Effect of pH on ammonium adsorption by natural Zeolite clinoptilolite

Abstract

Clinoptilolite, a zeolite mineral with a high cation exchange capacity and surface area, has ion‐exchange properties that can be utilized to adsorb NH₄ ⁺, protecting it from losses during composting of N‐rich animal manures. Ammonium adsorption by the natural zeolite clinoptilolite was studied to ascertain the effectiveness of the zeolite as an NH₄ ⁺ adsorbent at pH 4, 5, 6, and 7. The NH₄ ⁺ adsorption data were fitted to the one‐ and two‐surface Langmuir, Freundlich, and Temkin isotherms. All models described the NH₄ ⁺adsorption data successfully (r²≥0.939). The one‐surface Langmuir, Freundlich, and Temkin were converted to pH‐dependent forms. The amount of NH₄ ⁺ adsorbed increased as pH and initial NH₄ ⁺concentration increased. From the one‐surface Langmuir isotherm, the NH₄ ⁺adsorption capacity (X_m) of the zeolite increased linearly with pH (r²=0.994), and was estimated to be 9,660 mg N kg^‐1 at pH4, 11,220 mg N kg^‐1 at pH 5, 12,720 mg N kg^‐1 at pH 6, and 13,830 mg N kg^‐1 at pH 7. The adsorption of higher amounts of NH₄ ⁺with increasing pH and initial NH₄ ⁺concentration is an important characteristic of the zeolite that can be beneficial to minimizing N‐losses via NH₃volatilization during composting of N‐rich animal manures.     

Phosphate sorption by calcium‐bentonite as described by commonly used isotherms

Abstract

The one and two Langmuir, the Freundlich, and the Temkin isotherms were fitted to phsophorus (P) sorption data for P sorption by calcium (Ca)‐bentonite at different initial concentration and pH values of 3.8, 4.8, 6.0, 7.0, 8.0, and 9.0. Each was found to describe P sorption by Ca‐bentonite with comparable success. The effect of pH on P adsorption by Ca‐bentonite was studied and Langmuir, Temkin, and Freundlich isotherms were converted to the forms:

Langmuir: (Co‐X)X= 1/(0.0275–0.0025pH)(12.323–1.061pH) + (Co‐X)(12.323–1.016pH) Temkin: X = (2.45–0.211pH)In(AC) Freundlich: X = (1.324–0.146pH)C(^0.172+0044 _P ^H) where: X = (mmol P/kg) the amount of P sorbed per unit weight of soil, C = (μmol P/L) the P concentration in the equilibrium solution, and Co = ((μmol P/L) initial P concentration. It is noteworthy, that the maximum amount (Xm) of P that can be sorbed in a monolayer decreases by increasing of pH. Finally, the B constant of Temkin isotherms is indepented from pH changes.     

Evaluation of Adsorption Isotherm Models for Potassium Adsorption under Different Soil Types in Wolaita of Southern Ethiopia

