Long-term Fertilization Experiment Research Articles

Occurrence characteristics of Echinochloa and its response to long-term fertilization in paddy fields of yellow soil.

We studied the characteristics of Echinochloa and its response to variation of rice yield and soil properties under long-term fertilization in paddy field of yellow soil, based on a 23-year long-term fertilization experiment in Scientific Oberving and Experimental Station of Arable Land Conservation and Agricultural Environment (Guizhou), Ministry of Agriculture. The occurrence characteristics of Echinochloa (density, panicle number per plant, totle panicles, seed number per panicle, 1000-seed mass and seed mass per panicle) of ten treatments including CK, N, PK, NK, NP, NPK, 1/4MNP, 1/2MNP, M (manure), MNPK were examined. The results showed that the characteristics of Echinochloa significantly varied with long-term different fertilization. The highest density, panicle number per plant and total panicles of Echinochloa were attained in the MNPK treatment, followed by the 1/4MNP treatment. Compared with the NPK treatment, the density of Echinochloa was significantly decreased in no fertilizer treatment (CK) and unbalanced chemical fertilizer treatments (N, PK, NK, NP). The panicle number per plant significantly increased in organic fertilizer treatments (1/4MNP, 1/2MNP, M, MNPK). Both the density and total panicles of Echinochloa were positively correlated with rice yield. The occurrence characteristics of Echinochloa were positively correlated with soil organic matter, total N, total P, available N, available P and available K. Results from path analysis showed that soil total N had a direct positive effect on panicle number per plant and soil total P content was the main factor affecting the density and total panicles of Echinochloa. Soil available K content was the factor with strongest influence on seed number per panicle and seed mass per panicle. We concluded that the occurrence characteristics of Echinochloa varied with long-term different fertilization. The density, panicle number per plant and total panicles of Echinochloa could be increased with appling cow manure. Soil total P was the direct influencing factor for the variation of density and total panicle of Echinochloa in paddy field of yellow soil.

Biogeochemistry and forest composition shape nesting patterns of a dominant canopy ant.

Humans are increasing nutrient deposition across the globe, and we know little about how these changes influence consumer populations in tropical rainforests. We used a long-term fertilization experiment conducted in a Panamanian forest to explore how nutrient availability and tree traits affect abundance of a higher-level consumer. We added nitrogen, phosphorus and potassium in a factorial design for 18years. Given that phosphorus often limits ecosystem processes in lowland tropical forests, and addednitrogen reducesinsect abundance in our experiment, we first hypothesized that phosphorus addition would increase nest density and nest size of Azteca chartifex ants while nitrogen addition would have the opposite effects. We found 48% lower nest density in the canopy of nitrogen addition plots relative to plots that did not receive nitrogen. Phosphorus addition did not affect nest density or size. These nutrient effects were not diminished by the selectivity of host trees. In general, larger trees held more nests, despite their low frequencies across the forest, while some abundant species (e.g., palms) were rarely used. We further predicted higher nest frequency on trees with extrafloral nectaries, because this ant fuels its large colonies with extrafloral nectar. Despite the non-random distribution of A. chartifex nests, across tree species and nutrient treatments, trees with extrafloral nectaries did not host more nests. Our study suggests that areas of a tropical lowland forest which are not oversaturated with nitrogen, and contain large trees, have higher nest density. This could enable A. chartifex insimilar areas to outcompete other ants due to high abundance.

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.

Modeling the Effects of Soil Variability, Topography, and Management on the Yield of Barley

