Long-term Application Of Mineral Fertilizers Research Articles

Effects of LongTerm Application of Mineral Fertilizers and Manure on Agrochemical Properties of Gray Forest Soil, Crops Productivity and Carbon Sequestration

The effect of long-term application of increasing doses of mineral (from N90P75K100 to N360P300K400) and organic (cattle manure from 25 to 100 t/ha) fertilizers on the fertility of gray forest soil was studied in the micro-plot experiment. Over 9 years, 0.81–3.24 t/ha of nitrogen, 0.68–2.70 t/ha of P2O5 and 0.90–3.60 t/ha of K2O were applied with mineral fertilizers. Manure supplied 43–173 t/ha of dry matter, 16–65 t/ha of Corg, 0.85–3.41 t/ha of Ntot, 0.65–2.59 t/ha of P2O5 and 0.86–3.46 t/ha of K2O. In the yield the mineral fertilizer system exceeded the organic one by an average of 29%. At extreme doses (N360P300K400 and 100 t/ha of cattle manure) mineral fertilizers reduced crop productivity more strongly than organic fertilizers. A direct linear relationship was found between the doses of mineral and organic fertilizers and the increase in the content of available P2O5 and K2O in the soil. Application of extreme doses of fertilizers did not lead to saturation of the soil with available forms of phosphorus and potassium. Long-term application of organic fertilizers increased the soil pH(KCl) by 0.4–1.3 units and mineral fertilizers decreased it by 0.8–1.4 units. Annual application of mineral fertilizers increased soil Corg content by an average of 0.02–0.04% per year, and organic fertilizers – by 0.08–0.17% per year. Manure application at 100 t/ha over 9 years led to the saturation of the soil with organic carbon. The C : N ratio in the soil under a mineral fertilizer system was decreased, while it with the organic system was increased. An approach to calculate the carbon sequestration efficiency for the assessment of different agronomic practices is proposed. It is shown that the carbon sequestration efficiency of the organic fertilizers was 15% higher than that of the mineral fertilizers.

Replacing nitrogen in mineral fertilizers with nitrogen in maize straw increases soil water-holding capacity

Soil water-holding capacity decreases due to long-term mineral fertilizer application. The objective of this study was to determine how replacing mineral fertilizer with maize straw affected the soil water retention curve, soil water content, soil water availability, and soil equivalent pore size. Replacement treatments in which 25% (S25), 50% (S50), 75% (S75), and 100% (S100) of 225 kg ha−1 nitrogen from mineral fertilizer (CK) was replaced with equivalent nitrogen from maize straw were conducted for five years in the Loess Plateau of China. The Gardner model was used to fit the soil water retention curve and calculate the soil water constant and equivalent pore size distribution. The results indicated that the Gardner model fitted well. Replacing nitrogen from mineral fertilizer with nitrogen from straw increased soil specific water capacity, soil readily available water, soil delayed available water, soil available water, soil capillary porosity, and soil available water porosity over time. S25 increased field capacity and wilting point from the fourth fertilization year. S50 enhanced soil readily available water, soil delayed available water, soil available water, and soil available water porosity from the fifth fertilization year, whereas S25 and S75 increased these from the third fertilization year or earlier. Soil specific water capacity, soil readily available water, soil delayed available water, soil available water, soil capillary porosity, and soil available water porosity could better reflect soil water-holding capacity and soil water supply capacity compared with field capacity and wilting point.

Uranium Dissemination with Phosphate Fertilizers Globally: A Systematic Review with Focus on East Africa