Adsorption isotherm is essential for predicting its mechanisms, which are important for potassium (K) fertilizer application and to recommendation appropriate rates for acidic soils. Thus, the objective of this study was to evaluate K adsorption characteristic of the selected soils by comparing different adsorption models with soil properties of the soil in different districts (Sodo Zurie, Damot Gale, Damot Sore and Boloso Sore) in the Wolaita Zone of Southern Ethiopia. Four adsorption isotherms are: Langmuir, Freundlich, Temkin, and Van Huay were used to describe adsorption processes. Composite surface (0-20 cm) depth soil samples from four districts sites were collected. The results revealed that the K adsorption data coincide with both models with (r² = 0.99). However, Freundlich model was better in describing K adsorption than the other model. The adsorption maxima(ad_(max), distribution coefficient, buffer capacity (BC), and adsorption capacity(a_(capacity) values of soils ranged from -333 to334.5,0.54 to78.7,159.9 to 389.3, and 327 to 417mg Kkg^-1 respectively, these results showed that Sodo Zurie, Bolos Sore and Demote Sore were effective model parameters. Van Huay a_(capacity) 417mg Kkg^-1 while the bonding energy constant Langmuir is -0.075mg Kkg^-1 in Bolos Sore soil compared to other soils, which were found to be more valuable in discriminating between high K adsorption soils. Correlation between some soil properties with ad_(max) were positively a highly correlated with clay, pH, organic carbon (OC) and exchangeable potassium with r² = 0.92**, 0.93**, 0.95** and 0.96 ** respectively, but negatively correlated with bonding energy with r²= -0.79, -0.80,-0.77 and -0.72 respectively, while calcium carbonate (CaCO3) was very highly correlated with ad_(max) r²= 0.99***). The Freundlich constant, Temkin BC, and Van Hauy a_(capacity) were correlated with CaCO3 content soils with r²=0.12,-0.01,and 0.12,respectively, while slope (1/n) was significantly negatively correlated with soil cation exchange capacity (CEC), CaCO₃, clay contents and exchangeable K and Mg²⁺ with r²= 0.04, -0.67, -0.78, -0.69, and –0.69, respectively. These findings reveal the extent of K depletion in the soils of Wolaita providing a baseline for K rates required for crop production and validation of all models through real-time experiments in the field; this is recommended before the models are used on a large scale basis.     

Boron adsorption characteristics of some acidic alluvial soils in relation to soil properties

Abstract

We investigated boron (B) adsorption characteristics for 16 acid alluvial soils as a function of equilibrium B concentration (0–80 μg/mL) and the effect of soil properties on such adsorption. The adsorption data for the soils could be described by Freundlich, Temkin, and BET isotherm equations over the entire concentration ranges studied, and by Langmuir and Eadie‐Hofstee equations only over a limited range. In general, the B adsorption capacity and the energy of retention of the soils calculated from different equations are low, the average Langmuir adsorption maxima and bonding energy constant being 21.47 μg/g and 0.113 mL/μg, respectively, making B susceptible to leaching losses. Simple and multiple regression analysis show that the adsorption capacities are significantly influenced by organic carbon (C), cation exchange capacity (CEC), and different forms of aluminium (Al) content in soils. The energy related constants are also influenced by the forms of Al in soils. Existence of significant correlations between constants obtained from different equations confirmed the adsorption characteristics of the soils.     

Interactive effects from combining fertilizer and organic residue inputs on nitrogen transformations

Concerns about sustainability of agroecosystems management options in developed and developing countries warrant improved understanding of N cycling. The Integrated Soil Fertility Management paradigm recognizes the possible interactive benefits of combining organic residues with mineral fertilizer inputs on agroecosystem functioning. However, these beneficial effects may be controlled by residue quality. This study examines the controls of inputs on N cycling across a gradient of (1) input, (2) residue quality, and (3) texture. We hypothesized that combining organic residue and mineral fertilizers would enhance potential N availability relative to either input alone. Residue and fertilizer inputs labeled with ¹⁵N (40–60 atom% ¹⁵N) were incubated with 200 g soil for 545 d in a microcosm experiment. Input treatments consisted of a no-input control, organic residues (3.65 g C kg⁻¹ soil, equivalent to 4 Mg C ha⁻¹), mineral N fertilizer (100 mg N kg⁻¹ soil, equivalent to 120 kg N ha⁻¹), and a combination of both with either the residue or fertilizer ¹⁵N-labeled. Zea mays stover inputs were added to four differently textured soils (sand, sandy loam, clay loam, and clay). Additionally, inputs of three residue quality classes (class I: Tithonia diversifolia, class II: Calliandra calothyrsus, class III: Z. mays stover) were applied to the clay soil. Available N and N₂O emissions were measured as indicators for potential plant N uptake and N losses. Combining residue and fertilizer inputs resulted in a significant (P < 0.05) negative interactive effect on total extractable mineral N in all soils. This interactive effect decreased the mineral N pool, due to an immobilization of fertilizer-derived N and was observed up to 181 d, but generally became non-significant after 545 d. The initial reduction in mineral N might lead to less N₂O losses. However, a texture effect on N₂O fluxes was observed, with a significant interactive effect of combining residue and fertilizer inputs decreasing N₂O losses in the coarse textured soils, but increasing N₂O losses in the fine textured soils. The interactive effect on mineral N of combining fertilizer with residue changed from negative to positive with increasing residue quality. Our results indicate that combining fertilizer with medium quality residue has the potential to change N transformations through a negative interactive effect on mineral N. We conclude that capitalizing on interactions between fertilizer and organic residues allows for the development of sustainable nutrient management practices.     

