Effect of Long‐Term Fertilization on the Strontium Content of Soil

Abstract

The total and available strontium (Sr) contents of the experimental soil in the National Long‐Term Fertilization Trials set up in 1968 in Keszthely were compared in correlation to the Sr content of the Ramann‐type brown forest soil and different long‐term P‐fertilizer treatments. The Sr uptake by lettuce was also studied. Soil samples were taken from the 0‐ to 20‐cm depth in the 32nd year of the experiment from plots given different P fertilizer treatments (0–50–100–150–200 kg P₂O₅ ha^?1 y^?1). The total and available Sr content of soils were measured using ICP‐AES. A positive linear correlation was established between the total and available Sr contents of the experimental soils. The total and available soil Sr contents were significantly higher in large dose P‐fertilizer treatments than in case of lower doses. The Sr concentration of lettuce was four to eight times greater than the available Sr content of the soil samples, and Sr accumulation was observed in lettuce leaves.     

Tillage Effects on Soil Quality Indicators and Nematode Abundance in Loessial Soil under Long‐Term No‐Till Production

Abstract: Soil quality indicators and nematode abundance were characterized in a loessial soil under long‐term conservation tillage to evaluate the effects of no‐till, double‐disk, chisel, and moldboard plow treatments. Indicators included soil electrical conductivity (EC), soil texture, soil organic matter (SOM), and total particulate organic matter (tPOM). Nematode abundance was positively correlated with EC, silt content, and total POM and negatively correlated with clay content. Clay content was the main source of variation among soil quality indicators and was negatively correlated with nematode abundance and most indicators. The gain in SOM in the no‐till system amounted to 10887 kg over the 24 years or 454 kg ha^?1 year^?1, about half of this difference (45%) resulting from soil erosion in plowed soils. The balance of gain in SOM with no till (249 kg ha^?1 year^?1) was due to SOM sequestration with no till. No‐till management reduced soil erosion, increased SOM, and enhanced soil physical characteristics.     

Application of Near Infrared Reflectance Spectroscopy for the Assessment of Soil Quality in a Long‐Term Pasture

Abstract

The objective of the present study was to assess the ability of near infrared reflectance spectroscopy (NIRS) to analyze chemical soil properties and to evaluate the effects of different phosphorus (P) and potassium (K) fertilization rates on soil quality in different layers of a long‐term pasture. The NIRS calibrations were developed for humus, total Kjeldahl nitrogen (N_Kjeldahl), and several humic substances (HA1, “mobile” humic acids fraction; ΣHA, sum of humic acids; FA1, “mobile” fulvic acids; ΣFA, sum of fulvic acids, etc.) using soil samples of rather heterogeneous origin, collected during 1999–2003. Different spectral preprocessing and the modified partial least squares (MPLS) regression method were explored to enhance the relation between the spectra and measured soil properties. The equations were employed for the quality prediction of a sod gleyic light loam (Cambisol) in five PK fertilization treatments. The soil was sampled in 2000 and 2003 in three field replicates at depths of 0–10, 10–20, 20–30, and 30–50 cm, n=60 samples yr^?1. The best coefficients of correlation, R², between the reference and NIRS‐predicted data were as follows: for N_Kjeldahl, 0.965; humus, 0.938; HA1, 0.903; HA2, 0.905; HA3, 0.924; ΣHA, 0.904; and FA1, 0.911; and ΣFA, 0.885. Our findings suggest that it is feasible to use NIRS for the assessment of the effects of the inorganic PK fertilizer on the soil quality in different depths of a long‐term pasture.     

