High Quality Organic Resources are Most Efficient in Stabilizing Soil Organic Carbon: Evidence from Four Long-Term Experiments in Kenya
Loading...
Date
2022
Authors
Laub, Moritz
Corbeels, Marc
Couëde, Antoine
Ndungu, Samuel Mathu
Mucheru-Muna, Monicah Wanjiku
Mugendi, Daniel
Necpalova, Magdalena
Waswa, Wycliffe
Broek, Marijn Van De
Vanlauwe, Bernard
Journal Title
Journal ISSN
Volume Title
Publisher
Copernicus Publications G{\"o}ttingen, Germany
Abstract
In sub-Saharan Africa, long-term maize cropping with low external inputs has been associated with the loss of soil fertility.
While adding high-quality organic resources combined with mineral fertilizer has been proposed to counteract this fertility
loss, the long-term effectiveness and interactions with site properties still require more understanding. This study used repeated
5 measurements over time to assess the effect of different quantities and qualities of organic resource addition combined with
mineral N on the change of soil organic carbon concentrations (SOC) over time (and SOC stocks in the year 2021) in four
ongoing long-term trials in Kenya. These trials were established with identical treatments in moist to dry climates, on coarse to
clayey soil textures, and have been managed for at least 16 years. They received organic resources in quantities equivalent to
1.2 and 4 t C ha-1 per year in the form of Tithonia diversifolia (high quality, fast turnover), Calliandra calothyrsus (high quality,
10 intermediate turnover), Zea mays stover (low quality, fast turnover), sawdust (low quality, slow turnover) and local farmyard
manure (variable quality, intermediate turnover). Furthermore, the addition or absence of 240 kg N ha-1 per year as mineral N
fertilizer was the split-plot treatment. At all sites, a loss of SOC, rather than gain, was predominantly observed due to a recent
conversion from permanent vegetation to agriculture. The average reduction of SOC concentration over 19 years in the 0 to 15
cm depth ranged from 42% to 13% of the initial SOC concentration for the control and the farmyard manure treatments at 4 t
C ha-1 yr-1, respectively. Adding Calliandra or Tithonia at 4 t C ha-1 yr-1 15 limited the loss of SOC concentrations to about 24%
of initial SOC, while the addition of saw dust, maize stover (in 3 of 4 sites) and sole mineral N addition, showed no significant
reduction in SOC loss over the control. Site specific analyses, however, did show, that at the site with the lowest initial SOC
concentration (about 6 g kg-1), the addition of 4 t C ha-1 yr-1 farmyard manure or Calliandra plus mineral N led to a gain in
SOC concentrations. All other sites lost SOC in all treatments, albeit at site specific rates. While subsoil SOC stocks in 2021
20 were little affected by organic resource additions (no difference in 3 of 4 sites), the topsoil SOC stocks corroborated the results
1 for SOC concentrations. The relative annual change of SOC concentrations showed a higher site specificity in high-quality
organic resource treatments than in the control, suggesting that the drivers of site specificity in SOC buildup (mineralogy,
climate) need to be better understood for effective targeting of organic resources. Even though farmyard manure showed the
most potential for reducing SOC loss, our results clearly show that maintaining SOC with external inputs only is not possible at
25 organic resource rates that are realistic for small scale farmers. Thus, additional agronomic interventions such as intercropping,
crop rotations or strong rooting crops may be necessary to maintain or increase SOC.
Description
Article
Keywords
Citation
Laub, M., Corbeels, M., Couëdel, A., Mathu Ndungu, S., Mucheru-Muna, M. W., Mugendi, D., ... & Six, J. (2022). High quality organic resources are most efficient in stabilizing soil organic carbon: Evidence from four long-term experiments in Kenya. EGUsphere, 2022, 1-33.