Copper adsorption behavior of three Malaysian rice soils

Abstract

Copper (Cu) deficiency exists in different rice growing areas of Malaysia. A study on Cu adsorption was carried out in three Malaysian rice soils (Idris, Tebengau, and Kangar series) using six levels of Cu (0, 100, 200, 300, 400, and 500 ug g^‐1). The data on Cu adsorption were fitted into Langmuir, Freundlich, and Temkin equations. Adsorption data were also correlated with pH, cation exchange capacity, and organic matter content of the soils. The effect of Cu addition on redox potential (Eh) of the soils was also measured. The Eh values were correlated with equilibrium solution Cu concentrations. Copper adsorption increased gradually with increasing level of added Cu in all the soils. The rate of increase was the highest in Kangar series followed by Tebengau and Idris, respectively. Correlation between Cu adsorption and pH was significant (r=0.772) whereas correlation of adsorption with either organic matter content or cation exchange capacity was nonsignificant. Copper adsorption in two soils (Idris and Tebengau) fitted Langmuir, Freundlich, and Temkin equations whereas Cu adsorption in the Kangar soil fitted Freundlich and Temkin equations. Redox potential (Eh) of the soils increased gradually with increasing level of added Cu. The rate of increase was the highest in Idris followed by Kangar and Tebengau soils, respectively. The relationship between equilibrium solution Cu concentration and redox potential was significant. The results of this study indicated that copper adsorption is mainly dependent on soil pH. In soils with higher adsorption capacity, more Cu fertilizer may be needed to get immediate crop response.     

Do combined applications of crop residues and inorganic fertilizer lower emission of N2O from soil?

Emissions of N₂O were measured following addition of ¹⁵N‐labelled residues of tropical plant species [Vigna unguiculata (cowpea), Mucuna pruriens and Leucaena leucocephala] to a Ferric Luvisol from Ghana at a rate of 100 mg N/kg soil under controlled environment conditions. Residues were also applied in different ratio combinations with inorganic N fertilizer, at a total rate of 100 mg N/kg soil. N₂O emissions were increased after addition of residues, and further increased with combined (ratio) applications of residues and inorganic N fertilizer. However, ¹⁵N‐N₂O production was low and short‐lived in all treatments, suggesting that most of the measured N₂O‐N was derived from the applied fertilizer or native soil mineral N pools. There was no consistent trend in magnitude of emissions with increasing proportion of inorganic fertilizer in the application. The positive interactive effect between residue‐ and fertilizer‐N sources was most pronounced in the 25:75 Leucaena:fertilizer and cowpea:fertilizer treatments where 1082 and 1130 mg N₂O‐N/g residue were emitted over 30 days. N₂O (log_e) emission from all residue amended treatments was positively correlated with the residue C:N ratio, and negatively correlated with residue polyphenol content, polyphenol:N ratio and (lignin + polyphenol):N ratio, indicating the role of residue chemical composition in regulating emissions even when combined with inorganic fertilizer. The positive interactive effect in our treatments suggests that it is unlikely that combined applications of residues and inorganic fertilizer can lower N₂O emissions unless the residue is of very low quality promoting strong immobilisation of soil mineral N.     

