Comparing Nutrient Availability in Low-Fertility Soils using Ion Exchange Resin Capsules

Assessing the nutrient status of low-input, low-fertility desert soils poses some unique challenges. Commonly used soil analysis procedures and resin capsules generally assess nutrient status of fertile agricultural soils. Ion-exchange resin capsules (Unibest Company, Bozeman, Mont.) provide a viable alternative. A study was conducted to determine effectiveness of resin capsules to extract low levels of nutrients applied to native soils. Loamy sand and sandy clay loam desert soils from Utah were treated with combinations of four rates of nitrogen (N) as ammonium nitrate (34–0–0), three rates of phosphorus (P) as phosphoric acid (0–72–0), and two rates of iron sulfate (FeSO₄·7H₂O) and zinc sulfate (ZnSO₄·7H₂O) (include an untreated control). Each soil treatment was implanted with a resin capsule placed into either 250 or 1000 cm³ of soil after addition of water equivalent to 50% field capacity and incubated for either 60 or 120 days at 25 °C. After the appropriate incubation time, capsules were washed and extracted using 2 M hydrochloric acid (HCl), and the extract was used to measure iron (Fe), ammonium (NH₄)-N, nitrate (NO₃)-N, sulfur (S), and zinc (Zn). Conventional soil tests were completed on incubated soils (60 or 120 days). Resin capsules reflected NH₄-N and P fertilizer applied at low rates in the loamy sand but not in the sandy clay loam. Neither Fe nor Zn application was reflected in resin capsules, but the accompanying S was clearly quantified. In comparison to conventional soil test procedures, resin capsule NH₄-N was clearly a better indicator than KCl-extractable NH₄-N; resin capsule NO₃-N was effective, but not as good an indicator as water extraction; and resin capsule P was reflective of soil applied P in loamy sand but not in sandy clay loam, whereas sodium bicarbonate was effective in both soils. Resin capsules show promise for use in low-input conditions, but additional understanding of interactions in variable soils is needed.     

氮肥基追比对小麦产量、土壤水氮分布及利用的影响

为解决区域土壤质地类型针对性氮肥施用问题,在轻壤土和黏壤土上分别设置不施氮肥,氮肥基追比3∶7,4∶6,5∶5,6∶4和7∶3处理,研究小麦产量、水氮利用效率以及土壤含水量、贮水量、NH_4~+-N、NO_3~--N动态变化规律。结果表明:轻壤质土壤氮肥基追比4∶6的处理小麦产量、水分利用效率、氮肥生产效率最高分别为8 265.3 kg/hm~2,27.6 kg/(hm~2·mm),34.4 kg/kg。黏壤质土壤氮肥基追比5∶5的处理小麦产量、水分利用效率、氮肥生产效率最高分别为8 363.2 kg/hm~2,28.3 kg/(hm~2·mm),34.8 kg/kg。小麦不同生育期各土层含水量垂直分布变化较大,轻壤质土壤含水量在9.3%～26.2%,而黏壤质为9.7%～27.6%;小麦全生育期内土壤贮水量呈先升高后降低趋势,黏壤质土壤贮水量高于轻壤质。氮素追施量越多土壤表层NH_4~+-N与NO_3~--N含量越高,且随土层加深土壤NH_4~+-N与NO_3~--N含量降低,受降水影响轻壤质土壤NH_4~+-N与NO_3~--N更易于向土层深处淋溶,成熟期黏壤质各土层的NH_4~+-N和NO_3~--N含量均多于轻壤质。说明黏壤质土壤保水保氮肥能力强于轻壤质,氮肥基追比可以适当增加。     

灌溉施用氮肥后氮素在土壤中的转化及淋失状况: 土柱模拟研究

A soil column method was used to compare the effect of drip fertigation (the application of fertilizer through drip irrigation systems, DFI) on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation (SFI), and to study the leaching loss and transformation of three kinds of nitrogen fertilizers (nitrate fertilizer, ammonium fertilizer, and urea fertilizer) in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N (NH₄⁺-N + NO₃^--N) in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or ammonium fertilizer. Compared to the control (without urea addition), on the first day when soils were fertigated with urea, there were increases in NH₄⁺-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH₄⁺-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH₄⁺-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH₄⁺-N fixation or volatilization in the soil during the fertigation process.     