Crop Response to Long‐Term Potassium Application as Affected by Potassium‐Supplying Power of the Selected Soils in Northern China

Potash resources in China are very scarce. It is especially important to correctly evaluate the potential potassium‐supplying power of soils in northern China in order to use soil potassium sufficiently and potash fertilizer properly. Regional differences in crop yield responses to long‐term potassium application in northern China were determined in this study. Twenty‐five representative soil samples from 13 provinces, municipalities, and autonomous regions of major agricultural regions in northern China were collected from the surface layer (0–20 cm) before crop seeding in 1993. A soil potassium‐depletion study was carried out in a pot experiment with successive planting of corn seedlings for 10 harvests in the 25 soils. Since 1993, field trials on wheat and corn response to long‐term potassium application were conducted at the fixed sites of HLJ‐SC (Shuangcheng of Heilongjiang), JL‐LFZ (Liufangzi of Jilin), HB‐XJ (Xinji of Hebei), SX‐LF (Linfen of Shanxi), QH‐NKY (Nongkeyuan of Qinghai), and XJ‐CJ (Changji of Xinjiang). Soil‐available potassium, slowly available potassium, total potassium, main clay minerals, cation exchange capacity, particle size, other available nutrients, and potassium concentration in plants were measured. The results showed that potential potassium‐supplying powers of the 25 tested soils, which were respectively evaluated by the contents of slowly available potassium in soils and the amount of total net potassium uptake in the pot experiment, generally tended to increase from eastern to western regions in northern China. Significant wheat yield responses to long‐term potassium application in the field trials were found since 2000 in the north‐central region but not observed until 2004 in the northwestern region. Significant corn yield responses to long‐term potassium application in the field trials were found starting in soils of the northeastern region, following in soils of the north‐central region, and then in soils of the northwestern region. These were consistent with potential potassium‐supplying power of the soils, which tended to increase from east to west regions.     

Selective Dissolution Analysis of Major and Trace Elements in an Allophanic Andisol Acidified by Long‐Term Fertilizer Application

A long‐term (61 years) experimental field was used to examine the effect of acidification on the chemical composition of an allophanic Andisol in northeastern Japan. The pH values of the 1:10 water extract of the plow layer soils were 4.1, 4.7, and 6.2 for three fertilizer application treatments: chemical fertilizers only (CF), CF and compost (CFC), and CFC with liming, respectively. Three batch dissolution analyses were conducted to determine water‐soluble and exchangeable (D1), D1 plus, inorganically bound elements to noncrystalline clays and organically bound elements (D2), and total concentration of elements (TCE, 45 elements). The D1 fraction of 20 elements increased, and that of eight decreased with acidification. The D2 fraction of lithium increased, and that of eight elements decreased with acidification. Because the D2 fraction of many other elements and TCE were not strongly altered, present acidification of this soil can be restored with liming and other necessary amendments.     

Influence of Long‐Term Application of Organic and Inorganic Fertilizer to Build Up Soil Fertility and Nutrient Uptake in Mint‐Mustard Cropping Sequence

Abstract

Field experiment was conducted for 7 years continuously to evaluate the influence of combined application of organic and inorganic fertilizer on soil fertility buildup and nutrient uptake in mint (Mentha arvensis) and mustard (Brassica juncea) cropping sequence. Maximum organic carbon was observed under full supply of organic manure (T₂; FYM at 20 t ha^?1) averaged across all the Stages of cropping sequence. It was increased by 38, 50, and 51% in T₂ in Stages I (after mint harvest/presowing of dhaincha), II (after incorporation of dhaincha (Sesbania aculeata)/presowing of mustard), and III (after harvest of mustard/preplanting of mint), respectively, over their respective controls. In general, magnitude of organic carbon was recorded higher in Stage II after green manuring of Sesbania compared with Stages I and III. Nitrogen availability in treated plots was increased by 26.0–89.9, 15.2–64.5, and 4.9–52.0% in Stages I (after mint harvest/presowing of Sesbania), II (after incorporation of dhaincha/presowing of mustard), and III (after harvest of mustard/preplanting of mint), respectively, over their respective control. Average across all the three Stages showed a positive balance of nitrogen (N), phosphorus (P), and potassium (K) in soil under different treatments. Mean of the three Stages indicated that maximum available N, P, and K were increased by 36.1, 129.0, and 65.20% in T₄ (N:P:K: 133:40:40 and FYM at 6.7 t ha^?1), T₄ (N:P:K::133:40:40 and FYM at 6.7 t ha^?1), and T₃ (N:P:K::100:30:30 and FYM at 10 t ha^?1), respectively, over their initial status. Supply of organic and inorganic fertilizer (T₄; N:P:K::133:40:40 and FYM at 6.7 t ha^?1) was found most suitable combination with respect to N, P availability in soil, and productivity of mint and mustard crop.     

