N, P And K Research Articles

Long-term fertilization has different impacts on bacterial communities and phosphorus forms in sugarcane rhizosphere and bulk soils under low-P stress.

The application of phosphorus (P) fertilizer effectively improves soil P availability, but it also affects soil microbial communities. However, the responses of soil bacterial communities and P forms to long-term P fertilization, and the relationships of bacterial communities with soil P forms remain unclear in P-deficient field. In this study, the impacts of different P fertilization treatments (chemical nitrogen and potassium (NK); chemical N, P and K (NPK); and NPK plus straw (NPKS)) on the bacterial communities and P forms in sugarcane rhizosphere (RS) and bulk soils (BS) were evaluated. Compared with the NK, the NPK and NPKS treatments significantly (P<0.05) increased the yield and quality characters of sugarcane, especially under NPKS. Additionally, P fertilization significantly increased the available P (AP), soluble inorganic P (Pi) and retained Pi in both the RS and BS, but they significantly increased the Chao1 and Shannon index only in the BS; and almost all these indices were significantly higher in the RS than in the BS. The bacterial community compositions were also significantly altered by P fertilization, with major changes in the RS and minor changes in the BS. The bacterial genera that were enriched in the sugarcane rhizosphere mainly included Bradyrhizobium, Rhodanobacter, Pseudolabrys, Conexibacter, and Burkholderia-Caballeronia-Paraburkholderia, some of which potentially promote the plant growth. Compared to NK, functional groups involved in the cycling of carbon, N, and sulfur significantly increased or decreased with fertilizer P application. Moreover, the relative abundances of many bacterial species were significantly correlated with the soil P forms. In conclusion, long-term P fertilization altered bacterial structure and functions in P-deficient sugarcane soil, which could help the soil P cycling and suppling. The results provide useful information to stimulate the power of the microbes by fertilization measures to improve soil nutrients and crop production.

Interaction of soil microbial communities and phosphorus fractions under long-term fertilization in paddy soil

Understanding the impact of biological activities on the soil phosphorus (P) distribution under long-term fertilizer application can facilitate better soil P fertility management. Therefore, the primary objectives of this study were to investigate the effect of long-term (since 1981) fertilizer application on the soil P fractions and microbial community and to evaluate correlations between the microbial community structure and P distribution. The following treatments were implemented in a long-term field trial: no fertilization (CK), inorganic N and K (NK), inorganic P and K (PK), inorganic N, P and K (NPK) and manure+NPK (MNPK) fertilization. The study showed that the soil pH, soil organic carbon and total and available N and P concentrations were considerably higher in the MNPK treatment than in the CK treatment. The soil microbial biomass C, N and P concentrations were also significantly higher in the MNPK treatment than in the CK treatment. Among fertilization treatments, the β-1,4-glucosidase, α-1,4-glucosidase, urease, acid phosphatase and phosphodiesterase activities were the highest in the MNPK treatment. Compared to inorganic fertilization, the MNPK treatment increased the labile soil P fractions and decreased the residual soil P concentration. Continuous fertilization significantly affected the soil microbial composition. The total phospholipid fatty acid (PLFA) concentrations in the NK, PK, NPK and MNPK treatments were 23.3, 43.1, 48.7 and 87.7% higher, respectively, than in the CK treatment. A significant correlation was observed between the microbial community and soil P fractions. Moreover, the aggregated boosted tree (ABT) model showed that among the various soil biochemical properties, the total PLFA concentration was the factor that most influenced the active P pool, accounting for 35.4% of the relative influence of all soil biochemical properties examined. These findings reveal that combined manure and inorganic fertilizer application is a better approach than applying inorganic fertilizer alone for sustaining long-term P fertility by mediating soil biological activity.

Long-term change in phosphorus behavior and the degree of P saturation in typical cropland after different fertilization practices

