Long-term Fertilizer Application Research Articles

Evidence for the accumulation of toxic metal(loid)s in agricultural soils impacted from long-term application of phosphate fertilizer

Phosphate fertilizers may contain elevated concentrations of toxic metals and metalloids and therefore, their excessive application can result in the accumulation of both phosphorus (P) and metal(loid)s in agricultural soils. This study aims to investigate the occurrence, distribution, and potential plant-availability of metal(loid)s originating from phosphate fertilizer in a long-term experimental field at the Tidewater Research Station in North Carolina, where topsoil (10–20 cm deep) and subsoil (up to 150 cm deep) samples were collected from five plots with consistent and individually different application rates of P-fertilizer since 1966. We conducted systematic analyses of P and metal(loid)s in bulk soils, in the plant available fraction, and in four sequentially extracted soil fractions (exchangeable, reducible, oxidizable, and residual). The results show that P content in topsoils were directly associated with the rate of P-fertilizer application (ρ = 1, p < 0.05). Furthermore, P concentrations were highly correlated with concentrations of Cd, U, Cr, V, and As in the bulk topsoil (ρ > 0.58, p < 0.05), as well as the potential plant-available fraction (ρ > 0.67, p < 0.01), indicating the accumulation of the fertilizer-derived toxic metal(loid)s in the topsoil. Significant correlations (p < 0.001) of metal(loid)s concentrations between the bulk soil and the potential plant-available fraction raises the possibility that P-fertilizer application could increase the accumulation of toxic metal(loid)s in plants, which could increase human exposure. Results from sequential leaching experiments revealed that large portions of the trace elements, in particular Cd, occur in the soluble (exchangeable and reducing) fractions of topsoil with higher P-fertilizer input, whereas the levels of redox-sensitive elements (As, V, U, Cr) were higher in the reducible and oxidizable fractions of the soils. Overall, the data presented in this study demonstrate the effect of long-term P-fertilizer application on the occurrence and accumulation of a wide range of toxic metal(loid)s in agricultural topsoil.

Effects of Long-term Combined Application of Organic and Inorganic Fertilizers on Soil Carbon Pool and Greenhouse Gas Emissions in Orchards

Applying organic fertilizer can increase the contents of soil organic carbon (SOC) and active organic carbon, which are crucial for strengthening soil quality and fertility. Four treatments were established:no fertilization (CK), single application of organic fertilizer (M), single application of chemical fertilizer (NPK), and combined application of organic and inorganic fertilizers (MNPK). The changes in SOC and active components under long-term combined application of organic and inorganic fertilizers were investigated, as were the effects of various fertilization measures on greenhouse gas emissions. Moreover, we evaluated the variation in the soil carbon pool management index (CPMI). Total organic carbon (TOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidized organic carbon (EOC), and particulate organic carbon (POC) increased by 82.84%, 66.30%, 21.12%, 93.28%, and 145.80%, respectively, when compared to those in the CK treatment. The NPK treatment had no discernible effect on SOC and organic carbon components. The combined application of organic and inorganic materials could enhance LI, CPI, and the soil carbon pool management index, with the increase in LI and CPI being the primary reason for the increase in CPMI. Correlation analyses revealed that soil organic carbon components and CPMI were significantly positively correlated with greenhouse gas emissions. The combined application of organic and inorganic materials enhanced cumulative CO2 emissions and warming potential (GWP) but decreased GHGI and yielded a maximum of 56365 kg·hm-2. Compared with that in the CK treatment (29073 kg·hm-2), apple yield in MNPK increased by 93.87%. Therefore, applying organic and inorganic fertilizers in dryland apple orchards can improve the accumulation of organic carbon and stabilize the soil carbon pool, which is more beneficial to the sustainable development of orchards.

Long-term application of controlled-release fertilizer enhances rice production and soil quality under non-flooded plastic film mulching cultivation conditions

