dry matter (t ha−1) of yam tubers removed and yam shoots recycled in the 2002-2003 and 2004-2005 cropping seasons in four villages in Benin.
2002-2003 cropping seasons | 2004-2005 cropping seasons | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
T0 | TM | TMA | TMM | LSD | T0 | TM | TMA | TMM | LSD | |
|
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DM removed | 5.09 |
3.83 |
7.20 |
7.33 |
0.51 | 4.34 |
3.02 |
8.00 |
8.02 |
0.55 |
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Yam shoots | 1.27 |
0.96 |
1.80 |
1.83 |
0.13 | 1.09 |
0.76 |
2.00 |
2.00 |
0.14 |
Means with the same letter within row are not significantly different (
DM: dry matter; LSD: least square difference at 5%.
T0 (control 1): one-year fallow-yam rotation; TM (control 2): maize-yam rotation; TMA:
Nitrogen, phosphorus, and potassium content (kg ha−1) dry matter of plant parts removed in the crop harvest and those returned to the soil in yam-based cropping systems (2002-2003 and 2004-2005 cropping seasons, four cropping system treatments, four village sites, 32 farmers, Benin).
2002-2003 cropping seasons | 2004-2005 cropping seasons | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
T0 | TM | TMA | TMM | LSD | SD | T0 | TM | TMA | TMM | LSD | SD | ||
|
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Yam tubers | N | 19.35 |
14.57 |
27.37 |
27.84 |
1.95 | 2.98 | 16.49 |
11.48 |
30.41 |
30.47 |
2.08 | 3.18 |
P | 1.99 |
1.49 |
2.81 |
2.86 |
0.20 | 0.31 | 1.69 |
1.18 |
3.12 |
3.13 |
0.21 | 0.33 | |
K | 21.39 |
16.10 |
30.25 |
30.77 |
2.16 | 3.30 | 18.23 |
12.70 |
33.61 |
33.68 |
2.30 | 3.52 | |
Maize grains | N | 0.00 |
34.88 |
34.43 |
33.38 |
2.27 | 3.47 | 0.00 |
31.52 |
27.68 |
26.71 |
2.03 | 3.11 |
P | 0.00 |
5.30 |
5.24 |
5.08 |
0.35 | 0.53 | 0.00 |
4.79 |
4.21 |
4.06 |
0.31 | 0.47 | |
K | 0.00 |
4.34 |
4.28 |
4.15 |
0.28 | 0.43 | 0.00 |
3.92 |
3.44 |
3.32 |
0.25 | 0.39 | |
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Yam shoots | N | 14.01 |
10.54 |
19.81 |
20.15 |
1.41 | 2.16 | 11.72 |
8.16 |
21.60 |
21.65 |
1.48 | 2.26 |
P | 1.91 |
1.44 |
2.70 |
2.75 |
0.19 | 0.29 | 1.30 |
0.91 |
2.40 |
2.41 |
0.16 | 0.25 | |
K | 17.57 |
13.22 |
24.85 |
25.28 |
1.77 | 2.71 | 14.65 |
10.20 |
27.01 |
27.06 |
1.85 | 2.83 | |
Fallow stover | N | 47.63 |
0.00 |
0.00 |
0.00 |
3.86 | 5.91 | 47.03 |
0.00 |
0.00 |
0.00 |
4.22 | 6.46 |
P | 5.26 |
0.00 |
0.00 |
0.00 |
1.23 | 1.89 | 5.09 |
0.00 |
0.00 |
0.00 |
1.27 | 1.94 | |
K | 19.90 |
0.00 |
0.00 |
0.00 |
2.16 | 3.30 | 19.49 |
0.00 |
0.00 |
0.00 |
1.98 | 3.03 | |
Maize stover | N | 0.00 |
31.87 |
31.43 |
30.47 |
2.45 | 3.75 | 0.00 |
33.45 |
29.35 |
28.28 |
2.60 | 3.97 |
P | 0.00 |
4.56 |
4.51 |
4.37 |
0.39 | 0.60 | 0.00 |
4.65 |
4.08 |
3.95 |
0.45 | 0.68 | |
K | 0.00 |
17.48 |
18.57 |
16.76 |
1.86 | 2.84 | 0.00 |
17.42 |
15.30 |
14.80 |
1.42 | 2.17 | |
Aeschy. stover | N | 0.00 |
0.00 |
115.93 |
0.00 |
6.63 | 10.14 | 0.00 |
0.00 |
107.70 |
0.00 |
9.34 | 14.28 |
P | 0.00 |
0.00 |
8.15 |
0.00 |
0.97 | 1.49 | 0.00 |
0.00 |
8.76 |
0.00 |
0.69 | 1.05 | |
K | 0.00 |
0.00 |
36.25 |
0.00 |
1.33 | 2.03 | 0.00 |
0.00 |
34.53 |
0.00 |
1.70 | 2.60 | |
Mucuna stover | N | 0.00 |
0.00 |
0.00 |
138.92 |
6.53 | 9.99 | 0.00 |
0.00 |
0.00 |
133.25 |
5.28 | 8.07 |
P | 0.00 |
0.00 |
0.00 |
11.40 |
1.81 | 2.77 | 0.00 |
0.00 |
0.00 |
11.11 |
1.61 | 2.46 | |
K | 0.00 |
0.00 |
0.00 |
39.73 |
1.51 | 2.31 | 0.00 |
0.00 |
0.00 |
39.68 |
1.78 | 2.72 |
Means with the same letter within row are not significantly different (
T0 (control 1): one-year fallow-yam rotation; TM (control 2): maize-yam rotation; TMA:
Therefore, total plant N, P, and K (kg ha−1) dry matter removed in the crop harvest and those returned to the soil in yam-based cropping systems were significantly higher in TMA and TMM than in T0 and TM during both cropping seasons (Table
Total plant nitrogen, phosphorus, and potassium (kg ha−1) dry matter removed in the crop harvest and those returned to the soil in yam-based cropping systems (2002-2003 and 2004-2005 cropping seasons, four cropping system treatments, four village sites, 32 farmers, Benin).
2002-2003 cropping seasons | 2004-2005 cropping seasons | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
T0 | TM | TMA | TMM | LSD | SD | T0 | TM | TMA | TMM | LSD | SD | ||
Total nutrients removal through harvest (kg ha−1) | N | 19.35 |
49.44 |
61.80 |
61.22 |
2.91 | 4.46 | 16.49 |
43.01 |
58.09 |
57.18 |
2.90 | 4.44 |
P | 1.99 |
6.80 |
8.05 |
7.93 |
0.39 | 0.60 | 1.69 |
5.97 |
7.33 |
7.19 |
0.38 | 0.57 | |
K | 21.39 |
20.44 |
34.53 |
34.93 |
2.16 | 3.30 | 18.23 |
16.61 |
37.05 |
37.00 |
2.31 | 3.54 | |
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Total nutrients recycled through plant biomass (kg ha−1) | N | 61.64 |
42.41 |
167.17 |
189.54 |
10.68 | 16.33 | 58.75 |
41.61 |
158.66 |
183.17 |
11.59 | 17.72 |
P | 7.17 |
6.00 |
15.36 |
18.52 |
2.21 | 3.37 | 6.40 |
5.56 |
15.25 |
17.47 |
2.09 | 3.20 | |
K | 37.47 |
30.71 |
79.66 |
81.77 |
3.24 | 4.95 | 34.14 |
27.62 |
76.84 |
81.54 |
3.94 | 6.03 |
Means with the same letter within row are not significantly different (
T0 (control 1): one-year fallow-yam rotation; TM (control 2): maize-yam rotation; TMA:
Afterwards soil characteristics at the end of the experiment globally showed relatively low clay, silt, and relatively high sand concentration on different sites under different treatments (T0, TM, TMA, and TMM) in comparison with initial soil characteristics at the beginning of the experiment. Soil organic matter concentration was improved at 10–20 cm depth particularly in Miniffi (1.247%, 1.176%, 1.326%, and 1.409%) on T0, TM, TMA, and TMM, respectively, and Gomè (1.010%, 0.959%, 1.046%, and 1.126%). Globally, soil N and P concentrations were improved on different sites on treatments TMA and TMM in 0–10 cm or 10–20 cm depth (Tables
(a) Soil characteristics at the end of the experiment (December 2005), 0–10 and 10–20 cm layers, on 1-year fallow of
Akpéro | Gbanlin | Miniffi | Gomè | |||||
---|---|---|---|---|---|---|---|---|
Depth (cm) | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 |
“Plinthosols” | “Plinthosols” | “Luvisols ferriques” | “Luvisols ferriques” | |||||
Clay% | 5.927 | 6.101 | 5.276 | 5.227 | 6.078 | 6.143 | 6.004 | 6.239 |
Silt% | 10.482 | 10.755 | 5.425 | 5.446 | 6.329 | 6.568 | 15.950 | 16.089 |
Sand% | 83.587 | 83.143 | 89.293 | 89.325 | 87.587 | 87.287 | 78.046 | 77.671 |
C% | 0.996 | 0.909 | 0.686 | 0.672 | 0.756 | 0.723 | 0.625 | 0.587 |
N% | 0.080 | 0.087 | 0.0575 | 0.059 | 0.061 | 0.061 | 0.0588 | 0.058 |
C/N | 12.523 | 10.911 | 12.00 | 11.389 | 12.438 | 11.928 | 10.821 | 10.211 |
OM% | 1.713 | 1.563 | 1.180 | 1.157 | 1.301 | 1.247 | 1.076 | 1.010 |
PH | 6.364 | 6.095 | 6.020 | 6.278 | 5.934 | 6.020 | 5.934 | 5.848 |
Bray P | 20.440 | 18.880 | 5.646 | 5.743 | 9.073 | 6.688 | 5.668 | 3.693 |
K | 0.385 | 0.366 | 0.407 | 0.283 | 0.329 | 0.214 | 0.203 | 0.201 |
C%: soil carbon concentration; N%: soil nitrogen concentration; OM% (=1.72 × C%): soil organic matter content; C/N: index of biodegradability or ratio of soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K cmol kg−1: soil potassium.
