Zinc Application Effects on Yield and Seed Oil Content of Sunflower Grown on a Saline Calcareous Soil

ABSTRACT

Two field experiments (2000–2001 and 2001–2002) were conducted at two nearby fields in the Qanavat region of Qom province, central Iran, to investigate the effects of zinc (Zn) fertilization on production of sunflower. The experiment was conducted in a randomized complete block design with six treatments in three replicates. Treatments were: Zn₀ (non-Zn fertilized), Zn₁₀, Zn₂₀, Zn₃₀, and Zn₆₀ (soil application of 10, 20, 30, and 60 kg Zn ha^?1, respectively), and Zn_Spray (foliar spraying of 0.5 kg Zn ha^?1 using ZnSO₄). Seeds of sunflower (Helianthus annuus cv. ‘Record’) were planted on June 20, 2000 and June 15, 2001. At harvest, shoot and seed yields as well as concentration of Zn, iron (Fe), manganese (Mn), sodium (Na), and chloride (Cl) in leaves of sunflower were determined. Addition of 20 kg Zn ha^?1 significantly increased seed production and shoot dry-matter yield of sunflower, while other Zn treatments had no significant effect on shoot dry-matter yield, or decreased it. The thousand-seed weight was the yield component most affected by Zn fertilization, while plant height and head diameter did not change. The maximum content of seed oil was achieved under the Zn₁₀ treatment, then decreased at higher rates of soil-applied Zn such that oil content of seed under the Zn₃₀ and Zn₆₀, treatments was significantly lower than that of the control. Seed oil content was unaffected by foliar spraying of Zn. The concentration of Zn in sunflower leaves was increased with an increase in soil-added Zn of from 0 to 60 kg Zn ha^?1. The highest leaf concentrations of Zn (162 and 175 mg kg^?1 day matter (DM) in the first and second year, respectively) were achieved by foliar application of ZnSO₄. Leaf concentration of Fe was significantly increased in the Zn₂₀ treatment compared with the control but decreased at the higher rates of soil-added ZnSO₄. Soil addition of different levels of ZnSO₄ decreased concentration of Na and Cl in leaves. The lowest concentration of Na and Cl in leaves was observed under Zn₂₀. The results of this study suggest that soil application of a suitable amount of Zn has a positive effect on both quantitative and qualitative yield of sunflower in saline, calcareous soils.     

Soil amendment with city sewage sludge increases soil extractable cadmium,nickel and zinc more than tannery,pharmaceutical and paper mill wastes

Abstract

The distribution of DTPA-extractable Cd, Ni and Zn in four profile samples collected from areas contaminated with wastes from tannery, city sewage, pharmaceutical and paper mills located at different places in Bangladesh was investigated. Soil samples were analysed for the total and their DTPA-extractable metal contents. The total concentration of metals in the soil horizons ranged from 0.07 to 0.62 mg kg^?1 for Cd, 31 to 54 mg kg^?1 for Ni and 59 to 838 mg kg^?1 for Zn, respectively. These metal concentrations were highest in the surface and lowest in the subsurface horizons. This trend was also observed for the DTPA-extractable amounts of these metals. The relative extractability, expressed as the ratio of DTPA to total contents (aqua regia-extractable) was 33 to 46% for Cd, 2 to 10% for Ni and 3 to 28% for Zn, respectively, in the A1 horizon, while in the B and C horizons the ratios decreased gradually as did total concentration, indicating that metal contamination was primarily limited to the surface horizon. For all three metals, the above mentioned ratio was highest in the city sewage soil and the lowest in the paper mill soil. In general, the extent of contamination among the profiles investigated was in the following order: city sewage>tannery>pharmaceutical>paper mill soil. Higher ratios of DTPA-extractable Cd, Ni and Zn in the city sewage soil than the other soils may create a risk for the contamination of agricultural products and ground water.     