Agricultural practices that integrate plastic film mulching (PM) cultivation and controlled-release urea have been widely used to conserve water and increase crop yields. The interactive responses of rice productivity and soil quality to long-term plastic film mulching cultivation and controlled-release urea have not yet been comprehensively elucidated, and whether or not plastic film mulching cultivation combined with controlled-release urea is suitable for rice production remains unclear. A 12-year field experiment with two water regimes (continuously flooded [CF] and PM) and three nitrogen (N) fertilization treatments (no N fertilizer, urea, and controlled-release urea) was conducted to explore the long-term effects on rice yield, soil physicochemical and biological properties, and soil quality in a single rice cropping system. Compared to continuously flooded system, the plastic film mulching system maintained rice productivity (CF: 6.9 t ha−1; PM: 7.1 t ha−1) with higher water productivity (CF: 0.9 g L−1; PM: 2.0 g L−1). Controlled-release urea treatments improved rice yield by 11.9% and 44.6% compared to treatments with urea and no N fertilizer, respectively. Random forest analysis indicated that enzyme activity was the main factor affecting rice yield. Compared to continuously flooded system, the plastic film mulching system significantly increased soil pH by 3.4% and decreased soil organic matter content by 9.3%. Moreover, the plastic film mulching system exhibited significantly higher enzyme activity than the continuously flooded system. Principal coordinate analysis of enzyme activities showed that N fertilization influenced enzyme activities considerably more than water regime. According to Pearson’s analysis, soil fungal alpha diversity was more sensitive to soil physicochemical properties than bacterial alpha diversity. Overall, treatment with controlled-release urea in the plastic film mulching system resulted in the highest soil quality index values, which were positively correlated with rice yield (R2 = 0.61, p = 0.000). The positive direct effects induced by continuously flooded cultivation (i.e., satisfying the water requirements of rice) were counterbalanced by the negative indirect effects of altered enzyme activity. The N fertilizer type indirectly influenced rice yield by altering soil nutrients, enzyme activity, and microbial diversity. Therefore, controlled-release urea could maintain rice production with high soil quality under non-flooded plastic film mulching cultivation conditions.

The Effects of Long-Term Application of Stabilized and Coated Urea on Soil Chemical Properties, Microbial Community Structure, and Functional Genes in Paddy Fields

The addition of fertilizers is indispensable in agricultural production, and currently, there is a wide variety of new types of fertilizers available. For example, commonly used are stabilized fertilizers with inhibitors and coated slow-release fertilizers, among others. However, the long-term effects of these fertilizers, when applied continuously are still uncertain. This study will provide scientific and theoretical support for the development and promotion of these fertilizers. A 16-year paddy field with brown soil treated with different urease and nitrification inhibitors, sulfur-coated urea (SCU), and resin-coated urea (PCU) was studied. The study showed that long-term use of conventional urea nitrogen fertilizer resulted in a significant reduction in soil total phosphorus (TP). Long-term application of NBPT and conventional urea significantly increased soil organic matter (SOM). Moreover, except for HQ and NBPT+DMPP, the prolonged application of new urea fertilizers also significantly enhanced soil total potassium (TK). Application of SCU fertilizer in brown soil type paddy fields resulted in a significant decrease in soil pH over time. However, changes in pH had no effect on the abundance of ammonia-oxidizing bacteria (AOB), as AOB was mainly affected by soil-available N. DMPP, HQ+DCD, NBPT+DMPP, SCU, and PCU significantly reduced the 16S rRNA gene copy number of soil bacteria, with the greatest effect of coated urea fertilizer (SCU and PCU). Long-term application of stable urea fertilizer with HQ significantly reduced the bacterial community in paddy soil. Conversely, HQ+DCD-stabilizede urea fertilizer significantly increased the population structure and abundance of Basidiomycota fungi while decreasing the population structure and abundance of Rozellomycota fungi. DMPP-stabilized urea fertilizer notably increased the population structure and abundance of Ascomycota fungi while decreasing the population structure and abundance of Rozellomycota and Chytridiomycota fungi. Furthermore, HQ-stabilized urea fertilizer significantly reduced the population structure and abundance of Chytridiomycota fungi.

Long-term organic fertilization enhances potassium uptake and yield of sweet potato by expanding soil aggregates-associated potassium stocks

Crop straw return and organic manure application are effective and environmentally friendly methods used by farmers to improve soil structure, fertility and agricultural productivity. Sweet potato is a typical “potassium (K)-favoring” food crop and widely grown throughout the world. However, the regulation effects of long-term organic fertilization on soil aggregates-associated K stocks and K uptake by sweet potato are less understood. Herein, a long-term fertilization experiment since 2007 including chemical fertilizer (NPK), NPK combined with commercial manure (NPK+CM), NPK combined with pig manure (NPK+PM), and NPK combined with rice straw (NPK+RS) treatments under peanut-sweet potato crop rotation was employed. Long-term fertilizer application contributed to higher yield, yield stability, and K uptake of sweet potato. NPK+PM and NPK+RS treatments both showed the best promoting effect on plant growth. NPK+PM and NPK+RS treatments showed remarkable increasement of aggregate-associated exchangeable potassium (EK) and non-exchangeable potassium (NEK) stocks, particularly for small-macroaggregates (0.25–2 mm) and large-macroaggregates (> 2 mm). Total potassium (TK), EK and NEK stocks in large and small-macroaggregates displayed positive effects on K uptake and yield for sweet potato. Pearson's correlation and random forest model analysis revealed that EK and NEK stock in large-macroaggregate were the most key factors for K uptake and yield of sweet potato under long-term fertilization. Overall, our study highlights the prominent advantage of long-term organic fertilization.