Manure Nutrient Content on Vermont Dairy Farms: Long‐Term Trends and Relationships

Manure nutrient analysis is an important component of nutrient‐management planning on dairy farms. The University of Vermont Agricultural and Environmental Testing Laboratory analyzed more than 2,300 dairy manure samples from 1992 to 2006. Means of nutrient content were consistent with published values, but variability among the sample results supports the need for laboratory analysis to determine manure application rates. Phosphorus (P) content of manure decreased by about 30% from 1992 to 2004, presumably reflecting a shift in dairy diets to avoid feeding excess P, but P content increased in the following 2 years. The copper (Cu) content of liquid manure increased four‐fold, mostly after 1998, a change attributed to increased use of copper sulfate (CuSO₄) in foot baths. While not reliable for making nutrient‐management decisions on individual farms, long‐term summaries can be useful to detect trends and to put individual analytical results in context.     

Change of Organic Carbon Content and Its Fractions in Black Soil under Long‐Term Application of Chemical Fertilizers and Recycled Organic Manure

Abstract

Soil organic matter (SOM) is an important indicator for soil quality and sustainable agriculture, and agricultural practices may strongly affect SOM content and chemistry. Thus, a long‐term experiment was conducted in northeast China to study the effect of chemical fertilizers and recycled organic manure on the contents of SOM along its fractions of black soil (0–20‐cm depth). Eight treatments were used: 1) control, 2) recycled organic manure (ROM), 3) nitrogen (N) alone, 4) N+ROM, 5) N+phosphorous (P), 6) N+P+ROM, 7) N+P+potassium (K), and 8) N+P+K+ROM. The results showed that from 1985 to 2002; soil total organic carbon (TOC) decreased by 6.5% over the 18 years in control (33.25 g/kg in 1985), 5.6% in ROM treatment, and 5.1% in N‐alone treatment, and 1.5% in the N+P treatment but increased by 0.3% in the N+P+K treatment. In the three treatments of chemical fertilizers together with ROM (i.e., N+ROM, N+P+ROM, and N+P+K+ROM), soil TOC content in 2002 increased by 0.3%, 1.3%, and 2.8%, respectively, when compared with control in 1985. Compared with control in 2002, light fraction organic carbon (LFOC) content increased by 23% in N+ROM treatment, 24% in N+P+ROM, and 28% in N+P+K+ROM, and readily oxidized carbon (ROC) content increased by 24% 31%, and 39%, respectively, in these three treatments. The ROC was well correlated with soil TOC. Compared with the data from 18 years ago, in all eight treatments organic carbon of soil in the humic acid fraction decreased by 5.0–13% and in fulvic acid decreased by 1.4–14%; however, with chemical fertilizers and ROM applied together, the rate of decrease was reduced. Overall, ROM is effective for increasing the content of soil TOC and thus, its different active carbon fractions in black soil would help to maintain or increase soil productivity.     

Characterization of Organic Acids Recovered from Rhizosphere of Corn Grown on Biosolids‐Treated Medium