Leaching Methods Can Underestimate Mineralization Potential of Soils

Aerobic incubations to estimate net nitrogen (N) mineralization typically involve periodic leaching of soil with 0.01 M calcium chloride (CaCl₂), so as to remove mineral N that would otherwise be subject to immobilization. A study was conducted to evaluate the accuracy of leaching for analysis of exchangeable ammonium (NH₄⁺)-N and nitrate + nitrite (NO₃^?+ NO₂^–)-N, relative to conventional extractions using 2 M potassium chloride (KCl). Ten air-dried soils were used, five each from Illinois and Brazil, that had been amended with NH₄⁺-N (1 g kg^?1) and NO₃^–-N (0.6 g kg^?1). Both methods were in good agreement for inorganic N analysis of the Brazilian Oxisols, whereas leaching was significantly lower by 12–48% in recovering exchangeable NH₄⁺-N from Illinois Alfisols, Mollisols, and Histosols. The potential for underestimating net N mineralization was confirmed by a 12-wk incubation experiment showing 9–86% of mineral N recoveries from three temperate soils as exchangeable NH₄⁺.     

Environmental Implication of Soils Amended with Anaerobically Digested Sewage Sludge in Hong Kong

Rainfall leaching soil column trials wereused to characterize the downward movement ofpotential contaminants through a sandy loam and sandysoil following the application of an anaerobicallydigested sewage sludge at the rates of 10 and 25%(v/v). Leachate pH did not vary significantly withsludge application except for sandy loam with 25%sludge, while initial electrical conductivity (EC) anddissolved organic carbon (DOC) increased linearly withsludge application and declined shortly to levelsfound in soils without sludge. A higher initialleaching loss of ammonium (NH₄ ⁺) was found in sandy soilthan loamy sand due to its lower cation exchangecapacity. Nitrate (NO₃ ^-) was the dominant anion inleachates with an average in excess of 10 mg L^-1 NO₃ ^- at all loading rates after 12 weeks. The highestconcentration of NO₃ ^- occurred with the highest sludgeapplication rate. Leachate zinc (Zn) content increasedin loamy sand columns at the high sludge loading rateat the end of the experiment owing to the reduced pHfollowing nitrification. No significant difference inleachate copper (Cu) and phosphate (PO₄ ^3-) contents werenoted for both soils receiving various sludgeapplication rates. Evaluation of the soluble nutrientspresent in the soil profiles at the end of theleaching experiment showed that EC, NH₄ ⁺ and PO₄ ^3- increased according to sludge application rate up toa depth of 20 cm. Significant accumulation of NO₃ ^- wasfound in sandy loam with sludge application to thedepth of 50 cm. Analyses of leachates and soils forthe selected contaminants revealed that NO₃ ^- leaching islikely to occur without plant growth at the currentapplication rate. Therefore, the application rate forsludge should not exceed 10% (v/v), and the provisionof vegetation on the amended soil would reduce theleaching loss of NO₃ ^-.     

Nitrification Inhibitor,Fertilizer Rate,and Temperature Effects on Nitrous Oxide Emission and Nitrogen Transformation in Loamy Sand Soil

An incubation study investigated the effects of nitrification inhibitors (NIs), dicyandiamide (DCD), and neem oil on the nitrification process in loamy sand soil under different temperatures and fertilizer rates. Results showed that NIs decreased soil nitrification by slowing the conversion of soil ammonium (NH₄⁺)-nitrogen (N) and maintaining soil NH₄⁺-N and nitrate (NO₃^?)-N throughout the incubation time. DCD and neem oil decreased soil nitrous oxide (N₂O) emission by up to 30.9 and 18.8%, respectively. The effectiveness of DCD on reducing cumulative soil N₂O emission and retaining soil NH₄⁺-N was inconsistently greater than that of neem oil, but the NI rate was less obvious than temperature. Fertilizer rate had a stronger positive effect on soil nitrification than temperature, indicating that adding N into low-fertility soil had a greater influence on soil nitrification. DCD and neem oil would be a potential tool for slowing N fertilizer loss in a low-fertility soil under warm to hot climatic conditions.     

