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

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 RESEARCH TEAM

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. 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.

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

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 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

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

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

ACN Field layout Ridge tillage Conv. Tillage Ridge tillage Conv. Tillage F1

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

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 give %OM. 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 give %OM. Conversion of %OM to %OC is %OM/1.724 or simply 2. Conversion of %OM to %OC is %OM/1.724 or simply 2.

Effects of ridge tillage, conventional tillage systems, and fertilizer on maize yields (kg ha -1 ), Two year pull 2005 and 2006 in Western Gambia. FertilizerTillage systems RT*CTRTCT (kg ha -1 ) (Yield kg ha -1 ) Check (no fertilizer) NPK + 42 urea NPK + 86 urea NPK urea Analysis of variance SourceF-valueP-valueF-valueP-value Tillage system (T) 0.150> Fertilizer (F) 51.70< <0.001 T*F2.80<

Effects of ridge tillage, conventional tillage systems, and fertilizer on total soil carbon (t/ha) in 2005 and % carbon (%) in 2005, Western Gambia. Fertilizer Tillage systems 2005 RT*CTRTCT (kg ha -1 ) Total soil carbon (t/ha ) (%Carbon) Check (no fertilizer) NPK + 42 urea NPK + 86 urea NPK urea Analysis of variance SourceF-valueP-valueF-valueP-value Tillage system (T) 4.44> Fertilizer (F) 3.34< <0.001 T*F1.4>

Descriptive statistics of soil carbon in ridge and conventional tillage systems, StatisticRidge-tillageConventional tillage Mean Median Standard deviation Minimum Maximum Range CV (%)

Returns over variable cost of fertilizer on maize in ridge and conventional tillage systems in Western Gambia 2005 and FertilizerTillage systems RT*CTRTCT (kg ha -1 ) (Dalasis ha -1 ) Check (no fertilizer) NPK + 42 urea NPK + 86 urea NPK urea Statistics Mean Standard deviation CV Paired t-testP>0.05 P<0.057

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. 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.

Hypothesis e Suggests up to a 40% improvement in crop yields can be achieved with increased carbon storage Generic evidence to date suggest

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

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

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

F1: 21 days after planting 2003

F1: 21 days after planting 2005

F1: 21 days after planting 2006

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

Reflections

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