Akpéro | Gbanlin | Miniffi | Gomè | |||||
---|---|---|---|---|---|---|---|---|
Depth (cm) | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 |
“Plinthosols” | “Plinthosols” | “Luvisols ferriques” | “Luvisols ferriques” | |||||
Clay% | 5.363 | 5.666 | 5.020 | 5.006 | 5.913 | 5.811 | 5.780 | 5.959 |
Silt% | 10.820 | 10.951 | 5.393 | 5.573 | 6.271 | 6.358 | 16.226 | 16.348 |
Sand% | 83.816 | 83.381 | 89.581 | 89.423 | 87.815 | 87.834 | 77.997 | 77.697 |
C% | 1.015 | 0.9165 | 0.669 | 0.655 | 0.754 | 0.684 | 0.617 | 0.557 |
N% | 0.089 | 0.109 | 0.066 | 0.078 | 0.075 | 0.082 | 0.072 | 0.071 |
C/N | 11.419 | 8.575 | 10.113 | 8.520 | 10.223 | 8.355 | 8.591 | 7.786 |
OM% | 1.746 | 1.576 | 1.150 | 1.127 | 1.297 | 1.176 | 1.062 | 0.959 |
PH | 6.993 | 6.733 | 6.650 | 6.897 | 6.555 | 6.650 | 6.555 | 6.441 |
Bray P | 22.610 | 21.750 | 7.031 | 7.604 | 8.041 | 6.024 | 8.041 | 6.024 |
K | 0.582 | 0.493 | 0.466 | 0.353 | 0.376 | 0.239 | 0.271 | 0.235 |
C%: soil carbon concentration; N%: soil nitrogen concentration; OM% (=1.72 × C%): soil organic matter content; C/N: index of biodegradability or ratio of soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K cmol kg−1: soil potassium.
Akpéro | Gbanlin | Miniffi | Gomè | |||||
---|---|---|---|---|---|---|---|---|
Depth (cm) | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 |
“Plinthosols” | “Plinthosols” | “Luvisols ferriques” | “Luvisols ferriques” | |||||
Clay% | 6.509 | 6.752 | 5.455 | 5.999 | 6.245 | 5.882 | 5.567 | 5.390 |
Silt% | 10.581 | 10.811 | 5.513 | 5.608 | 6.310 | 6.396 | 15.85 | 15.866 |
Sand% | 82. 910 | 82.438 | 89.033 | 88.394 | 87.445 | 87.721 | 78.748 | 78.744 |
C% | 1.1248 | 1.0583 | 0.732 | 0.685 | 0.781 | 0.771 | 0.635 | 0.608 |
N% | 0.107 | 0.124 | 0.073 | 0.084 | 0.084 | 0.092 | 0.079 | 0.076 |
C/N | 10.707 | 8.654 | 10.115 | 8.197 | 9.300 | 8.417 | 8.082 | 8.006 |
OM% | 1.935 | 1.820 | 1.260 | 1.178 | 1.344 | 1.326 | 1.092 | 1.046 |
PH | 7.371 | 7.221 | 7.112 | 7.237 | 7.034 | 7.087 | 6.997 | 7.031 |
Bray P | 23.890 | 22.930 | 8.929 | 8.540 | 9.364 | 6.900 | 9.364 | 6.900 |
K | 0.687 | 0.604 | 0.509 | 0.436 | 0.452 | 0.297 | 0.332 | 0.298 |
C%: soil carbon concentration; N%: soil nitrogen concentration; OM% (=1.72 × C%): soil organic matter content; C/N: index of biodegradability or ratio of soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K cmol kg−1: soil potassium.
