Long-term Organic Amendments Research Articles

Comparative evaluation of 16S rRNA primer pairs in identifying nitrifying guilds in soils under long-term organic fertilization and water management.

Compared with 454 sequencing technology, short-read sequencing (e.g., Illumina) technology generates sequences of high accuracy, but limited length (<500 bp). Such a limitation can prove that studying a target gene using a large amplicon (>500 bp) is challenging. The ammonia monooxygenase subunit A (amoA) gene of ammonia-oxidizing archaea (AOA), which plays a crucial part in the nitrification process, is such a gene. By providing a full overview of the community of a functional microbial guild, 16S ribosomal ribonucleic acid (rRNA) gene sequencing could overcome this problem. However, it remains unclear how 16S rRNA primer selection influences the quantification of relative abundance and the identification of community composition of nitrifiers, especially AOA. In the present study, a comparison was made between the performance of primer pairs 338F-806R, 515F-806R, and 515F-907R to a shotgun metagenome approach. The structure of nitrifier communities subjected to different long-term organic matter amendment and water management protocols was assessed. Overall, we observed higher Chao1 richness diversity of soil total bacteria by using 515F-806R compared to 338F-806R and 515F-907R, while higher Pielou's evenness diversity was observed by using 515F-806R and 515F-907R compared to 338F-806R. The studied primer pairs revealed different performances on the relative abundance of Thaumarchaeota, AOB, and NOB. The Thaumarchaeota 16S rRNA sequence was rarely detected using 338F-806R, while the relative abundances of Thaumarchaeota detected using 515F-806R were higher than those detected by using 515F-907R. AOB showed higher proportions in the 338F-806R and 515F-907R data, than in 515F-806R data. Different primers pairs showed significant change in relative proportion of NOB. Nonetheless, we found consistent patterns of the phylotype distribution of nitrifiers in different treatments. Nitrosopumilales (NP) and Nitrososphaerales (NS) clades were the dominant members of the AOA community in soils subject to controlled irrigation, whereas Ca. Nitrosotaleales (NT) and NS clades dominated the AOA community in soils subject to flooding irrigation. Nitrospira lineage II was the dominant NOB phylotype in all samples. Overall, ideal 16S rRNA primer pairs were identified for the analysis of nitrifier communities. Moreover, NP and NT clades of AOA might have distinct environmental adaptation strategies under different irrigation treatments.

Soil organic carbon pools under long-term mineral and organic amendments: a multisite study

Soil organic carbon (SOC) has various pools with different stabilization mechanisms. It is unclear how these SOC pools respond to various mineral and organic amendments depending on a large climate-soil gradient. Here, we studied in three zonal soils: Ferralic Cambisol (subtropic), Calcaric Cambisol (warm-temperate) and Luvic Phaeozem (mid-temperate) under 23-year mineral, straw and manure amendments. Six SOC sub-pools were isolated: unprotected, physically, chemically, biochemically, physico-chemically and physico-biochemically protected pools. Compared to initial level, SOC and most sub-pools increased in the three soils under manure application (p < 0.05), but little under straw and mineral amendments. The Luvic Phaeozems had much higher sequestration efficiencies of bulk SOC (27%) and its five sub-pools (5–7%) more than the Calcaric Cambisol (9%, 1–2%) and Ferralic Cambisol (9%, 0.5–1%). In contrast, Ferralic Cambisol had highest sequestration efficiency of unprotected pool (7%). The Calcaric Cambisol had divergent patterns of the six SOC pools compared with Luvic Phaeozems and Ferralic Cambisol, due to the low clay content. With the build-up of bulk SOC, the building-up abilities of non-protected, physically-, chemically- and biochemically-protected pools depended on soil type, while the building-up abilities of physico-chemically- and physico-biochemically-protected pools were convergent (12–19%) among soils. In conclusion, the Luvic Phaeozems had much higher build-up ability of bulk SOC and most sub-pools than the other two soils. With the build-up of SOC, the physico-chemically- and physico-biochemically-protected pools (most stable) had convergent response rates among soils, while the other pools had divergent response rates.Graphical