Growing concern has been expressed about uranium (U) accumulation in agricultural soils caused by the long-term application of mineral fertilizers. More than 80% of naturally occurring U transfers from phosphate rock (PR), the raw material used in mineral fertilizer production, to phosphorus (P) fertilizers. These fertilizers are then distributed on agricultural soils, where the U could accumulate over time and become a risk to the environment. The objective of this work was to review the reported content of U in P fertilizers, its potential dispersion in soils, and its uptake by plants in different countries in the world as reported in the literature. The articles for this systematic review were selected from the Scopus database published between 2003 and 2022. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) protocol were used. A total of 54 articles were assessed based on the standard inclusion and exclusion criteria. U concentrations in P fertilizers, agricultural soil dissemination, and plant uptake for available data were obtained and assessed. In order to compare a set of related data from the collected articles, box and whisker plots showing the distribution of U in P fertilizers are presented by region. The results from the reviewed articles show that the U concentrations in P fertilizer were in the range of 0.1–653 mg kg−1. Interestingly, Minjingu P fertilizers from Tanzania, which are used in six East African countries, showed the highest U concentrations (159 to 653 mg kg−1, average 390 mg kg−1). The reported U concentrations for these fertilizers are, in fact, comparable to those of conventional low-grade uranium deposits mined in Namibia and elsewhere. Additionally, approximately 96% of the reviewed articles indicate that fertilized soil has higher U concentrations than non-fertilized soils, hinting at a measurable effect of mineral fertilizer use. The review recommends U extraction during mineral fertilizer production so that potential environmental risks can be reduced and U resources that would otherwise be lost can be recovered and used to substitute conventional U mining elsewhere.

Decadal application of mineral fertilizers alters the molecular composition and origins of organic matter in particulate and mineral-associated fractions

The extent to which long-term application of mineral fertilizers regulates the quantity, quality, and stability of soil organic matter (SOM) in soil matrices remains unclear. By combining four biomarkers, i.e., free and bound lipids, lignin phenols and amino sugars, we characterized the molecular composition, decomposition and origins of SOM in response to 10-year fertilization (400 kg N ha−1 yr−1, 120 kg P ha−1 yr−1 and 50 kg K ha−1 yr−1) in a cropland in North China. We focused on two contrasting fractions: particulate organic matter (POM), and mineral-associated organic matter (MAOM). Fertilization increased soil organic carbon (SOC) by 23% in MAOM, and altered its composition and origins, despite having a limited effect on bulk SOC levels. Fertilization increased plant-derived terpenoids by 46% in POM and long-chain lipids (≥C20) by 116% in MAOM but decreased short-chain lipids (<C20) by 54% in the former fraction. Fertilization reduced suberin-derived lipids by 56% in POM and 30% in MAOM but increased lignin-derived phenols by 74% in POM and 31% in MAOM, implying that crop residues were preferentially stored via the POM form. Fertilization decreased the contribution of microbial residues to SOC in both the fractions. Overall, mineral fertilizers tended to reduce certain labile components within POM (e.g., short-chain lipids), leading to the accrual of recalcitrant molecules (e.g., long-chain lipids, cutin-derived lipids, and lignin-derived phenols) in the MAOM fraction. Collectively, our study suggests that mineral fertilizers can increase SOM stability and persistence by modifying their molecular composition and preservation in the mineral-organic associations in a temperate agroecosystem.

Gross nitrogen mineralization and nitrification at an optimal phosphorus input level in southern Chinese red soil with long-term fertilization