A better understanding of processes involved in crop production as well as the use of models as tools for managing agricultural systems are main reasons for the development of growth models. During the last three decades, the complexity of models increased from simple input-output relationships to highly sophisticated mechanistic process oriented models. Nevertheless, today, the simpler crop yield models have received a wider application, e.g., in management oriented decisions for plant production and in the evaluation of field experiments at multiple scales. The spatial variability considerably influences the experimental error variance which is particularly relevant in highly managed production experiments and in breeding nurseries. Therefore, the purpose of this study was to predict the yield of barley based on regressions and analysis of variance/covariance (ANOVA, ANCOVA) in a long-term static nitrogen fertilizer experiment receiving six different forms of nitrogen and three levels of nitrogen. The factors were the level of fertilization and the applied N-fertilizer forms. As covariates, the apparent soil electrical conductivity (ECa), relief parameters, and location coordinates were used. These covariates were served as proxies for site conditions. The apparent conductivity was measured with different sensors (EM38, EM38-MK2) and in all possible configurations. The ANOVA indicated smaller R2-values and higher root mean square differences (RMSD) in comparison to the ANCOVA ((fertilized plots ANOVA: R2 = 0.21, RMSD = 5.23 dt ha−1; ANCOVA: R2 = 0.845, RMSD = 2.30 dt ha−1). Besides the form and level of fertilization, conductivity readings were the most important covariates accounting for the averaged long-term yields. Looking at the individual years, ECa occurred in the ANCOVA models in five of 11 years, whereas topographic covariates (mainly variables with the parameter slope in the derivation) appeared in eight years in the models. The introduction of plot-wise, time-invariant soil and relief parameters improved the discrimination of testing and modelling the treatment performance within the long-term field trial. The high degree of explanatory power in yield prediction delivered by static soil parameters makes them highly attractive and can contribute to an improved evaluation of production oriented field experiments.

Mitigation of soil acidification through changes in soil mineralogy due to long-term fertilization in southern China

Soil acidification is a natural process, and it is well known that soil acidification can be accelerated by long-term fertilization (LTF). Nevertheless, how this acidification occurs and how the mineralogies of iron oxides as the important active clay components in red soil respond to the acidification is still less understood. In this study, soil samples from 23 years (1990–2013) of long-term fertilization experiments were collected from the Qiyang Red Soil Experimental Station in southern China. The physicochemical properties of the soil samples were analyzed. A significant negative linear correlation between soil pH and log(Alpy) (complex-state aluminum) as well as log(Alexch) (exchangeable Al3+) illustrate that Alpy and Alexch are the most sensitive species to soil acidification compared with the other factors. In addition, the mineralogical characteristics of the iron oxides in five typical LTF treatments, including the control, chemical fertilizer N, NPK, NPK plus manure and manure were analyzed using the synchrotron differential XRD patterns (DXRD). The results obtained revealed that the LTF treatment with chemical N reduced the total content of iron oxides and the ratio of goethite to hematite (G/H value), and the transformation of iron oxides and accumulation of hematite in the soil would reduce the soil's buffering capacities to acidification. In contrast, the LTF treatments with manure (NPKM and M) presented the opposite trends. In addition, a positive relationship between soil pH and the IOsAlmol% (isomorphous substitution ratio of Al for Fe in iron oxides) was also found. Therefore, the potential acid Al3+ ions in soil are reduced through the ionic substitution of Al for Fe in the structure, which may further mitigate the process of soil acidification. These results provide new insights for further understanding the soil acidification processes induced by LTF and how those iron oxides respond to soil pH during soil acidification.

Selected persistent organic pollutants (POPs) in the rhizosphere of sewage sludge-treated soil: implications for the biodegradability of POPs

ABSTRACTThe impact of regular application of sewage sludge or farmyard manure on the organic contaminant loads in soil was assessed in a model rhizobox experiment. Two soils originating from a long-term field crop rotation and fertilizer experiment running since 1996 were used. The total polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), organochlorinated pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), perfluorooctanoic acid (PFOA), and perfluorooctane sulfonate (PFOS) contents were determined in the rhizosphere and bulk soil. The results showed low but still detectable contents of PCBs and OCPs in the soil, substances which were banned a few decades ago. Among the OCPs, dichlorodiphenyltrichloroethane (DDT) and its metabolites reaching up to 18.2 µg kg−1 of the soil even exceeded the preventive levels for these compounds in agricultural soils, i.e. 7.5 µg kg−1 of soil. For PBDEs, PFOA, and PFOS, their contents in the soil significantly increased with sewage sludge application. The enhancement of the potential biodegradability of the POPs in the rhizosphere was confirmed only for hexachlorocyclohexane (γ-HCH), where, the level of γ-HCH increased significantly in the rhizosphere soil compared to bulk soil. Thus, natural attenuation of POPs in the soil-plant system seems to be insufficient for most of the investigated compounds.