Contrasting response of soil microbiomes to long-term fertilization in various highland cropping systems

Soil microbiomes play important roles in supporting agricultural ecosystems. However, it is still not well-known how soil microbiomes and their functionality respond to fertilization in various cropping systems. Here we examined the effects of 36 years of phosphorus, nitrogen, and manure application on soil bacterial communities, functionality and crop productivity in three contrasting cropping systems (i.e., continuous leguminous alfalfa (AC), continuous winter wheat (WC), and grain-legume rotation of winter wheat + millet - pea - winter wheat (GLR)) in a highland region of China’s Loess Plateau. We showed that long-term fertilization significantly affected soil bacterial communities and that the effects varied with cropping system. Compared with the unfertilized control, fertilization increased soil bacterial richness and diversity in the leguminous AC system, whereas it decreased those in the GLR system. Fertilization, particularly manure application, enlarged the differences in soil bacterial communities among cropping systems. Soil bacterial communities were mostly affected by the soil organic carbon and nitrogen contents in the WC and GLR systems, but by the soil available phosphorous content in the AC system. Crop productivity was closely associated with the abundance of fertilization-responsive taxa in the three cropping systems. Our study highlights that legume and non-legume cropping systems should be disentangled when assessing the responses of soil microbial communities to long-term fertilizer application.

Soil properties and microbial functional attributes drive the response of soil multifunctionality to long-term fertilization management

Fertilization is a vital management practice to improve soil fertility and promote agricultural production. However, there is limited knowledge about the interactive effects between soil abiotic and biotic factors and soil multifunctionality after long-term fertilization. There has been little research on determining whether the application of organic fertilizers can improve the functional potential of microorganisms to maintain multifunctional stability. In this study, we integrated soil physicochemical properties, extracellular enzyme activities, bacterial community characteristics, and the abundance of functional genes related to carbon (C) and nitrogen (N) cycling to evaluate the mechanism of soil functional potential response to 13 years of fertilization management. Four treatments were compared, including no fertilizer (CK), conventional fertilization (CF), formulated fertilization by soil testing (SF), SF with organic fertilizer (SFO). The addition of organic fertilizer enhanced the soil electrical conductivity, N-cycling enzyme activities, contents of macroaggregate and associated C, and soil nutrients, while decreasing the content of microaggregates compared with other treatments. The co-application of chemical and organic fertilizer led to significant increases in soil multifunctionality and the bacterial Shannon index compared with the CK and CF treatments. Soil abiotic factors are the key predictors for shaping soil multifunctionality. The addition of organic fertilizer could increase the abundance of functional genes related to C- and N-cycling mediated by the contents of nutrients and the aggregates associated with nutrients. Additionally, treatment with organic fertilizer can mitigate the decrease in genes for C-cycling function caused by the long-term application of chemical fertilizer (SF). In addition, the structural equation models revealed that the fertilization positively affected soil multifunctionality indirectly by changing the bacterial diversity and community composition, as well as the functional potential related to N-cycling. Overall, soil properties and microbial functional attributes jointly drive the response of soil multifunctionality to long-term fertilization management. These results suggest that the combination of organic and chemical fertilizer is worth popularizing to improve multifunctionality and its stability to maintain agricultural sustainability.