In China, phosphorus (P) is recognized as a “key limiting nutrient” for crop production, and its overuse results in underground leaching, ecosystem alterations and risks to humans, such as degraded surface water quality. The coupling of nitrogen (N) and P implies that soil N dynamics are largely affected by P availability. However, how the addition of P affects soil N transformations remains less understood. To determine the optimal P-input level, we performed an incubation experiment on an upland soil from Jinxian in China after long-term mineral fertilizer application and P addition. The two treatments without N addition T1 (no fertilizer) and T2 (inorganic potassium fertilizer) and the two treatments with N addition T3 (inorganic nitrogen fertilizer) and T4 (inorganic nitrogen and potassium fertilizer) were selected from the long-term experiment that involved scientific management at five P-input levels (0, 25, 50, 75, and 100 kg P2O5 ha−1) with three replications. The results showed that soil organic matter (SOM) increased in the T3 and T4 treatments compared with the T1 and T2 treatments. The T4 treatment resulted in the maximum N concentration of 1.28 g kg−1, followed by that in the T3 treatment (1.25 g kg−1), T2 (0.16 g kg−1) and that in the T1 treatment (0.10 g kg−1), in the soil. Among the different treatments, soil microbial biomass carbon (SMBC) and nitrogen (SMBN) were significantly higher (492.69 mg kg−1 and 73.36 mg kg−1, respectively) in the T3 treatment than in the other treatments, while soil microbial biomass phosphorus (SMBP) was higher in the T4 treatment (17.55 mg kg−1). With the addition of P, the gross N mineralization rate was substantially enhanced when N and K were applied. After the 90-day incubation period, with higher concentrations of NO3--N and NH4+-N in the T4 treatment than in the other treatments, the concentrations were significantly increased by P addition, specifically T4P4 by 11.27% and 37.37%, T4P3 by 12.64% and 30.29%, T4P2 by 22.94% and 64.53%, and T4P1 by 3.93% and 11.09%, compared with those of T4P0, respectively; these results indicated a maximum N mineralization potential (No) and mineralization rate constant, k (NMR). As a result of the increased gross nitrogen mineralization rates and associated NH4+ substrate availability, the gross nitrification rate was also increased by P addition. Based on the polynomial regression analysis, the inclusion of P at the rate of 60 kg P2O5 ha−1 can be used effectively to obtain maximum gross N mineralization rates in soil. Additionally, to fully understand why P addition is more effective under specific soil and environmental conditions, more research is necessary to determine the underlying mechanisms.

Mineral fertilizers, lime and green manuring in crop rotation under conditions of the Baikal region

The results of research on the effect of long-term application of mineral fertilizers, lime and green manuring on soil acidity and crop productivity are presented. The experiment was conducted in a long-term (2017-2020) stationary field experiment in the fifth rotation of a four-field crop rotation: corn, barley + clover, clover, spring wheat. The soil of the experimental plot is gray forest heavy loam. The following variants were studied: without fertilizers, N90Р60, Р60К90, N90К90, N90Р60К90 on two backgrounds - without liming and with the introduction of 0.5 Ng of lime (5.7 t/ha). It was found that 5 times use of ameliorant helped to decrease acidity of gray forest soil: рНKCl increased by 0,9-1,5 in comparison with the initial indicator (4,5-4,9), hydrolytic acidity decreased by 6,1-8,3 mg-eq./100 g, the degree of base saturation increased by 20,0-25,5%. Due to the use of green manuring in the crop rotation, рНKCl grew by 0.4-0.6; hydrolytic acidity fell by 2.3-4.1 mg-eq./100 g of soil, the degree of base saturation raised by 9.2-13.3%. The mineral fertilizers at the applied rates had no effect on changing the soil acidity, both on non-lime- and lime-fertilized backgrounds. The productivity of crop rotations by experiment variants increased by 0.23-0.69 tons of grain units per hectare (tgru/ha) (7-21%) and was the greatest with the combined effect of total mineral fertilizer (N90P60K90) and lime. The recoupment of 1 kg rate of application of mineral fertilizers to agricultural products was 6.1-11.5 kg of grain, 1 ton of lime - 2.5-3.2 kg of grain.

Concentration of lanthanides in the Estonian environment: a screening study

Lanthanides (Ln) are crucial for several future green technologies, such as wind turbines, solar panels and electric cars. However, the current use of Ln is already remarkable and they are considered emerging contaminants. To evaluate the hazard of Ln to ecosystems the data on their environmental concentrations are needed. This study aimed to provide new information on concentration of Ln for Estonian environment where oil-shale industry may be considered a potential pollution source of Ln. In the sampled riverine sediments the Ln concentrations varied in the range of 39-117 mg/kg dry wt and in the riverine macrophytes from 1.7 to 14 mg/kg dwt being higher near the potential pollution sources. In the leaves of silver birch Betula pendula the Ln concentrations ranged from 0.1 to 0.7 mg/kg dwt. In particular, we showed that the use of the oil-shale fly ash for soil amelioration may lead to the Ln accumulation in the plants and the long-term application of mineral fertilizers may increase Ln concentrations in the plants growing near the arable land.