Long-term organic amendments increase the vulnerability of microbial respiration to environmental changes: Evidence from field and laboratory studies

Organic amendments can improve soil fertility and microbial diversity, making agroecosystems more resilient to stress. However, it is uncertain whether organic amendments will enhance the functional capacity of soil microbial communities, thereby mitigating fluctuations in microbial respiration caused by environmental changes. Here, we examined the impacts of long-term organic amendments on the dynamics of microbial catabolic capacity (characterized by enzyme activities and carbon source utilization) and microbial respiration, as well as their interrelationships during a period with fluctuating temperature and rainfall in the field. We then subjected the field soil samples to laboratory heating disturbances to further evaluate the importance of microbial catabolic capacity in explaining patterns of microbial respiration. In both field and laboratory experiments, organic amendments tended to increase the stability of microbial catabolic capacity, but significantly increased the vulnerability of microbial respiration to environmental changes. However, the direction and driving factors of microbial respiration affected by environmental changes differed between the field and laboratory experiments. Environmental changes in the field suppressed the promotional effects of organic amendments on microbial respiration mainly through reducing microbial catabolic capacity, while laboratory heating further enhanced microbial respiration mainly due to increased soil resource availability. Together, these findings suggest that increased microbial respiration variations under organic amendments may potentially increase the uncertainty in predicting soil carbon emissions in the scenario of ongoing climate/anthropogenic changes, and highlight the necessity of linking laboratory studies on environmental changes to field conditions.

Long-Term Organic Amendment Application Improves Soil Fertility Status, Nutrient Accumulation and Crop Productivity Under Rice-Wheat Cropping System

ABSTRACT The major issue in modern agriculture is long-term sustainability. Nutrient management by integrating organic manures and inorganic fertilizers may play a vital role in improving and sustaining crop productivity. A long-term field experiment (since 1984) comprising 11 treatments with different combinations of inorganic and organic fertilizers such as farm yard manure (FYM), wheat cut straw (WCS) and Dhaincha (Sesbania aculeata L.) as green manure (GM) was conducted to evaluate their effects on crop yield, nutrient accumulation and soil fertility status under a rice – wheat cropping system. The maximum grain yield of wheat was recorded in T6, i.e. 50% recommended dose of fertilizers (RDF) + 50% nitrogen through FYM in rice and 100% RDF in wheat (4291 kg ha−1) as compared to chemically fertilized plots T5, i.e. 100% RDF in both rice and wheat (3441 kg ha−1). The application of organic manures in combination with chemical fertilizers reduced soil pH and bulk density from 7.40 to 7.23 and 1.49 to 1.37 g cm−3, respectively. Soil organic carbon (SOC), available soil nutrients and nutrient accumulation by crop were higher in integrated nutrient management-treated plots as compared to control. A positive and significant correlation was observed between SOC and available soil nitrogen (r = 0.987), phosphorus (r = 0.913) and potassium (r = 0.921). The results clearly suggest that integrated use of chemical fertilizers and organic manures on a long-term basis improves soil fertility and crop productivity with the potential to enhance soil sustainability

Long-Term Organic Amendments Combined with Nitrogen Fertilization Regulates Soil Organic Carbon Sequestration in Calcareous Soil

Organic amendments have been widely confirmed to support soil health and agricultural sustainability. However, the effects and mechanisms of long-term organic amendments combined with chemical fertilizers on soil organic carbon (SOC) sequestration and soil macroaggregate formation are still unclear. Therefore, this study aimed to explore the interaction between soil carbon sequestration and soil agglomeration after 12 years of fertilization. Seven treatments within a field experiment were selected to conduct the research, including nitrogen (N) application by farmers, optimized N management, biochar and/or straw, manure, compost or biogas residue plus optimized N management. The results showed that the addition of organic materials significantly enhanced the SOC by 29.6–119.8% and 10.3–36.3% in 0–15 and 15–30 cm soil layers compared to N application by farmers, respectively. Meanwhile, the soil humus carbon pools in the 0–15 cm soil layer were increased by 14.7–205.2%, particularly humin carbon (HUC), which could be considered as a useful indicator of the soil carbon sequestration process. Among the organic materials, the addition of biochar was the most effective strategy due to its high aromatic carbon content that resisted biodegradation. The addition of organic materials also improved the soil labile carbon fractions, and the contents of microbial biomass carbon (MBC), dissolved organic carbon (DOC), particulate organic carbon (POC) and KMnO4-oxidizable carbon (ROC) were enhanced by 120.5%, 92.3%, 217.2% and 85.5% on average, respectively, and the amount of exchangeable Ca2+ and Mg2+ cations and Fe and Al oxides in the soil increased significantly whilst the Na+ content declined in the 0–15 cm soil layer. These indicators showed a significant correlation with the mean weight diameter (MWD). Our results revealed that the addition of organic materials could be an effective management practice to promote soil carbon sequestration and soil macroaggregate formation in calcareous soil.