Nitrogen transformations in cold and frozen agricultural soils following organic amendments

Though microbial activity is known to occur in frozen soils, little is known about the fate of animal manure N applied in the fall to agricultural soils located in areas with prolonged winter periods. Our objective was to examine transformations of soil and pig slurry N at low temperatures. Loamy and clay soils were either unamended (Control), amended with ¹⁵NH₄-labeled pig slurry, or amended with the pig slurry and wheat straw. Soils were incubated at −6, −2, 2, 6, and 10 °C. The amounts of NH₄, NO₃ and microbial biomass N (MBN), and the presence of ¹⁵N in these pools were monitored. Total mineral N, NO₃ and ¹⁵NO₃ increased at temperature down to −2 °C in the loam soil and −6 °C in the clay soil, indicating that nitrification and mineralization proceeded in frozen soils. Nitrification and mineralization rates were 1.8-4.9 times higher in the clay than in the loamy soil, especially below freezing point (3.2-4.9), possibly because more unfrozen water remained in the clay than in the loamy soil. Slurry addition increased nitrification rates by 3-14 times at all temperatures, indicating that this process was N-limited even in frozen soils. Straw incorporation caused significant net N immobilization only at temperatures ≥2 °C in both soils; the rates were 1.4-3.4 higher in the loam than in the clay soil. Nevertheless, up to 30% of the applied ¹⁵N was present in MBN at all temperatures. These findings indicate that microbial N immobilization occurred in frozen soils, but was not strong enough to induce net immobilization below the freezing point, even in the presence of straw. The Q₁₀ values for estimated mineralization and nitrification rates were one to two orders-of-magnitude larger below 2 °C than above this temperature (13-208 versus 1.5-6.9, respectively), indicating that these processes are highly sensitive to a small increase in soil temperature around the freezing point of water. This study confirms that net mineralization and nitrification can occur at potentially significant rates in frozen agricultural soils, especially in the presence of organic amendments. In contrast, net N immobilization could be detected essentially above the freezing point. Our results imply that fall-applied N could be at risk of overwinter losses, particularly in fine-textured soils.     

Crop yield and SOC responses to biochar application were dependent on soil texture and crop type in southern Quebec,Canada

Changes to soil nutrient availability and increases for crop yield and soil organic C (SOC) concentration on biochar‐amended soil under temperate climate conditions have only been reported in a few publications. The objective of this work was to determine if biochar application rates up to 20 Mg ha^?1 affect nutrient availability in soil, SOC stocks and yield of corn (Zea mays L.), soybean (Glycine max L.), and switchgrass (Panicum virgatum L.) on two coarse‐textured soils (loamy sand, sandy clay loam) in S Quebec, Canada. Data were collected from field experiments for a 3‐y period following application of pine wood biochar at rates of 0, 10, and 20 Mg ha^?1. For corn plots, at harvest 3 y after biochar application, 20 Mg biochar ha^?1 resulted in 41.2% lower soil NH on the loamy sand; the same effect was not present on the sandy clay loam soil. On the loamy sand, 20 Mg biochar ha^?1 increased corn yields by 14.2% compared to the control 3 y after application; the same effect was not present on the sandy clay loam soil. Biochar did not alter yield or nutrient availability in soil on soybean or switchgrass plots on either soil type. After 3 y, SOC concentration was 83 and 258% greater after 10 and 20 Mg ha^?1 biochar applications, respectively, than the control in sandy clay loam soil under switchgrass production. The same effect was not present on the sandy clay loam soil. A 67% higher SOC concentration was noted with biochar application at 20 Mg ha^?1 to sandy clay loam soil under corn.     