Does long-term application of mineral fertilizers improve physical properties and nutrient regime of sandy soils?

In modern agriculture, mineral fertilizers are considered to be a significant enhancing factor. They promote soil fertility, particularly in sandy soils. Farmers should be aware of the effects of fertilizers on the soil environment. Here, we report the results of three long-term experiments with durations of 25, 41 and 94 years conducted in a sandy soil at the experimental station of the Warsaw University of Life Sciences – SGGW in Skierniewice, Poland. The soil physical properties and nutrient regime were monitored under a set of experimental treatments: Control – no fertilizer, NPK – NPK fertilizers, CaNPK – CaNPK fertilizers in the 41-year and 94-year-long experiments, and FYM – farmyard manure as control, FYM+NPK – farmyard manure+NPK fertilizers and FYM+CaNPK – farmyard manure+CaNPK fertilizers in the 25-year-long experiment. Only the 41-year-long experiment showed a significant decrease in bulk density by 7% under NPK treatment compared to control. Total and available P increased significantly across experiments and fertilization treatments compared with the corresponding controls, most remarkably in the 41-year-long experiment. In the 94-year-long experiment, total Ca and Mg rose by 168% and 45% under CaNPK treatment, respectively, relative to the control. Total organic carbon increased considerably across experiments. Similarly, total N and S increased in NPK treatment significantly by 67% and 56%, respectively compared with the control in the 41-year-long experiment. Overall, the highest number of correlations between soil physical properties and nutrient content was determined in the 94-year-long experiment. The obtained results show positive effects of FYM on the content of soil nutrients.

Effects of Long-Term Mineral Fertilizer Application on Soil Nutrients, Yield, and Fungal Community Composition

Effects of Long-Term Mineral Fertilizer Application on Soil Nutrients, Yield, and Fungal Community Composition

Оцінка основних показників родючості темно-сірого опідзоленого ґрунту за тривалого систематичного застосування добрив

Goal. Based on observations in the system of range agroecological monitoring to identify changes in the natural cycle of nutrients and toxic elements due to anthropogenic factors. Methods. General scientific methods of materialist dialectics, scientific abstraction, analysis and synthesis, logical thinking, and special: range agroecological monitoring, mathematical and statistical. Results. The results of studies conducted on dark gray podzolized soil of the Right-Bank Forest-Steppe with long-term application of mineral fertilizers and the background of by-products of the predecessor during 1987–2017 are shown. It is fixed that humus content has increased by 0.2–0.3%, while the indices of exchange and potential acidity, as well as the amount of the absorbed bases compared to the ecotope without the use of fertilizers, have dropped. That is the indication of the acidifying action of the applied fertilizers and the need for liming. The number of compounds of light hydrolysis and mineral nitrogen in fertilized ecotopes was at very low and low levels. When applying a double dose of mineral fertilizers N75P74K83 on the background of organic levels, the content of mobile phosphates and potassium was respectively very high and high, which provided optimal conditions for phosphorus and potassium nutrition of crop rotation plants. None of the ecotopes exceeded the maximum allowable concentration (MAC) and the background content of mobile forms of lead, cadmium and nickel for the soils of Ukraine. The content of copper in the soil was low and medium, and the content of zinc was very low and low. Conclusions. During long-term anthropogenic loading for 30 years in the grain-crop rotation of the Right-Bank Forest-Steppe with the application of 232–349 kg/ha NRK on the background of plowing of by-products of plant growing there was an expanded reproduction of fertility of dark-gray podzolized soil as to humus, mobile forms of phosphorus and potassium. But a tendency was observed of accumulation of mobile forms of cadmium with a simultaneous deepening of copper and zinc deficiency.