广东主要母质发育水稻土对硅的吸附特性

Silicate adsorption in eight paddy soils developed from four different parent materials in Guangdong Province, China was examined to obtain fundamental knowledge of silicate adsorption to improve the efficacy of silicate fertilizer use in these areas. A correlation analysis showed that silicate adsorption did not obey the Langmuir equation （r = -0.664- 0.301） but did obey the Freundlich and Temkin equations （P〈0.01, r = 0.885-0.990）. When the equilibrium silicate concentration （Ci） was less than 45 mg SiO2 kg^-1, the adsorption capacity was in the following decreasing order of paddy soils： basalt-derived 〉 Pearl River Delta sediment-derived 〉 granite-derived 〉 sand-shale-derived. Stepwise regression and path analysis showed that for the investigated paddy soils amorphous MnO and Al2O3 were the two most important materials that affected silicate adsorption. Moreover, as Ci increased, amorphous Al2O3 tended to play a more important role in silicate adsorption, while the effects of amorphous MnO on silicate adsorption tended to decrease.     

Effect of soil moisture and transpiration on mineral content in leaves and berries of cabernet sauvignon grapevine

Leaf and berry transpiration ratio in grapevine (Vitis vinifera L.) was found to be affected by soil moisture. With the condition of diminished soil moisture, berry transpiration is higher prior to vèraison compared to conditions when the water content in the substrate is higher and berry transpiration decreases with an increase of leaf transpiration. Studies were conducted in 1993 and 1994 to investigate the link between soil moisture, traspiration, and accumulation of certain mineral elements in leaves and berries on plants of the Cabernet sauvignon cultivar grafted on Kober 5 BB rootstock. Leaf and berry transpiration and mineral accumulation were evaluated by gaseous exchange measurements, soil sampling and moisture analysis, and leaf and berry sampling and analysis of mineral content. Observations were repeated at about 15‐day intervals between full bloom and berry ripening. Transpiration per unit of surface area (mmol H₂O m^‐2 s^‐1) was always higher in leaves than in berries. Leaf transpiration varied from 5.62 mmol H₂O m^‐2 s^‐1 to 2.92 mmol H₂O m^‐2 s^‐1 in 1993 in the period between the 8th and 86th day after full bloom (DAFB), and from 6.49 mmol H₂O m^‐2 s^‐1 to 4.37 mmol H₂O m^‐2 s^‐1 in 1994 between the 12th and 94th DAFB. Berry transpiration ranged between 3.86 mmol H₂O m^‐2 s^‐1 and 1.04 mmol H₂O m^‐2 s^‐1 in 1993 and between 4.34 mmol H₂O m^‐2 s^‐1 and 0.5 mmol H₂O m^‐2 s^‐1 in 1994. Leaf transpiration was not correlated with the mineral element content in the leaves, whereas berry transpiration was directly correlated with the nitrogen (N), calcium (Ca), potassium (K), and phosphorus (P) content in berries. Leaf mineral composition was affected only for iron (Fe) content by the variation on soil moisture, whereas the berry N, P, K, and Ca contents were positively correlated with soil water content. The leaf and berry Ca content appeared to be greater with high soil moisture, i.e., in conditions which favor intense metabolism of the whole plant.     

Anaerobic Digestate Administration: Effect on Soil Physical and Mechanical Behavior

A field experiment was conducted on an alluvial soil with winter lettuce [Lactuca sativa (L.) cv. Bacio] plants to study, in the second year of testing and in both field and laboratory conditions, the effects of fertilizers—compost by farm residues [(FC, 2.0% nitrogen (N)], mineral (MIN, 21% N), organomineral (OM, 10% N), mycorrhizas inoculum (MYC), wine-production residue [distiller's residue (DR, 3.6% N), anaerobic digestate (AD), and mycorrhizas (ADM)—on soil physical and mechanical parameters. Application of DR plus mycorrhizas improved the available phosphorus (P) and copper (Cu) contents of the surface (0–0.20 m) soil. The soil surface macroporosity increased significantly (>20%) in treatments FC, MYC, and OM, compared to the control. Results of the oedemeter test showed that with a load of 10 daN the compression susceptibility was greater in the compost treatment compared to other fertilizers, whereas with a load of 200 daN this parameter was lower in FC, AD, MYC, and ADM treatments. The least penetration resistance in the 0- to 20-cm layer of AD and MYC treatments showed lesser values and only in treatment AD in the 20- to 40-cm layer. Hydraulic conductivity values were enhanced in AD, MYC, and ADM plots.     