ABSTRACT Soils with continuous application of fertilizer phosphorus (P) may present high accumulations of P and may be at high risk of P loss. In this study, we investigated the effects of different fertilization strategies on soil P dynamics in three typical cropland soils over broad spatiotemporal scales in China. The soil P speciation (characterized both by Hedley fractionation and 31P nuclear magnetic resonance (31P NMR)) and soil P sorption characteristics were examined under five fertilization treatments: unfertilized control (CK); chemical nitrogen (N) and potassium (K) (NK); N, P and K (NPK); NPK plus straw (NPKS); and NPK plus manure (NPKM). We found that with an increase of 100 kg ha−1 in the cumulative P budget, the increases in Olsen-P and CaCl2-P contents ranged in 1.98–7.35 mg kg−1 and 0.46–1.46 mg kg−1, respectively, among the three soils. The recovery rates of P in Hedley fractionation (87–111%) were much higher than those of 31P NMR spectroscopy (40–91%). More percentage of organic P was detected in Hedley fractionation than 31P-NMR in acidic soil, while more percentage of organic P was detected in 31P-NMR than Hedley fractionation in neutral and alkaline soils. Chemical fertilizer combined with manure or straw can decrease the bond strength (k) values compared to chemical fertilizer alone, while change trends in the maximum P sorption capacity (Qm) were dependent on the soil types. Moreover, the degree of P saturation (DPS) was significantly correlated with the cumulative P budget in each site. A change point in the relation between DPS and soil organic carbon (SOC) was found. After the change point, the DPS increased by 0.63–1.06% as the SOC increased by 0.1 g kg−1. Agricultural measures that increased the contents of SOC and available P could increase DPS values effectively, especially manure amendment, which should be carefully considered to reduce P loss risk.

Combined Fertilization Could Increase Crop Productivity and Reduce Greenhouse Gas Intensity through Carbon Sequestration under Rice-Wheat Rotation

Quantifying greenhouse gas intensity (GHGI) and soil carbon sequestration is a method to assess the mitigation potential of agricultural activities. However, the effects of different fertilizer amendments on soil carbon sequestration and net GHGI in a rice-wheat cropping system are poorly understood. Here, fertilizer treatments including PK (P and K fertilizers); NPK (N, P and K fertilizers), NPK + OM (NPK plus manure), NPK + SR (NPK plus straw returning), and NPK + CR (NPK plus controlled-release fertilizer) with equal N input were conducted to gain insight into the change of soil organic carbon (SOC) derived from the net ecosystem carbon budget (NECB), net global warming potential (GWP), and GHGI under rice-wheat rotation. Results showed that compared with NPK treatment, NPK + OM significantly increased wheat yield and NPK + SR caused significant increase in rice yield. Meanwhile, NPK + SR and NPK + CR treatments reduced net GWP by 30.80% and 21.83%, GHGI by 36.84% and 28.07%, respectively, which suggested that improved grain production could be achieved without sacrificing the environment. With the greatest C sequestration, lowest GHGI, the NPK plus straw returning practices (NPK + SR) might be the best strategy to mitigate net GWP and improve grain yield and NUE in the current rice-wheat rotation system.

Trade-off between soil aggregate stability and carbon decomposition under 44 years long-term integrated nutrient management in rice-wheat-jute system

ABSTRACT Soil stability, yield decline and higher carbon decomposition are the key issues in intensive agriculture. Long-term integrated nutrient management (INM) influences carbon (C) dynamics and maintains the soil aggregate stability, which driven by the type of cropping system and climatic zone. Therefore, the specific effects of rice-wheat-jute cropping system on soil aggregate distribution, C-stability, and trade-off between C-storage and decomposition rate were studied of a long-term INM trial in the sub-tropical zone. We investigated the effect of four long-term nutrient management practices that include, control, N (nitrogen (N) and no phosphorus (P), and potassium (K)), NPK (N, P and K) and INM (N, P, K + farmyard manure (FYM)). Results showed that the addition of FYM with NPK improved macro-aggregates by 71%, and associated C-pools by 30%. The INM enhanced C-storage (20%), however, the decomposition rate was also higher (28%) over control at 35 °C at field capacity. A trade-off exists between the soil-aggregate stabilization and C-decomposition rate. The proportion of C-storage was higher than decomposition in INM. Further, the C-sequestration varied (0.17 to 0.26 t ha−1 y−1) under different treatments and were found highest in INM, indicating long-term soil stability and yield sustainability in the rice-wheat-jute system.

Long-Term Fertilization and Lime-Induced Soil pH Changes Affect Nitrogen Use Efficiency and Grain Yields in Acidic Soil under Wheat-Maize Rotation