螃蟹对闽江河口互花米草湿地土壤活性养分变化的影响

为阐明螃蟹活动对湿地土壤活性养分含量变化的影响,对闽江河口湿地不同潮滩螃蟹干扰下的土壤DOC、MBC、NH_4~+-N、NO_3~--N、Fe及其价态含量特征进行测定和分析。结果表明:有螃蟹组土壤DOC和MBC含量分别为95.98,11.13mg/kg,对照组含量分别为106.99,7.54mg/kg,螃蟹组土壤DOC含量略低于对照组(P0.05),螃蟹组土壤MBC含量高于对照组(P0.05);两者含量最高值和最低值分别出现在夏季和冬季,且夏季显著高于其他季节(P0.05)。螃蟹组土壤NH_4~+-N和土壤NO_3~--N含量分别为22.45,1.08mg/kg,对照组含量分别为23.65,1.44mg/kg,螃蟹组土壤NH_4~+-N含量低于对照组(P0.05),螃蟹组土壤NO_3~--N含量低于对照组(P0.05);不同季节,土壤NH_4~+-N和NO_3~--N含量存在显著差异(P0.01)。螃蟹组土壤总铁含量略高于对照组(P0.05);螃蟹组土壤Fe2+含量显著高于对照组(P0.05);螃蟹组和对照组土壤Fe3+含量差异不明显(P0.05)。不同季节,土壤总Fe、Fe~(2+)和Fe~(3+)含量存在显著差异(P0.01)。     

Effects of 4-amino 1,2,4-triazole, dicyandiamide and encapsulated calcium carbide on nitrification inhibition in a subtropical soil under upland and flooded conditions

 Nitrification inhibition of soil and applied fertilizer N is desirable as the accumulation of nitrates in soils in excess of plant needs leads to enhanced N losses and reduced fertilizer N-use efficiency. In a growth chamber experiment, we studied the effects of two commercial nitrification inhibitors (NIs), 4-amino 1,2,4-triazole (ATC) and dicyandiamide (DCD), and a commonly available and economical material, encapsulated calcium carbide (CaC₂) (ECC) on the nitrification of soil and applied NH₄ ⁺-N in a semiarid subtropical Tolewal sandy loam soil under upland [60% water-filled pore space (WFPS)] and flooded conditions (120% WFPS). Nitrification of the applied 100 mg NH₄ ⁺-N kg^–1 soil under upland conditions was retarded most effectively (93%) by ECC for up to 10 days of incubation, whereas for longer periods, ATC was more effective. After 20 days, only 16% of applied NH₄ ⁺-N was nitrified with ATC as compared to 37% with DCD and 98% with ECC. Under flooded soil conditions, nitrates resulting from nitrification quickly disappeared due to denitrification, resulting in a tremendous loss of fertilizer N (up to 70% of N applied without a NI). Based on four indicators of inhibitor effectiveness, namely, concentration of NH₄ ⁺-N and NO₃ ^–-N, percent nitrification inhibition, ratio of NH₄ ⁺-N/NO₃ ^–-N, and total mineral N, ECC showed the highest relative efficiency throughout the 20-day incubation under flooded soil conditions. At the end of the 20-day incubation, 96%, 58% and 38% of applied NH₄ ⁺-N was still present in the soil where ECC, ATC and DCD were used, respectively. Consequently, nitrification inhibition of applied fertilizer N in both arable crops and flooded rice systems could tremendously minimize N losses and help enhance fertilizer N-use efficiency. These results suggest that for reducing the nitrification rate and resultant N losses in flooded soil systems (e.g. rice lowlands), ECC is more effective than costly commercial NIs. Received: 25 May 2000     

Nutrient cycling and greenhouse gas emissions from soil amended with biochar-manure mixtures