Divergent responses of aggregate stability to long-term mineral and organic amendments between upland and paddy soils

Divergent responses of aggregate stability to long-term mineral and organic amendments between upland and paddy soils

Effect of Long-Term Organic Amendment Application on the Vertical Distribution of Nutrients in a Vertisol

Soil nutrients in deep soils are important for nutrient cycling and plant growth. Organic amendments have been widely used for enhancing soil health and crop yield. However, little is known about the effects of organic amendments on the vertical distributions of soil nutrients. Based on a 32-year long-term organic amendment experiment, the objective of this study was to evaluate changes in the vertical distribution of nutrients in a soybean–wheat system Vertisol. The results showed that NPK with manure or straw application significantly increased soil organic carbon (SOC), total N, total P, alkali-hydrolyzable N, available P and available K above the 40 cm soil layer. Variations in soil micronutrients primarily occurred above the 20 cm soil layer, and the highest contents were observed for NPKWS and NPKPM, respectively. Nevertheless, large amounts of NO3−−N contents accumulated in the 120–200 cm depth with manure but not straw application, indicating a high potential risk of nitrate leaching in manure treatments. These findings suggested that the application of organic amendment (manure or straw) could be recommendable for improving soil nutrients along the soil profile. Straw incorporation could be used as an alternative option for sustainable agriculture in regions with inadequate manure resources or severe nitrate leaching.

Organic amendments increase the flow uniformity of energy across nematode food webs

Energy dynamics within ecological communities are important in delivering ecosystem services. However, it remains elusive how the energy fluxes within soil food webs respond to agricultural fertilization regimes. Here, we studied the effects of long-term organic amendments and mineral fertilizers on the energetic structure of soil nematodes from a food-web perspective. We replicated our experiment in a rice paddy and in an upland maize cropping system. Results showed that the abundance of most trophic groups was higher in organically amended soils compared with mineral fertilizer treatments in both systems. Organic amendments, but not mineral fertilizers, increased the energy flux of total nematodes and most trophic groups compared with the no-fertilizer treatment. Furthermore, organic amendments increased the relative allocation of energy flux to microbivores but decreased the relative allocation to herbivores, supporting a higher flow uniformity than mineral fertilizers. We further found that organic amendments favored a higher total energy flux by supporting a greater nematode diversity, while sustained a higher flow uniformity by altering nematode community composition. Taken together, the result provides the evidence that a complex and species-rich community could transfer more energy to support ecosystem services. A broader perspective on linkages of biodiversity and energy dynamics spanning multitrophic groups is crucial for sustainable management, particularly in the light of non-random species loss under future environmental change.

Mechanisms controlling the stabilization of soil organic matter in agricultural soils as amended with contrasting organic amendments: Insights based on physical fractionation coupled with 13C NMR spectroscopy