Nitrogen regime of soddy-podzolic soil with long-term use of different types and combinations of mineral fertilizers

The purpose of the work is to study the effect of various types and combinations of mineral fertilizers on the fractional composition of nitrogen in soddy-podzolic soil in a long-term stationary experiment and compare it with a virgin analogue. The studies were carried out in 2016 and 2018 on the experimental field of the Perm Research Institute of Agriculture after harvesting barley in an eight-field crop rotation deployed on soddy-podzolic heavy loamy soil. The experiment scheme: without fertilizers: N90; Р90; К90; N90P90; N90K90; P90K90; N90Р90К90. To assess the effect of nitrogen, phosphorus, potash fertilizers and their combinations on the nitrogen regime of soddy-podzolic soil, the arable soil was compared with the virgin analogue. The nitrogen fund of soddy-podzolic soil of a long-term stationary experiment is represented by 64…71 % non-hydrolyzable and 17…22 % hardly hydrolyzable forms of nitrogen. Long-term use of various types and combinations of mineral fertilizers did not significantly change the ratio of nitrogen fractions characteristic of virgin soils of this type. Nitrogen fertilizers, both with one-sided application and in combination with potassium chloride (N90К90) and superphosphate (N90P90), contributed to an increase in the total nitrogen content in the arable soil layer by 10…20 % relative to the control, mineral nitrogen compounds - by 2…3 times. Unilateral application of potash fertilizer provided an increase in the content of total nitrogen in the soil by 12 %, the introduction of superphosphate did not have a signi cant effect on the nitrogen regime of the soil. Long-term use of complete mineral fertilizer (N90P90K90) only in this way: (N90P90К90) contributed to maintaining total nitrogen at the level of virgin soil - 1490 mg/kg. Long-term unilateral application of nitrogen fertilizers increased the content of nitrate nitrogen in the soil over the entire meter layer by 1.5-2.5 times, ammonium - by 1.5-14.6 times. The reserves of mineral nitrogen in the variants N90P90, N90K90, and N90P90K90 in the 0-20 cm layer increased 2-3 times, in the 0-100 cm layer - 2 times relative to the control variant.

The Effects of Localized Plant–Soil–Microbe Interactions on Soil Nitrogen Cycle in Maize Rhizosphere Soil under Long-Term Fertilizers

Long-term fertilization can result in changes in the nitrogen (N) cycle in maize rhizosphere soil. However, there have been few reports on the impacts of plant–soil–microbe regulatory mechanisms on the N cycle in soil. In this study, soil samples were collected from a long-term experimental site located at Jilin Agricultural University, Changchun City, Jilin Province, Northeast China. We then analyzed the changes in the functional genes related to the N cycle, soil enzyme activity, and maize root exudates under long-term fertilizer application using metagenomics and liquid chromatography analysis. We aimed to investigate the response of the N cycle to long-term fertilizers, the interaction among plant, soil, and microbes, and the effect of the plant–soil–microbe system on the N cycle. Long-term fertilization had a significant effect on soil N contents, N2O emissions, and enzyme activity related to the N cycle in maize rhizosphere soil. The functional genes of the N cycle were mainly enriched in the N degradation pathway in maize rhizosphere soil. N fertilizer application decreased the abundance of functional genes related to N fixation and degradation, denitrification, and assimilatory nitrate reduction (ANRA) and increased the abundance of functional genes participating in dissimilatory nitrate reduction (DNRA) and anaerobic ammonia oxidation/hydroxylamine oxidation. The soil environment was positively related to soil enzyme activity and negatively related to the microbial community composition and amino acids in root exudates. The contribution rate of microorganisms to the N cycle was the highest (r2 = 0.900), followed by amino acids (r2 = 0.836) and the soil environment (r2 = 0.832). Therefore, we concluded that N fertilizer is the main factor limiting the soil N cycle and that microorganisms are the main factor regulating the N cycle in the plant–soil–microorganism system.

Effect of Reducing Nitrogen Fertilization and Adding Organic Fertilizer on Net Photosynthetic Rate, Root Nodules and Yield in Peanut.

Long-term excessive application of chemical fertilizers can cause many problems, such as soil degradation and environmental pollution. Therefore, we reduced conventional nitrogen fertilization and added organic fertilizers in some cases to investigate the response of photosynthetic characteristics, root nodules and yield on reduced nitrogen fertilization. Compared to conventional nitrogen fertilization, the 25% and 35% nitrogen reduction treatments reduced the leaf area index, net photosynthetic rate, 100-fruit weight, 100-kernel weight and the yield of peanut, but had no significant effect on the kernel rate. With constant N fertilizer, adding organic fertilization alone increased leaf area index, chlorophyll, net photosynthetic rate and yield of peanut. In compounded treatments of nitrogen and organic fertilizer, the highest yields were achieved in the 25% N reduction with the 3000 kg/hm-2 organic fertilizer treatment (T3) and the 4500 kg/hm-2 organic fertilizer treatment (T4); furthermore, the net photosynthetic rate, leaf area index, yield and fertilizer contribution were significantly higher in these two treatments than in the conventional fertilizer treatments. Nitrogen fertilizer had significant effects on the quantity and fresh weight of root nodules. Concretely, nitrogen reduction increased the quantity and fresh weight of root nodules of peanut in the early stage of fertility but decreased them in the harvest stage. Nitrogen reduction with an additional organic fertilizer in the late stage of fertility increased the quantity and fresh weight of root nodules of peanut. Considering the property of root nodules was significantly positively correlated with net photosynthetic rate and yield, the arguments above may be the mechanism of the highest yields found in T3 and T4. This work can provide empirical and instructional support for a balanced fertilization strategy in peanut agriculture and high-yielding and efficient cultivation of peanut.