Long-term combined application of manure and chemical fertilizer sustained higher nutrient status and rhizospheric bacterial diversity in reddish paddy soil of Central South China

Bacteria, as the key component of soil ecosystems, participate in nutrient cycling and organic matter decomposition. However, how fertilization regime affects the rhizospheric bacterial community of reddish paddy soil remains unclear. Here, a long-term fertilization experiment initiated in 1982 was employed to explore the impacts of different fertilization regimes on physicochemical properties and bacterial communities of reddish paddy rhizospheric soil in Central South China by sequencing the 16S rRNA gene. The results showed that long-term fertilization improved the soil nutrient status and shaped the distinct rhizospheric bacterial communities. Particularly, chemical NPK fertilizers application significantly declined the richness of the bacterial community by 7.32%, whereas the application of manure alone or combined with chemical NPK fertilizers significantly increased the biodiversity of the bacterial community by 1.45%, 1.87% compared with no fertilization, respectively. Moreover, LEfSe indicated that application of chemical NPK fertilizers significantly enhanced the abundances of Verrucomicrobia and Nitrospiraceae, while manure significantly increased the abundances of Deltaproteobacteria and Myxococcales, but the most abundant Actinobacteria and Planctomycetes were detected in the treatment that combined application of manure and chemical NPK fertilizers. Furthermore, canonical correspondence analysis (CCA) and the Mantel test clarified that exchangeable Mg2+ (E-Mg2+), soil organic carbon (SOC) and alkali-hydrolyzable nitrogen (AN) are the key driving factors for shaping bacterial communities in the rhizosphere. Our results suggested that long-term balanced using of manure and chemical fertilizers not only increased organic material pools and nutrient availability but also enhanced the biodiversity of the rhizospheric bacterial community and the abundance of Actinobacteria, which contribute to the sustainable development of agro-ecosystems.

Soil microbial community composition closely associates with specific enzyme activities and soil carbon chemistry in a long-term nitrogen fertilized grassland

Due to the profound impact of nitrogen (N) input on soil systems, linking the activity and composition of soil microbial communities to soil organic carbon (SOC) is crucial to reveal the microbial-driven mechanisms underlying SOC decomposition by nitrogen fertilization. A long-term nitrogen fertilization experiment with 6 urea fertilizer gradients (0, 2, 4, 8, 16, and 32 g N m−2 yr−1) was conducted on a temperate grassland. The soil basic characteristics, microbial community DNA sequences, five soil enzymes including C, N, and phosphorus cycling, and soil C fractions were measured after 14 years of N addition. N fertilization significantly modified both the bacterial and fungal community composition, with larger variations at higher N levels. N fertilization increased the proportion of copiotrophic bacteria and saprotrophic fungi. Specific enzyme activities standardized by microbial biomass carbon among N fertilizing gradients demonstrated that the potential of labile C acquisition was stable, but the potential of N and P acquisition and recalcitrant C degradation were increased. Recalcitrant soil C fractions including alkyl C and aromatic C significantly differed among N levels, despite the stable SOC concentration. The variations of bacterial phyla and fungal trophic guilds were both associated with specific enzyme activities; meanwhile, fungal phyla were more related to soil C fractions, as the Basidiomycota abundance echoed the proportion of aromatic C at 4–16 g N m−2 yr−1. In conclusion, this study indicates that the changes in microbial community composition by N fertilization can have far-reaching impacts on SOC turnover and nutrient acquisition.

Soil organic carbon sequestration as influenced by long-term manuring and fertilization in the rice-wheat cropping system

Fertilization is a feasible approach to increase the soil organic carbon. To investigate the effect of fertilization on crop biomass carbon, dynamics of soil organic carbon and soil carbon sequestration rate in the (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system under the middle reach of the Yangtze River, central China, a thirty-three years (1981 − 2013) long-term fertilizer experiment was conducted with nine treatments, including no amendment addition treatment (control), nitrogen (N), phosphorus (P), potassium (K) fertilizer treatments (N, NP, NPK), manure (M) and manure combined with chemical fertilizer treatments (MN, MNP, MNPK, hMNPK). The results indicated that average crop biomass carbon was increased by 39.9 − 77.2% compared to unfertilized control (4.43 t ha−1 yr−1) due to fertilizer application, the highest crop biomass carbon was 7.85 t ha−1 yr−1 in the hMNPK treatment and the lowest crop biomass carbon was 5.21 t ha−1 yr−1 in the N alone treatment. The annual total organic carbon input were 4.14 t ha−1 yr−1 in the M treatment and 5.80 t ha−1 yr−1 in the hMNPK treatment, which was 1.95 − 2.74 times of those in the NPK treatments (2.12 t ha−1 yr−1). Total organic carbon input of soil were increased by 10.2 − 23.3 kg C ha−1 yr−1, and increment rate in the appended manure treatments were much higher than those in the control and inorganic fertilizer treatments. Soil organic carbon retention in the topsoil (0 − 20 cm) decreased by 0.11 − 0.14 t ha−1 yr−1 in the control, N and NP treatments; nevertheless, soil organic carbon sequestration rates varied from 0.03 to 0.20 t ha−1 yr−1 in the NPK and appended organic manure treatments. These results demonstrate that organic manure use or integrated organic manure with chemical fertilizer application can be important strategies for increasing soil organic carbon sequestration and maintaining soil quality in the rice-wheat cropping system of China.