Soil organic matter (SOM) has vital roles in the global carbon (C) cycle and the use of organic amendments (OAs) to maintain or improve SOM levels is a promising practice. However, the mechanisms underlying SOM stabilization in OA-amended soils remain insufficiently resolved. For more effective understanding on such issues, we examined soil samples from a long-term experimental plot (26–31 years) that included six treatments, namely, a chemical fertilizer (CF) alone (CF), a bark compost plus CF (BC + CF), a coffee residue compost plus CF (CRC + CF), a cattle manure compost plus CF (CMC + CF), and a cattle manure (CMC) or sewage sludge compost (SSC) alone at a higher application rate, using physical fractionation. In the fractionation, free particulate SOM (fSOM), free SOM occluded in aggregates (oSOM), and SOM weakly bound to minerals (wSOM; s.g. 1.6–2.0 g cm−3) and strongly (sSOM; s.g. >2.0 g cm−3) were separated and characterized using 13C nuclear magnetic resonance (NMR) along with OAs and bulk soil samples. The long-term OA applications enhanced the total C accumulation and the amount of C accumulated as oSOM, wSOM, and sSOM correlated positively with the total C content. The application of BC or CRC resulted in a greater accumulation of fSOM. Conversely, the continuous application of SSC or CMC, which has a high N content and a low C/N ratio, led to a greater accumulation of C, mainly as wSOM. Our findings suggest that both the quality and quantity of OAs control the forms of C that accumulate and this involves different mechanistic pathways. We suggest that the abundant alkyl C in the wSOM and sSOM fractions was SSC-derived SOM in the SSC soil while in the case of the CMC soil, this was due to the increased contribution of microbial-derived SOM.

Assessing Factors Controlling Structural Changes of Humic Acids in Soils Amended with Organic Materials to Improve Soil Functionality

Humic acids (HAs) regulate soil chemical reactivity and improve many soil functions. The amendment of soil with organic materials increases soil organic matter (SOM) content and promotes the formation of HAs. However, the effect of the type, frequency and duration of amendment, and pedoclimatic conditions on SOM transformation and HA structural changes remains unclear. Herein, four experimental field sites (S1–4) with short-to-long-term organic fertilisation schemes were used to assess the effects of such factors, i.e., S1: loamy sand amended once with farmyard manure (FYM), brown coal waste (BCW), and biochar (BIO) for 0.5 and 1.5 years; S2: silt loam amended once with BIO for 8 years; S3: loamy sand amended every 5 years with FYM for 94 years; and S4: clayey silt amended every 2 years with FYM for 116 years. All HAs were extracted and analysed for structural differences by elemental analysis (EA), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), solid-state cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C-NMR), and differential scanning calorimetry (DSC). Results from EA, FTIR, and NMR showed that the long-term samples from S3 (treatments, T9–T10) and S4 (T11–T12) had the greatest aromatic characteristics, which increased with FYM amendment (T10 and T12). These agreed with DSC data, which indicated lower aliphatic contents compared with other samples. Samples from S2 (T7–T8), with receded amendment effects, had less aromatic and greater aliphatic characteristics compared with the short-term samples, S1 (T1–T6). In S1, structural changes were limited, but aromaticity increased with BIO (T3 and T6) compared with corresponding FYM (T1 and T4) and BCW (T2 and T5) amendments due to inherently high aromatic groups in the former. Overall, the results showed that the site (due to differences in pedoclimatic conditions), field age of OM, and amendment frequency were the main factors that influenced HA structure, and hence SOM transformation. Regular, long-term organic amendment increases the aromatic characteristics of HAs, which can improve soil functionality, but short-term structural improvements are achievable only when amending material is rich in aromatic compounds.

Long-term combined application of chemical fertilizers and organic manure shapes the gut microbial diversity and functional community structures of earthworms