Effect of long-term application of mineral fertilizers and FYM on microbial dynamics, yield and quality of FCV tobacco (Nicotiana tabacum) grown in vertisols

A long term manurial experiment (Permanent Manurial Trial) with the objective to study the effect of continuous application of organic manure (FYM) and inorganic fertilizers (NPK) on microbial diversity, yield and quality of Flue-cured Virginia (FCV) tobacco (Nicotiana tabacum L. ) as monocrop was carried out at CTRI Farm, Katheru, for 53 years commencing from 1956-57 to 2008-09. The results obtained before the closing of the experiment (2003- 2008) are discussed in this paper. The microbial dynamics expressed in terms of culturable microbial populations, i.e. bacteria, fungi, actinomycetes, Azotobacter and PSB were measured after 53 years of continuous application of mineral fertilizers and organic amendments to vertisols. The population of bacteria, actinomycetes, Azotobacter and PSB were maximum in plots treated with mineral fertilizers and FYM while fungal population was maximum in mineral fertilizers treated plots. The population of bacteria, actinomycetes, Azotobacter and PSB increased in the treatments with the addition of P and K fertilizers alone or in combination. The fungal population decreased with the addition of NPK along with the FYM. Bacillus, Pseudomonas species of bacteria and Trichoderma, Aspergillus and Rhizopus species of fungi, Streptomyces species of actinomycetes were the main dominating culturable microorganisms in all the treatments. The FYM amended plots sustained crop productivity and microbial populations at higher levels than rest of the mineral fertilizer treatments. The average cured leaf yields indicated that only farm yard manure and inorganic nitrogen application has exerted pressure in increasing the cured leaf yields by 24. 52% and 26. 97% respectively in VT-1158 variety of tobacco in vertisols. The nitrogenous fertilizers alone had the most deleterious effect on crop productivity and the biological soil environment. The results of the present study support the concept of balanced fertilization and integrated nutrient management practices for improving the soil quality and sustained crop productivity.

How relationships between soil organic matter parameters and soil structure characteristics are affected by the long-term fertilization of a sandy soil

Refining our understanding of how soil structure develops is important because soil structure has a major influence on plant growth. Recent studies show positive correlations between soil organic matter and soil structure. However, the question remains: how are the relationships between soil organic matter (SOM) parameters and soil structure characteristics affected by the long-term fertilization of a sandy soil? In contrast to most other studies on SOM vs. soil structure, the present study is composed of long-term field experiments (a total of 3 experiments) with durations of 25, 41 and 94 years. In this paper, the impact of the long-term application of mineral fertilizers and manure on the SOM and soil structure of a sandy soil is quantified, and the relationships between the SOM and soil structure of a sandy soil with a dependence on the length of fertilizer application are determined. Soil samples were collected from all three long-term field experiments in central Poland, which were located at Skierniewice experimental station including a 94-year-old experiment with mineral fertilization, a 41-year-old experiment with mineral fertilization and a 25-year-old experiment with mineral fertilization + farmyard manure (FYM) in a 4-year cycle. In the spring of 2017, soil samples were collected (Co – no fertilizers, NPK – NPK fertilizers, CaNPK – CaNPK fertilizers). In the 94-year-old experiment, the content of soil organic carbon (SOC) in Co, NPK and CaNPK was 4.07, 5.89 and 5.99 g kg−1, respectively. An increase in the SOC content under fertilization was also found in the other two experiments. In the 25-year-old experiment, the SOC contents in FYM, FYM + NPK and FYM + CaNPK were 6.07, 8.36 and 7.63 g kg−1, respectively, and in the 41-year-old experiment, the SOC contents in Co, NPK and CaNPK were 6.38, 10.1 and 7.80 g kg−1, respectively. The content of labile carbon (CL) increased significantly in the fertilized treatments only in the 94-year-old experiment. The contents of humic substances significantly increased in the soil of fertilized treatments in the 25- and 41-year-old experiments. In all fertilized treatments, the humus quality significantly decreased. After 94 years of mineral fertilization, the content of water-stable macroaggregates (WSAma) in size fractions > 5 and 5–2 mm was significantly higher in the NPK than in the Co and CaNPK treatments. After 94 years of mineral fertilization, the mean weight diameter of aggregates for dry sieving (MWDd) differed between Co (0.41) and both treatments of mineral fertilization (NPK: 0.88; CaNPK: 1.70). The application of FYM with CaNPK resulted in a statistically significant decrease in aggregate stability (Sw) in the 25-year-old experiment. For Co and NPK treatments in the 41-year-old experiment, the contents of WSAma > 5 mm were 41% and 51% lower, respectively, whereas the content of WSAma 5–3 mm was lower by 40% and 50%, respectively, which was higher than that for the CaNPK treatment. The aggregate stability significantly decreased due to NPK application in the soil of the 41-year-old experiment. The number of correlations between SOM parameters and the soil structure decreased in the following order: 94-year-old experiment with mineral fertilization > 41-year-old experiment with mineral fertilization > 25-year-old experiment with mineral fertilization + FYM.