Micronutrient status of calcareous paddy soils and rice products: implication for human health

Modern agricultural systems have to provide enough micronutrient output to meet all the nutritional needs of people. Accordingly, knowledge on micronutrient status in soil and crop edible tissues is necessary. This study was carried out to investigate zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu) concentration of calcareous paddy soil and the relative rice grain. Rice crops (straw, hull, and grain) and associated surface soils (0–25 cm) were collected from 136 fields and analyzed for total and diethylene triamine pentaacetic acid (DTPA) available Zn, Fe, Mn, and Cu. The DTPA-Zn concentration in more than 50% of paddy soils was less than its critical deficiency concentration (2 mg kg⁻¹), while the concentrations of DTPA Fe, Mn, and Cu were sufficient. The grain Zn concentration of more than 54% of the rice samples was less than 20 mg kg⁻¹. About 55% and 49% of the rice samples were deficient in Mn and Cu, respectively, while the Fe concentration in rice grains was sufficient. A significant negative correlation was found between the CaCO₃ content and soil DTPA-extractable Zn, Fe, Mn, and Cu. There were significant relationships between the total soil phosphorus and DTPA-extractable micronutrient concentrations. By considering the average daily rice consumption of 110 g per capita, the Zn, Fe, Mn, and Cu intake from rice consumption was estimated to be 2.4, 7.7, 1.6, and 0.7 mg for adults, respectively.     

The potential of using 15N natural abundance in changing ammonium-N and nitrate-N pools for studying in situ soil N transformations

Purpose

This study examined the usefulness of ¹⁵N natural abundance (δ¹⁵N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning.

Materials and methods

In situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L^?1 NO₃^?-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ¹⁵N of NH₄⁺-N and NO₃^?-N in the top 5 cm soil before and after the incubation, and δ¹⁵N of NO₃^?-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes.

Results and discussion

The significant decrease in δ¹⁵N of NH₄⁺-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ¹⁵N of NH₄⁺-N and significant increase in δ¹⁵N of NO₃^?-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes.

Conclusions

The δ¹⁵N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ¹⁵N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes.

     

Tracing the source and fate of dissolved organic matter in soil after incorporation of a C labelled residue: A batch incubation study

While dissolved organic matter (DOM) in soil solution is a small but reactive fraction of soil organic matter, its source and dynamics are unclear. A laboratory incubation experiment was set up with an agricultural topsoil amended with ¹³C labelled maize straw. The dissolved organic carbon (DOC) concentration in soil solution increased sharply from 25 to 186 mg C L⁻¹ 4 h after maize amendment, but rapidly decreased to 42 mg C L⁻¹ and reached control values at and beyond 2 months. About 65% of DOM was straw derived after 4 h, decreasing to 29% after one day and only 1.3% after 240 days. A significant priming effect of the straw on the release of autochthonous DOM was found. The DOM fractionation with DAX-8 resin revealed that 98% of the straw derived DOM was hydrophilic in the initial pulse while this hydrophilic fraction was 20-30% in control samples. This was in line with the specific UV absorbance of the DOM which was significantly lower in the samples amended with maize residues than in the control samples. The δ¹³C of the respired CO₂ matched that of DOC in the first day after amendment but exceeded it in following days. The straw derived C fractions in respired CO₂ and in microbial biomass were similar between 57 and 240 days after amendment but were 3-10 fold above those in the DOM. This suggests that the solubilisation of C from the straw is in steady state with the DOM degradation or that part of the straw is directly mineralised without going into solution. This study shows that residue application releases a pulse of hydrophilic DOM that temporarily (<3 days) dominates the soil DOM pool and the degradable C. However, beyond that pulse the majority of DOM is derived from soil organic matter and its isotope signature differs from microbial biomass and respired C, casting doubt that the DOM pool in the soil solution is the major bioaccessible C pool in soil.     

Impact of soil organic matter on calcium carbonate equilibrium and forms of Pb in water extracts from Kastanozem complex

Purpose

Accounting for ionic strength and ion association, the degree of calculated supersaturation with CaCO₃ of gleyic solonetz and molic solonetz soil solution is high. The purpose of the research was to reveal the effect of the water-dissolved organic matter (DOM) on the calcium carbonate equilibrium (CCE) in soil solution, to create a thermodynamic model of carbonate association and complexation with DOM and heavy metals (HMs), and to correct the principal of soil management.

Materials and methods

Object of research—Kastanozem complex of the dry steppe, Rostov Oblast, Russia. The water extraction of soluble salts was made at the water-to soil-ratio 5:1 and analyzed using standard methods. DOM content was determined by Strosser (J Agrobiol 27:49–60, 2010). The soil solution macro-ion equilibrium composition was calculated using ION-2 program (Endovitsky et al. 2009). DOM role in soil solution supersaturation with СаСО₃ was assessed, comparing C content in real solution and in identical artificial solution prepared without organic matter. Taking into account the ion association, the molar fractions of free and bound HM ion were calculated using microelement association coefficient, k_as(ME). The soil liquid-phase saturation with CaCO₃ was characterized by the ratio of the real solubility product (S) to the thermodynamic solubility product (S⁰): К?=?S/S⁰.