Earthworms are crucial regulators of many soil ecosystem processes; however, the effects of fertilization regimes on earthworm gut microbiota remains poorly understood. Here, we investigated the effects of 10 years of fertilization on the gut microbiota of two different earthworm species, Metaphire californica and Amynthas phaselus, belonging to anecic and endogeic ecological groups, respectively. Five fertilization treatments were designed as follows: non-nitrogen fertilizer (CK), nitrogen fertilizer only (NPK), and the combined application of inorganic fertilizers and three different application rates of pig manure (NPKM1, NPKM2, NPKM3). We observed that, compared with the CK and NPK treatments, the organic manure treatments had strong effects on both earthworm gut microbial communities and the associated metabolic functions. The lower application rate of organic manure significantly increased the gut microbial diversity of both earthworm species, which may have further improved their gut microbial metabolic potential, especially for the metabolism of various carbon resources. With the increasing application of organic fertilizers, the abundance of several bacterial families, such as Comamonadaceae, Oxalobacteraceae, and Cytophagaceae, significantly increased in the gut of M. californica. These families have also been identified as the primary indicator taxa of high organic matter inputs and play a crucial role in regulating microbial community functionalities. However, a similar trend was not observed in the gut of A. phaselus, indicating that A. phaselus might be less sensitive to fertilization regimes because it lives deeper in the soil and has a long digestive tract compared with those of M. californica. Our results demonstrated that long-term organic amendment application significantly shapes earthworm gut microbial communities and results in greater decomposition potential of the earthworm gut. Furthermore, our study found that lower application rates of organic matter may be beneficial for earthworm gut microbial diversity and functional structures.

Eight years organic amendment application alters N2O emission potential by increasing soil O2 consumption rate

Organic amendments are efficient measures that can be employed to increase both nitrogen use efficiency and soil organic carbon (SOC) content. However, the long-term effects of such measures on soil N2O emission and the associated underlying mechanisms are still unclear. Here, we sampled soils that were part of two long-term trials after eight years of different amounts and types of organic amendment addition, and investigated the response of soil N2O emissions to different types of mineral N addition under oxic condition. Further, we selected two soil samples with a large difference in SOC content and investigated the responses of soil CO2, N2O, NO, and N2 emissions as well as O2 consumption to NH4+, NO3−, and nitrification inhibitor addition under limited O2 diffusion condition and anoxic condition. Results showed that long-term organic amendments significantly increased SOC content, while the stimulated effect on N2O and N2 emissions owing to increased SOC contents was more pronounced with NH4+ addition under limited O2 diffusion condition than under oxic or anoxic conditions. Further, in all treatments under limited O2 diffusion condition, soil O2 concentration and N2O production showed significant inverse relationships, suggesting that O2 directly regulates N2O production. We speculated that the decrease in O2 availability with higher SOC contents owing to enhanced soil respiration, instead of the increased supply of electron donors, is primarily responsible for the stimulated N2O emissions. This implied that practices which reduce limited O2 diffusion conditions might help to minimize the stimulated N2O emissions from increased SOC content.

Responses of soil microbial community composition and enzyme activities to long-term organic amendments in a continuous tobacco cropping system

Organic amendment may be an effective management practice for alleviating soil degradation in continuous cropping systems. However, few studies focus on the effects of long-term organic amendments on soil microbial community and microbial nutrient status in continuous tobacco fields. Here, an 11-year field experiment was conducted to investigate the effects of organic amendments on plant and soil physiochemical properties, microbial communities, ecoenzymatic stoichiometry, and glomalin-related soil protein (GRSP) accumulation in a continuous tobacco field. Five treatments were applied: CK (no fertilizer); CF (chemical fertilizer only); CFS (chemical fertilizer plus corn straw); CFO (chemical fertilizer plus oilseed residues); CFM (chemical fertilizer plus composted pig manure). Organic amendments increased soil microbial abundances. Application of organic fertilizers significantly reduced gram-positive to gram-negative bacterial ratios, but significantly increased fungi/bacteria ratios, probably because gram-negative bacteria and fungi are the dominant decomposers of increased available nutrients and recalcitrant materials, respectively. Organic amendments significantly enhanced soil enzyme activities, except for the difference in β-1,4-N-acetylglucosaminidase, Leucine aminopeptidase, and polyphenol oxidase (PPO) activities between the CF and CFO. The lowest soil organic carbon (SOC) content in CFS among organic amendments treatments was probably because the positive priming effects of straw and the highest peroxidase and PPO activities increased stable SOC mineralization rates due to the high C:N:P ratio of nutrients input. Microbial activities were limited by carbon, nitrogen, and phosphorus in CFS, while carbon and phosphorus were the limiting factors in CK, CF, CFO, and CFM. Relative to CF, CFO significantly enhanced microbial carbon and phosphorus limitation, whereas CFM significantly decreased microbial carbon limitation. CFM had the highest GRSP content among treatments. Our results demonstrated that combined application of composted pig manure and chemical fertilizers is a consistently effective measure for alleviating soil degradation in continuous tobacco fields.

