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Soil organic carbon and nitrogen dynamics under long-term conservation agriculture systems in Cambodia

Authors:
Vira Leng at Institut Agro Montpellier
Vira Leng
Rémi Cardinael at Cirad - La recherche agronomique pour le développement
Rémi Cardinael
Vang Seng at Murdoch University
Vang Seng
Florent Tivet at Cirad - La recherche agronomique pour le développement
Florent Tivet
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Abstract

This study quantified soil organic carbon (SOC) and soil total nitrogen (STN) changes in three long-term (14 years) experiments comparing conventional tillage (CT) and different no-till (NT) cropping systems using a diachronic approach and an equivalent soil mass approach. The three experiments were established in 2009 in a randomized complete block design with three replicates and comprise maize (MaiEx)-, soybean (SoyEx)-, and cassava (CasEx)-based cropping systems. Soil samples were collected in 2021, 10 years after the first sampling (2011), at 7 depths: 0-5, 5-10, 10-20, 20-40, 40-60, 60-80, and 80-100 cm. At 0-10 cm depth, NTs significantly increased SOC stock at a rate of 0.35, 0.51 and 0.73 Mg C ha-1 y-1 for CasEx, SoyEx and MaiEx, respectively. CT exhibited a positive trend only on CasEx with an accumulation rate of 0.14 Mg C ha-1 y-1 (0-10 cm). A significant SOC accumulation was observed under NT cropping systems for CasEX and MaiEx up to 60-80 and 80-100 cm depth, respectively. By contrast, STN stock significantly increased under NT cropping systems only at 0-5 cm depth with an accumulation rate of 13.9, 22.9 and 34.0 kg N ha-1 y-1 under CasEx, SoyEx and MaiEx, respectively. A depletion of N stocks was observed under CT and NT cropping systems at deeper soil layers. Over 10 years of time, SOC accumulation rate of NT, at 0-100 cm depth, reached 1.08 and 1.73 Mg C ha-1 yr-1 for CasEx and MaiEx, respectively while non-significant change was observed under NT SoyEx and CT of the three experiments. The findings suggest that long-term NT cropping systems with high amount of biomass-C inputs and crop rotation enhance SOC sequestration even at deeper soil layers. However, these results raise questions about the dynamics of N under NT cropping systems.
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Soil organic carbon and nitrogen dynamics
under long-term conservation agriculture systems in Cambodia
Vira LENGa,b*, Rémi CARDINAELc, Vang SENGa, Florent TIVETa,c, d ,
Pascal LIENHARDc , d , Phearum Marka, Johan SIXe, Lyda HOKf, Stéphane Boulakiac,
Laurent THURIESg
a: Cambodian Conservat ion Agr i cul t ur e R esearch for Develop m ent C en ter , Department of Agr icu ltu ral Lan d
Res o urce s Man ag em ent, General Direct ora t e of Agriculture, Ministry of Ag ricult ur e , Forestry, and Fish eries,
Ph nom Pen h, C a mbodia
b: D o ctor al Sc hool GAIA, SupAgro Mon tpell i er, U ni versity of Montpelli er, Mo nt pe llier, France
c: AI DA , Univ Montpellier, CIRA D , M ont pellier, France
d: A g roec o logy and Safe Food System Tr an sitions in Southeast A sia Pro j ect (ASSET)
e: De partment of Environmenta l Systems Sciences, E TH Zur ich, 8092, Switzerland
f: Royal University of A gricu l tur e, Fa cult y of Agronomy and C enter of Excellence o n Su s taina ble Agricultural
Int ens ifi cat i on and Nutrition, Phnom P enh , Cambodia
g: CI RAD , U R Rec y cling and Risk, Avenue Agropolis, 34398, Mo ntp elli er , France
* C orrespo ndi n g a ut hor : leng vira@yahoo.com
This study quantified soil organic carbon (SOC) and soil total nitrogen (STN) changes in three long-
term (14 years) experiments comparing conventional tillage (CT) and different no-till (NT) cropping
systems using a diachronic approach and an equivalent soil mass approach. The three experiments
were established in 2009 in a randomized complete block design with three replicates and comprise
maize (MaiEx)-, soybean (SoyEx)-, and cassava (CasEx)-based cropping systems. Soil samples were
collected in 2021, 10 years after the first sampling (2011), at 7 depths: 0–5, 5–10, 10–20, 20–40, 40–