Effects of Long-Term Straw Returning and Nitrogen Fertilizer Reduction on Soil Microbial Diversity in Black Soil in Northeast China

Returning straw to the field, coupled with fertilizer application, is an effective means to improve the fertility of black soil in Northeast China. Previous studies have mainly focused on the physical and chemical properties of soil structure and fertility. However, few efforts have been made to study the impact of straw returning on the microbial community of black soil in Northeast China. Here, we studied the typical northeast black soil in Heilongjiang Province to characterize the effects of long-term chemical fertilizer application and straw returning on its bacterial community structure. High-throughput sequencing was conducted to characterize the bacterial community of northeast black soil under different agricultural fertilization treatments, and the main factors affecting the bacterial community of northeast black soil were revealed through bioinformatic analyses. The results of high-throughput sequencing analyses demonstrated that the main bacterial phyla in the black soil in Northeast China were Actinomycetes, Proteobacteria, Acidobacteria, Chloroflexus, and Bacteroidetes. Long-term application of chemical fertilizers significantly increased the fertility and crop yield of black soil in Northeast China but led to significant changes in bacterial community structure and a significant decrease in diversity. Although straw returning improved soil fertility, it did not alleviate the adverse effects of the long-term application of chemical fertilizers on soil bacterial communities. Furthermore, our results demonstrated that changes in soil pH were the main factor leading to variations in soil bacterial communities. Returning straw to the field based on fertilizer application can improve black soil fertility in Northeast China but fails to alleviate the adverse effects of fertilizer-induced soil acidification on the composition and diversity of soil bacterial communities. This suggests that returning straw to the field may not have a significant beneficial impact on the microbial ecology of the black soil of Northeast China. Therefore, further research is needed to establish new straw return strategies to maximize agricultural yields while minimizing ecological impacts.

Manganese losses induced by severe soil acidification in the extensive Lei bamboo (Phyllostachys violascens) plantation stands in Eastern China

Manganese (Mn) is a critical element in soils, essential to plant growth. Long-term and intensively managed Lei bamboo (Phyllostachys violascens) stands are usually subjected to severe soil acidification and Mn activation. However, Mn migration from topsoil to deep soil induced by severe soil acidification was poorly recognized and studied. The distribution and changes of the total and the operationally defined Mn forms in soil profiles and its potential stress and environmental effect were investigated in a chronosequence of Lei bamboo stands (0, 2, 6, 11, and 16 years of stand age). The results showed that the Mn amount was significantly decreased in topsoil and accumulated in subsoil with the long-term and intensive fertilizer application. Soil exchangeable Mn and superphosphate extractable Mn demonstrated large different variation to total Mn, whereas their sum was largely higher than and highly correlated with 8-hydroxyquinoline (HQN) extractable Mn. Soil organic carbon, pH value, exchangeable bases, and soil redox simultaneously controlled soil Mn depletion. In conclusion, long-term and intensive fertilizer application leads to soil acidification and accelerated soil Mn depletion in bamboo stand soil, promoting Mn accumulation in bamboo shoots.