Results and discussion

The soil solution supersaturation with CaCO₃ was characterized by the product of analytical concentrations (S), equilibrium concentrations [accounting ion activity (S^I), ion association (S^II), ion association and complexation (S^III)], and the thermodynamic solubility product (S⁰). To evaluate the role of DOM in soil solution supersaturation with CaCO₃, the initial pure Ca (HCO₃)₂ solution series was prepared. The humic and fulvic acids from the illuvial horizon of gleyic solonetz with concentrations of 20 mg C L^?1 and 120 mg C L^?1 decreased the CaCO₃ precipitation compared with initial soil solution. The release of CaCO₃ from soil water extracts containing water-soluble organic matter was 1.2–1.9 times less compared with identical artificial solution not containing organic matter. The HM binding by carbonates is proportional to the DOM content.

Conclusions

In molic solonetz and gleyic solonetz, the neutralization of the soda should be assessed by the soil solution supersaturation with CaCO₃. To calculate the degree of HM passivation in soil solution containing DOM, the coefficient of soil solution oversaturation with CaCO₃ is proposed. For reducing soil organic matter and DOM mobility and loss from soil, as well as for Pb passivation, intra-soil mechanical processing, intra-soil waste management, and intra-soil watering are proposed.

     

Biochar reduced soil extractable Cd but increased its accumulation in rice (Oryza sativa L.) cultivated on contaminated soils

Purpose

This study focused on the effects and mechanisms of biochar amendment to Cd-contaminated soil on the uptake and translocation of Cd by rice under flooding conditions.

Materials and methods

Pot and batch experiments were conducted using Cd-contaminated soil collected from a field near an ore mining area and a cultivar of Oryza sativa ssp. indica. Biochar derived from rice straw under anaerobic conditions at 500 °C for 2 h was mixed with the soil at the rate of 0, 2.5, and 5%.

Results and discussion

The application of 5% biochar reduced CaCl₂-extractable soil Cd by 34% but increased Cd concentration in brown rice by 451%. Biochar amendment decreased water-soluble Fe²⁺ in soils and formation of Fe plaques on roots and weakened the Fe²⁺-Cd²⁺ competition at adsorption sites on the root surface. Biochar increased water-soluble Cd in the soil and consequently Cd uptake by rice roots by releasing water-soluble Cl^?. Biochar application also reduced the proportion of cell wall-bound Cd in the root, which caused easier Cd translocation from the cortex to the stele in the root and up to the shoot.

Conclusions

Rice straw biochar (with high concentration of water-soluble Cl^?) reduced CaCl₂-extractable soil Cd but increased Cd concentration in rice under flooding condition.

     

Two-year fluctuation of Cd bioavailability in a remediated rice field under different water managements

Purpose

Based on two consecutive years of field-scale trials, under different water managements, we illustrated the persistence of remediation effect of palygorskite on a Cd-polluted rice field.

Materials and methods

The Cd uptake by a plant, pH and Cd chemical extractability, available P/K, and extractable Zn/Cu in paddy soils were used to evaluate the influence of palygorskite on Cd immobilization and soil fertility index.

Results and discussion

In contrast to the 1st year, at 0–1.5% palygorskite applied dose in soils, 0.025 M HCl–extractable Cd in continuous flooding reduced by 12.1–19.0%, and that in wetting irrigation increased by 10.9–18.9% in the 2nd year (p?<?0.05). The toxicity characteristic leaching procedure Cd reduction of 3.0–11.4% and increase of 8.9–12.0% were obtained under above-mentioned water managements (p?<?0.05). Compared with the 1st year, at different clay additional concentrations, grain Cd in continuous flooding reduced by 7.0–11.3%, and that in wetting irrigation increased by 6.5–10.8% in the 2nd year (p?<?0.05). Although trace elements in clay treated soils declined, they had no influence on the grain yield due to a minimum value higher than the critical value of 1.5 mg kg^?1 for Zn and 2.0 mg kg^?1 for Cu. The available P in continuous flooding took on a maximum increase of 8.2% in the 2nd year (p?<?0.05).