Integrating biochar into cattle diets has recently emerged as a potential management practice for improving on-farm productivity.Yet,information concerning the cycling of biochar-manure mixtures is scarce.A 70-d incubation experiment was conducted within two surface(0–15 cm)Mollisols with contrasting textures,i.e.,sandy clay loam(Raymond)and clayey(Lethbridge),to evaluate the effects of biochar(3 Mg ha^-1)on cumulative greenhouse gas(GHG)emissions and related fertility attributes in the presence or absence of cattle manure(120 Mg ha^-1).Five treatments were included:i)non-amended soil(control,CK),ii)soil amended with pinewood biochar(B),iii)soil amended with beef cattle manure(M)(manure from cattle on a control diet),iv)soil amended with biochar-manure(BM)(manure from cattle on a control diet,with pinewood biochar added at 20 g kg^-1of diet dry matter),and v)soil amended with B and M at the aforementioned rates(B+M).A total of 40 soil columns were prepared and incubated at 21℃and 60%–80%water-holding capacity.On average,total CO₂fluxes increased by 2.2-and 3.8-fold under manure treatments(i.e.,M,BM,and B+M),within Raymond and Lethbridge soils,respectively,relative to CK and B.Similarly,total CH4 fluxes were the highest(P<0.05)in Raymond soil under B+M and BM relative to CK and B,and in Lethbridge soil under M and BM relative to CK and B.In Lethbridge soil,application of BM increased cumulative N₂O emissions by 1.8-fold relative to CK.After 70-d incubation,amendment with BM increased(P<0.05)PO_4-P and NO_3-N+NH_4-N availability in Raymond and Lethbridge soils compared with B.A similar pattern was observed for water-extractable organic carbon in both soils,with BM augmenting(P<0.05)the occurrence of labile carbon over CK and B.It can be concluded that biochar,manure,and/or biochar-manure have contrasting short-term effects on the biogeochemistry of Mollisols.At relatively low application rates,biochar does not necessarily counterbalance manure-derived inputs.Although BM did not mitigate the flux of GHGs over M,biochar-manure has the potential to recycle soil nutrients in semiarid drylands.     

Effects of freeze–thaw cycles and the soil water content on carbon and nitrogen changes in different soil types of Heilongjiang Province,China

To reveal the influence of freeze–thaw cycles (FTCs) on soil carbon and nitrogen changes, six typical soils in Northeast China were selected as the research objects to conduct a FTC simulation test in an artificial climate chamber. Three soil volumetric water contents (10%, 20%, 30%) and eight FTCs (0, 2, 4, 6, 8, 10, 15, 20) were set. The results showed that the soil organic carbon (SOC) and microbial biomass carbon (MBC) contents of different soil types under the FTCs initially exhibited a downward and then an upward trend, while the dissolved organic carbon (DOC) content exhibited an upward and then a downward trend. Otherwise, the fourth and sixth FTCs were the key points of change. The SOC, MBC and DOC contents in paddy fields were higher than those in dry fields, showing upward and then downward trends spatially from northeast to southwest. The SOC and MBC contents in each soil type were the highest at the 20% water content, and the DOC content gradually increased with increasing water content. The ammonium nitrogen (NH₄⁺-N) content in different soil types at different water contents under the FTCs showed an upward trend first, then a downward trend and finally an upward trend. The NH₄⁺-N content in paddy fields was higher than that in dry fields. The nitrate nitrogen (NO₃^‒-N) content showed a downward trend first, then an upward trend and finally a downward trend. The NO₃^‒-N content in dry fields was higher than that in paddy fields. The NH₄⁺-N contents in the three soil types on the Sanjiang Plain were significantly higher than those on the Songnen Plain. The NH₄⁺-N and NO₃^‒-N contents showed upward trends with increasing water content, but the differences were not significant. The results have implications for the study of different types of soils and provide references for research on the mechanism of soil carbon and nitrogen transformation in typical farming areas in Northeast China.     

Fate of Chinese-fir litter during decomposition as a result of inorganic N additions

We conducted a controlled experiment to evaluate Chinese-fir litter decomposition and its response to the addition of inorganic N. Litter-derived CO₂, microbial biomass carbon (MBC), and dissolved organic carbon (DOC) were monitored during an 87-d incubation of a mixed soil–litter substrate using the ¹³C tracer technique. Litter C was mostly converted to CO₂ (47.4% of original mass), followed by MBC (3.6%), and DOC (1.0%), with 48% remaining unaltered in the soil. The litter decomposition rate significantly increased with the addition of inorganic N, although the effect depended on whether N was added as NH₄⁺ or NO₃⁻. Soil-derived CO₂, MBC, and DOC also increased following the combined addition of litter and N. The results showed that only a small percentage of litter C was retained as MBC or DOC and that the conversion rate depended, in part, on the form of inorganic N added to the Chinese-fir plantation soil.     

