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

Transcription

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 1 Montpellier Session.3.1 C: Closing the yield gap

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 (CD) : soil fertility restoration project (SODECOTON, CIRAD) What determines current yield gaps, how wide are they, and how to close them? Preliminary phase of the project: Building resilience in cotton-based farming systems of N Cameroon (SODECOTON-CIRAD) Data mining ( old and long term trials) Exploratory agrarian system study

3 Decline in productivity Seed-cotton yield (kg ha -1 ) Seed-cotton yield (kg ha -1 ) Cotton yield and fertiliser use at national level Cotton yield and fertiliser use at Garoua, Cameroon Global fertiliser productivity at Garoua, N Cameroon Seed-cotton yield (kg ha -1 ) r =.7 15 r = Period Period Yield = * t (r =.4) Aggregated seed-cotton yield G Fertiliser Year applied (kg ha -1 ) Year Fertiliser applied (kg ha -1 ) Fertiliser applied (kg ha -1 )

4 Discontinuous/ insufficient fertiliser use Responsive soils Crop productivity Restoration Hysteresis Degradation Poorly responsive soils Fertiliser use

5 Hysteresis of land rehabilitation - Kenya 7 Manure application A 7 C Manure + fertiliser application Biomass yield (t ha -1 ) r d h Time (seasons) Time (seasons) Tittonell et al., 8, Agronomy Journal 1

6 La mémoire du sol Phases of depletion and restoration (Benin) 5 Maize grain yield (kg ha -1 ) Seed-cotton yield (kg ha -1 ) Time (yr) Time (yr) 1 75 Relative Control yields (%) Mulch + Manure + Fertiliser 5 5 Restauration of control (M+M+F) Aplahoué,

7 What determines current yield gaps? Network of on-farm trials in 199 Seed-cotton yield (kg ha -1 ) Seed-cotton yield (kg ha -1 ) Average response to fertiliser by cotton in 199 Response to fertiliser by cotton per quintile Cotton response to mineral fertilisers (N,P,K,S) farmer fields around Garoua 5 Soils -3% Clay + silt; 65 ±8 mm 15, 15, 5, 375, 5 kg ha a 5 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 What determines current yield gaps? SOM (%) Coarse sand (%) Soil organic matter 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 ) Coarse sand Fine sand Clay + fine silt Late.9sowing 1. Soil organic matter 5.7 (%) Soil productivity without fertiliser Cmol (+) kg -1 Clay+silt (%) mg P kg -1 Yield = 587 SOM - 88 r =.98 ph scale Seed-cotton yield without fertiliser (kg ha -1 ) 5.1 Q4 Qq Seed-cotton yield without fertiliser (kg ha -1 ) Q Q ph (water 1:.5) Exchangeable Al 5 1 Q Early sowing Early sowing Qq Modal sowing 5 3 Modal sowing Late sowing Soil organic matter (%) Cmol (+) K kg -1 Cmol (+) Al kg -1

9 Soil carbon losses and productivity decline Seed-cotton yield (kg ha -1 ) A positive feedback Clearence of native savannah vegetation Continuous cultivation with poor C restitution Productivité Soilphysico-chemicaldegradation et durabilité dans les savanes cotonnières d Afrique de l Ouest CO Productivity decline (less biomass, less soil cover, less C back to soil) Yield without fertiliser Exportation Système de de résidus culture de et récolte matière organique du sol rendement kg/ha Response parameters, efficiency, yield gaps and soil organic matter Attainable yield (full fertiliser) Récolte photosynthèse 1.5-4T.6-1 T Résidus de Culture 1-3 T CO Humification K % 6 Matière Organique du Sol T Teneur en carbone (mg/g) horizon - cm minéralisation K 6% Valeurs obtenues par analyse 5.7 Valeurs simulées par le modèle F F1 F F1 F F1 résidus exportés résidus restitués res.rest.+ pailles MOS% mais 7-8 coton 7-8 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. (9) L abandon de la culture du cotonnier est-il momentané ou définitif? AgroParisTech

11 Diversity at local scale: how to define yield potential? Decline in livestock numbers Diversity of farming trajectories and styles History of land occupation and use: current heterogeneity Number of livestock heads Debru, J. (9) L abandon de la culture du cotonnier est-il momentané ou définitif? AgroParisTech

12 Summary Discontinuous/ insufficient fertiliser use widens yield gaps through cumulative effects positive feedbacks, poor resilience Irreversibility/ hysteresis of crop response to fertiliser beyond a threshold of soil degradation la mémoire du sol Organic resource management as key to restoring soil productivity and closing yield gaps Complexity of local land use systems must be embraced Are potential yields at plot scale relevant reference at landscape level? Should such heterogeneity be maintained, reinforced or evened out? To what extent could crop-livestock interactions be intensified? Policy innovation: e.g. could policy enforce crop rotation or fallows? Data mining as a method to inform yield gap analysis

13 Thanks for your attention