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

Abstract

Locally available organic inputs to soil, solely or in combination with inorganic fertilizers, are used to reverse declining soil fertility and improve soil organic matter content (SOM) in smallholder farms of most Sub-Saharan Africa (SSA) countries. Soil organic matter characterization can indicate soil organic input, carbon (C) sequestration potential, or even an authentication tool for soil C dynamics in C stocks accounting. This study determined the effects of the long-term application of selected integrated soil fertility management (ISFM) technologies on SOM functional group composition and maize yields. The study was carried out on an ongoing long-term soil fertility field experiment established in 2004 in Mbeere South sub-county, the drier part of upper Eastern Kenya. The experimental design was a randomized complete block design. The ISFM treatments were 60 kg ha −1 nitrogen (N) from goat manure (GM60); 30 kg ha −1 inorganic 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. The C compositions of ground soil samples and organic amendments were analyzed using 13 C solid-state NMR. The GM60, GM30+IF30, LC60, and TD60 treatments had much higher Alkyl and O-Alkyl C SOM functional groups than 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 7.03–14.50 mg kg −1 for inorganic fertilizers, organic fertilizers, and organic + inorganic fertilizers, respectively. The mean 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 2.98–4.60 Mg ha −1 for inorganic fertilizers, organic fertilizers, and organic + inorganic fertilizers, respectively. The results showed that a long-term application of sole organic fertilizers or combined with inorganic fertilizers increases maize yield and soil C sequestration potential. The increase was attributed to high Alkyl and O-Alkyl C SOM functional groups. Hence, knowing the C fraction content of organic inputs is vital in determining the best-fit management technologies for ameliorating soil fertility and sustaining and/or improving crop yields.

Advancing the science and practice of ecological nutrient management for smallholder farmers

“…Compared to organic amendments, N i has the smallest impact on C org accrual (Han et al, 2016;Luo et al, 2018). In cases where greater C org is detected in F i treatments compared to zero input controls is often due to a reduced rate of SOM loss rather than net SOM accrual (Ladha et al, 2011;Ndung'u et al, 2021;Tiefenbacher et al, 2021). Use of organic amendments, either alone or paired with F i , accelerates SOM accrual, and provides other benefits including increases in microbial abundance/activity, including beneficials such as arbuscular mycorrhizae fungi (Figure 5; Jiang et al, 2021).…”

“…Use of organic amendments, either alone or paired with F i , accelerates SOM accrual, and provides other benefits including increases in microbial abundance/activity, including beneficials such as arbuscular mycorrhizae fungi (Figure 5; Jiang et al, 2021). While fertilizers often improve crop yields in smallholder systems, sole reliance on F i does not provide expected yield boosts (Jayne et al, 2018) or deliver substantive soil health benefits (Ndung'u et al, 2021;Young et al, 2021). A study of over one thousand smallholder fields in Malawi is a case in point; management factors associated with soil C org levels included crop diversity, weeds and organic residue incorporation, but not fertilizers (Tu et al, 2022).…”

Roots prime microbes to extract nitrogen and stabilize soil organic matter

“…In contrast to plants, soil microbes are primarily understood to be energy, or carbon, limited (Soong et al, 2020). As such, organic fertilizer that contains C and N can prime microbial activity and decomposition relative to inorganic N fertilizer (Cui et al, 2022;Ndung'u et al, 2021). However, uncertainty remains in the extent to which the priming of microbial activity leads to net soil C losses by enhancing decomposition or net C gains by promoting the production of microbial necromass that can form more stable SOM.…”

Nutrient management and bioaugmentation interactively shape plant–microbe interactions inMiscanthus × giganteus

“…Inorganic fertilization provides readily available mineral nutrients to plants and can reduce plant investment in and reliance on rhizosphere microbes (Fan et al, 2019; Lourenço et al, 2018; Pan et al, 2014). On the other hand, organic amendments like dairy manure include nutrients and carbon contained within organic matter and require further breakdown by microbes to be available to plants, which may be linked to the positive impacts of organic fertilization on microbial activity and soil carbon (Ndung'u et al, 2021). As such, these two types of fertilization may differentially affect the relationship of Miscanthus with its rhizosphere microbiome (Ai et al, 2015; Lourenço et al, 2018).…”