Effects of N placement,carbon distribution and temperature on N2O emissions in clay loam and loamy sand soils

Changes in the profile distribution of soil C stocks for conventional versus no‐tillage can affect N₂O losses. Uncertainty remains whether deep N placement into a wetter layer in humid areas would affect N₂O losses. This study evaluated the effects of soil carbon profile distribution (inverted, normal), depth of nitrogen placement (5 cm, 15 cm), temperature (10, 20 and 30 °C) and soil texture (clay loam, loamy sand) on N₂O emissions from soil cores in a 216‐h incubation after simulated rainfall. N₂O losses were larger from the clay loam than from the loamy sand, and cumulative N₂O emissions from the inverted profile, with greater C levels at depth, were more than those from the profile with more C near the upper surface. Cumulative N₂O losses from the inverted clay loam profile with deep N placement (1.16 mg N per kg dry soil; 0.71% of applied N) on average were almost double those in the loamy sand (0.62 mg N per kg dry soil; 0.42%). The smallest N₂O losses were measured from the profiles with more C close to the upper surface with a shallow placement of N for the clay loam (0.19 mg N per kg dry soil; 0.12%) and loamy sand (0.33 mg N per kg dry soil; 0.23%). An exponential relationship between N₂O fluxes and temperature was measured. We conclude that large N₂O losses may occur under the combination of greater soil C content at deeper layers (ploughed soils) and moist profiles after N application (humid regions). Deep N placement appears to aggravate rather than ameliorate these concerns.     

控释氮肥养分控释效果及合理施用研究

试验采用{3,3}单形重心设计方法,研究了普通尿素和2种包膜尿素D90、D60配比对土壤NH4+-N、NO3--N及矿质态氮(Nmin)含量的影响。结果表明,供试的7种包膜肥料初期溶出率均12.0%,微分溶出率在0.26%～2.49%之间。各处理土壤NH4+-N含量均随时间逐渐降低,而NO3--N和Nmin含量随时间逐渐增加。整个培养期内单独施用尿素处理,土壤NH4+-N、NO3--N及Nmin含量最高;2种控释肥单施或其配比施用土壤NH4+-N、NO3--N及Nmin含量最低;尿素与控释肥配合施用,土壤NH4+-N、NO3--N及Nmin含量居中。不同时期内土壤NH4+-N的来源不同,0～20d内,尿素对土壤NH4-N含量贡献最大;30～50d内,土壤NH4+-N主要来自D60;整个培养期内尿素对土壤NO3--N和Nmin的贡献均最大。肥料配比中随着尿素比例的减少,土壤NH4+-N、NO3--N及Nmin均逐渐减少。研究结果初步验证了混料设计在肥料配比研究中的可行性。     

Estimating soil ammonium adsorption using pedotransfer functions in an irrigation district of the North China Plain

Extensive use of chemical fertilizers in agriculture can induce high concentration of ammonium nitrogen(NH4⁺_-N) in soil. Desorption and leaching of NH4⁺_-N has led to pollution of natural waters. The adsorption of NH4⁺_-N in soil plays an important role in the fate of the NH4⁺_-N. Understanding the adsorption characteristics of NH4⁺_-N is necessary to ascertain and predict its fate in the soil-water environment, and pedotransfer functions(PTFs) could be a convenient method for quantification of the adsorption parameters. Ammonium nitrogen adsorption capacity, isotherms, and their influencing factors were investigated for various soils in an irrigation district of the North China Plain. Fourteen agricultural soils with three types of texture(silt, silty loam, and sandy loam) were collected from topsoil to perform batch experiments. Silt and silty loam soils had higher NH4⁺_-N adsorption capacity than sandy loam soils.Clay and silt contents significantly affected the adsorption capacity of NH4⁺_-N in the different soils. The adsorption isotherms of NH4⁺_-N in the 14 soils fit well using the Freundlich, Langmuir, and Temkin models. The models’ adsorption parameters were significantly related to soil properties including clay,silt, and organic carbon contents and Fe²⁺ and Fe³⁺ ion concentrations in the groundwater. The PTFs that relate soil and groundwater properties to soil NH4⁺_-N adsorption isotherms were derived using multiple regressions where the coefficients were predicted using the Bayesian method. The PTFs of the three adsorption isotherm models were successfully verified and could be useful tools to help predict NH4⁺_-N adsorption at a regional scale in irrigation districts.     