Conclusions

Two consecutive years of field-scale in situ demonstration tests revealed that continuous flooding was a preferable water management regime for Cd immobilization using palygorskite in the rice field. There were no remarkable differences in extractable Zn/Cu between 2 years.

     

Long-Term Influence of Nutrient Management on Carbon and Nutrients In Typic-Ustochrept Soils

ABSTRACT

Continuous incorporation of green manure (GM) and rice straw residue (RSR) over a long period of time generally improved soil physico-chemical properties. To generate this information, laboratory studies were conducted during 2014 on the soil samples collected from an on-going long-term experiment on rice–wheat sequence in progress since 2001. The results of the study reported improvement in bulk density, water holding capacity, and total porosity with green manuring. The maximum organic carbon build up was recorded in manure @ 15 t ha^?1 which was applied through GM. The application of fertilizers, GM and RSR incorporation improved the buildup of the available and total N, P, and K contents of surface soil. The data further indicated that the DTPA-extractable and total Zn, Cu, Fe, and Mn in soil increased significantly in all the fertilizer and manurial treatments over recommended practice. The integrated use of GM and RSR in combination with chemical fertilizers improved the soil fertility status, as well as its physical environment. To sustain the soil health of rice–wheat system in loamy sand soil, it is imperative to apply GM and RSR in combination with chemical fertilizers. Also the increase in DTPA-extractable and total Zn, Cu, Fe, and Mn may be attributed to chelating action of organic compounds released from manures applied in the form of GM and RSR under rice–wheat system.     

Biochar and biochar with N fertilizer as a potential tool for improving soil sorption of nutrients

Purpose

Biochar usually has a large specific surface area, and due to this, it increases the sorption capacity of the soil where it was applied. The objectives of this study were to (i) quantify the effects of biochar and biochar in combination with N fertilizer on the soil sorption parameters and (ii) quantify the effects of soil organic matter on the sorption parameters after application of biochar with and without N fertilizer.

Materials and methods

The experiment was established on Haplic Luvisol at the locality of Dolná Malanta (Slovakia) in 2014. The soil samples were collected once a month from the depth 0–0.2 m during 2014 to 2016. The field experiment included three rates of biochar application (B0?=?no biochar, B10?=?biochar at the rate of 10 t ha^?1, B20?=?biochar at the rate of 20 t ha^?1) and three levels of N fertilization (N0?=?no nitrogen, N40?=?nitrogen at the rate of 40 kg ha^?1, N80?=?nitrogen at the rate of 80 kg ha^?1).

Results and discussion

Overall, the decrease of the average values of hydrolytic acidity due to biochar and biochar combined with N fertilization resulted on average in an increase of sum of basic cation (SBC), cation exchange capacity (CEC), and sorption capacity of soil organic matter (CEC_SOM) in all treatments. However, this effect was the most intensive in B10N40. Despite the fact that the average values of sorption parameters improved, its dynamics during the investigated period were different. A significant decrease in CEC was observed from 2014 to 2016 in all treatments, except B0N0 and B10N0. A stable trend in CEC_SOM was observed only in B10N40. Humic substances and humic acids had a statistically significant positive effect on the SBC, CEC, and CEC_SOM only in B20N0 treatment. Negative correlations between the above mentioned parameters were observed in B10N80 treatment.

Conclusions

We conclude that the application of biochar and biochar combined with N fertilization had a positive influence on sorption parameters. However, its effects on SBC, CEC, and CEC_SOM decreased over time after its application.

     

Decarboxylation of organic anions to alleviate acidification of red soils from urea application

Purpose

Decarboxylation of organic anions in crop straw is recognized as one of the mechanisms for increasing pH in acidified soils. However, the effectiveness of specific compounds in alleviating soil acidification from nitrification has not been well determined. This study examined three organic anions commonly found in crop straws and their effect on soil acidity and N transformation processes following urea application to a red soil (Ferralic Cambisol).

Materials and methods

A 35-day incubation experiment was conducted using soil after receiving 26 years of two different nutrient treatments: (1) chemical nitrogen, phosphorus, and potassium fertilization (NPK, pH 4.30) and (2) NPK plus swine manure (NPKM, pH 5.88). Treatments included three rates (0.25, 0.5, and 1.0 g C kg^?1) of calcium citrate, 0.5 g C kg^?1 calcium oxalate, 0.5 g C kg^?1 calcium malate, urea-only (control) soil, and a non-treated soil as a reference. Soil acidity, mineral N species, decarboxylation, and their correlations were determined.