Soil Nematode Abundances were Increased by an Incremental Nutrient Input in a Paddy-upland Rotation System.

SummaryTo study the effect of fertilization on soil nematode communities in a paddy-upland rotation system, an ongoing thirty-three years long-term fertilizer experiment is conducted which includes seven treatments; an unfertilized treatment (control), nitrogen (N), phosphorus (P), potassium (K) fertilizer treatments (N, NP, NPK) and organic manure (M) combined with chemical fertilizer treatments (MN, MNP, and MNPK). The soil nematode community structure and crop yields were determined in 2012 and 2013. Overall total nematode abundance was increased by an incremental nutrient input both in the rice and wheat fields. Total number of nematode was 1.25 – 2.37 times greater in the rice field and was 1.08 – 2.97 times greater in wheat field in the fertilization treatments than in the unfertilized treatment. Soil free-living nematode abundances was significantly (P < 0.001) increased in organic manure combined with chemical fertilizer treatments in rice field. Fungi-feeders and plant-feeding nematodes abundances were not significantly different among treatments in rice and wheat fields. Omnivorous and predatory nematodes were the most dominant groups in the present study. Omnivores, predators and Prodorylaimus abundances were significantly (P < 0.05) higher in organic manure combined with NPK fertilizer treatments than in chemical fertilizer alone and unfertilized treatments both in rice and wheat fields. Stepwise regressions revealed that soil free-living nematodes were significant predictors of rice grain yields (R2 = 0.56, P < 0.001) and omnivorous and predatory nematodes were significant predictors of the wheat grain yield (R2 = 0.89, P < 0.001). Therefore, long-term application of organic manure combined with chemical fertilizer could increase nematode abundances and crop yields. Organic manure combined with chemical fertilizer application was recommended in agricultural ecosystem.

The stability mechanism for organic carbon of aggregate fractions in the irrigated desert soil based on the long-term fertilizer experiment of China

Soil samples from the Hexi Corridor located in the arid regions of Northwestern China were collected from a 24–year–old field experiment. The distribution of organic carbon (OC) in the different size water stable aggregate (WSA) fractions and the stability mechanism of OC in WSA size fractions were studied. The results showed that long-term application of solo organic manures or in combination with inorganic N fertilizer significantly increased the OC concentrations of different size WSA fractions compared to the CK, while long-term application of solo N fertilizer had no significant effect. After fertilization for 24 years, the OC concentrations of 0.25–2 mm WSA fraction was significantly positively correlated with the percentages of this WSA fraction, while the OC concentrations of >2 mm, 0.053–0.25 mm and <0.053 mm were not significantly correlated with their corresponding percentages of WSA fractions (P > 0.05). In addition, the OC concentrations of loosely, stably and tightly bound humus in 0.25–2 mm WSA fraction were significantly higher than those in other size WSA fractions, which were also significantly correlated with the corresponding chemical components, e.g. different forms of calcium, in 0.25–2 mm WSA fraction (P < 0.05). It could be explained that affinities of OC to chemical components in 0.25–2 mm WSA fraction were stronger than those in other size WSA fractions. The results of NMR analysis also showed that the aromaticity and alkyl/O-alkyl ratio for the 0.25–2 mm WSA fractions were significantly lower than those for other size WSA fractions (P < 0.05). These results demonstrated that the 0.25–2 mm WSA fraction played an important role in stabilizing soil OC and protecting OC from degradation in the irrigated desert soil.

