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Active Al, Fe and Si (i.e., oxalate extractable fraction: Alo, Feo, Sio) strongly affect soil physical, chemical and biological properties. This study examined the pedogenic factors affecting Alo, Feo and Sio contents across a soil weathering sequence in the Cameroon volcanic line. We investigated the B horizon (∼50-cm depth) from 26 soils formed in basaltic materials at different elevations (110–2570 m) incorporating a wide range of temperature (14–27 °C) and precipitation (1520–3130 mm). The weathering sequence ranged from weakly weathered Andisols in the southwest region grading to strongly weathered Oxisols on the central highlands. We assumed pyrophosphate extractable Al/Fe (Alp/Fep) as organo-Al/Fe complexes, and Sio, (Alo − Alp) and (Feo − Fep) as short-range-order (SRO) minerals. Factor analysis of climatic (e.g., temperature and precipitation/leaching metrics) and soil geochemical properties (e.g., weathering indices) identified three independent factors representing temperature/dry season intensity, weathering degree and precipitation/leaching as the primary determinants of Alo, Feo and Sio concentrations. Organo-metal complexes (Alp and Fep) were negatively correlated with the temperature/dry season intensity factor, whereas the SRO mineral phases (Sio, Alo − Alp and Feo − Fep) were negatively correlated with weathering degree. The precipitation/leaching factor positively correlated with Alo, Feo and Sio. Our analysis infers that low temperature promotes the formation and preservation of organo-Al/Fe complexes, whereas weathering degree is more critical for SRO minerals. Further, increased weathering and a drier climate enhance the formation of crystalline clay minerals at the expense of SRO minerals. Allophanic materials (Sio) were evident (Sio: 9–43 g kg−1) only in weakly weathered soils. However, low allophanic contents were found in more highly weathered soils (Sio: 2–7 g kg−1) accompanied by high Alp and Fep, suggesting the importance of volcanic parent materials as a direct source of Al and Fe via weathering for the formation of organo-metal complexes. In sum, we clarified the discriminatory effects of climatic factors and degree of weathering in regulating the composition of the active Al, Fe and Si fractions along the Cameroon volcanic line.

Climate and parent material are considered the primary factors determining the distributions of soil clay (secondary) minerals, but their influence has not been rigorously elucidated for tropical volcanic soils. Herein, we investigated soil secondary mineral distributions in volcanic regions of Java and Sumatra islands representing large variations in climatic (mean annual temperature (MAT): 13 to 27°C; precipitation: 1910 to 3950 mm) and parent material conditions (rhyolitic-to-basaltic tephra). Soil secondary minerals were assessed by selective extractions, X-ray diffraction analysis, and differential thermal analysis. Moreover, the thermodynamic stabilities of minerals were evaluated based on the ion activities of equilibrated soil–water suspensions. Factor analysis of climate and soil geochemical (e.g., total Si, Fe and K) properties identified temperature, dry season intensity, and parent material as the primary factors regulating secondary mineral distributions. A negative correlation between oxalate extractable Al and Fe (Alo and Feo) and the temperature factor indicates low temperature promoted the formation and preservation of short-range-order (SRO) minerals and organo-Al/Fe complexes, which resulted in Alo + 1/2Feo ≥ 20 g kg−1 (andic property criterion) at MAT

The rice-wheat cropping system (RWCS) provides the world's population with staple foods, and it is crucial to maintain global food demand and security. Food systems are a complex ecosystem and sustain many feedback mechanisms. Crop residue management is one of those feedback mechanisms that was assessed under conservation agriculture, and a decomposition study was analyzed for the rice-wheat cropping system using rice, wheat, and maize crop residue for decomposition rate and nutrients release under agricultural practices (zero till, raised beds). Different zero tillage techniques in Samastipur demonstrated an accelerated decomposition trend, which was especially noticeable in the straw from wheat and rice. At the same time, permanent bed systems showed a relatively larger residue mass, especially in the case of wheat and maize straw. Permanent bed systems (wheat-maize system), particularly those using wheat straw, held the largest amounts of residue mass when the total residue mass throughout the sites was taken into account. Samastipur showed higher nutrient release for all the rice residue in wheat, rice residue in maize, and wheat residue in rice except maize residue in rice as compared to the Karnal sites. Decomposition kinetics, modeled via a first-order exponential decay function, showed high correlations (R2: 0.941 to 0.996) across treatment methods. The research underscores the significant effect of agroecological factors on residue decomposition and nutrient release, irrespective of residue type, highlighting the importance of tailored residue management practices for enhanced nutrient cycling and sustainability. These findings contribute to the optimization of residue management strategies in RWCS, promoting sustainable agriculture practices in the face of climate change and increasing food security demands. [ABSTRACT FROM AUTHOR]

This study evaluates the impact of conservation agriculture (CA) on soil carbon sequestration and crop productivity in the Indo-Gangetic Plains, focusing on short-term effects over 3 and 5 years. Conducted at two distinct sites, Karnal and Samastipur, the research compares zero tillage, permanent raised beds, and conventional tillage systems across diverse cropping patterns. Initial findings after 3 years showed no significant differences in carbon and nitrogen stocks at Karnal, while Samastipur's maize-mustard-mungbean rotation on permanent raised beds showed increased carbon stocks. Notably, after 5 years, significant differences in soil carbon stocks emerged at both sites, with improved organic matter input indicated by coarse particulate organic matter (cPOM) formation. The study confirms the potential of POXC and POC as early indicators for carbon sequestration in CA systems, highlighting the role of CA practices in enhancing soil health and crop productivity sustainably. [ABSTRACT FROM AUTHOR]

To investigate how the long-term application of inorganic fertilizer and organic amendments affects the turnover rates of organic matter in physico-chemically fractionated components in paddy soils and how their rates are related to their amounts, we studied the effect of variable management of inorganic fertilizer and organic amendments for > 50 years on the ∆14C values of accumulated soil organic carbon (SOC) in fractionated components of 5 soil samples from three paddy fields. SOC was fractionated into four components based on their physico-chemical properties: (1) light fraction (LF) derived from plant residues, (2) heavy fraction (HF) containing stable aggregates, (3) oxidizable fraction (OxF) and (4) non-oxidizable fraction (NOxF) forming organo-mineral complexes with fine-textured minerals. The ∆14C values were determined by accelerator mass spectrometry using graphitized samples. The ∆14C values of SOC in NOxF (from −305‰ to − 90.5‰) were much lower than those of HF (from −123‰ to − 3.7‰) and OxF (from −215‰ to 21.0‰). Lowest values for NOxF suggested slowest turnover rates as expected, and higher and comparable values for OxF and HF implied much faster turnover rates of SOC in OxF compared with upland soils. This could be one of the characteristics of SOC dynamics in paddy soils, probably reflecting repeated puddling of plow layer soils. ∆14C values in all the fractions increased in response to the application of inorganic fertilizer and organic amendments, suggesting faster turnover rate. Soils with clayey and weathered characteristics had the lowest ∆14C values, or slowest turnover rates among the study fields. The relationship between the ∆14C value and the amount of accumulated C for HF, OxF and NOxF indicated that the more the SOC accumulated, the faster the turnover rate of the SOC was, regardless of the fractions, and the relationship of the HF was considerably different from those of OxF and NOxF. In conclusion, these results can be the basis for understanding the C dynamics and for improving soil fertility status and soil C sequestration in paddy soils. [ABSTRACT FROM AUTHOR]