Long-term nitrogen balance for pearl millet (Pennisetum glaucum L.) in an acid sandy soil of Niger

On acid sandy soils of Niger (West Africa) fertilizer N recovery by pearl millet (Pennisetum glaucum L.) is often more than 100 per cent in years with normal or above average rainfall. Biological nitrogen fixation (BNF) by N₂-fixing bacteria may contribute to the N supply in pearl millet cropping systems. For a long-term field experiment comprising treatments with and without mineral fertilizer (F) and with and without crop residue application (CR) a N balance sheet was calculated over a period of six years (1983-1988). After six years of successive millet cropping total N uptake (36-77 kg N ha^?1 yr^?1) was distinctly higher than the amount of fertilizer N applied (30 kg N ha^?1 yr^?1). The atmospheric input of NH₄-N and NO₃-N in the rainwater was about 2 kg N ha_?1 yr^?1, 70 % in the form of NH₄-N. Gaseous NH₃ losses from urea (broadcast, incorporated) were estimated from other experiments to amount to 36 % of the fertilizer N applied. Nitrogen losses by leaching (15 to > 25 kg N ha^?1 yr^?1) were dependent on the treatment and on the quantity and distribution of single rainfall events (>50 mm). Decline in total soil N content (0-60 cm) ranged from 15 to 48 kg N ha^?1 yr^?1. The long-term N balance (1983-1988) indicated an annual net gain between 6 (+CR-F) and 13 (+CR+F) kg N ha^?1 yr^?1. For the control (-CR-F) the long-term N balance was negative (10 kg N ha^?1 yr^?1). In the treatment with crop residues only, the N balance was mainly determined by leaching losses, whereas in treatments with mineral fertilizer application the N balance depended primarily on N removal by the millet crop. The annual net gain in the N balance increased from 7 kg ha^?1 with mineral fertilizer to 13 kg ha^?1 in the combination mineral fertilizer plus crop residues. In both the rhizosphere and the bulk soil (0-15 cm), between 9 and 45% of the total bacterial population were N₂-fixing (diazotrophic) bacteria. The increased N gain upon crop residue application was positively correlated with an increase in the number of diazotrophic and total bacteria. The data on bacterial numbers suggest that the gain of N in the longterm N balance is most likely due to an N input by biological nitrogen fixation. In addition, evidence exists from related studies that the proliferation of diazotrophs and total bacteria in the rhizosphere due to crop residue application stimulated root growth of pearl millet, and thus improved the phosphorus (P) acquisition in the P deficient soil.     

柠檬酸存在下施硅对土壤磷吸附和解吸特性影响

以棕壤为研究对象,采用室内培养的方法,通过加硅酸钙处理、硅酸钙+1 mmol/L柠檬酸处理和硅酸钙+2 mmol/L柠檬酸处理,研究了柠檬酸存在下施硅对棕壤中磷素吸附和解吸特性的影响,并用Langmuir方程、Freundlieh方程与Temkin方程对其进行拟合分析,其中磷吸附解吸试验采用恒温批处理平衡法.结果表明,Langmuir与Temkin模型对处理后棕壤磷的吸附拟合效果最好.硅酸钙+1 mmol/L柠檬酸处理的棕壤对磷的吸附量最大,为500mg/kg;硅酸钙+2 mmol/L柠檬酸处理的棕壤对磷的解吸量及解吸率最大,最大解吸率可达45.2％.因此,硅酸钙+1 mmol/L柠檬酸处理的棕壤对磷肥的储存能力最强,硅酸钙+2 mmol/L柠檬酸处理的棕壤对磷活化能力最强,即供磷能力最强.     