60, 60–80, and 80–100 cm. At 0–10 cm depth, NTs significantly increased SOC stock at a rate of
0.35, 0.51 and 0.73 Mg C ha-1 y-1 for CasEx, SoyEx and MaiEx, respectively. CT exhibited a positive
trend only on CasEx with an accumulation rate of 0.14 Mg C ha-1 y-1 (0-10 cm). A significant SOC
accumulation was observed under NT cropping systems for CasEX and MaiEx up to 60-80 and 80-
100 cm depth, respectively. By contrast, STN stock significantly increased under NT cropping
systems only at 0–5 cm depth with an accumulation rate of 13.9, 22.9 and 34.0 kg N ha-1 y-1 under
CasEx, SoyEx and MaiEx, respectively. A depletion of N stocks was observed under CT and NT
cropping systems at deeper soil layers. Over 10 years of time, SOC accumulation rate of NT, at 0-
100 cm depth, reached 1.08 and 1.73 Mg C ha-1 yr-1 for CasEx and MaiEx, respectively while non-
significant change was observed under NT SoyEx and CT of the three experiments. The findings
suggest that long-term NT cropping systems with high amount of biomass-C inputs and crop rotation
enhance SOC sequestration even at deeper soil layers. However, these results raise questions about
the dynamics of N under NT cropping systems.
... Since N.C. A&T, has developed a vast strength on CAPS modeling; soil carbon sequestration study using EPIC (Le, 2017;Le et al., 2018); CAPS veggies study (Edralin et al., 2016;Edralin et al., 2017;Edralin, 2015); CAPS grains study (Hok, 2014;Hok et al., 2015;Hok et al., 2018), it is recommended that N.C. A&T strengthen its partnership with Texas A&M and other groups for further CAPS modeling research. ...
Experimental and Modeling Evaluation of Conservation Agriculture with Drip Irrigation for Small-Scale Agriculture in Sub-Saharan Africa
Thesis
Full-text available
  • May 2018
Food and nutrition insecurity continues to be the main challenges in Sub-Saharan Africa (SSA). The traditional tillage practice with a rainfed system, and poor soil and water management resulted in soil degradation and low productivity. In this study; field experiments, biophysical models, and spatial analysis were used to identify and evaluate a potential solution for small-scale agriculture in the region; particularly in Ethiopia, Ghana, and Tanzania. Multi-Criteria Evaluation (MCE) technique was used to assess irrigable land and the feasibility of water-lifting technologies for the Lake Tana Basin of Ethiopia, followed by determining irrigation potential. Biophysical data were collected from the field experiment in SSA to evaluate the impacts of conservation agriculture (CA) with drip irrigation on vegetable yield and irrigation water use. The Agricultural Policy /Environmental eXtender (APEX) model was verified using field-scale data and used to evaluate the impacts of CA with drip irrigation on water management and crops. The APEX model and MCE technique were to upscale field-scale crop production to the national level, followed by determining the irrigation potential of groundwater. About 345,000 ha and 135,000 ha of lands in Lake Tana Basin were found irrigable from surface and groundwater sources; low-flow of rivers and groundwater can satisfy up to about 1.2% and 3.5% of the irrigable lands, respectively. The Rope pump has the highest applicability in Lake Tana Basin (26%) for the use of groundwater. From the field experiment, a significant vegetable yield increase was observed in Ethiopia (9-184%) and Ghana (18-99%) under CA; except in Tanzania possibly due to waterlogging. On the other hand, CA significantly reduced irrigation water use (18-47%) for various vegetables. The model result depicted the improvement of water management; the reduction of evapotranspiration (up to 49%) and runoff (up to 62%), and the increase in soil moisture and percolation. The average fresh vegetable yield ranges from 1.8–2.8 t/ha; 1.4–2.2 t/ha; 5.5–15.7 t/ha. and 8.3–12.9 t/ha for garlic, onion, tomato, and cabbage, respectively. Groundwater can support about 1.4 - 3.5 Mha of land to produce vegetables. CA with drip irrigation has the potential to intensify food production in SSA
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