Abstract

Organic acid production by plants and microorganisms was quantified in sand media amended with biosolids in the presence and absence of corn (Zea mays L.) in a sand‐culture hydroponic medium. Total quantities of organic acids were greatest in treatments containing both plants and biosolids, with lesser amounts in treatments with plants alone, biosolids‐treated media alone, and a nutrient solution–irrigated blank medium. Biosolids enhanced organic acid production in the rhizosphere and influenced the composition of organic acid mixtures. Only lactic, acetic, butyric, and oxalic acids were detected in media without plants. When the medium was planted, additional organic acids were recovered including tartaric, maleic, succinic, valeric, glutaric, pyruvic, and propionic. Lactic, acetic, and butyric acids were predominant in solutions recovered from the planted media and collectively accounted for 0.65 to 0.75 of the COO^? mole fraction. Oxalic, maleic, and tartaric acids were the second most abundant and varied from 0.05 to 0.1 of the mole fraction, followed by succinic, valeric, glutaric, propionic, and pyruvic acids, comprising ≤0.05 of the mole fraction. Plant growth stage had no effect on relative proportions of organic acids but did influence the total quantities of organic acids recovered. Biosolids sources did not have a significant effect on either the quantity or composition of organic acids in any media. The predominance of organic acids that are microbial fermentation products suggests that the carbon contained in root exudates and biosolid amendments was transformed into a mixture of various fermentation products that accumulated in the rhizosphere solution and sand medium as a result of microbial growth and activity.     

Bioavailability of Heavy Metals in Biosolids‐Amended Soil

Abstract

A single biosolids application was made to 1.5×2.3 m confined plots of a Davidson clay loam (Rhodic Kandiudult) in 1984 at 0, 42, 84, 126, 168, and 210 Mg ha^?1. The highest biosolids application supplied 750 and 600 kg ha^?1 of Cu and Zn, respectively. Corn (Zea mays L.), from 1984 to 2000, and radish (Raphanus sativus L.) and romaine lettuce (Lactuca sativa var. longifolia), from 2001 to 2004, were grown at the site to assess heavy‐metal bioavailability. Extractable (0.005 diethylenetriamine (DTPA) and Mehlich 1) Cu and Zn were determined on 0 to 15‐cm depth samples from each plot. Corn yield increased with biosolids rate each year until 1993 to 1997, when yield decreased with biosolids rate because of phytotoxicity induced by low (<5.0) soil pH. The corn yield reduction was reversed between 1998 and 2000 upon raising the soil pH to approximately 6.0 by limestone addition following the 1997 season. Between 2001 and 2004, radish and lettuce yields were either not affected or slightly increased with biosolids rate, even as soil pH declined to below 5.5. Plant‐tissue metal concentrations increased with biosolids rate and as pH declined but were always within the normal range of these crops. Mehlich 1 and DTPA extractable metals increased linearly with biosolids rate. Extractability of Cu and Zn decreased approximately 50% over the past 20 years despite a decrease in soil organic matter concentration and greater than 95% conservation of the metals.     

Plant Availability of Soil Phosphorus Forms accumulated from Long‐Term Superphosphate Applications to Irrigated Pastures

Abstract: In recent years, many pastoral farmers in New Zealand reduced or withheld phosphorus (P) fertilizer application to their pasture in response to rising fertilizer costs and falling prices in farm produce. When P fertilizer application is withheld, pasture and animal production relies on the P reserves accumulated in the soil from the previous P fertilizer applications. A field‐plot experiment superimposed on irrigated pastures that had received long‐term annual superphosphate (SP) fertilizer applications for 25 years was conducted to examine the forms of P accumulated from the previous SP applications contributing to plant‐available P. The long‐term SP applications were withheld, and the soil was subjected to treatments of no fertilizer (nil), P only, sulphur (S) only, or both P and S, each with P and S at two rates in a split‐plot design with four replicates that ran for 6 years. Soil samples (0–75 mm deep) collected from the trial each year were subjected to a sequential P fractionation scheme. Results showed that most of the P forms extracted by the different extractants showed no significant differences between treatments. Only the inorganic P (Pi) extracted by sodium bicarbonate (NaHCO₃), sodium hydroxide (NaOH) I, and hydrochloric acid (HCl) showed significant differences, and these were related to plant‐available P. However, it was not possible to isolate an individual P form as the dominant P form accumulated from previous SP applications as the plant‐available P form.     