Nitrogen balance in a soil‐wheat system under plow‐ and no‐tillage in the argentine humid pampa

Abstract

Changing conventional tillage to conservation tillage systems affects nitrogen (N) cycling in agroecosystems. Our objective was to evaluate the role of soil organic pools, specially plant residues, as sources‐sinks of nitrogen in an humid and warm temperate environment cropped to wheat, under plow‐ and no‐tillage. The experimental site was in the Argentine Pampa on a Typic Hapludoll. A balance‐sheet method was used: Nupt+Nres=Nsow+Nmin, where Nupt=N uptake by the crop at harvest; Nsow=soil mineral N as NH₄ and NO₃ at 0–90 cm depth, one month before sowing, plus N added as fertilizer; Nres=residual soil mineral N as NH₄ and NO₃ at 0–90 cm depth, at harvest; Nmin=N mineralized from humus and plant residues during wheat growing period. Nupt did not differ between tillage systems. Nitrogen supply by the mineral N pool, estimated by the difference Nsow‐Nres, was ca. 150 kg N ha^‐1 in both tillage systems. Plant residues decomposed and released N under both treatments. This organic N pool decreased 77% along the crop cycle. Nmin, calculated using the balance equation was 83 kg N ha^‐1, and did not differ between tillage managements, representing 35% of Nupt. This results highlight the importance of the organic pools as sources of N for wheat in the Humid Pampa. They also brink our attention on the importance for evaluate residue decomposition and humus mineralization in warm‐temperate regions when fertilizer requirements are determined, in order to minimize environmental hazard and economic losses by overfertilization.     

Potential methods for estimating nitrogen fertilizer value of organic residues

New organic fertilizers based on waste products are continually being introduced in agriculture. Their nitrogen (N) fertilizer value of their total N and mineral N content varies widely, creating a demand for standardized laboratory methods. This study evaluated some potential methods for estimating the N fertilizer value of different kinds of organic fertilizers. The methods were evaluated against the N fertilizer value obtained from a ryegrass pot experiment. Fifteen fertilizers were tested, including different kinds of manure, powders from meat, bone, blood and feathers, rapeseed cake, lucerne pellets, sewage sludge, biogas residue, vinasse and mussel compost. Mineral fertilizer equivalents (MFE) were calculated as the fraction of total N (MFE) or organic N (MFE_org) out of total N that has the same availability to plants as inorganic N. Mineral N content (% of total N added with organic residue) after 4 weeks of incubation of soil was correlated to MFE (r² = 0.78), but was on average 17% lower. Warm water‐extractable N, amino acid N and crude fibre analysis all proved to be unsatisfactory as methods for estimating MFE or MFE_org. However, the carbon/nitrogen ratio accurately reflected short‐term plant‐available N through a negative linear relationship (r² = 0.83) and would thus be a very useful method for estimating MFE, with MFE decreasing by 5% per unit increase in C/N ratio. The results also indicated that the analysis of near infrared reflectance (NIR) spectra can be an even quicker and cheaper method to estimate MFE of organic residues, but this issue requires further research.     

Saline water and municipal solid waste compost application on tomato crop: Effects on plant and soil