Akpéro | Gbanlin | Miniffi | Gomè | |||||
---|---|---|---|---|---|---|---|---|
Depth (cm) | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 | 0–10 | 10–20 |
“Plinthosols” | “Plinthosols” | “Luvisols ferriques” | “Luvisols ferriques” | |||||
Clay% | 6.180 | 6.539 | 5.724 | 6.045 | 6.371 | 6.191 | 5.561 | 5.440 |
Silt% | 10.556 | 10.789 | 5.519 | 5.579 | 6.330 | 6.373 | 15.714 | 15.841 |
Sand% | 83.264 | 82.673 | 88.758 | 88.376 | 87.299 | 87.436 | 78.725 | 78.719 |
C% | 1.244 | 1.150 | 0.757 | 0.729 | 0.819 | 0.810 | 0.655 | 0.619 |
N% | 0.127 | 0.138 | 0.083 | 0.086 | 0.088 | 0.094 | 0.085 | 0.078 |
C/N | 9.959 | 8.425 | 9.224 | 8.545 | 9.239 | 8.457 | 7.707 | 7.944 |
OM% | 2.140 | 1.978 | 1.303 | 1.253 | 1.409 | 1.393 | 1.126 | 1.064 |
PH | 7.225 | 7.162 | 6.963 | 6.912 | 6.875 | 6.975 | 7.062 | 6.888 |
Bray P | 23.110 | 22.700 | 10.015 | 10.393 | 11.665 | 7.755 | 11.665 | 7.755 |
K | 0.746 | 0.663 | 0.552 | 0.494 | 0.479 | 0.338 | 0.367 | 0.315 |
C%: soil carbon concentration; N%: soil nitrogen concentration; OM% (=1.72 × C%): soil organic matter content; C/N: index of biodegradability or ratio of soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K cmol kg−1: soil potassium.
Soil characteristics | Depth | T0 | TM | TMA | TMM | LSD |
---|---|---|---|---|---|---|
Clay% | 0–10 cm | 5.821 |
5.519 |
5.944 |
5.959 |
0.111 |
10–20 cm | 5.928 |
5.611 |
6.006 |
6.054 |
0.124 | |
|
||||||
Silt% | 0–10 cm | 9.546 |
9.678 |
9.522 |
9.530 |
ns |
10–20 cm | 9.714 |
9.807 |
9.670 |
9.645 |
ns | |
|
||||||
Sand% | 0–10 cm | 84.628 |
84.802 |
84.534 |
84.511 |
ns |
10–20 cm | 84.357 |
84.584 |
84.324 |
84.301 |
ns | |
|
||||||
C% | 0–10 cm | 0.766 |
0.764 |
0.818 |
0.869 |
0.037 |
10–20 cm | 0.723 |
0.703 |
0.780 |
0.827 |
0.033 | |
|
||||||
N% | 0–10 cm | 0.064 |
0.076 |
0.086 |
0.095 |
0.003 |
10–20 cm | 0.066 |
0.085 |
0.094 |
0.099 |
0.004 | |
|
||||||
C : N | 0–10 cm | 11.947 |
10.087 |
9.551 |
9.032 |
0.272 |
10–20 cm | 11.109 |
8.309 |
8.319 |
8.343 |
0.211 | |
|
||||||
MO% | 0–10 cm | 1.317 |
1.313 |
1.408 |
1.495 |
0.063 |
10–20 cm | 1.244 |
1.209 |
1.342 |
1.422 |
0.057 | |
|
||||||
Bray P (mg kg−1) | 0–10 cm | 10.210 |
11.840 |
13.430 |
14.346 |
1.126 |
10–20 cm | 8.750 |
10.660 |
11.410 |
12.290 |
1.217 | |
|
||||||
K+ cmol kg−1 | 0–10 cm | 0.331 |
0.424 |
0.495 |
0.536 |
0.026 |
10–20 cm | 0.266 |
0.330 |
0.409 |
0.453 |
0.028 | |
|
||||||
PH water | 0–10 cm | 6.063 |
6.688 |
7.129 |
7.031 |
0.055 |
10–20 cm | 6.060 |
6.680 |
7.144 |
6.984 |
0.053 |
Means with the same letter within row are not significantly different (
C%: soil carbon concentration; N%: soil nitrogen concentration; OM% (=1.72 × C%): soil organic matter content; C : N: ratio of soil carbon to nitrogen; Bray P (mg/kg-soil): soil phosphorus; K+ cmol kg−1: soil potassium; LSD: least square difference at 5%; SD: standard deviation.