Liming (L) is a common practice to mitigate soil acidification and enhance soil quality and crop productivity. However, in acidic soil, it is not clear how long-term application of lime and nitrogen (N)-based fertilizer affects soil chemical properties, the wheat and maize grain yields (GY), and N-use efficiency (NUE). Thus, to investigate the effects of N-based fertilizations without L (−L) and with L (+L) on wheat and maize GY and NUE through their effects on soil chemical properties, we analyzed a 28-year field experiment in acidic soil under a wheat-maize system in South China. The analysis was carried out between 1991 and 2010 (before L) and between 2011 and 2018 (after L). We categorized the treatments into (1) no fertilizer (C); nitrogen (N); N and phosphorus (NP); N and potassium (NK); N, P and K (NPK); and NPKCR, NPK and crops residue (CR) applications (NPKCR), before L; and (2) C; N−L; N+L; NP−L; NP+L; NK−L; NK+L; NPK−L; NPK+L; NPKCR−L and NPKCR+L, after L. The effects of long-term fertilization resulted in lower soil pH by 15%, soil available K (AK) by 19%, POlsen by 6%, NO3−-N by 15%, soil organic matter (SOM) by 16%, total N by 16%, and C:N ratio by 13% in −L soil than in +L soil. However, the accumulation of NH4+-N was higher by 40% in −L soil than in +L soil. Wheat and maize GY, N recovery efficiency (REN), and N partial factor productivity (PEPN) were more adversely affected by 8-year fertilizations in −L compared with fertilizations before L and in +L primarily because of the significantly decreased soil pH. Conversely, improvements in wheat and maize yields, REN, and PFPN by 8-year fertilizations in +L were related to increasing soil pH, exchangeable base cations such as Ca2+, Mg2+, and the alleviated toxicity of Al3+. Overall, improvement of GY and NUE from the acidified soil in South China requires the long-term integrated use of fertilizer (NPK), retention of CR, and the +L (i.e., NPKCR+L).

Long-term effects of inorganic fertilizers and organic manures on the structure of a paddy soil

Inorganic fertilizers and organic manures have been widely used to maintain crop yields. Leguminous green manures are usually used in the paddy fields in southern China. But the effect of green manures or combination of green manures with other fertilizers on soil physical properties, especially soil pore structure, is unclear. Based on a 34-year field experiment, we investigated the effects of different fertilization strategies on soil structural properties of a paddy soil. Four treatments were selected: no amendment as a control (CK), inorganic fertilization of N, P and K (NPK), combined application of inorganic fertilizers and green manure (GM), and combined application of inorganic fertilizers, green manure and swine manure (GSM). Results showed that relative to the CK treatment, the NPK, GM and GSM treatments increased SOC content by 7.9 %, 17.8 % and 25.7 %, respectively (P < 0.05). The increase of SOC content led to increased aggregate water stability in the GSM treatment (P < 0.05) but not in the GM and NPK treatments (P > 0.05). Consistent with SOC, soil bulk density was reduced by 5.6 %, 7.4 % and 17.6 %, respectively, for the NPK, GM and GSM treatments (P < 0.05). Total porosity was significantly increased in all the fertilized treatments (P < 0.05). Detailed pore size distribution analysis revealed that the NPK treatment mainly increased < 25 μm pores (total porosity minus porosity of pores that are > 25 μm), while the GM and GSM treatments mainly increased > 25 μm pores. The GSM treatment also significantly increased the connectivity and fractal dimension of macropores (P < 0.05). The penetration resistance of the paddy soil was not affected by the different fertilization strategies, with a low (< 0.4 MPa) value at the plough layer (0−15 cm) and a high value (up to 1.6 MPa) at the plough pan (15−25 cm). Overall, this study indicated that inorganic fertilizers had beneficial, but limited effects on paddy soil structure. Green manure and swine manure can further improve soil pore structure and soil aggregation.

Effects of Long-Term Application of Chemical Fertilizers and Organic Fertilizers on Heavy Metals and Their Availability in Reddish Paddy Soil

To investigate the effects of long-term fertilization on the accumulation and availability of heavy metals in reddish paddy soil and to analyze the major influencing factors, soil samples were collected after the later rice was harvested in 2018 from a long-term fertilization field experiment that began in 1984. Six treatments were selected, namely CK (control without fertilization), PK (P and K fertilizer), and NPK (N, P, and K fertilizer), and different proportions of organic fertilizer plus chemical fertilizer (M1NPK: 30%M+70%NPK; M2NPK: 50%M+50%NPK; and M3NPK: 70%M+30%NPK), soil chemical properties, total and available heavy metal contents, and the relationships between the available forms of heavy metals and soil chemical parameters and total heavy metals (THM) were analyzed. The results showed that ① long-term fertilization changed the soil chemical properties; compared with those of CK, PK significantly increased the contents of soil available phosphorus (AP) and available potassium (AK), NPK significantly increased the soil organic matter (SOM), cation exchange capacity (CEC), AP, and AK, and the organic fertilizer treatments significantly increased the contents of SOM, CEC, AP, AK, and nitrate (NO3--N). ② There were slight variations in the THM contents under the chemical fertilizer treatments (PK and NPK), whereas the organic fertilizer treatments significantly increased the total contents of Cu, Zn, and Cd. ③ The chemical fertilizer treatments significantly increased the available Cr and As, whereas the organic fertilizer treatments significantly increased the available Cu, Zn, Cr, Cd, As, and Fe. ④ There were significant positive correlations between the available Cu, Zn, Cr, Cd, As, and Fe and the SOM, CEC, AP, and NO3--N. In addition, the available Zn and Cd were significantly positively correlated with the soil pH, whereas the available Pb was significantly negatively correlated with soil pH, SOM, CEC, and NO3--N. ⑤ There were significant positive correlations between the available and total contents of Cu, Zn, and Cd, whereas there were significant negative correlations between the available and total contents of Cr and Fe. ⑥ Redundancy analysis showed that SOM and pH accounted for 80.7% and 5.5% of the variation in THM, whereas the soil CEC, AP, and pH accounted for 81.1%, 4.9%, and 3.3% of the variation in the available heavy metals, respectively. ⑦ The partial least squares path model analysis showed that the path coefficients of the THM, CEC, and AP on the available state of heavy metals were 0.459, 0.417, and 0.293, respectively. Long-term application of organic manure, such as pig manure, significantly improved the soil chemical properties and affected the availability of heavy metals, and soil CEC and AP may play key roles in regulation.