The effect of mineral fertilizers and farmyard manure on winter wheat grain yield and grain quality

This study evaluated how organic manures and mineral fertilizers affect winter wheat grain and straw yields and grain quality properties. The analysed period of the long-term fertilizer experiment was established in Čáslav, Czech Republic, in 1955 and covers the seasons 2011–2014. The fertilizer treatments were: control; farmyard manure (FYM); FYM + P; FYM + K; FYM + PK; FYM + N&lt;sub&gt;1&lt;/sub&gt;; FYM + N&lt;sub&gt;2&lt;/sub&gt;; FYM + N&lt;sub&gt;1&lt;/sub&gt;PK; FYM + N&lt;sub&gt;2&lt;/sub&gt;PK and FYM + N&lt;sub&gt;3&lt;/sub&gt;PK. The highest grain yields were recorded in the FYM + P and FYM + N&lt;sub&gt;3&lt;/sub&gt;PK treatments (8.9 t/ha). The highest straw yields were recorded in the FYM + N&lt;sub&gt;3&lt;/sub&gt;PK treatment (6.52 t/ha). The lowest yields were provided in the unfertilized control and FYM treatments. Qualitative parameters were evaluated in the control, FYM and FYM + N&lt;sub&gt;3&lt;/sub&gt;PK treatments between the years 2011 and 2013. The best quality of wheat grain was provided by the FYM + N&lt;sub&gt;3&lt;/sub&gt;PK treatment. Combination of the farmyard manure with NPK is the best way to achieve high grain yields with good quality and leads to sustainable food production.

Characteristics of Organic Carbon Changes in Brown Earth under 37-year Long-Term Fertilization

To investigate the impacts of different fertilization on characteristics of organic carbon (OC) changes in brown earth (Hapli-Udic Cambisol), an experiment was conducted with long-term located fertilization experiment from 1979–2015. The experiment field divided into chemical fertilization group, low levels of organic manure group and high levels of organic manure group. The results showed that: the OC was mainly stored in >1.0 mm size aggregates. As the organic fertilizers application grew, the mass percentage of the water-stable aggregates (WSA) for >1.0 mm aggregates significantly increased by 2.3–30.1 times and when the organic and inorganic fertilizers were combined to be applied, the mass percentage of >2.0 mm aggregates and carbon preservation capacity (CPC) increased significantly. Over 37 years of fertilization, the organic carbon concentration, stock and rate of change in brown soil presented the following rank: high-levels of organic manures group > low-levels of organic manures group> chemical fertilization group. Based on the experimental data over the last 37 years, we examined the relationship between total carbon input and the change of organic carbon stock, and constructed a curve: y = 0.153x–0.129.

Assessing the ability of soil tests to estimate labile phosphorus in agricultural soils: Evidence from isotopic exchange

Efficient phosphorus (P) fertilization strategies are essential for intensive crop production with minimal negative environmental impacts. A key factor in sustainable P use is assessment of the plant available soil P pool using soil P tests. This study determined isotopically exchangeable P after six days of reaction with 33PO4 (P-E (6 d)) to determine how accurately two commonly used P tests, Olsen and AL (acid ammonium acetate lactate) can quantify the amount of labile P. Soil samples were taken from both highly P-amended and unamended plots at six sites within the Swedish long-term soil fertility experiments. According to P K-edge XANES spectroscopy, the P speciation was dominated by Al-bound P and organic P, with additional contributions from Fe-bound P and Ca phosphates in most soils. The results showed that the AL test overestimated P-E (6 d) by a factor of 1.70 on average. In contrast, the Olsen test underestimated P-E (6 d), with the mean ratios of P-Olsen to P-E (6 d) being 0.52 for high-P and 0.19 for low-P soils. The 33P/31P ratio in the Olsen extract of a 33PO4 spiked soil was closer to that of a 0.005 mol L−1 CaCl2 soil extract than the corresponding ratio in the AL extract, suggesting that AL extraction solubilized more non-labile P. In conclusion, the AL and Olsen methods are not suitable for direct quantification of the isotopically exchangeable soil P pool after 6 days of equilibration. However, based on the results, Olsen may be superior to AL for classification of soil P status, due to its even performance for calcareous and non-calcareous soils and lower extraction of non-labile P.

