Fig1 : Improving SOC budget with High manure application increases sorghum yield
(limit value ~ 6.0 mgC g-1) Agronomic and
environmental goals are in accordance
Results
Under Sudano-Sahelian climatic conditions, the level of soil organic carbon (SOC) is a critical, if not vital, component of fertility. Given the low nutrient status and the drought constraint, the level of soil organic matter is a key factor to ensure sustainable plant productivity.
The aim of our research was to evaluate the stocks of SOC in a ferric Acrisol of Burkina Faso under different farming systems including manuring and crop residues restitution to the soil. The fractionation of soil organic matter (SOM) allowed us to assess the degree of SOM protection.
Context
Materials and methods
Conclusions
0 1000 2000 3000 4000 5000 0.0 5.0 10.0 15.0 C soil (0-20 cm) ( mg g-1) S or g h um Y ie ld ( k g h a -1 ) ( 4 0 y e ar s T re at m e nt s)Control Crop residues Manure Low
Fert. Low Manure High Fert. High
border line
Fig2 : 22 years cultivation general losses of SOC from the 20 first cms of soil stock (Control -44%) , restricted by organic inputs, specially animal manure.
0% 20% 40% 60% 80% 100% Sorghum Straw Manure aerobic compost Anaerobic compost O rg an ic s in pu t co m po si ti on ( % o f to ta l O .M
.) Soluble Hemi cell. Cell. Lignin
C so il af te 2 2 y ea rs : -2 8 % C so il af te r 2 2 y ea rs : -3 2 % C so il af te r 2 2 y ea rs : -2 8 % C so il af te r 2 2 y ea rs : -1 5 %
After 10 years of application, soil tillage does not affect SOC stock on first 40 cm layer and this, with or without manure input. Futhermore, soil tillage is
beneficial for the crop.
Plant Yield and S O C content
Fig 3a : High level manure improve C storage in (0-20 µm) fraction that is protected to the mineralization.
soil C fraction
0.0 2.0 4.0
Control min. Fert Manure Low Manure High C s oi l (m g g -1 ) Soluble (0-20) µm (20-2000) µm
Fractions SOC budget (0-10 cm) after 40 years of application
-0.50 -0.25 0.00 0.25 0.50
Control Manure High
D el ta C s ol ( m g g -1 ) Soluble (0-20) µm (20-2000) µm
Fig 3b : Nitrogen fertilizer effect (urea) is reversed in case of manure input at high level. C storage in the fraction < 20 µm is improved .
‘’Quality’’ of SOC stock induced by O M inputs
Increasing the storage of C in the soil is possible with the current farming practices but their optimisation has to be achieved.
This study opens onto possible actions and concludes on the necessity to take into account the macrofauna and microbial activities in interaction with the organic matter for a better control of the organic flows.
(1) : Université de Ouagadougou, Burkina Faso, email: edmondhien@hotmail.com ; (2) : CIRAD-PERSYST UPR « risques et recyclage » ; (3) : IRD-UR 179 SEQBio ; (4) INRA UR
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E. Hien(1) ; F. Ganry(2) ; R. Oliver(2) ; C.Feller (3); J. Balesdent(4)
Long-term evolution of organic matter modified by cultural practices
in a cultivated Acrisol - consequences on soil organic carbon stocks
This study has used samples and results from some plots of the long-term experiment of Saria (Burkina Faso) settled in 1960 (Sedogo, 1993).
Treatments differed in the rates of mineral fertilization, level and nature (sorghum straw, farm manure (Man.) of organic restitutions application and the tillage practices (scrapping and ploughing) under a continuous sorghum crop since 1960.
Soil is a ferric Acrisol, mean annual temperature is 28.0°C and mean annual precipitation 800 mm. The duration of soil moisture deficit is 8 to 9 months.
Measurements and observations concerned: (i) in the field the soil morphological characterization, bulk density and crops yields, (ii) in the laboratory the organic matter (OM) characterization (biochemical composition) and soil C, N, and particle-size fractionation.
The model RothC 26.3 (Coleman and Jenkinson, 1999) was run to check predicted values with measured SOC stocks for the different treatments.
0 5 10 15 20 25 30 1960 1970 1980 1990 2000 Year S to ck C (t h a-1)
Control min. fert. Man. Low Man. High
Obsv. Control Obsv. Fert Obsv. man. Low Obsv. Man High Manure t ha-1 (annual input until 76 after every 2 years)
Fig 4 : RothC modelization of SOC stock between 1960 and 2000 shows that the high level manure only is able to store carbon in the soil. However it’s necessary to apply an attenuation coefficient of 0.34 to fit observed and calculated values. Soil macrofauna activity (termites) and manure characteristics may explain this.
Half-life of “labile” SOC is about 17 years (Soil fractions decomposition rate simulation).
5 Low: 5t ; High: 40 t ha-1