Long-term differences in nutrient management under intensive cultivation alter potassium supplying ability of soils

Despite removal of potassium (K) by crops in large quantities, often exceeding that of nitrogen (N), K fertilization has long been neglected compared with N and phosphorus (P) in Indian agriculture leading to mining of soil K. We, therefore, studied the effect of long-term fertilization (with or without K) on K supplying ability of two major soil orders of India, viz. Inceptisol and Vertisol after more than four decades of cultivation. Soil samples (0–15 and 15–30 cm) were collected after the completion of 43 (Inceptisol) or 42 (Vertisol) cropping cycles from on-going long-term experiments located at New Delhi (Inceptisol) and Jabalpur (Vertisol), India, from six treatments, viz. no-fertilization (control), recommended N (N), N and P (NP), N, P and K (NPK), 150% NPK and NPK + farmyard manure (NPK + FYM), along with adjacent uncultivated land. Ammonium acetate extractable K (Kex), non-exchangeable K (NEK), quantity-intensity relationship and K release kinetics along with grain yields and K uptake by crops were studied. The Kex and K-saturation of exchange complex in both soils and NEK in the Inceptisol were the lowest under NP followed by N. Cropping without K input resulted in lower quantity (non-specifically and specifically held K i.e. –ΔK0 and Ks) and intensity (equilibrium activity ratio i.e. AReK) of K in both soils. More negative values of standard free energy of exchange (ΔG0) under cultivation without K in both soils indicated increased affinity of soil solids for K+ owing to K omission. The gap between equilibrium exchangeable K (EK0) and minimum exchangeable K (EKmin) was significantly lower under cropping without K than with K in the Vertisol. Imbalanced fertilization (N or NP) also showed noticeably smaller cumulative K releases and slower rates of replenishment of solution K by solid phase K in both soils. Interestingly, even under cropping with K fertilization at either experimental site, several K supply parameters showed decline compared with adjacent uncultivated soil. Grain yields of wheat and total K uptake by all crops (maize and wheat in Inceptisol; soybean and wheat in Vertisol) showed significant and positive response to K application. The study showed variable effect of long-term intensive cropping with or without K input on the K supplying ability of an Inceptisol and a Vertisol. The findings underlined inadequacy of the existing K fertilizer recommendations, and the need for their refinement to minimize native K mining and sustain K supplying ability of soils.

Impact of forty-seven years of long-term fertilization and liming on soil health, yield of soybean and wheat in an acidic Alfisol

ABSTRACT Fertilization with suitable amendment in acidic soil is crucial to achieve long-term high crop yield without deteriorating soil health in intensive cropping system. We studied the chemical and biological properties of soil, soybean, and wheat yield after 47 years of long-term fertilization in an acidic Alfisol. Treatments were: unfertilized (control); recommended N dose (N); recommended N and P (NP); recommended N, P and K (NPK); NPK + hand weeding (NPK + HW); NPK + 10 Mg ha−1 farmyard manure (NPK + FYM) and NPK + 0.40 Mg ha−1 lime (NPK + lime). Long-term application of NPK + FYM significantly enhanced the soil cation exchange capacity (CEC), organic carbon, available NPK and microbial functions compared to NPK. Application of NPK + lime increased soil pH, dehydrogenase activity (DHA) and bacterial population by 15.7%, 38.8% and 145% respectively, over NPK. Continuous inorganic-P fertilizer application leads to substantial build-up of available-P in soil. Fertilization of FYM/lime with NPK recorded higher crops yield compared to NPK. Soil DHA, bacterial population and CEC were most influencing factors governing grain yield. Overall, long-term application of NPK with FYM/lime improved soil health and crop yield, but rate of inorganic-P input should be curtailed in an Alfisol.