Surface Liming and Zinc Availability in a Long‐Term Experiment under No‐Till System

No‐till (NT) system with crop rotation is one of the most effective strategies to improve agricultural sustainability in tropical and subtropical regions. To control soil acidity in NT, lime is broadcast on the surface without incorporation. The increase in soil pH due to surface liming may decrease zinc (Zn) availability and its uptake by crops. A field experiment was performed in Paraná State, Brazil, on a loamy, kaolinitic, thermic Typic Hapludox to evaluate Zn bioavailability in a NT system after surface liming and re‐liming. Dolomitic lime was surface applied on the main plots in July 1993 at the rates of 0, 2, 4, and 6 Mg ha^?1. In June 2000, the main plots were divided in two subplots to study of the effect of surface re‐liming at the rates of 0 and 3 Mg ha^?1. The cropping sequence was soybean [Glycine max (L.) Merrill] (2001–2 and 2002–3), wheat (Triticum aestivum L.) (2003), soybean (2003–4), corn (Zea mays L.) (2004–5), and soybean (2005–6). Soil samples were collected at the following depths: 0–0.05, 0.05–0.10, and 0.10–0.20 m, 10 years after surface liming and 3 years after surface re‐liming. Soil Zn levels were extracted by four extractants: (i) 0.005 mol L^?1 diethylenetriaminepentaacetic acid (DTPA) + 0.1 mol L^?1 triethanolamine (TEA) + 0.01 mol L^?1 calcium chloride (CaCl₂) solution at pH 7.3 (DTPA–TEA), (ii) 0.1 mol L^?1 hydrochloric acid (HCl) solution, (iii) Mehlich 1 solution, and (iv) Mehlich 3 solution. Zinc concentrations in leaves and grains of soybean, wheat, and corn were also determined. Soil pH (0.01 mol L^?1 CaCl₂ suspension) varied from 4.4 to 6.1, at the 0‐ to 0.05‐m depth, from 4.2 to 5.3 at the 0.05‐ to 0.10‐m depth, and from 4.2 to 4.8 at the 0.10‐ to 0.20‐m depth, after liming and re‐liming. Zinc concentrations evaluated by DTPA–TEA, 0.1 mol L^?1 HCl, Mehlich 1, and Mehlich 3 solutions were not changed as a result of lime rate application. Re‐liming increased Zn concentrations extracted by 0.1 mol L^?1 HCl at 0–0.05 m deep and by DTPA–TEA at 0.05–0.10 m deep. Surface‐applied lime promoted a decrease in Zn concentrations of the crops, mainly in grains, because of increased soil pH at the surface layers. Regardless of the liming treatments, levels of Zn were sufficient to soybean, wheat, and corn nutrition under NT.     

Dissolved and Soil Organic Carbon after Long‐Term Conventional and No‐Tillage Sorghum Cropping

Abstract

Distribution of dissolved (DOC) and soil organic carbon (SOC) with depth may indicate soil and crop‐management effects on subsurface soil C sequestration. The objectives of this study were to investigate impacts of conventional tillage (CT), no tillage (NT), and cropping sequence on the depth distribution of DOC, SOC, and total nitrogen (N) for a silty clay loam soil after 20 years of continuous sorghum cropping. Conventional tillage consisted of disking, chiseling, ridging, and residue incorporation into soil, while residues remained on the soil surface for NT. Soil was sampled from six depth intervals ranging from 0 to 105 cm. Tillage effects on DOC and total N were primarily observed at 0–5 cm, whereas cropping sequence effects were observed to 55 cm. Soil organic carbon (C) was higher under NT than CT at 0–5 cm but higher under CT for subsurface soils. Dissolved organic C, SOC, and total N were 37, 36, and 66%, respectively, greater under NT than CT at 0–5 cm, and 171, 659, and 837% greater at 0–5 than 80–105 cm. The DOC decreased with each depth increment and averaged 18% higher under a sorghum–wheat–soybean rotation than a continuous sorghum monoculture. Both SOC and total N were higher for sorghum–wheat–soybean than continuous sorghum from 0–55 cm. Conventional tillage increased SOC and DOC in subsurface soils for intensive crop rotations, indicating that assessment of C in subsurface soils may be important for determining effects of tillage practices and crop rotations on soil C sequestration.     

