A.K. Jarju * , M. Faye, C. Bojang, M. Suso, Y. Sanneh, B. Jobe, A. Bittaye, F atajo

1. Effect of Watershed (ACN) and Fertilizer Management on Soil Organic Carbon (SOC) Conservation in Maize-based cropping systems in The Gambia.

2. RESEARCH TEAM A.K. Jarju*, M. Faye, C. Bojang, M. Suso, Y. Sanneh, B. Jobe, A. Bittaye, F atajo National Agriculture Research Institute (NARI), PMB 526, Serekunda, The Gambia and C. Yamoah, R. Kablan, R. S.Yost* SM-CRSP Carbon Project, University of Hawaii Department of Plant and Soil Science, University of Hawaii, Honolulu, USA

3. Introduction A watershed management experiment was initiated in the Gambia from 2002 to 2006 to test the hypothesis that ridge tillage retains rainfall and interacts with fertilizer to produce greater maize grain and biomass yields than conventional watershed management.

4. Objective To evaluate existing and improved cropping systems for increased Carbon storage as soil Carbon and sustainable increased crop production.

5. Methodology A split plot design with three replications was used for the experiment. The main plots were ridge-tillage and conventional tillage watershed management. Subplots were four fertilizer rates

6. Methodology Treatments: Main plots • 1.      Ridge-tillage • 2. Conventional tillage

7. Methodology Sub-plots • 1.      check with no fertilizer • 2.     200 kg ha-1 NPK fertilizer + 16 kg ha-1 of urea (approximately half the national recommended rate) • 3.     200 kg ha-1 NPK fertilizer + 43 kg ha-1 of urea (full the national recommended rate) • 4.     200 kg ha-1 NPK fertilizer + 150 kg ha-1 of urea (double the national recommended rate.)

8. ACN Field layout Ridge tillage Conv. Tillage F1

9. Determination of soil carbon The widely recognized method to estimate soil carbon in cropping systems for assessment of carbon sequestration is the dry-combustion procedure (SM-CRSP, 2002).

10. Determination of soil carbon For the Gambian upland soils, 5g-soil is pre-dried to 105 C and later to 360 C. The product of percent LOI at 360 C and 0.717 give %OM. Conversion of %OM to %OC is %OM/1.724 or simply 2.

11. Fertilizer Tillage systems 2005 2006 RT* CT RT CT (kg ha-1) (Yield kg ha-1) Check (no fertilizer) 431 530 632 586 200 NPK + 42 urea 1153 1052 2422 2134 200 NPK + 86 urea 1136 941 2226 1702 200 NPK + 258 urea 1105 1193 2134 1842 Analysis of variance Source F-value P-value F-value P-value Tillage system (T) 0.150 >0.05 31.29 0.030 Fertilizer (F) 51.70 <0.001 280.867 <0.001 T*F 2.80 <0.05 6.588 0.007 Effects of ridge tillage, conventional tillage systems, and fertilizer on maize yields (kg ha-1),Two year pull 2005 and 2006 in Western Gambia.

12. Fertilizer Tillage systems 2005 2005 RT* CT RT CT (kg ha-1) Total soil carbon (t/ha) (%Carbon) Check (no fertilizer) 8.73 7.91 0.72 0.63 200 NPK + 42 urea 8.90 7.83 1.26 0.95 200 NPK + 86 urea 9.96 7.70 1.12 1.02 200 NPK + 258 urea 10.05 8.61 1.10 0.98 Analysis of variance Source F-value P-value F-value P-value Tillage system (T) 4.44 >0.05 43.52 0.022 Fertilizer (F) 3.34 <0.05 54.49 <0.001 T*F 1.4 >0.05 7.47 0.004 Effects of ridge tillage, conventional tillage systems, and fertilizer on total soil carbon (t/ha) in 2005 and % carbon (%) in 2005, Western Gambia.

13. Statistic Ridge-tillage Conventional tillage Mean 0.87 0.73 Median 0.90 0.79 Standard deviation 0.17 0.11 Minimum 0.57 0.53 Maximum 1.09 0.88 Range 0.52 0.35 CV (%) 19.2 15.0 Descriptive statistics of soil carbon in ridge and conventional tillage systems, 2005.

14. Fertilizer Tillage systems 2005 2006 RT* CT RT CT (kg ha-1) (Dalasis ha-1) Check (no fertilizer) 2115 2600 2728 2508 200 NPK + 42 urea 3680 3000 9820 7312 200 NPK + 86 urea 3420 2540 7520 5234 200 NPK + 258 urea 2814 2500 5922 4646 Statistics Mean 2814 2638 6457 4925 Standard deviation 858 250 2979 1925 CV 0.31 0.09 0.458 0.401 Paired t-test P>0.05 P<0.057 Returns over variable cost of fertilizer on maize in ridge and conventional tillage systems in Western Gambia 2005 and 2006.

15. Plans for 2007 Work with both the national extension staff and international NGOs to train farmers in the installation of the ADOs and to intensify the replicate ACN on farm program and farmer-to-farmer field visits.

16. Hypothesis

17. Scaling up realized benefits of ACN on farmers field Replicated on farm ACN technology 2007/2008 Determination post rain vegetable production in ACN water shed sites in western and north bank region 2008 and beyond

18. Conventional Tillage Road beranch toward Kerr cherino Conventional Tillage Road to Kerr Cherino Ridge ttillage Fass Chaw Village Mosque Road from Madina sering Mass Road in middle of the Village

19. The basket - Gambia experience FARMER INNOVATION AND ACN CROSS BOARDER FACTOR FIVE YEARS OF EXPERIMENTATION AND CROP RESIDUE MANAGEMENT IMPACT ON CROP YIELD FERTILIZER FREE PLOTS

20. F1: 21 days after planting 2003

21. F1: 21 days after planting 2005

22. F1: 21 days after planting 2006

23. On farm discussions for adoption and options “ ridging vs no ridging” in ACN

24. Reflections

25. Successful research is backed by a committed work force at community level

26. Thank you