Effect of perfluorooctanoic acid on microbial activity in wheat soil under different fertilization conditions

Perfluorooctanoic acid (PFOA) is an emerging persistent organic pollutant which has been identified at significant levels in soils. Existed ecotoxicological studies have mainly employed earthworms to evaluate the toxicity of PFOA. However, little information do we know about the toxicity of PFOA regarding soil microorganisms. Accordingly, the adverse effects of PFOA on microbial activity in a wheat soil under four fertilization treatments were investigated in this study. The microcalorimetric results revealed that the toxicity of PFOA on soil microbial activity in four treatments followed a descending sequence: Control (no fertilization), NK (no P fertilizer, but N and K fertilizers were used), PK (no N fertilizer, but P and K fertilizers were used), and NPK (N, P and K fertilizers were used). The soil sample with higher available P content had higher resistant to PFOA. There were significant differences in urease activity and alkaline phosphatase activity among the four fertilization treated soils. Molecular modeling studies clearly demonstrated that the binding of PFOA with alkaline phosphatase was more stable than with urease through electrostatic interaction, van der Waals force, and hydrogen bonds. These results are expected to provide more comprehensive information in toxicity of PFOA in soil environment.

Variation of soil dissolved organic carbon under long-term different fertilizations and its correlation with maize yields

There have been many studies about the effects of long-term fertilizations on crop yields and soil organic carbon. However, little attention has been paid to the response of soil dissolved organic carbon (DOC) to fertilization practices. The aims of this work were to investigate the variations of the content and the chemical composition of soil DOC under long-term different fertilizations and to evaluate their correlations with maize yields. A long-term fertilization experiment under a double maize cropping system was established in 1986 in acidic Ultisols of southern China. Soil samples were collected in April 2014 from the following ten treatments: (1) CK (non-fertilization), (2) N (only N fertilization), (3) P (only P fertilization), (4) K (only K fertilization), (5) NP (N and P fertilization), (6) NK (N and K fertilization), (7) NPK (N, P, and K fertilization), (8) HNPK (double doses of NPK fertilization amount), (9) OM (only organic manure), and (10) NPKM (NPK fertilization plus organic manure). The soil basic chemical properties including the content of DOC were determined. Then, the chemical composition of soil DOC was assessed through three-dimensional excitation-emission matrix (3DEEM) and parallel factor analysis (PARAFAC). The results showed that long-term application of organic manure significantly increased the content of soil DOC and obviously changed the chemical composition of soil DOC. Based on the 3DEEM and PARAFAC, organic manure treatments (OM, NPKM) had higher proportions of tryptophan-like components and lower proportions of tyrosine-like components as compared with other treatments (CK and inorganic fertilizer treatments). For the fluorescence indices, organic manure treatments showed significantly higher humification index (HIX) and lower biological index (BIX) and McKnight index than other treatments. Aggregated boosted trees analysis revealed that the DOC content explained 24.6% of the total variance in maize yields and ranked first among all tested soil chemical properties. Furthermore, all fluorescence properties of DOC were correlated with maize yields, in which the HIX index was the most important factor. This research demonstrated that not only the content of DOC but also the chemical composition of DOC in acidic Ultisols were significantly correlated to maize yields. It may be an effective way to improve soil quality and productivity by increasing DOC content and HIX index. From the perspective of soil DOC, our results proved again that application of organic manure could be the most suitable fertilization practice in acidic Ultisols of southern China.

Long-term fertilization decreases chemical composition variation of soil humic substance across geographic distances in subtropical China

Many previous research have investigated the spatial distribution of the content of soil organic matter (SOM) and soil humic substance (HS), while few work focused on the chemical composition variation of HS across geographic distance. Paddy soils, collected from different long-term fertilization treatments across a wide geographic area in subtropical China, were used to evaluate the spatial variation of HS chemical composition. The 3-dimensional fluorescence spectroscopy combined with parallel factor analysis was used to evaluate the chemical composition of the soil extractable humic substance (EHS, including humic acid and fulvic acid). Analysis of distance-decay relationship (DDR) was introduced here to study the spatial variation of the chemical compositions of these EHSs. It was found that geographic location impose greater impact on the compositional variation of soil EHS than fertilization practice. Fertilization treatments including NPK (mineral N, P and K fertilizers) and NPKS (NPK fertilizers plus straw return) exhibited significant flattened DDR slopes as compared to CK (no fertilizers), which indicated fertilization (NPK and NPKS) decreased the variation of EHS chemical composition in paddy soils across geographic distance. A positive correlation was found between variations of soil bacterial community and EHS chemical composition, and fertilization (NPK and NPKS) enhanced their relationships. This work demonstrated that although the geographic location mainly dominated the spatial variation of the soil EHS chemical composition across geographic distance, the same long-term fertilization practice could gradually domesticate the paddy soils to display more similar EHS composition.