Effects of long-term organic amendment on the fertility of soil, nodulation, yield, and seed quality of soybean in a soybean-wheat rotation system

Organic amendment has long been recognized as an effective approach to improve soil fertility and plant nutrition. Most studies on long-term organic amendment in fields have focused on cereals. The effects of long-term organic amendment on legumes remain largely unknown. Here we studied the impact of organic amendments, including straw and manure on the soil fertility, nodulation, seed yield, and seed quality in a 27-year experiment. The long-term fertilizer treatments were laid out using a randomized complete block design designed with three replications in the first year of experimentation (1990). Fertilization treatments were CK (no fertilization), NPK (inorganic nitrogen, phosphorus and potassium fertilizers), NPKS (Straw together with inorganic N, P, and K fertilizers), and NPKM (manure together with inorganic N, P, and K fertilizers). The layout was subsequently maintained in the following years to clearly understand the effect of long-term application of each treatment. Maize (Zea mays L.)-wheat (Triticum aestivum L.) rotation was the main long-term experiment cropping system from 1990 to 2011; from 2012 it becomes wheat-soybean (Glycine max L.) rotation. We found that NPKS, NPKM, and NPK increased organic matter by 34.7%, 36.24%, and 17.17%, respectively, and total nitrogen by 28.9%, 29.7%, and 25.2%, respectively, in comparison with CK. Organic amendment also increased enzymatic activity of phenol oxidases and β-1,4-glucosidases. The NPKS and NPKM increased soybean yields by 30.8% and 29.6%, respectively, in comparison with NPK alone and CK. The soybean yields significantly correlated with NO3-N, available phosphorus, available potassium and soil organic matter. Both the inorganic fertilizers and organic amendments did not significantly alter soybean nodule number and size. NPKS and NPKM applications significantly reduced fat content by 1.17% and 1.26%, respectively, as opposed to NPK fertilized treatments alone (0.34%), compared with those under CK, but did not affect soybean protein. Overall, the combination of straw returning with inorganic fertilizers and manure with inorganic fertilizers improves soil fertility and increases soybean productivity. However, organic amendments together with inorganic fertilizers might have an undesirable effect on soybean fat content. Organic amendments combined with NPK application have the highest value of protein content and increased nitrogen to the soil. High nitrogen reduced fat and increased protein content. Therefore, rate of N inputs should be adjusted under the application of organic amendments together with inorganic fertilizers in fluvo-aquic soil.

Organic amendments drive shifts in microbial community structure and keystone taxa which increase C mineralization across aggregate size classes

Organic amendments can stimulate soil organic carbon (SOC) mineralization and soil aggregation simultaneously, which can improve C sequestration and soil fertility. However, the microbial mechanism governing C mineralization at the aggregate level remains uncertain. Here, we investigate how long-term organic amendments change SOC mineralization via affecting the microbial community composition and their co-occurrence pattern from micro-to macroaggregates. Four fertilization regimes from an 8-year field experiment were selected to study this mechanism, i.e., no fertilization (CK); inorganic NPK fertilizer (NPK); NPK + straw (NS); and NPK + straw and manure (NSM). Our results indicated that organic amendments significantly modified the C dynamics, bacterial and fungal community composition and network topological patterns in all aggregate sizes. Specifically, for microbial community composition, organic amendments increased the relative abundance of most Gram-negative bacteria and saprotrophic fungi. For microbial network relationships, organic amendments shifted keystone taxa from oligotrophs to copiotrophs in the bacterial network, and from Eurotiales to Sordariales in the fungal network, respectively. In addition, organic amendments alleviated competitive interactions coupled with keystone taxa in the bacterial network. These microbial changes were responsible for the increase of C mineralization in all aggregates, but the dominant microbial mechanisms varied with aggregate size. The alleviated competitive interactions coupled with keystone taxa of the bacterial network dominated the increases of C mineralization in macroaggregates, while the bacterial community composition did so in microaggregates. However, the fungal community composition only showed a significant impact on altering C mineralization in macroaggregates. Overall, our study provides a fundamental understanding of the microbial regulation of C dynamics at the aggregate level and highlights the importance of network topological patterns.

