The influence of organic and inorganic nutrient inputs on soil organic carbon functional groups content and maize yields

Authors: NDUNG'U, M - University Of Nairobi; NGATIA, LUCY - Florida A & M University; ONWONGA, R - University Of Nairobi; MUCHERU-MUNA, M - Kenyatta University; FU, R - Florida State University; Moriasi, Daniel; NGETICH, K - University Of Nairobi

Submitted to: Heliyon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2021
Publication Date: 9/15/2021
Citation: Ndung'U, M., Ngatia, L.W., Onwonga, R.N., Mucheru-Muna, M.W., Fu, R., Moriasi, D.N., Ngetich, K.F. 2021. The influence of organic and inorganic nutrient inputs on soil organic carbon functional groups content and maize yields. Heliyon. 7(8):e07881. https://doi.org/10.1016/j.heliyon.2021.e07881.
DOI: https://doi.org/10.1016/j.heliyon.2021.e07881

Interpretive Summary: Application of organic fertilizers singly or in combination with inorganic fertilizers is essential to increasing soil organic matter (SOM) and improving soil fertility in smallholder farming systems of Sub-Saharan Africa and other countries. The goal of this study was to determine the long-term effects of selected integrated soil fertility management treatments on SOM functional groups composition and maize grain yield based on field experiment established in 2004 in the Central Highlands of Kenya. The 12 fertilizer application treatments comprised: 1) 60 kg ha-1 nitrogen (N) goat manure; 2) 30 kg ha-1 inorganic N fertilizer; 3) 60 kg ha-1 inorganic N fertilizer; 4) 30 kg ha-1 N goat manure + 30 kg ha-1 inorganic N fertilizer; 5) 90 kg ha-1 inorganic N fertilizer; 6) 60 kg ha-1 N from lantana; 7) 30 kg ha-1 N lantana plants + 30 kg ha-1 inorganic N fertilizer; 8) 60 kg ha-1 N from mucuna beans; 9) 30 kg ha-1 N mucuna beans + 30 kg ha-1 inorganic N fertilizer; 10) 60 kg ha-1 N from Mexican sunflower; 11) 30 kg ha-1 N Mexican sunflower + 30 kg ha-1 inorganic N fertilizer; and 12) control with no inputs. Soil and organic amendment samples were collected and analysed for carbon compositions. Long-term application of organic and inorganic soil fertility inputs enhanced soil carbon and maize yields. The long-term average soil carbon for the control, organic fertilizers, inorganic fertilizers and the combined organic and inorganic fertilizer application treatments was 7.47, 5.89, 13.37, and 9.63 mg kg-1, respectively. The average maize grain yield for the control, organic fertilizers, inorganic fertilizers and the combined organic and inorganic fertilizer application treatment was 0.56, 1.80, 3.09, and 3.56 Mg ha-1, respectively, which generally correlated with soil carbon. These results show that long-term application of organic fertilizers individually or in combination with inorganic fertilizers increases maize grain yield and the carbon sequestration potential. Knowledge of carbon fraction content of organic soil inputs is important in determining the best management practices to improve soil fertility in order to sustain and/or improve crop yields.

Technical Abstract: In most smallholder farming systems of Sub-Saharan Africa (SSA), locally available organic soil inputs solely or in combination with limited amounts of inorganic fertilizers are used to reverse declining soil fertility and improve soil organic matter content (SOM). Characterization of SOM after long-term application of organic and inorganic inputs can serve as an indicator of soil organic input carbon (C) sequestration potential or even as a verification tool for soil C changes in C stocks accounting. In this study, we determined the long-term effects of selected integrated soil fertility management technologies on SOM functional groups composition and how it affects maize (Zea mays) grain yields in the Central Highlands of Kenya. The study was based on an ongoing long-term soil fertility field experiment established in 2004 in Mbeere South sub-county, the drier part of the Central Highlands of Kenya. The treatments arranged in a randomised complete block design comprised of: 60 kg ha-1 N from goat manure (GM60); 30 kg ha-1 inorganic nitrogen (N) fertilizer (IF30); 60 kg ha-1 inorganic N fertilizer (IF60); GM30 + IF30; 90 kg ha-1 inorganic N fertilizer (IF90); 60 kg ha-1 N from lantana (Lantana camara) (LC60); LC30+ IF30; 60 kg ha-1 N from mucuna beans (Mucuna pruriens) (MP60); MP30 + IF30; 60 kg ha-1 N from Mexican sunflower (Tithonia diversifolia) (TD60); TD30 + IF30, and a control with no inputs. We used 13C solid-state NMR to analyze C compositions of ground soil samples and organic amendments. The GM60, GM30 + IF30, LC60, and TD60 treatments had much higher Alkyl and O-Alkyl C SOM functional groups compared with the control and other treatments. The average soil C for the control was 7.47 mg kg-1 and ranged from 5.03 to 7.37, 9.57 to 18.77, and 7.03 to 14.50 mg kg-1 for inorganic fertilizers, organic fertilizers, and organic + inorganic fertilizers, respectively. The average maize grain yield for the control was 0.56 Mg ha-1 and ranged from 1.51 to 1.99, 1.94 to 4.16, and 2.98 to 4.60 Mg ha-1 for inorganic fertilizers, organic fertilizers, and organic + inorganic fertilizers, respectively. These results show that long-term application of organic fertilizers individually or in combination with inorganic fertilizers increases maize grain yield and the C sequestration potential, which could be attributed to high Alkyl and O-Alkyl C SOM functional groups. Hence, the knowledge of C fraction content of organic soil inputs is vital in determining the best-fit management technologies to ameliorate of soil fertility in order to sustain and/or improve crop yields.