Effects of long-term organic fertilization on soil microbiologic characteristics, yield and sustainable production of winter wheat

We investigated the soil microbiologic characteristics, and the yield and sustainable production of winter wheat, by conducting a long-term fertilization experiment. A single application of N, P and K (NPK) fertilizer was taken as the control (CK) and three organic fertilization treatments were used: NPK fertilizer+pig manure (T1), NPK fertilizer+straw return (T2), NPK fertilizer+pig manure+straw return (T3). The results showed that all three organic fertilization treatments (T1, T2 and T3) significantly increased both soil total N (STN) and soil organic carbon (SOC) from 2008 onwards. In 2016, the SOC content and soil C/N ratios for T1, T2 and T3 were significantly higher than those for CK. The three organic fertilization treatments increased soil microbial activity. In 2016, the activity of urease (sucrase) and the soil respiration rate (SRS) for T1, T2 and T3 were significantly higher than those under CK. The organic fertilization treatments also increased the content of soil microbial biomass carbon (SMBC) and microbial biomass nitrogen (SMBN), the SMBC/SMBN ratio and the microbial quotient (qMB). The yield for T1, T2 and T3 was significantly higher than that of CK, respectively. Over the nine years of the investigation, the average yield increased by 9.9, 13.2 and 17.4% for T1, T2 and T3, respectively, compared to the initial yield for each treatment, whereas the average yield of CK over the same period was reduced by 6.5%. T1, T2, and T3 lowered the coefficient of variation (CV) of wheat yield and increased the sustainable yield index (SYI). Wheat grain yield was significantly positively correlated with each of the soil microbial properties (P<0.01). These results showed that the long-term application of combined organic and chemical fertilizers can stabilize crop yield and make it more sustainable by improving the properties of the soil.

Changes in soil aggregate‐associated enzyme activities and nutrients under long‐term chemical fertilizer applications in a phosphorus‐limited paddy soil

AbstractPaddy soils in subtropical China are usually deficient in phosphorus (P) and require regular application of chemical fertilizers. This study evaluated the effects of chemical fertilizers on the distribution of soil organic carbon (SOC), total nitrogen (N) and available P, and on the activity of the associated enzymes in bulk soil and aggregates. Surface soils (0–20 cm) were collected from a 24‐yr‐old field experiment with five treatments: unfertilized control (CK), N only (N), N and potassium (NK), N and P (NP), and N, P and K (NPK). Undisturbed bulk soils were separated into &gt;2, 1–2, 0.25–1, 0.053–0.25 and &lt;0.053 mm aggregate classes using wet sieving. Results showed that both NP‐ and NPK‐treated soils significantly increased mean weight diameter of aggregates, SOC, available P in bulk soil and aggregates, as compared to CK. Most SOC and total N adhered to macro‐aggregates (&gt;0.25 mm), which accounted for 64–81% of SOC and 54–82% of total N in bulk soil. The activities of invertase and acid phosphatase in the 1–2 mm fraction were the highest under NPK treatment. The highest activity of urease was observed in the &lt;0.053 mm fraction under NP treatment. Soil organic carbon and available P were major contributors to variation of enzyme activities at the aggregate scale. In conclusion, application of NP or NPK fertilizers promoted the formation of soil aggregates, nutrient contents and activities of associated enzymes in P‐limited paddy soils, and thus enhanced soil quality.

Manure substitution of mineral fertilizers increased functional stability through changing structure and physiology of microbial communities