Effects of Long‐Term Irrigation using Industrial Wastewater on Soil Properties and Elemental Contents of Rice,Spinach, Clover,and Grass

Abstract

Application of industrial wastewater on agricultural lands increased the amounts of elements in soil and plants. To investigate the effects of wastewater on soil properties and element content in soil and plants, wastewaters of three industries (chrome chemical, wood and paper, and textiles) were examined in 2005. At harvest time, the soil samples were taken from depths of 0–15 and 15–30 cm, and the roots and shoots of rice, spinach, clover, and grass and grain of rice in an industrial wastewater–treated area and untreated area were sampled. Results indicated that the concentrations of zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) increased in river water when wastewater was discharged into it. Use of the river water, influenced by industrial wastewater, for irrigation of rice and other plants increased the amounts of organic matter and available Zn, Cu, Mn, and Fe in soil. Cation exchange capacity was correlated with available Cu and Fe in soil (+0.431** and +0.499**, respectively). Soil organic matter was correlated with available Zn, Cu, Mn, and Fe in soil. However, the clay content in soil did not correlate with these elements. Meanwhile, in roots, shoots, and grains of rice and roots and shoots of spinach, clover, and grasses of agricultural land influenced by industrial wastewater, the amounts of Zn, Cu, Mn, and Fe increased. Therefore, by increasing the amount of Mn in the soil, the concentration of Zn in rice grain decreased and the concentration of Cu and Mn increased. Transferred Zn concentrations to rice grain and shoots of spinach, clover, and grass were more than Cu and Mn and increased in rice grain.     

Evaluation of Agronomic and Environmental Soil P Test Methods in a Network of Hungarian Long‐Term Field Trials

Abstract

Winter wheat shoot weight and phosphorus (P) concentrations, corn leaf weight and P concentrations, and soil AL, Olsen, H₂O, Bray 1, Pi (Fe-oxide impregnated paper strip) and AERM (anion exchange resin membrane) contents were determined in a network of uniform Hungarian national long‐term field trials. P application had a significant effect on soil P test values at different P levels and sites. The relationship between the different soil P test methods was studied separately for different soil groups (all, acid, and calcareous soils). Corn leaf weight was influenced by the sites much more than by soil P supply level, whereas corn leaf P percentage was influenced by both sites and P levels. For winter wheat, both sites and soil P levels had a positive effect on wheat shoot weight. Wheat shoot P percentage was influenced by the soil P supply much more than by the sites. Correlation between corn leaf P percentage and the Pi or AERM extractable P and between wheat shoot P percentage and the Pi and AERM P values was logarithmic.     

Influence of Long‐Term Sodic‐Water Irrigation,Gypsum, and Organic Amendments on Soil Properties and Nitrogen Mineralization Kinetics under Rice–Wheat System

Abstract

Influence of long‐term sodic‐water (SW) irrigation with or without gypsum and organic amendments [green manure (GM), farmyard manure (FYM), and rice straw (RS)] on soil properties and nitrogen (N) mineralization kinetics was studied after 12 years of rice–wheat cropping in a sandy loam soil in northwest India. Long‐term SW irrigation increased soil pH, exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR) and decreased organic carbon (OC) and total N content. On the other hand, application of gypsum and organic amendments resulted in significant improvement in all these soil properties. Mineralization of soil N ranged from 54 to 111 mg N kg^?1 soil in different treatments. Irrigation with SW depressed N mineralization. In SW‐irrigated plots, two flushes of N mineralization were observed; the first during 0 to 7 d and the second after 28 d. Amending SW irrigated plots with GM and FYM enhanced mineralization of soil N. Gypsum application along with SW irrigation reduced cumulative N mineralization at 56 days in RS‐amended plots but increased it under GM‐treated, FYM‐treated, or unamended plots. Nitrogen mineralization potential (N_o) ranged from 62 to 543 mg N kg^?1 soil. In the first‐order zero‐order model (FOZO), the easily decomposable fraction ranged from 5.4 to 42 mg N kg^?1 soil. Compared to the first‐order single compartment model, the FOZO model could better explain the variations in N mineralization in different treatments. Variations in N_o were influenced more by changes in pH, SAR, and ESP induced by long‐term SW irrigations and amendments rather than by soil OC.     