Is CO2 evolution in saline soils affected by an osmotic effect and calcium carbonate?

Salt-affected soils are widespread, particularly in arid climates, but information on nutrient dynamics and carbon dioxide (CO₂) efflux from salt-affected soils is scarce. Four laboratory incubation experiments were conducted with three soils. To determine the influence of calcium carbonate (CaCO₃) on respiration in saline and non-saline soils, a loamy sand (6.3% clay) was left unamended or amended with NaCl to obtain an electrical conductivity (EC) of 1.0 dS?m^?1 in a 1:5 soil/water extract. Powdered CaCO₃ at rates of 0%, 0.5%, 1.0%, 2.5%, 5.0% and 10.0% (w/w) and 0.25-2 mm mature wheat residue at 0% and 2% (w/w) were then added. Cumulative CO₂-C emission from the salt amended and unamended soils was not affected by CaCO₃ addition. To investigate the effect of EC on microbial activity, soil respiration was measured after amending a sandy loam (18.8% clay) and a silt loam (22.5% clay) with varying amount of NaCl to obtain an EC_1:5 of 1.0–8.0 dS?m^?1 and 2.5 g glucose C?kg^?1 soil. Soil respiration was reduced by more than 50% at EC_1:5?≥?5.0 dS?m^?1. In a further experiment, salinity up to an EC_1:5 of 5.0 dS?m^?1 was developed in the silt loam with NaCl or CaCl₂. No differences in respiration at a given EC were obtained between the two salts, indicating that Na and Ca did not differ in toxicity to microbial activity. The effect of different addition rates (0.25–2.0%) of mature wheat residue on the response of respiration to salinity was investigated by adding NaCl to the silt loam to obtain an EC_1:5 of 2.0 and 4.0 dS?m^?1. The clearest difference between salinity levels was with 2% residue rate. At a given salinity level, the modelled decomposition constant ‘k’ increased with increasing residue addition rate up to 1% and then remained constant. Particulate organic carbon left after decomposition from the added wheat residues was negatively correlated with cumulative respiration but positively correlated with EC. Inorganic N (NH ₄ ⁺ -N and NO ₃ ^? -N) and resin P significantly decreased with increasing salinity. Resin P was significantly decreased by addition of CaCl₂ and CaCO₃.     

施肥时机对土壤水氮运移转化规律的影响

为揭示不同施肥时机（全过程、前1/2和后1/2入渗水量施肥）下土壤水氮运移转化规律,以砂壤土和黏壤土质地的一维垂直肥液（尿素）入渗试验为基础,重点分析不同施肥时机下土壤水氮分布与再分布过程中的运移转化规律,并量化比较其对土壤中氮素含量的影响。结果表明,施肥时机对土壤累积入渗量和湿润体中水分分布影响微小,但对不同形态氮素运移转化影响显著;砂壤土和黏壤土入渗结束时刻,全过程和后1/2入渗水量施肥时,其尿素态氮、铵态氮（NH₄⁺—N）和硝态氮（NO₃^-—N）含量均随土层深度增大而减小;前1/2入渗水量施肥时,尿素态氮和NO₃^-—N含量在湿润体边缘累积,NH₄⁺—N呈先增大后减小趋势,且主要分布在5—25 cm土层;再分布阶段,全过程和后1/2入渗水量施肥时,砂壤土和黏壤土中尿素态氮分别在再分布3天和5天时基本水解完成,同时NH₄⁺—N含量达到峰值,NO₃^-—N含量再分布10天内未出现下降趋势;前1/2入渗水量施肥时,尿素态氮再分布10天时基本水解完成,NH₄⁺—N含量再分布5~10天达到峰值,NO₃^-—N含量则呈先增加后减小趋势;后1/2入渗水量和全过程施肥条件下,砂壤土和黏壤土再分布10天时0—40 cm土层中NH₄⁺—N和NO₃^-—N含量均大于前1/2入渗水量施肥,说明其氮素潜在利用效率高,故推荐畦（沟）灌合理施肥时机为后1/2入渗水量或全过程施肥。研究结果可为农田畦（沟）灌施肥系统的设计和管理提供理论基础和技术支撑。     