Soil function, such as decomposition of organic materials, is of crucial importance to sustain soil fertility and may be enhanced through soil management. We hypothesized that manure amendment would increase soil functional stability more effectively than mineral fertilization when soil nutrients were not limited. By using a 22-yr field experiment, the objectives were 1) to determine the effects of manure substitution and reduction of mineral fertilizers on soil physio-chemical properties, soil microbial community structure, and soil biological functional stability; 2) to isolate the effects of organic amendment from those of mineral fertilization on soil biologic functional stability; and 3) to elucidate the controlling mechanisms on the soil functional stability. Soils were sampled from the field treatments, no fertilization (CK), mineral N, P and K (NPK), two doses of NPK (2NPK), manure amendment (OM) and OM in combination with NPK (NPK + OM). The nutrient inputs were similar in treatments OM and 2NPK. The functional stability was quantified by measuring the decomposition rate of crop litter added to the soils following Cu addition and heating. Soil nutrients, organic carbon and pH increased due to mineral fertilization and organic amendment. The principal component analysis of phospholipid fatty acid (PLFA) profiles demonstrated that the structure of soil microbial communities shifted between the mineral-fertilized soils and manure-amended soils and the shifts were not due to nutrient limitation because the soil microbial communities were not separated between the treatments of NPK and 2NPK. The manure amendment enhanced the resistance and resilience to Cu and heating more than the mineral fertilization, to a larger extent in treatment NPK + OM than in treatment OM. The resistance and resilience to Cu addition was positively correlated with soil organic matter, soil aggregate stability, while only the resistance to heating was positively correlated to soil aggregate stability. Moreover, the resistance and resilience were correlated with the shifts of functional and physiological structure of soil microbial communities due to long-term manure amendment and mineral fertilization. In conclusion, the partial substitution of mineral fertilizers with manure (NPK + OM) increased soil functional stability to heavy metal pollution and global warming through altered structure and physiology of soil microbial communities due to improved soil aggregation with higher soil organic matter.

Effect of twelve years integrated nutrient management practices on soil fertility and performance of upland rice in terraced land

A long-term field experiment was started in 2001 on newly constructed bench terraces at the Department of Soil and Water Conservation in the experimental farm of School of Agricultural Science and Rural Development (SASRD), Nagaland University (NU), Medziphema, Nagaland to study the long term effects of various nutrients management practices on performance of upland rice and fertility of terraced land under rainfed condition. Twelve treatments involving N, P and K (NPK) fertilizers, farmyard manure (FYM), poultry litter, forest litter, Azospirillum and Zn either alone or in combinations were applied continuously for twelve years to evaluate the effect of integrated nutrient management practices on available N, P and K content and performance of upland rice in a terraced land. The available N and K content increased significantly in all the treatments whereas, available P content increased significantly in all the treatments except Forest litter burned+ ½ FYM over control. The highest accumulation of available N, P and K was found in NPK+ Poultry litter, NPK+ FYM and ½N+ PK+ ½N Forest litter treatments, respectively. The rate of build up of available N, P and K in different nutrient management practices varied from 3.57 to 22.5, 0.19 to 1.09 and 3.35 to 13.3 kg ha -1 yr -1 , respectively. Maximum plant height was recorded in NPK+ FYM+ Zn treatment. The number of productive tillers per plant was also highest in NPK+ FYM+ Zn treatment. The highest straw yield was recorded in NPK+ FYM followed by NPK+ Poultry litter treatment. The highest grain yield was recorded in NPK+ FYM+ Zn followed by NPK+ Poultry litter treatment. Compared with NPK, grain yield in NPK+ FYM+ Zn, NPK+ Poultry litter and NPK+ FYM treatments increased significantly and were 38.1, 34.43 and 32.6 per cent higher, respectively. Among different nutrient management practices, NPK+ FYM+ Zn proved to be the best practices followed by NPK+ Poultry litter and can suitably be recommended for use not only to build up available N, P and K levels but also to produce higher grain yield in terraced land under upland rice cultivation.

Response of paddy soil organic carbon accumulation to changes in long-term yield-driven carbon inputs in subtropical China

A decrease in C inputs from the return of crop residues to soil has occurred in many regions worldwide in recent years. The effects of this decline in C inputs could provide valuable information for assessing the long-term impact of litter C inputs on soil organic C (SOC) in rice paddy soils. The present study aimed to evaluate the response of rice paddy SOC accumulation to changes in actual C inputs in subtropical China, with emphasis on the response of C accumulation to declining C inputs. For this, we used a long-term field experiment on paddy soil in a rice-rice (Oryza sativa L.) cropping system running from 1990 to 2014. The four treatments were CK (control, no fertilizer), OM (organic matter application), NPK (N, P, and K fertilizer application), and NPKOM (NPK and organic matter application). Organic matter application for the OM and NPKOM treatments included rice straw and green manure that were left in the field after harvest and chopped, along with rice residues with stubbles and roots. In all treatments, C sequestration showed an increasing trend (from 0.207 to 0.880gkg−1yr−1) in the early and middle stages of the experiment (1990–2006) followed by a decreasing trend (from −0.429 to −0.064gkg−1yr−1) in the late stage (2007–2014). The trends were more pronounced for the OM and NPKOM treatments than for their CK and NPK counterparts. The changes in SOC stocks were consistent with changes in C inputs (p<0.01). During the late stage, yield and litter inputs from crop residues and green manure decreased, quickly affecting SOC stock in paddy soils. This declining trend in annual rice yields was mainly caused by the decline in first rice yields, accounting for 42.3–91.5% of the decrease in annual C inputs. Insufficient P or N and K supply and unfavorable climatic factors (decreases in sunshine duration and both maximum and minimum temperatures) are possible reasons for the decline in first rice yields and green manure biomass in the late stage. Collectively, the results suggest that C stocks in high-productivity paddy soils respond very sensitively to a decline in C inputs. This raises the risk of loss of C stock in paddy soil if, in the long run, a large return of C to soil with crop residues or by other sources, e.g., green manure, cannot be achieved.