Genetic yield gains of winter wheat in Germany over more than 100 years (1895–2007) under contrasting fertilizer applications

For highly productive regions such as Germany, the increase of wheat grain yields observed throughout the 20th century is largely attributed to the progress in crop breeding and agronomic management. However, several studies indicate a strong variability of the genetic contribution across locations that further varies with experimental design and variety selection. It is therefore still unclear to which extent management conditions have promoted the realization of the breeding progress in Germany over the last 100+ years. We established a side-by-side cultivation experiment over two seasons (2014/2015 and 2015/2016) including 16 winter wheat varieties released in Germany between 1895 and 2007. The varieties were grown using 24 different long-term fertilization treatments established since 1904 (Dikopshof, Germany). Averaged over all cultivars and treatments mean yields of 6.88 t ha−1 and 5.15 t ha−1 were estimated in 2015 and 2016, respectively. A linear mixed effects analysis was performed to study the treatment-specific relation between grain yields and year of variety release. Results indicate a linear increase in grain yields ranging from 0.025 to 0.032 t ha−1 yr−1 (0.304 to 0.387% yr−1) in plots that were treated with combined synthetic-organic fertilizers without signs of a leveling-off. Yields from low or unfertilized plots do not show a significant progress in yield. Responsiveness of mean yields to fertilizer management increases with year of release and indicates small yield penalties under very low nutrient supply. Results highlight the need to consider the importance of long-term soil fertilization management for the realization of genetic gains and the value of long-term fertilization experiments to study interactions between genetic potential and management.

Phosphorus adsorption and desorption characteristics of different textural fluvo-aquic soils under long-term fertilization

Phosphorus (P) fertilizer has been widely applied to improve crop yields in the North China Plain; however, most of applied P fertilizer is disabled due to the strong sorption/fixing processes in the soil. This study evaluates the change characteristics of soil properties on different textural soils and their relationships with the P adsorption and desorption under long-term fertilization to do a favor to make strategies for improving the P availability of the soil. Five textural fluvo-aquic soils including gritty sand, silt sand, sandy loam, medium loam, and light clay were investigated in a 27-year (1990–2017) long-term fertilization experiment at Zhengzhou (Henan province) of China. Soil samples were collected in 1990, 1999, and 2017 at 0–20 cm to measure soil properties (i.e., soil mechanical composition) and P adsorption and desorption characteristics. The clay and silt contents decreased and sand content increased in the light clay soil with the cultivation years, the opposite situation for the gritty sand and silt sand soils. The contents of total P, Olsen–P, and organic matter (SOM) in the five textural soils were increased over time. There were stronger P absorption capacity and weaker desorption ability for the light clay soil relative to others, which was reflected in the largest P maximum buffer capacity (MBC) and the lowest β value; however, the P adsorption capacity tended to decrease over time for the light clay soil. Clay and silt fractions were positively correlated with MBC, while negatively correlated with β (P < 0.01); similar disciplines were found in the contents of SOM, total iron (Fe), and free Fe oxides (FeDCB). The mechanical composition of five textural fluvo-aquic soils changed to some extent under the long-term cultivation, thereby improved P absorption and desorption capacity. The clay and silt fractions as well as SOM and FeDCB contents were the major factors for the P adsorption, but sand content was the major factor for the P desorption.

Mechanisms for increasing soil resistance to acidification by long-term manure application

Soil pH buffering capacity (pHBC) plays a crucial role in determining soil acidification rates and the amount of lime required to ameliorate soil acidity. However, it remains poorly understood how soil organic matter affects soil pHBC. Here, Alfisol and Ultisol samples from long-term fertilization experiments (control, chemical N, P, and K (NPK), manure only (M), 1/2 NPK plus 1/2 M (1/2NPKM), and NPK plus M (NPKM)) were used to investigate the effects and underlying mechanisms of manure application on the pHBC and soil resistance to acidification through simulated acidification experiments. The results indicated that the application of manure increased pHBC and the resistance of soils to acidification in both the Alfisol and Ultisol. The pHBC of the Alfisol in the M and NPKM treatments was increased by 81 and 60% compared with the control, respectively. Similarly, the pHBC of the Ultisol in the NPKM treatment was 66% higher than that of the control. The extent of protons consumption by the Alfisol followed the order: M > NPKM > 1/2NPKM > NPK ≈ control during stimulated acidification, which was consistent with their pHBC. These results suggested that manure application increased the resistance of the Alfisol to acidification by increasing soil pHBC. The protonation of organic anions from the dissociation of weakly acidic functional groups on soil organic matter to form neutral molecules was the main mechanism responsible for the increase in pHBC and soil resistance to acidification induced by manure application. During this process, some exchangebale base cations were released from negatively charged sites on organic matter into soil solution. This mechanism was confirmed by the experimental observations: the release of base cations from soils increased, while soil exchangeable base cations and effective CEC decreased as soil pH decreased. The results are of fundamental significance for understanding the role of organic matter in retarding soil acidification through long-term manure application.