Phosphorus loss through surface runoff and leaching in response to the long-term application of different organic amendments on sloping croplands

Sustaining crop yield and decreasing the environmental risk of phosphorus (P) loss are key challenges for P fertilization management, which is helpful for achieving the goals for agriculture sustainable development. The effects of the long-term application of different organic amendments on P loss through surface runoff and leaching on sloping croplands have not been studied until now. We simultaneously measured the P loss based on a long-term fertilization experiment using a lysimeter (8 × 4 m2) with four treatments: control (no fertilizer; CK), mineral fertilizer (MF), mineral fertilizer combined with swine manure (MFSM), and mineral fertilizer combined with crop straw (MFCS). Annual P loss loads through surface runoff and leaching in the MF treatment were 90.3 ± 29.4 and 39.2 ± 13.2 mg m−2, respectively. The quantitative relationship between soil P surplus and total P loss load was described by a positive linear function, which suggested that a total P loss of approximately 2.9 kg ha−1 occurred with each 100 kg ha−1 of P surplus. P recovery efficiencies in the MFSM and MFCS treatments increased obviously by 24.0% and 34.5%, whereas soil P surplus decreased by 10.5% and 62.4%, respectively. Overall, the yield-scaled total P losses for the MFSM and MFCS treatments decreased significantly by 71% and 200%, respectively, compared with the MF treatment (0.12 ± 0.04 kg t−1). Long-term organic amendment application, especially for crop straw, effectively decreased P surplus and P loss, thereby increasing P efficiency. We recommend the combined application of mineral fertilizer with crop straw as a sustainable agronomic P management practice to achieve sustainable goals for development of the United Nations and the land degradation neutrality challenge.

Effect of long-term organic amendments on the full-range soil water retention characteristics of a Vertisol

Enhancement of soil water holding capability is of great interest for the management of agro-ecosystems to increase water use efficiency and crop yields. Application of organic amendments has been reported to affect the wet range of the soil water retention characteristic (SWRC, pF ≤ 4.2) differently and knowledge of the impact on the dry range of the SWRC (pF > 4.2) is limited. In this study, we evaluated the effect of 33 years application of inorganic fertilizer and organic amendments, including wheat straw, cow and pig manure on the full range of the SWRC of a Vertisol. Results showed that long-term application of inorganic fertilizer did not significantly affect soil water retention. The addition of organic amendments, i.e. wheat straw, pig or cow manure in combination with inorganic fertilizer significantly increased the wet range of the soil water retention, which was attributed to improved soil structure by increased SOC content. However, plant available water content was not significantly improved by organic amendments. Application of organic amendments decreased or had no effect on soil water retention at pF > 5.5, indicating the hygroscopic water was less impacted by SOC content. Our results showed that the effects of organic amendments mainly improved the retention of the capillary water but not the adsorption of hygroscopic water. This provides new insights on the understanding of water behaviors in Vertisols.

Impact of long-term chemical fertilizer and organic amendment to Fusarium root rot of soybean

Soil suppressiveness to Fusarium root rot of soybean had been observed in a black soil field after a long-term fertilization with nitrogen (N) and phosphorus (P) fertilizer combined with pig manure as organic amendment (NPM), rather than that with only nitrogen and phosphorus fertilizer (NP) or no fertilizer (NF). To determine the microbial role on this suppressiveness, fungal and bacterial community characteristics in NPM, NP and NF treatments were investigated by qPCR and DGGE. Compared with the similar bacterial community characteristics among 3 treatments, fungal community, especially Fusarium population size and community composition in NPM treatment were different with those of NP and NF groups. Based on the isolation and pathogenicity test, pathogenic F. oxysporum, F. graminearum, F. verticillioide and F. lateritium absolutely dominated Fusarium community in NF and NP groups. Nonpathogenic F. avenaceum, F. equiseti, F. culmorum, F. redolens, F. solani and F. tricinctum dominated Fusarium community in NPM group. Isolation rate of pathogenic Fusarium in NPM reduced from 100% to 38% in NF. These results suggested that the dominance of soil non-pathogenic Fusarium population induced by organic amendment might play an important role on suppressing Fusarium root rot in the tested field.