Вплив тривалого внесення мінеральних добрив на вміст обмінних катіонів у ґрунті

Вплив тривалого внесення мінеральних добрив на вміст обмінних катіонів у ґрунті

Effect of long-term mineral fertilizer application on soil enzyme activities and bacterial community composition

Soil bacteria are critical to maintain soil fertility. In this study, soil chemical properties, enzyme activities and soil bacterial community from a long-term fertilizer experiment (37 years) were analysed to elaborate the effects of long-term mineral fertilizer application on soil enzyme activities and bacterial community composition. Compared with control treatment, bacterial community richness was reduced in low nitrogen (N) fertilizer and high N fertilizer treatments and increased in high N fertilizer and phosphorus (P), high N fertilizer and potassium (K) (N2K), and high N fertilizer, P and K (N2PK) treatments. The distribution of each phylum and genera was obviously changed and the range of the dominant phyla was not affected in all fertilization treatments. Principal component analysis showed that soil bacterial community in the N2K treatment was clearly different than in the N2PK treatment. The N2PK treatment had much higher available P, total organic carbon, invertase, urease and phosphatase activities than the N2K treatment, which might change soil bacterial community composition. In conclusion, fertilization with combined application of P, K and N in appropriate proportions is an optimum approach for improving soil quality and soil bacterial community abundance in non-calcareous fluro-aquic soils in the North China Plain.

Correction to: Phosphorus addition enhances gross microbial N cycling in phosphorus-poor soils: a 15N study from two long-term fertilization experiments

The tight coupling between nitrogen (N) and phosphorus (P) suggests that P availability may affect soil microbial N dynamics in terrestrial ecosystems. However, how P addition affects the internal N transformations in P-deficient agricultural soil remains poorly understood. We hypothesized that an increase in gross microbial N rates in P-deficient soil should occur after long-term P inputs in agricultural soils. We thus conducted a 15N pool dilution experiment to quantify the gross microbial N transformation rates after long-term mineral fertilizer applications in an upland fluvo-aquic soil (from Fengqiu with pH 8.55) and upland red soil (from Qiyang with pH 5.49) in China. We found that P addition significantly enhanced the gross N mineralization and immobilization rates when N and K were also applied, probably due to the increased soil total C and N concentrations at both soils. Also, gross nitrification rate was stimulated by P addition, perhaps because of enhanced gross N mineralization rates and associated NH4+ substrate availability. Our results showed that long-term P addition may stimulate soil gross N dynamics and hence increase overall N availability for crops in P-deficient agricultural soils.

The effect of application of organic manures and mineral fertilizers on the state of soil organic matter and nutrients in the long-term field experiment