Changes of some soil chemical and microbiological characteristics in a long-term fertilization experiment in Hungary

Agricultural management practices – directly or indirectly – influence soil properties.&#x0D; Fertilization rates and crop rotation can strongly affect soil pH, soil nutrient supply and soil organic matter content due to the changes of microbial processes. The objective of this study was to compare the effects of different fertilization doses in monoculture and tri-culture of maize (monoculture: only maize grown since 1983, tri-culture: it is a three-year crop rotation system: pea – winter wheat – maize) on selected soil characteristics. The long-term fertilization experiments were set up in 1983 in Eastern Hungary. These experiments are situated west of Debrecen in Hajdúság loess region, on calcareous chernozem (according to WRB: Chernozems).&#x0D; The test plant was maize (Zea mays L.). One-one pilot blocks were selected from monoculture and tri-culture of the long-term experiments. The observed soil samples were taken in the 30th year of the experiment, in 2013. The doses of NPK fertilizers increased parallel together, so the effects of N-, P- and K-fertilizers cannot be separated.&#x0D; With the increasing fertilizer doses, the soil pH has decreased in both crop production systems and, in parallel, the hydrolytic acidity has significantly increased. A close negative correlation was proved between the pHH2O, pHKCl and hydrolytic acidity. An increased nutrient content in soil was recorded in every NPK treatment and the available phosphorus and nitrate content increased in higher proportion than that of potassium. Of the measured parameters of C-and N-cycles, fertilization has mostly had a positive effect on the microbial activity of soils. Besides the effects of fertilizer doses, correlation were looked for between soil microbiological properties. Evaluating the ratios among the measured parameters (organic carbon and microbial biomass carbon, OC/MBC ratio; carbon-dioxide and microbial biomass carbon; CO2/MBC proportion), the fertilization rate seems to be favoured by the increase of amounts of organic compounds

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Effects of arbuscular mycorrhizal fungus Rhizoglomus intraradices on active and passive pools of carbon in long-term soil fertility gradients of maize based cropping system

ABSTRACTA potculture study was conducted in soils collected from long-term fertilizer experiment (LTFE) being kept up as far the past 40 years to determine whether arbuscular mycorrhizal fungus (AMF) Rhizoglomus intraradices colonization changes the active and passive pools of carbon in a maize (Zea mays) – finger millet (Eleusine crocana)- cowpea (Vigna sinensis) cropping sequence in the Experimental Farm of the Tamil Nadu Agricultural University, Coimbatore, India. Soil samples were processed, sterilized and maize plants were grown in various fertility gradients in the absence (M-) or presence (M+) of AMF (Rhizoglomus intraradices) inoculation. The data have clearly shown that M+ soils had consistently higher active pools such as water soluble carbon, hot water soluble carbon and biomass carbon (M- 189; M + 305 mg kg−1), and passive pools such as soil organic carbon (M- 4.17; M + 4.31 mg g−1) and total glomalin. Among the fertility gradients, 100% NPK + Farm Yard Manure (FYM) with or without mycorrhizal fungal inoculation registered higher values for both active and passive pools of C but the response was more pronounced in the presence AMF inoculation. Overall, the data suggest that mycorrhizal fungal inoculation assists in effective carbon sequestration in an intensive cereal-legume cropping system.Abbreviations: AMF: Arbuscular mycorrhizal fungi; DAS: Days After Sowing; LTFE: Long-Term Fertilizer Experiment; WSC: Water soluble organic carbon; HA: Humic acid; FA: Fulvic acid; HWSC: Hot water soluble carbon