T0 (control 1): one-year fallow-yam rotation; TM (control 2): maize-yam rotation; TMA:
Data are the means.
The end of study soil analysis showed soil chemical properties (SOM%, N%, P (mg/kg-soil), K+ cmol kg−1, and pH water) significantly higher in TMA and TMM than in traditional systems T0 and TM (
The highest biomass dry matter (DM) amount recycled was recorded on
DM of yam shoots recycled on TMA and TMM were significantly higher in 2005 (dry year) than in 2003 (humid year). The chemical fertilizers applied and the above biomass DM of intercropping maize and herbaceous legume recycled and accumulated in 2002, 2003, and 2004 could have resulted in a combined beneficial effect of water, nutrient use, and plant growth in 2005. DM amounts of
The nutrient (N, P, and K) levels removed or recycled fit the DM production (tubers and shoots) and then varied according to treatment and cropping season.
Most of the soils as mentioned above are tropical ferruginous soils, originally from Precambrian crystalline rocks (granite and gneiss) and classified as plinthosols (Gbanlin and Akpéro) and luvisols (Miniffi and Gomè). Miniffi and Akpéro are located on a plateau (well-drained soils) while Gomè is on lowland (more poorly drained soils). Gbanlin is located on an undulating plateau with concretions. Soil chemical analysis showed that the soil was deficient in N, P, and K and soil organic matter (SOM). This could be due to the mining agriculture and also a consequence of the mechanical destruction of the soil structure during the ridging for yam crop. In fact yam is a demanding crop in terms of organic matter and nutrients. Research [
Nitrogen is the most deficient component of these soils grown with low organic matter content. Total nitrogen deficiency of these soils lies in the fact that nitrogen is the only major nutrient that does not exist in the bedrock. Further, the transfer of atmospheric nitrogen to the soil by biological and chemical process is slow. Losses of nitrogen in these soils are common because of the high volatility and solubility of this nutrient. Nitrogen is generated by the breakdown of inherent organic matter and needs to be supplemented with other sources of organic materials or mineral fertilizer. Many studies focusing on these elements conclude that there is an indisputable need to correct the lack of N and P in the soil in Africa [
It is possible to reduce or stop ongoing soil degradation and the decrease in yield with such rotations including improved short fallows or intercropping with herbaceous legumes. The use of legumes improves levels of concentration of the soil parameters. The improvement of the clay concentration at the end of the perennial experiment could be due to the process of the composite soil samples collected on the ridges resulting from the brewing of the soil deep layer relatively rich in clay and the soil horizon surface after ridging. Indeed, ridging allows increasing the volume of the soil deep layer and contributes to the incorporation of organic residues into the soil.
Significant differences in total SOM and nutrients increase with treatments TMA and TMM in comparison with T0 and TM could be due to the faster decomposition of fermentable green manure (herbaceous legumes) with low humification coefficient (5%) added to the moderate decomposition of lignified maize stover on relatively degraded soils [
Our results showed that legumes improved soil P. Legumes fallows with
The soil K concentrations were improved in our study (Table
The field of interest of the study is to determine the impact of yam-based systems with herbaceous legumes on dry matter production (tubers and shoots), nutrients removed and recycled, and the soil fertility changes. Yam tuber dry matter production was significantly improved in yam-based systems with legumes in comparison with traditional systems. Treatment × Farmer and Year × Treatment interactions influenced significantly the yam tuber dry matter production. Amounts of N, P, and K recycled in yam shoot were significantly higher in yam-based systems with legumes than in traditional systems. The nutrient (N, P, and K) levels removed or recycled fit the DM production (tubers and shoots) and then varied according to treatments and cropping seasons. The end of study soil analysis showed soil chemical properties (SOM%, N%, P (mg/kg-soil), K+ cmol/kg, and pH water) significantly higher in treatments with legumes than in traditional systems. We then propose to promote durable and replicable yam-based systems with legumes, through a favorable legislative, economic, and political environment to support local initiatives. Collaborations between farmers, research, development, and extension structures should also be favored to support the development and dissemination of innovations.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors express their sincere appreciation and thanks for the Cooperation Program for Academic and Scientific Research (CORUS). Finally, the authors greatest appreciation goes to farmers who freely agreed to participate in trials and make part of their fields available for the research.