Soil Properties and Macro Cations Status impacted by Long‐Term Applied Poultry Litter

Abstract

Most ethnic populations worldwide consume poultry products. Whereas poultry litter (PL) is a traditionally inexpensive and effective fertilizer to improve soil quality and agricultural productivity, overapplication to soils has raised concerns because excess nutrients in runoff could accelerate the eutrophication of fresh bodies of water. A long‐term field experiment of land application of PL to soils used for pasture growth has been maintained for nearly two decades in the Sand Mountain region of north Alabama, USA. In this work, several soil parameters impacted by the long‐term applied litter were characterized. The findings clearly support previous general observations that long‐term applied litter on pasture soils altered soil properties and macrocation levels. Unlike other studies, however, the effects of applied litter at multiple rates and years were examined, thus revealing the dynamic impacts on soil properties. Hay yields increased with the increase of years of PL application, regardless of the applied rate. This observation was consistent with previous observations that the labile phosphorus (P) portion in these soils increases with application years whereas total P increases with the cumulative applied PL amounts. Poultry litter application did not markedly affect soil electric conductivity, bulk density, or sodium (Na) or potassium (K) levels, especially at the soil surface (0–20 cm). Soil pH, carbon (C), C/nitrogen (N) ratio, calcium (Ca), and magnesium (Mg) were profoundly affected at all three soil depths (0–20, 20–40, and 40–60 cm). Most soil parameters analyzed in this study reached peak values with 10–15 years of applied litter. This observation suggests that there was a turning point of impact for applied litter around 10 years: prior to that the soil macrocations were altered positively as a result of accumulative functions. Continuous litter application may negatively alter a soil's capacity to retain macrocations, leading to less impact observed in this study. In other words, pasture soils with more than 10 years of applied litter would have higher potential for leaching and runoff. Our observation suggested that best management practices for land application of PL should take into consideration the different effects of PL application history.     

Changes in the Soil Phosphorus Content of a Long‐Term Fertilization Field Trial Studied in Laboratory Incubations

Abstract

The importance of different soil phosphorus (P) compounds and their transformation influenced by several soil and other factors is well established. However, the dynamics of short‐term processes taking part in the long‐term changes of soil P including immobilization and mobilization is still not completely documented. Laboratory incubation experiments were carried out at 10°C and 40°C for studying the influence of incubation on the availability of residual and freshly applied P in samples of a long‐term fertilization field trial conducted on a brown forest soil (U.S. taxonomy: Orthic Eutrochrept; FAO taxonomy: Eutric Cambisol). Samples showing three levels of P resulting from 10 years of intensive P fertilization (referred as P0, P1 and P2, respectively), were collected 30 years after fertilization ceased. Available P contents of soil samples were determined using three approaches: in water (modified Murphy–Riley method), sodium bicarbonate (Olsen, pH=8.5), and ammonium lactate (AL, pH=3.7) extract. Changes in the amounts of P were determined after 2 and 60 days of incubation in four freshly applied new treatments with increasing additions of P: 0, 100, 500, and 1000 mg of P₂O₅ per kg of soil, representing agronomic and extreme P rates. From the results of our experiments, it was suggested that after 2 days of incubation, at 10°C, both agronomic and extreme P rates resulted in significant increases in P content in each extract. On the other hand, after 60 days, even higher values were obtained. Decreases found in water‐P values after 60 days of incubation were considerable compared to either the Olsen‐P or the AL‐P values, indicating the decline of water‐soluble P forms and further evidence of immobilization with increasing incubation time and temperature. Correlation between water‐P, Olsen‐P, and AL‐P values were significant at both temperatures.     

