Fertiliser use, soil responsiveness and yield gaps in cotton-based cropping systems of N Cameroon

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1 Fertiliser use, soil responsiveness and yield gaps in cotton-based cropping systems of N Cameroon Michel Cretenet, Pablo Tittonell CIRAD-Persyst Yield Gap Symposium, AGRO 21 Montpellier

2 Background Productivity decline in cotton-based cropping systems of West and Central Africa: impact on regional economies Price fluctuations lead to discontinuous/ insufficient fertiliser use in the long term: impact on soil productivity Cameroon National debt funds (C2D) : soil fertility restoration project (SODECOTON, CIRAD) What determines current yield gaps, how wide are they, and how to close them? Data mining: reanalysis of old and long term trials

3 Decline in productivity Cotton yield and fertiliser use at national level Cotton yield and fertiliser use at Garoua, N Cameroon Global fertiliser productivity at Garoua, N Cameroon r 2 = r 2 = Period Period Yield = * t (r 2 =.4) G Fertiliser Year applied (kg ha -1 ) Year Fertiliser applied (kg ha -1 ) Fertiliser applied (kg ha -1 )

4 Discontinuous fertiliser use Crop productivity Restoration Discontinuation Fertiliser use

5 Hysteresis of land rehabilitation - Kenya Manure application A C Manure + fertiliser application Biomass yield (t ha -1 ) r d h Time (seasons) Time (seasons) Tittonell et al., 28, Agronomy Journal 1

6 La mémoire du sol Phases of depletion and restoration (Benin) Maize grain yield (kg ha -1 ) Time (yr) Time (yr) 1 75 Relative Control yields (%) Mulch + Manure + Fertiliser Restauration of control (M+M+F) Aplahoué,

7 Closing yield gaps through fertiliser use Network of on-farm trials in 199 Average response to fertiliser by cotton in 199 Response to fertiliser by cotton per quintile 2 Cotton response to mineral fertilisers (N,P,K,S) 3 25 farmer fields around Garoua (n = 135) 2 Soils 2-3% Clay + silt; 65 ±8 mm 1, 125, 25, 375, kg ha -1 1 a Observed Model Y = a + b * e -x/ Fertiliser applied (kg ha -1 ) Fertiliser applied (kg ha -1 ) n=7 n=34 n=66 b n=31 n=6

8 Closing yield gaps through fertiliser use SOM (%) Coarse sand (%) Soil organic matter 2 Olsen P Exchangeable CaManagement practices 4. affect attainable Exchangeable K yields Exchangeable Mg Cation exchange capacity Seed-cotton Yield without yield fertiliser (kg ha -1 (kg ) ha -1 ) 1 2 Coarse sand Fine sand Clay + fine silt Late.9sowing 1. 2 Soil organic matter 5.7 (%) 1 2 Soil productivity without fertiliser Cmol (+) kg -1 Clay+silt (%) mg P kg -1 Yield = 587 SOM r 2 =.98 ph scale Seed-cotton yield without fertiliser (kg ha -1 ) Q4 Qq Seed-cotton yield without fertiliser (kg ha -1 ) Q3 1 5 Q2 6.9 ph (water 1:2.5) Exchangeable Al Q1 Early sowing Early sowing Qq1 6.3 Modal sowing 3 Modal sowing Late sowing Soil organic matter (%) Cmol (+) K kg -1 Cmol (+) Al kg -1

9 Soil carbon losses and productivity decline A positive feedback Clearence of native savannah vegetation Continuous cultivation with poor C restitution Productivité Soil physico-chemical et durabilité dans degradation les savanes cotonnières d Afrique de l Ouest CO Productivity decline (less biomass, less soil cover, less C back 2 to soil) Yield without fertiliser Exportation de résidus de récolte Système de culture et matière organique du sol rendement kg/ha Response parameters, efficiency, yield gaps and soil organic matter Attainable yield (full fertiliser) Récolte photosynthèse.6-1 T Résidus de Culture 1-3 T 1.5-4T CO 2 Humification K % 6 2 Matière Organique du Sol T Teneur en carbone (mg/g) horizon -2 cm minéralisation K 2 6% Valeurs obtenues par analyse.7 Valeurs simulées par le modèle F F1 F F1 F F1 résidus exportés résidus restitués res.rest.+ pailles MOS% mais 72-8 coton 72-8 moy -3 cm Soil organic matter (%) Fertiliser use efficiency Yield gap Age de défriche

10 National policies with local consequences Local land use systems Organic matter and nutrient flows at village scale Land tenure, diversity of livelihoods and ethnicity How to determine reference yield levels (potential?) over such heterogeneous agricultural landscapes? Debru, J. (29) L abandon de la culture du cotonnier est-il momentané ou définitif? AgroParisTech

11 Diversity at local scale: how define yield potential? Decline in to livestock numbers Number of livestock heads Diversity of farming trajectories and styles History of land occupation and use: current heterogeneity Debru, J. (29) L abandon de la culture du cotonnier est-il momentané ou définitif? AgroParisTech

12 Concluding remarks Discontinuous/ insufficient fertiliser use widens yield gaps through cumulative effects Lack of reversibility in fertiliser response beyond a certain threshold of soil degradation hystereis or la mémoire du sol Soil organic matter as key to restoring soil productivity, but complexity of local land use systems must be embraced Policy innovation: e.g. could policy enforce crop rotations or fallows? Data mining as a method to inform yield gap analysis

13 Thanks for your attention

14 Number of livestock heads Decline in livestock numbers

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16 National policies with local consequences Faible intégration dans l enseignement 5 juillet 21

17 Decline in productivity Cotton yield and fertiliser use at Garoua, N Cameroon Fertiliser applied (kg ha -1 ) Year 5

18 Discontinuous fertiliser use 2 Fertiliser applied (kg ha -1 ) 1 Yields study region (kg ha -1 ) Period r 2 =.8 r 2 =.7 1 Garoua Est Garoua Ouest 1 Yields N Cameroon (kg ha -1 ) Observed Model Y = a + b * e -x/ r 2 =.7 H r 2 =.6 Period Period

19 Average response to fertiliser by cotton in a Observed Model Y = a + b * e -x/ b Fertiliser applied (kg ha -1 )

20 Response to fertiliser by cotton per quintile n=7 n=34 n=66 n=31 n= Fertiliser applied (kg ha -1 )

21 Soil productivity without fertiliser 3 Yield without fertiliser (kg ha -1 ) Yield = 587 SOM r 2 =.98 Qq4 1 Q4 Q3 Q2 Q1 Qq Soil organic matter (%)

22 Management practices affect attainable yields Early sowing Early sowing Modal sowing Modal sowing Late sowing Late sowing Soil organic matter (%)

23 Response parameters, efficiency, yield gaps and soil organic matter 3 Yield without fertiliser 2 Attainable yield (full fertiliser) Fertiliser use efficiency Yield gap Soil organic matter (%)

24 Discontinuous fertiliser use Global fertiliser productivity at Garoua, N Cameroon r 2 =.7 1 r 2 = Period Period Fertiliser applied (kg ha -1 )