Results and discussion

All three organic anions significantly increased pH in both soils and the effectiveness was positively correlated with application rate. The change in total exchangeable soil acidity was dominated by aluminum concentration in the NPK soil, but by proton concentration in the NPKM soil. At ≥?0.5 g C kg^?1, the anions decreased soil exchangeable acidity by 25–68% in NPK soil and by 63–88% in NPKM soil as compared with control. Oxalate was the most effective in increasing soil pH by 0.70 and 1.31 units and reducing exchangeable acidity by 3.79 and 0.33 cmol₍₊₎ kg^?1 in NPK and NPKM soils, respectively, and also resulted in the highest CO₂ production rate. Addition of organic anions led to a lower nitrification rate in NPKM soil relative to the NPK soil.

Conclusions

These results imply that crop straws rich in organic anions, especially oxalate, would have a higher potential to alleviate soil acidification.

     

Residual effects of soil Zn fertilization on soil characteristics,yield and quality of Platycodon grandiflorum

ABSTRACT

Zinc (Zn) deficiency is common worldwide and is a major limiting factor in the cultivation of Platycodon grandiflorum because most P. grandiflorum is cultivated on soils with slight or severe levels of Zn deficiency in China. To investigate the effects of soil Zn fertilization on P. grandiflorum and its residual effects on soil characteristics, a randomized complete block design was conducted at the experimental station of Shandong Agricultural University China in 2016–2018. In 2016, ZnSO₄ · 7H₂O was used as Zn fertilizer. The fertilizer levels of Zn fertilizer were designed as 0, 4, 6, 8 and 10 kg ha^?1 and were denoted as CK, Zn₄, Zn₆, Zn₈ and Zn₁₀. No Zn fertilizer was used in 2017 and 2018. The results showed that soil Zn fertilization increased the quantity of soil bacteria, and actinobacteria, Zn₈ and Zn₁₀ treatments increased the soil fungal quantity in 2017, whereas the effect was observed only in the Z₁₀ treatment in 2018. Soil Zn fertilization enhanced the activity of polyphenol oxidase, decreased that of phosphatase, and did not influence the invertase activity in both 2017 and 2018. Both the yield and the quality of P. grandiflorum in the succeeding three years increased due to the soil Zn fertilization in 2016. Overall, soil Zn application is a suitable approach to the cultivation of P. grandiflorum, and the residual effects of a one-time soil Zn fertilization could last at least two years.     

Application of VNIR and machine learning technologies to predict heavy metals in soil and pollution indices in mining areas

Purpose

Soil pollution indices are an effective tool in the computation of metal contamination in soil. They monitor soil quality and ensure future sustainability in agricultural systems. However, calculating a soil pollution index requires laboratory measurements of multiple soil heavy metals, which increases the cost and complexity of evaluating soil heavy metal pollution. Visible and near-infrared spectroscopy (VNIR, 350–2500 nm) has been widely used in predicting soil properties due to its advantages of a rapid analysis, non-destructiveness, and a low cost.

Methods

In this study, we evaluated the ability of the VNIR to predict soil heavy metals (As, Cu, Pb, Zn, and Cr) and two commonly used soil pollution indices (Nemerow integrated pollution index, NIPI; potential ecological risk index, RI). Three nonlinear machine learning techniques, including cubist regression tree (Cubist), Gaussian process regression (GPR), and support vector machine (SVM), were compared with partial least squares regression (PLSR) to determine the most suitable model for predicting the soil heavy metals and pollution indices.

Results

The results showed that the nonlinear machine learning models performed significantly better than the PLSR model in most cases. Overall, the SVM model showed a higher prediction accuracy and a stronger generalization for Zn (R²_V?=?0.95, RMSE_V?=?6.75 mg kg^?1), Cu (R²_V?=?0.95, RMSE_V?=?8.04 mg kg^?1), Cr (R²_V?=?0.90, RMSE_V?=?6.57 mg kg^?1), Pb (R²_V?=?0.86, RMSE_V?=?4.14 mg kg^?1), NIPI (R²_V?=?0.93, RMSE_V?=?0.31), and RI (R²_V?=?0.90, RMSE_V 3.88). In addition, the research results proved that the high prediction accuracy of the three heavy metal elements Cu, Pb, and Zn and their significant positive correlations with the soil pollution indices were the reason for the accurate prediction of NIPI and RI.