A field experiment was conducted in Southern Italy to evaluate the effects of different water quality and fertilizers on yield performance of tomato crop. In mineral nitrogen (N) fertilizer and irrigation with fresh water (Electrical Conductivity, EC, = 0.9 dS m^?1) (FWF); mineral N fertilizer and irrigation with saline water (EC = 6.0 dS m^?1) (SWF); municipal solid waste (MSW) compost and irrigation with fresh water (EC = 0.9 dS m^?1) (FWC); MSW compost and irrigation with saline water (EC = 6.0 dS m^?1) (SWC). At harvest, weight and number of fruits and refractometric index (°Brix) were measured, total and marketable yield and dry matter of fruit were calculated. The results indicated that MSW compost, applied as amendment, could substitute the mineral fertilizer. In fact, in the treatments based on compost application, the tomato average marketable yield increased by 9% compared with treatments with mineral fertilizer. The marketable yield in the SWF and SWC treatments (with an average soil EC in two years to about 3.5 dS m^?1) decreased respectively of 20 and 10%, in respect to fresh water treatments. At the end of the experiment, application of compost significantly decreased the sodium absorption rate (SAR) of SWC treatment in respect of SWF (?29.9%). Significant differences were observed among the four treatments both on soil solution cations either exchangeable cations. In particular compost application increased the calcium (Ca) and potassium (K) contents in saturated soil paste respect to the SWF ones (31.4% and 59.5%, respectively). At the same time saturated soil paste sodium (Na) in SWC treatment recorded a decrease of 17.4% compared to SWF.     

Nitrous oxide flux from komatsuna (Brassica rapa) vegetated soil: a comparison between biogas digested liquid and chemical fertilizer

Biogas production generates digested slurry as a by-product. It can be used as fertilizer especially after its conversion into digested liquid. A microcosm-based study was conducted in order to compare the effects of single application of digested liquid or chemical fertilizer on N₂O flux and crop yield of komatsuna vegetable. Analysis revealed that digested liquid-treated soils released almost equal cumulative N₂O (0.43 g?N m^?2) compared to chemical fertilizer (0.39 g?N m^?2). The uncropped soils treated with the digested liquid and chemical fertilizer released more N₂O compared to corresponding cropped soils. The N₂O emission factor and soil mineral N contents were similar for the digested liquid and chemical fertilizer-treated soils. Plant biomass in the first crop after digested liquid application was significantly higher (5.59 g plant^?1) than that after applied chemical fertilizer (4.78 g plant^?1); but there was no significant difference for the second crop. Nitrogen agronomic efficiency was improved by the digested liquid compared to chemical fertilizer. This study indicates that cumulative N₂O flux was similar after application of the digested liquid and chemical fertilizer, while the overall yield from both croppings was increased in the digested liquid-treated soil compared to chemical fertilizer-treated soil.     

High N fertilizer application to irrigated wheat in Northern Mexico for conventionally tilled and permanent raised beds: Effects on N balance and short term N dynamics

Nitrogen (N) surpluses from fertilizer application can cause major environmental harm including pollution of surface water, groundwater, and air. To assess such negative externalities, N balances are a complex but useful tool to predict surpluses and to measure effects of nutrient optimization strategies in agriculture. The Yaqui Valley in north‐western Mexico is representative for thousands of square kilometres of intensive, irrigated wheat production under arid conditions worldwide and has been targeted for conservation agriculture in recent years. For these cropping systems, detailed N balances are scarce and often incomplete. To help fill this knowledge gap, data from a long‐term experiment were collected in 2013/14 on a Vertisol to examine the impact of three tillage‐straw management practices (CTB: conventionally tilled beds; PB‐straw: permanent raised beds with residue retention; PB‐burn: permanent raised beds with residue burning) on N dynamics. Tillage had significant effects on soil NO₃‐N, NH₄‐N, and total N contents across the cropping period. Soil total N content was at all sampling depths lowest in CTB. Soil NO₃‐N in the 0–90 cm profile was highest in PB‐burn over the cropping period and ranged from 77 kg ha^?1 in the bed before pre‐planting fertilizer application up to 269 kg ha^?1 in the furrow after the second fertilizer application. Annual simple N balances were +59 kg N ha^?1 in CTB, +39 kg N ha^–1 in PB‐straw, and +46 kg N ha^?1 in PB‐burn. Residual mineral soil N was significantly affected by tillage‐straw management and lowest for PB‐straw (+205 kg N ha^?1) and highest for CTB, and for PB‐burn (+283 kg N ha^?1 each) in the 0–90 cm soil profile. Soil NO₃‐N moved out of the effective wheat root zone, as indicated by the high residual NO₃‐N content at 30–90 cm depth, which is an important pathway of N leaching. Quantifiable N losses through leaching and volatilization averaged 100 kg N ha^?1. Our findings suggest that there is potential for substantial reductions in N inputs in all tillage‐straw systems to decrease N losses and to reduce mineral residual soil N, but care should be taken to avoid reducing grain protein content, which in PB straw was already below the quality standard. A knowledge transfer of the European “N_min” concept is advisable in this region to regulate N fertilizer over‐application.     