Soil organic matter (SOM) plays an important role in terrestrial ecosystems and agroecosystems. Changes in the agricultural sector in the Czech Republic within the past 25 years have had a negative impact on SOM content and contribute to gradual soil degradation. The aim of this study is to estimate the effect of long-term application of different mineral fertilizers (NPK) and organic manures (manure, cattle slurry) on soil chemical properties (quality of humus, available nutrients, and soil reaction). Soil samples were collected from Luvisol during two selected periods 1994–2003 and 2014–2016 from long-term field experiment carried out in Prague-Ruzyně (Czech Republic). Average annual temperature is 8.5 °C, and annual precipitations are 485 mm. Different fertilization regimes have been applied for 62 years. The crop rotation was as follows: cereals (45%), root crops (33%) and legumes (22%). Soil analysis—soil organic carbon (SOC) was determined by oxidimetric titration method. Short fractionation method for evaluation of humic substance (HS), humic acid (HA) and fulvic acid (FA) content was used. Absorbance of HS in UV-VIS spectral range was measured by Varian Carry 50 Probe UV-VIS spectrometer. Degree of humification (DH) and color index (Q4/6) were calculated from fractional composition data. Soil reaction was measured by potentiometric method. Available nutrients (phosphorus, potassium, magnesium, calcium) were determined by Mehlich II and Mehlich I methods and by ICP-OES. For data analysis, the following are used: exploratory data analysis, ANOVA, and principal component analysis (PCA). PCA analysis differentiated fertilizers into two categories: (1) variant NPK (lower quality of humus)—higher acidity, lower SOC and HS content, predomination of FA, higher DH and lower content of available nutrients; (2) variants with organic manures (higher quality of humus)—lower acidity, higher SOC and HS content, predomination of HA, middle DH, and high content of available nutrients. The main result of presented study is to give a synthesis of effect of different type of fertilizers on a sustainable organic matter management in arable soils, with respect to yields, food security and adaptation to predict climate changes. Long-term application of mineral fertilizers (NPK) without organic matter input can accelerate humus mineralization and soil quality degradation with all negative consequences such as (nitrogen leaching, higher availability of toxic element for plants, slow energy for soil microorganisms etc.). Application of organic fertilizers (manure and cattle slurry) helps to achieve the long-term stable yields while maintaining soil at optimum quality (long-term sustainable management with SOM). Principal component analysis is a useful tool for evaluation of soil quality changes.

Specific Responses of Soil Microbial Residue Carbon to Long-Term Mineral Fertilizer Applications to Reddish Paddy Soils

Mineral nutrient inputs to soil may alter microbial activity and consequently influence the accumulation of microbial residues. In this study, we investigated the effects of application rates and ratios of mineral fertilizers on the microbial residue carbon (MRC) of reddish paddy soils after long-term (15-year) fertilizer applications in southern China. Contents of three soil amino sugars as microbial residue contents were determined and MRC were calculated based on amino sugars. Results showed that three individual amino sugar contents increased as fertilizer application rates increased until maximum values were reached at a rate of 450-59-187 kg ha−1 year−1 (N-P-K). The three amino sugar contents then declined significantly under the highest mineral fertilizer application rate of 675-88-280 kg ha−1 year−1 (N-P-K). In addition, to enhance the microbial residue contents, it was more beneficial to double P (N:P:K = 1:0.26:0.41) in fertilizers applied to the P-deficient reddish paddy soils than to double either N (N:P:K = 2:0.13:0.41) or K (N:P:K = 1:0.13:0.82). The contents of the three individual amino sugars and microbial residues under different fertilizer application rates and ratios were significantly and positively correlated with soil organic carbon (SOC), total N, total P, and pH. Increases in values of the fungal C to bacterial C ratios showed that soil organic matter (SOM) stability increased because of the fertilizer applications over the past 15 years. The contents and ratios of amino sugars can be used as indicators to evaluate the impact of mineral fertilizer applications on SOM dynamics in subtropical paddy soils. The results indicated that fertilizer applications at a rate of 450-59-187 kg ha−1 year−1 (N-P-K) may improve crop yields, SOC contents, and SOC stability in subtropical paddy soils.