Understanding how long-term organic amendments increase soil phosphatase activities: Insight into phoD- and phoC-harboring functional microbial populations

In context of the use of organic materials as alternatives for mineral fertilizer, it is important to understand how organic amendments influence soil extracellular phosphatase activities which accelerate the mineralization of organic phosphorus (P). To address this, the current study investigates the influence of organic amendments on acid (ACP) and alkaline (ALP) phosphatase activities in soils and how organic amendments influence these activities from the perspective of microbially-mediated pathways. Herein, a comprehensive meta-analysis of 599 measurements from 106 published studies around the world was performed as well as a field component sourced from a 30-year-old field experiment on fertilization. Based on meta-analysis, organic amendments increased average extracellular ACP and ALP activities by 22% and 53%, respectively, in comparison to the mineral-only fertilization. Observed increases in activities were consistent with significant increases in soil organic carbon (C), total nitrogen (N) and available P contents, and microbial biomass C and N pools. According to the data from the long-term field experiment, we found phoD-harboring species encoding ALP were more closely correlated with phoC-harboring species encoding ACP in organically amended soils, and more network hubs were also observed by organic amendment. Soil C:P and N:P ratios, and microbial biomass C were the main predictors of the abundance, diversity, and composition of the phoC- and phoD-harboring populations. Further analysis revealed that the soil C:P ratio was identified as the dominant predictor of potential ACP and ALP activities. Our work highlights the importance in understanding how soil C:N:P stoichiometry mediates phosphatase-harboring populations in order to determine the downstream consequences of using organic amendments for increasing phosphatase activities.

Effects of Organic Amendments on the Transformation of Fe (Oxyhydr)Oxides and Soil Organic Carbon Storage

Organic amendments from animal production are commonly used for promoting soil fertility, and their impacts on the residual soil organic carbon (SOC) are of both agricultural and environmental interest. Iron (Fe) in the form of (oxyhydr)oxides has been proposed to play a critical role in long-term SOC preservation by forming Fe-organic associations, though currently a comprehensive understanding of how these Fe-organic associations are regulated by long-term organic amendments is limited. Here, we synthesize information to link Fe (oxyhydr)oxides, SOC sequestration, and long-term organic inputs from both field and laboratory studies. The results show that vigorous Fe mobilization can be regulated by long-term application of organic amendments, and these organically amended soils contained significantly higher concentrations of poorly crystalline Fe that was closely related to SOC storage in both upland and paddy soils. Potential mechanisms are proposed as follows: (1) DOM from the organically-amended soils is more likely to co-precipitate with poorly crystalline Fe, and DOM from the inorganically-fertilized soils is to a larger extent adsorbed on poorly crystalline Fe. The co-precipitated Fe-OM complexes are more resistant to desorption than the adsorbed OM. (2) DOM extracts from soils treated with organic amendments exhibit a stronger inhibitory effect on the crystallization of poorly crystalline Fe than DOM from inorganically fertilized soils, which may be the consequence of increased numbers of aromatic functional groups. Organic acids in root exudates increased soil mineral availability and the formation of poorly crystalline minerals. Compared to inorganic fertilizers, organic amendments significantly increase (> 20%, p < 0.05) the concentration of poorly crystalline minerals in the presence of actual roots. (3) Microbially-mediated Fe cycling is strongly linked to the Fe mineralogy in soils, and regulated by long-term organic amendments. Greater consumption of poorly crystalline Fe was observed in inorganically-fertilized soil than that in organically amended soil, due to a higher relative abundance of Fe(III) reducers. Conversely, Fe(II) oxidizers were more abundant, and produced higher levels of poorly crystalline Fe under organic amendments. In conclusion, continuous organic amendments initialize a positive feedback loop for the maintenance of poorly crystalline Fe in soils, which can contribute to enhanced SOC storage.