Fatty‐Acid Profiles and Enzyme Activities in Soil Particle‐Size Fractions under Long‐Term Fertilization

Core Ideas Organic treatments significantly enhanced soil organic C, total N, and most enzymes activities. The highest soil organic C, total N, and enzyme activities were existed in 200‐ to 63‐μm fraction. Soil organic C, total N, C/N ratio, α‐glucosidase, sulfatase, β‐glucosidase, β‐cellobiohydrolase, and phenol oxidase activities were significantly correlated with phospholipid fatty acids. A long‐term experiment was established in 1981 to examine the influence of mineral and organic fertilizer on soil organic carbon (SOC), total nitrogen (TN), enzyme activities, and microbial community composition. In this study, we considered 33 yr of the following fertilizer treatments: no fertilizer (control, CK), fertilizer N (N), fertilizer N and P (NP), fertilizer N, P and K (NPK), manure plus fertilizer N, P and K (NPKM), and manure (M). We focused on yellow‐brown paddy soil and its particle‐size fractions of &gt;2000 µm (large macroaggregate sized), 2000–200 µm (coarse sand sized), 200–63 µm (fine sand sized), 63–2 µm (silt sized), and 2–0.1 µm (clay sized). Nutrient concentrations and enzymes, affected by fertilizer treatment and particle fraction, were unevenly active throughout the soils which showed significantly highest concentration and activity in the fine sand fraction, except sulfatase (Sul). However, the coarse sand fraction contributed the largest SOC, TN, and enzyme pools to bulk soil, followed by silt‐sized and large macroaggregate‐sized fractions. Compared with NPK, NPKM, and M treatments significantly improved SOC, TN, phosphatase (Pho), β‐glucosidase (βG), β‐cellobiohydrolase (βCB), N‐acetyl‐glucosaminidase (NAG), β‐xylosidase (βX), phenol oxidase (PhOx), peroxidase activities, and the total phospholipid fatty acids (PLFAs) abundance of soil fractions. Manure also accelerated SOC, TN, and most enzymes accumulation in coarse sand fraction at the expense of clay fraction. Principal component analysis (PCA) of microbial community composition showed a smaller variability in particle‐size fractions than treatments which suggested a considerable effect of soil nutrient availability on microbial community composition. Redundancy analysis (RDA) also convinced SOC, TN, C/N ratio, α‐glucosidase (αG), Sul, βG, βCB, and PhOx activities significantly governed microbial community in this study. Our results conveyed long‐term application of organic fertilizers contributed to the increase of SOC, TN, and most enzyme activities in bulk soil and particle fractions, along with abundant and diverse microbial community in fine sand fraction and other organic treated soil fractions.

Impact of long term nutrient management on soil fertility determinants and performance of rice in terraced land

The impact of long term nutrient management practices on soil fertility determinants and performance of upland rice after thirteen years of continuous cultivation on terraced land were studied in a field experiment conducted on the experimental farm of the School of Agricultural Sciences and Rural Development under rainfed conditions. Twelve treatments involving N, P and K (NPK) fertilizers, FYM, poultry litter, forest litter, Azospirillum and Zn either alone or in combinations were applied for thirteen years and rice crop cultivated continuously. The organic C content, available N, P and K, number of productive tillers, grain and straw yield increased significantly in all the treatments. The highest accumulation of available N, P and K was observed in NPK+ poultry litter, NPK+ FYM and ½N + PK + ½N forest litter treatments, respectively. After thirteen years the rate of build up of available N, P and K in different nutrient management practices ranged from 5.2 to 16.9, 0.33 to 0.80, and 1.96 to 7.03 ha -1 yr -1 , respectively. Addition of FYM and poultry litter with NPK increased 28.7 and 25.9 per cent in grain yield and 50.3 and 49.4 per cent in straw yield, respectively as compared to NPK alone.