Soil Nitrogen Fractions in Relation to Rice-Wheat Productivity: Effects of Long-Term Application of Mineral Fertilizers and Organic Manures

ABSTRACTMajor portion of soil N, present as organic fractions (SON), plays an indirect but vital role in N nutrition of plants. The SON fractions are sensitive to management practices, including fertilization. The nature and distribution of different forms of soil N were studied under long-term use of mineral fertilizers and organic manures in a rice (Oryza sativa)-wheat (Triticum aestivum) cropping system. Long-term fertilizer treatments included control (T1), 100% N (T2), 100% NP (T3), 100% NPK (T4), 150% NPK (T5), 100% NPK plus straw (T6), 100% NPK plus green manure (T7), and 100% NPK plus farmyard manure (T8). Prolonged application of fertilizers and organic manures differentially influenced mineral N (NO3–-N and NH4+-N), organic N fractions, and total N in soils. Organic N fractions constituted about 94.2% of total N as compared with 5.8% share of mineral N. Nitrate N was the dominant mineral N fraction in the soil, which was 4.4 times higher than NH4+-N fractions. Application of fertilizers improved available N in soil. Hydrolyzable-N increased with the application of organic manures. Of the total hydrolyzable-N fractions in soils, ammonia-N was 25%, amino sugar-N 9.9%, amino acid-N 25.2%, and hydrolyzable unknown-N 39.8%. A significant positive correlation was recorded between crop yield and N uptake. Amino acid-N and amino sugar-N explained 82.9% of the variation in rice yield and 73.4% of the variation in wheat yield. Integrated use of organic manures and inorganic fertilizers improved the N fractions in the soil, which should help increase rice and wheat production.

Seasonal dynamics of the microbiome of chernozems of the long-term agrochemical experiment in Kamennaya Steppe

The seasonal variability (spring–summer–autumn) of the taxonomic structure of prokaryotic microbiomes in chernozems of Kamennaya Steppe was studied using sequencing of the 16S rRNA gene. The samples were collected from the topsoil (0–20 cm) horizons of a long-term fallow and croplands differing in the rates of application of mineral fertilizers (NPK). The seasonal dynamics of the prokaryotic community in the soils of the fallow and croplands were similar: the summer samples significantly differed from the spring ones; in autumn, the microbiome structure approached that in spring; these changes were probably related to corresponding changes in the temperature and moisture conditions of the growing season. For all the plots, significant seasonal changes in the proportions of Thaumarchaeota (Cranarchaeota), Acidobacteria, Bacteroidetes, Firmicutes, and Verrucomicrobia phylogenetic groups were observed. The significant changes in the structure of the microbiomes (especially in the number of representatives of the Firmicutes, Cemmatiomonadetes, and Verrucomicrobia phyla) were revealed in the arable and fallow soils irrespectively of the season. The phylogenetic diversity estimated by the Shannon index, the number of the operating taxonomic units found, and the Chao1 index differed little in the soils of the studies plots. The long-term application of mineral fertilizers at different rates had little effect on the taxonomic structure and diversity of prokaryotic communities in the agrochernozems.

The impact of mineral fertilizers and lime on the transformation of humic acids in a soddy-podzolic heavy loamy soil of the Cis-Ural region

The composition and structure of humic acids in a soddy-podzolic heavy loamy soil (Retisol) of the Cis-Ural region after the long-term application of mineral fertilizers and lime was studied by the methods of elemental analysis, infrared spectroscopy, and thermogravimetry. It was found that mineral fertilizers and lime did not change the ranges of C, H, O, and N contents and general structure typical of humic acids in soddy-podzolic soils. The long-term anthropogenic impact on the soil resulted in some transformation of the composition and properties of humic acids. Clear absorption bands in the area of 1700 cm−1 (C=O of carbonyl group) and 1620 cm−1 (C=C of aromatic rings), which characterize the benzenoid structures of molecules, were found in the infrared spectra of humic acids from the soil treated with lime at the rate to compensate for the total acidity. Soil liming favored the accumulation of thermodynamically stable fragments of the central part of humic acid molecules and the destruction of peripheral radicals. The application of mineral fertilizers resulted in the enrichment of humic acids with aliphatic fragments. The combined application of mineral fertilizers and lime increased the portion of aromatic structures and, at the same time, enriched humic acids in aliphatic fragments less resistant to pyrolysis. These fragments are biologically and chemically active and can be readily involved in the element turnover processes, thus protecting the stable part of humus from the biological destruction.