Response of Soil Absolute and Specific Enzyme Activities to Long-Term Application of Organic Fertilizer to Solonetz in Northeast China

Soil organic carbon (SOC) and microbial biomass carbon (MBC) are highly correlated with enzyme activities. Specific enzyme activities can exclude the autocorrelation between enzyme activity and SOC and MBC. However, the responses of absolute and specific enzyme activities to saline–alkali properties remains unclear. In this study, the absolute and specific enzyme activities of cellobiose hydrolase, β-glucosidase, arylsulfatase, alkaline phosphatase, and urease were measured in soils with 10, 15, 18, 21, and 26 years of organic fertilizer application in contrast to soils without organic fertilizer application. The results showed that long-term organic fertilizer application led to significantly increased in the absolute and specific enzyme activity and decrease in pH, electrical conductivity (EC), exchangeable sodium percentage (ESP), as well as sodium adsorption ratio (SAR5:1). In the structural equation model (SEM), the EC extremely limited the geometric mean of specific enzyme activity per unit of MBC (MBC-GMSEA) (path coefficient, −0.84, p &lt; 0.001). Pearson’s correlation analysis showed that the correlations between EA/MBC and pH, EC, ESP, and SAR5:1 were higher than between the absolute soil enzyme activity and pH, EC, ESP, and SAR5:1. Of the parameters tested, EA/MBC was a more sensitive index to reflect the improvement effect of organic fertilizer on soils and evaluate the saline–alkali barrier.

Effect of Long-Term Use of Fertilizers on Soil-Dwelling Micromycetes of Meadow Chernozem Soil in Wheat Crops

The effect of long-term systematic application of fertilizers on the mycobiota of meadow chernozem soil in a stationary field experiment (Amur region) was studied for the first time. Information about cultivated soil microscopic fungi is given, an annotated list including 26 species is compiled. It was revealed that the application of nitrogen fertilizers (N30) for wheat against the background of long-term use of fertilizers caused an increase in the total number of soil fungi relative to the control variant by an average of 30–68%, whereas with their aftereffect, a less significant increase in the number of mushroom germs was observed (23–29%). The intervals of the optimal content of macronutrients for the active increase of the pool of microscopic fungi in meadow chernozem soil were determined: phosphorus – 50–65, potassium – 195–210, nitrogen – ≥10 mg/kg with optimal soil moisture of 22–24%. The aftereffect of long-term application of fertilizers, especially organo-mineral fertilizers, as well as the application of mineral fertilizers (N30) directly in the year of the study had a positive effect on species diversity, frequency of occurrence and dynamics of the number of fungal germs in the soil. Negative rearrangements of micromycete complexes as a result of prolonged use of mineral fertilizers in the agrocenoses of meadow chernozem soils were not detected, the introduction of nitrogen-phosphorus fertilizers contributed to a significant decrease in the pool of phytopathogenic fungi.

Long-term application of nitrogen and phosphorus fertilizers changes the process of community construction by affecting keystone species of crop rhizosphere microorganisms

Keystone species of microbial communities play a very important role in community structure and ecosystem function; however, the effect of long-term nitrogen (N) and phosphorus (P) fertilizers on key taxa and the mechanisms of community construction of rhizosphere microbial communities remain unclear. In this study, the effect of nine fertilization treatments (N0P0, N0P1, N0P2, N1P0, N1P1, N1P2, N2P0, N2P1, and N2P2) on soil microbial community diversity, keystone species, and construction methods in the crop rhizosphere were studied in a loess hilly area after 26 years of fertilization. The results showed that fertilization significantly increased the nutrient contents of the rhizospheric soil and root system and significantly affected microbial community composition (based on the Bray-Curtis distance) and community construction process (β-nearest taxon index: βNTI). The decrease in the abundance of oligotrophic bacteria (from phyla Acidobacteriota and Chloroflexi) in the keystone species of bacterial communities shifted the community construction process from homogenizing dispersal to variable selection process and was significantly regulated by soil factors (total P and carbon-N ratio). However, the decrease in the abundance of keystone species (from phylum Basidiomycota) in the fungal communities did not have a significant effect on community construction, which was mainly affected by root characteristics (root N content and soluble sugar). This study found that long-term N and P fertilization changed the keystone species composition of bacterial communities by affecting the nutrient content of the rhizospheric soil, such as total P, so that the construction mode of communities changed from a stochastic to a deterministic process, and the N2 fertilization, especially the N1P2 treatment was better for increasing network stability (modularity and clustering coefficient).

STATE AND PROSPECTS OF MINERAL FERTILIZERS USE IN AGRICULTURE OF KAZAKHSTAN

The article is a dedicated analysis of the production and use of mineral fertilizers globally, focusing on the agriculture of Kazakhstan. From 1950 to 2020, the fertilizer use ranged between 3.6–29.0 kg of NPK per hectare in arable agricultural land of Kazakhstan. The maximum benefit of fertilizers happened in 1986 in Kazakhstan, with 1,039 t of mineral fertilizers (active substances) applied at an area of 47% of the total arable land, while in 1965, the fertilized area was only 6.6% of the entire sown field. In Kazakhstan, the annual recommended need for mineral fertilizers is one million tons (active ingredient). The paper also discussed the influence of the long-term application of fertilizers on the leading indicators of soil fertility and crop productivity. Employing regression analysis also explored a high degree of probability of a positive relationship among the four viable factors, i.e., fertilizer use intensity, agrochemical indicators of the soil, crop plants yields, and their quality.