Effect of fertilization on respiration from different sources in a sandy soil of an agricultural long-term experiment

Annual changes in stocks of soil organic carbon may be detected by measurement of heterotrophic respiration, but field studies of heterotrophic respiration in long-term fertilization experiments on sandy soils are scarce. Our objectives were to: (1)investigate the influence of fertilizer type on mineralization of soil organic carbon and crop residue, and (2) show how fertilization treatments affect the annual C balance (net ecosystem carbon balance, NECB; negative values indicate a CO₂-source) in the sandy soil of the Darmstadt experiment. Treatments were long-term mineral fertilization with cereal straw incorporation (MSI) and application of rotted farmyard manure (FYM), both treatments receiving 14 g N m^?2 year^?1. This study used δ¹³C natural abundance after introduction of a C₄ crop to distinguish between different sources of respiration. Mineralization derived from C₃ sources was similar for MSI and FYM treatments (～270 g C m^?2 year^?1). The rate of residue mineralization in MSI treatments was higher, resulting in a mineralization of 49 and 37% of initial residue C in the soil of MSI and FYM treatments, respectively. The NECB (g C m^?2 year^?1) indicated the MSI treatment (approximately ?190) as a stronger source compared with the FYM treatment (～?30).     

Mechanisms of soil N dynamics following long-term application of organic fertilizers to subtropical rain-fed purple soil in China

In this study, a ¹⁵N tracing incubation experiment and an in situ monitoring study were combined to investigate the effects of different N fertilizer regimes on the mechanisms of soil N dynamics from a long-term repeated N application experiment. The field study was initiated in 2003 under a wheat-maize rotation system in the subtropical rain-fed purple soil region of China. The experiment included six fertilization treatments applied on an equivalent N basis (280 kg N ha⁻¹), except for the residue only treatment which received 112 kg N ha⁻¹: (1) UC, unfertilized control; (2) NPK, mineral fertilizer NPK; (3) OM, pig manure; (4) OM-NPK, pig manure (40% of applied N) with mineral NPK (60% of applied N); (5) RSD, crop straw; (6) RSD-NPK, crop straw (40% of applied N) with mineral NPK (60% of applied N). The results showed that long-term repeated applications of mineral or organic N fertilizer significantly stimulated soil gross N mineralization rates, which was associated with enhanced soil C and N contents following the application of N fertilizer. The crop N offtake and yield were positively correlated with gross mineralization. Gross autotrophic nitrification rates were enhanced by approximately 2.5-fold in the NPK, OM, OM-NPK, and RSD-NPK treatments, and to a lesser extent by RSD application, compared to the UC. A significant positive relationship between gross nitrification rates and cumulative N loss via interflow and runoff indicated that the mechanisms responsible for increasing N loss following long-term applications of N fertilizer were governed by the nitrification dynamics. Organic fertilizers stimulated gross ammonium (NH₄⁺) immobilization rates and caused a strong competition with nitrifiers for NH₄⁺, thus preventing a build-up of nitrate (NO₃⁻). Overall, in this study, we found that partial or complete substitution of NPK fertilizers with organic fertilizers can reduce N losses and maintain high crop production, except for the treatment involving application of RSD alone. Therefore, based on the N transformation dynamics observed in this study, organic fertilizers in combination with mineral fertilizer applications (i.e. OM, OM-NPK, and RSD-NPK treatments) are recommended for crop production in the subtropical rain-fed purple soils in China.