竹生物质炭和竹凋落物对毛竹林土壤营养元素和酶活性的影响

以广西壮族自治区桂林市华江乡内广泛分布的毛竹林土壤为研究对象,以竹生物质炭和竹凋落物作为外源碳,设置对照（CK）、低添加量生物质炭（1% BC）、高添加量生物质炭（2% BC）、低添加量凋落物（1% L）、高添加量凋落物（2% L）5个处理,进行为期两个月的室内培养试验,研究不同外源碳添加对毛竹林土壤营养元素和酶活性的影响。结果表明：与对照相比,竹生物质炭和竹凋落物添加均显著提高了土壤pH;竹生物质炭添加显著降低了而竹凋落物添加显著提高了土壤铵态氮（NH₄⁺-N）含量（P<0.05）,且高添加量（2% BC和2% L）的降低或提高作用更明显;不同外源碳添加均显著提高了土壤硝态氮（NO₃^–-N）含量,且凋落物添加的提高作用更明显;不同外源碳添加均显著提高了土壤有效磷（AP）含量,且高添加量的提高作用更明显;竹生物质炭添加对土壤可溶性有机碳（DOC）含量没有显著影响,但降低了土壤可溶性氮（DN）含量,而竹凋落物添加显著提高了土壤DOC和DN含量;不同外源碳添加对土壤微生物生物量碳（MBC）和氮含量（MBN）均没有显著影响,但降低了土壤蔗糖酶和脲酶活性。相关性分析表明,土壤pH、NH₄⁺-N、NO₃^–-N、DOC和DN是影响竹林土壤酶活性的关键性因子。     

Effect of Raw and NH4+-enriched Zeolite on Nitrogen Uptake by Wheat and Nitrogen Leaching in Soils with Different Textures

Leaching of nutrients in soil can change the surface and groundwater quality. The present study aimed at investigating the effects of raw and ammonium (NH₄⁺)-enriched zeolite on nitrogen leaching and wheat yields in sandy loam and clay loam soils. The treatments were one level of nitrogen; Z₀: (100 kg (N) ha^?1) as urea, two levels of raw zeolite; Z₁:(0.5 g kg^?1 + 100 kg ha^?1) and Z_2: (1 g kg^?1 + 100 kg ha^?1), and two levels of NH₄⁺-enriched zeolite; Z₃: (0.5 g kg^?1 + 80 kg ha^?1) and Z₄: (1 g kg^?1 + 60 kg ha^?1). Wheat grains were sown in pots and, after each irrigation event, the leachates were collected and their nitrate (NO₃^?) and NH₄⁺ contents were determined. The grain yield and the total N in plants were measured after four months of wheat growth. The results indicated that the amounts of NH₄⁺ and NO₃^? leached from the sandy loam soil were more than those from the clay loam soil in all irrigation events. The maximum and minimum concentrations of nitrogen in the drainage water for both soils were observed at control and NH₄⁺-zeolite treatments, respectively. Total N in the plants grown in the sandy loam was higher compared to plants grown in clay loam soil. Also, nitrogen uptake by plants in control and NH₄⁺-zeolite was higher than that of raw-zeolite treatments. The decrease in the amount of N leaching in the presence of NH₄⁺-zeolite caused more N availability for plants and increased the efficiency of nitrogen fertilizers and the plants yield.