Impact of Boron on Biomass Production and Nutrition of Aluminum‐Stressed Apple Rootstocks

Abstract

The aim of the experiment was to examine the effect of boron (B) on biomass production and nutrition of aluminum (Al)‐stressed apple (Malus sp.) rootstocks. The study was carried out under greenhouse conditions on Polish rootstock (P22) and Malling 26 (M.26) planted singly into 1‐L plastic pots filled with perlite and supplied with Hoagland's medium at pH 4.5 without or with Al (100 µM as AlCl₃). Boron was added into the Al‐containing medium at 20, 40, or 60 µM whereas into the medium without Al only at 20 µM as boric acid. The results showed that the presence of Al in the medium reduced biomass production of P22 and M.26 rootstocks by 22% and 41%, respectively. Rates of uptake and translocation of phosphorus (P), magnesium (Mg), and calcium (Ca) to aerial plant parts were decreased for Al‐treated rootstocks. Aluminum‐stressed P22 rootstocks grown in nutrient solution at 40 and 60 µM B had higher dry weight of leaves and roots, and also higher ability to take up P, Mg, and Ca and lower Al than those grown in the presence of Al at 20 µM B in the medium. Rates of absorption and transport of B to aerial plant parts corresponded with B level in the medium. These results suggest that on acid soils with high Al availability, supra‐optimal B concentrations in soil solution (40–60 µM) can prevent/alleviate Al toxicity in apple trees grafted on P22 rootstocks.     

Carbon Dioxide Emission from Black Soil as Influenced by Land‐Use Change and Long‐Term Fertilization

Land‐use change and soil management play a vital role in influencing losses of soil carbon (C) by respiration. The aim of this experiment was to examine the impact of natural vegetation restoration and long‐term fertilization on the seasonal pattern of soil respiration and cumulative carbon dioxide (CO₂) emission from a black soil of northeast China. Soil respiration rate fluctuated greatly during the growing season in grassland (GL), ranging from 278 to 1030 mg CO₂ m^?2 h^?1 with an average of 606 mg CO₂ m^?2 h^?1. By contrast, soil CO₂ emission did not change in bareland (BL) as much as in GL. For cropland (CL), including three treatments [CK (no fertilizer application), nitrogen, phosphorus and potassium application (NPK), and NPK together with organic manure (OM)], soil CO₂ emission gradually increased with the growth of maize after seedling with an increasing order of CK < NPM < OM, reaching a maximum on 17 August and declining thereafter. A highly significant exponential correlation was observed between soil temperature and soil CO₂ emission for GL during the late growing season (from 3 August to 28 September) with Q₁₀ = 2.46, which accounted for approximately 75% of emission variability. However, no correlation was found between the two parameters for BL and CL. Seasonal CO₂ emission from rhizosphere soil changed in line with the overall soil respiration, which averaged 184, 407, and 584 mg CO₂ m^?2 h^?1, with peaks at 614, 1260, and 1770 mg CO₂ m^?2 h^?1 for CK, NPK, and OM, respectively. SOM‐derived CO₂ emission of root free‐soil, including basal soil respiration and plant residue–derived microbial decomposition, averaged 132, 132, and 136 mg CO₂ m^?2 h^?1, respectively, showing no difference for the three CL treatments. Cumulative soil CO₂ emissions decreased in the order OM > GL > NPK > CK > BL. The cumulative rhizosphere‐derived CO₂ emissions during the growing season of maize in cropland accounted for about 67, 74, and 80% of the overall CO₂ emissions for CK, NPK, and OM, respectively. Cumulative CO₂ emissions were found to significantly correlate with SOC stocks (r = 0.92, n = 5, P < 0.05) as well as with SOC concentration (r = 0.97, n = 5, P < 0.01). We concluded that natural vegetation restoration and long‐term application of organic manure substantially increased C sequestration into soil rather than C losses for the black soil. These results are of great significance to properly manage black soil as a large C pool in northeast China.