Effect of long-term application of bioorganic fertilizer on the soil property and bacteria in rice paddy

The application of novel bioorganic fertilizer (BIO) has been established as a weed biocontrol strategy, and reduce herbicides pollution and negatively effects on agricultural ecosystems. However, its long-term influences on soil bacterial communities are unknown. Here, 16 S rRNA sequencing to identify the changes that occur in soil bacterial community and enzyme under BIO treatments after five years in a field experiment. BIO application effectively controlled weeds, however no obvious differences between treatments were observed under BIO-50, BIO-100, BIO-200 and BIO-400 treatment. Anaeromyxobacter and Clostridium_ sensu_ stricto_1 were the two dominant genera among BIO-treated soil samples. The BIO-800 treatment had a slight influence on the species diversity index, which was more remarkable after five years. The seven significantly-different genera between BIO-800 treatment and untreated soils included C._sensu_stricto_1, Syntrophorhabdus, Candidatus_Koribacter, Rhodanobacter, Bryobacter, Haliangium, Anaeromyxobacter. In addition, BIO application had different effects on soil enzymatic activities and chemical properties. The extractable P and pH saliency correlated with Haliangium and C._Koribacter, and C._sensu_stricto_1 observably correlated with exchangeable K, hydrolytic N and organic matter. Taken together, our data suggest that BIO application effectively controlled weeds and a slight influence on soil bacterial communities and enzymes. These findings expand our knowledge of the application of BIO as widely used as a sustainable weed control in rice paddy.

Influence of long-term fertilization on soil aggregates stability and organic carbon occurrence characteristics in karst yellow soil of Southwest China.

Current research has long focused on soil organic carbon and soil aggregates stability. However, the effects of different long-term fertilization on the composition of yellow soil aggregates and the characteristics of the occurrence of organic carbon in the karst region of Southwest China are still unclear. Based on a 25-year long-term located experiment on yellow soil, soil samples from the 0-20 cm soil layer were collected and treated with different fertilizers (CK: unfertilized control; NPK: chemical fertilizer; 1/4 M + 3/4 NP: 25% chemical fertilizer replaced by 25% organic fertilizer; 1/2 M + 1/2 NP: 50% chemical fertilizer replaced by organic fertilizer; and M: organic fertilizer). In water-stable aggregates, soil aggregates stability, total organic carbon (TOC), easily oxidized organic carbon (EOC), carbon preservation capacity (CPC), and carbon pool management index (CPMI) were analyzed. The findings demonstrated that the order of the average weight diameter (MWD), geometric mean diameter (GWD), and macro-aggregate content (R0.25) of stable water aggregates was M > CK > 1/2M +1/2NP > 1/4M +3/4NP> NPK. The MWD, GWD, and R0.25 of NPK treatment significantly decreased by 32.6%, 43.2%, and 7.0 percentage points, respectively, compared to CK treatment. The order of TOC and EOC content in aggregates of different particle sizes was M > 1/2M +1/2NP > 1/4M +3/4NP> CK > NPK, and it increased as the rate of organic fertilizer increased. In macro-aggregates and bulk soil, the CPC of TOC (TOPC) and EOC (EOPC), as well as CPMI, were arranged as M > 1/2M +1/2NP > 1/4M +3/4NP> CK > NPK, but the opposite was true for micro-aggregates. In bulk soil treated with organic fertilizer, the TOPC, EOPC, and CPMI significantly increased by 27.4%-53.8%, 29.7%-78.1%, 29.7-82.2 percentage points, respectively, compared to NPK treatment. Redundancy analysis and stepwise regression analysis show that TOC was the main physical and chemical factor affecting the aggregates stability, and the TOPC in micro-aggregates has the most direct impact. In conclusion, the primary cause of the decrease in SOC caused by the long-term application of chemical fertilizer was the loss of organic carbon in macro-aggregates. An essential method to increase soil nutrient supply and improve yellow soil productivity was to apply an organic fertilizer to increase aggregates stability, storage and activity of SOC in macro-aggregates.

Effects of Combined Application of Chemical Fertilizer and Biochar on Soil Physio-Biochemical Properties and Maize Yield

Excessive, long-term chemical fertilizer application adversely affects soil quality and maize yield. The combined application of biochar with chemical fertilizer can increase maize yield and improve soil fertility. A four-year field experiment was conducted to determine soil physio-biochemical properties and maize yield under a soybean–maize rotation in the black soils of Northeast China. There were five treatments, including no fertilization (CK), fertilizer (NPK), fertilizer + biochar (15.75 t·hm−2, BC1), fertilizer + biochar (31.50 t·hm−2, BC2), and fertilizer + biochar (47.25 t·hm−2, BC3). Compared with CK, the number of macroaggregates and the average weight diameter of soil aggregates in BC2 treatment increased significantly by 10.3% and 24.5%, respectively. The soil pH in the study area was 7.03, and it increased in all treatments except for BC1. The highest pH of 7.17 was recorded in NPK and BC2 treatments, which was around the optimal soil pH. In contrast to the CK and NPK treatments, the biochar application increased soil organic carbon (SOC) and total nitrogen (TN) content. The BC2 treatment improved soil C/N and increased the copy number of soil bacteria by 25.6% compared to CK. The combined application of chemical fertilizer and biochar was better than NPK treatment alone, and improved soil mechanical composition and fine soil particle contents (powder and clay). Mixed biochar with chemical fertilizer application also significantly increased maize yield and the weight of 100 grains increased from 9.5% to 10.9% compared to CK. The maize yield of the three fertilizer and biochar treatments was higher than treatments with applied chemical fertilizer alone, in the order of BC2 &gt; BC3 &gt; BC1 &gt; NPK &gt; CK (BC2 treatment increased by 34.8%). Additionally, the maize yield was significantly and positively correlated with soil aggregates, organic carbon and total nitrogen (p &lt; 0.05) as well as the 100-grain weight (p &lt; 0.01). The application of 31.50 t·hm−2 (BC2 treatment) of biochar can enhance soil physicochemical properties and improve maize yield.

Effects of Long-Term Application of Cl-Containing Fertilizers on Chloride Content and Acidification in Brown Soil

Chloride is a necessary micronutrient for plant growth, and with long-term application of chlorine-containing fertilizer, significant amounts of Cl− are introduced into farmland ecosystems. Many recent studies have focused on chlorinated fertilizers’ effects on crop yield and quality, while few studies have examined their effects on soil properties. To determine the effects of the long-term application of chlorinated fertilizer on soil Cl− ions and soil acidification, we conducted a 35 year long-term study of chlorine-containing fertilizer in a peanut–corn rotation (since 1984). We chose three of eight experimental treatments: (1) no fertilization (CK), (2) urea + monoammonium phosphate + potassium chloride (lower Cl), and (3) urea + ammonium chlorophosphite + potassium chloride (higher Cl). We measured the Cl− concentrations, pH, cation exchange capacity (CEC), exchangeable H+ and Al3+, and exchangeable alkali ions (K+, Na+, Ca2+, and Mg2+) at different soil depths (0–20, 20–40, and 40–60 cm). Compared to CK, chlorine-containing fertilizer application significantly increased the content of Cl− in the soil profile. Compared to the control, the Cl− content of lower Cl treatment of 0–20, 20–40, and 40–60 cm soil layers increased 11.08, 9.01, 15.21 mg kg−1 respectively, and the higher Cl treatment increased 38.71, 34.71, 32.05 mg kg−1 respectively. Compared to CK, chlorine-containing fertilizer application significantly reduced the soil pH by 0.41, 0.17, and 0.25 and 1.25, 0.91, and 0.88, respectively, in the 0–20, 20–40, and 40–60 cm soil layers. The higher chlorine treatment significantly increased the exchangeable Al3+ content in the 0–20, 20–40, and 40–60 cm soil layers by 2.79, 1.64, and 0.94 mg kg−1, respectively, significantly increasing the risk of aluminum toxicity. Furthermore, the soil exchangeable Ca2+ and Mg2+ contents and soil base saturation were significantly reduced. Although the Cl− content in the high-chlorine-treated soil was far from endangering crop growth, it accelerates soil acidification and the loss of base ions and increases the risk of Al3+ toxicity, which will not only affect the topsoil, but also the subsoil. Therefore, the long-term application of high content chloride fertilizers should be avoided in agricultural production.