Conclusion

Using VNIR to obtain soil pollution indices quickly and accurately is of great significance for the comprehensive evaluation, prevention, and control of soil heavy metal pollution.

     

Effect of long-term balanced and imbalanced inorganic fertilizer and FYM application on chemical fraction of DTPA-extractable micronutrients and yields under rice–wheat cropping system in mollisols

The imbalanced use of chemical fertilizers under intensive cultivation practices over a period of years leads to various soil-associated problems particularly nutrient availability. Thus, to examine the effect of long-term application of balanced and imbalanced inorganic fertilizer and farm yard manure (FYM) application on the chemical fraction of DTPA-extractable micronutrients under rice–wheat cropping system after 29 years, the observations were recorded from the ongoing field experiment at Govind Ballabh Pant University of Agriculture and Technology, Pantnagar, India. An application of balanced inorganic fertilizer with FYM in rice, while without FYM in wheat significantly improved the DTPA-extractable Zn, Fe, Mn and Cu after rice and wheat crops in both the surface and sub-surface soil layers. Lowest DTPA-extractable Zn, Fe, Mn and Cu were recorded, in surface and sub-surface soil under rice and wheat crops in control. The highest DTPA-extractable Zn, in both surface and sub-surface layers of rice (3.31, 1.62 mg kg⁻¹, respectively) and wheat (2.96, 0.99 mg kg⁻¹, respectively) was recorded because of application of N₁₈₀+P₈₀+K₄₀+Zn(F) + FYM in rice and N₁₈₀+P₈₀+K₄₀+Zn(F) in wheat. However, the DTPA-extractable Fe, Mn and Cu were highest in rice and wheat because of N₁₂₀+P₄₀+K₄₀+FYM and N₁₂₀+P₄₀+K₄₀ application, respectively. The balanced use of inorganic fertilizer with FYM (N₁₈₀+P₈₀+K₄₀+Zn(F) + FYM) in rice and without FYM [N₁₈₀+P₈₀+K₄₀+Zn(F)] in wheat supported the highest rice (6.74 t ha⁻¹) and wheat (3.50 t ha⁻¹) grain yields, while lowest in control. Based on the study results, long-term application of FYM at 5 tonnes ha⁻¹ in rice crop sustained the availability of DTPA-extractable cationic micronutrients to rice and wheat in Mollisols.     

Application of white mustard and oats in the phytostabilisation of soil contaminated with cadmium with the addition of cellulose and urea

Purpose

Determination of the effectiveness of white mustard and oats in immobilising cadmium as a soil contaminant and determining the role of cellulose and urea in restoring homeostasis in soil under pressure from Cd²⁺.

Materials and methods

Soil samples were contaminated with cadmium (CdCl₂·2¹/₂H₂O) at 0, 4, 8 and 16 mg Cd²⁺ kg^?1. In order to reduce the negative impact of Cd²⁺, cellulose was introduced to the soil at the following rates: 0 and 15 g kg^?1 and urea at 80 and 160 mg N kg^?1. The yield of the above-ground parts and roots was determined on days 40 and 80 of the experiment, along with the cadmium content in the plant material. The enzyme activity was also determined, and the physical and chemical properties of the soil were determined on the day of the oats’ (aftercrop) harvest.

Results and discussion

Contamination of soil with Cd²⁺ at 4 to 16 mg kg^?1 d.m. of soil reduced the yield of white mustard and oats. The tolerance index (TI) values indicate that oats (aftercrop) is more tolerant than white mustard of soil contamination with Cd²⁺. Cadmium accumulated more intensely in roots compared with the above-ground parts of the plants. The translocation index (TF) indicates smaller Cd²⁺ translocation from roots to above-ground parts, as it was below 1 in both plants. An addition of cellulose and nitrogen offsets the adverse impact of cadmium on plants. Arylsulphatase was the most sensitive to soil contamination with Cd²⁺, followed by dehydrogenases, catalase, β-glucosidase and urease, and alkaline phosphatase and acid phosphatase were the least sensitive. Contamination of soil with Cd²⁺ changed its physical and chemical properties only slightly.

Conclusions

White mustard and oats have phytostabilisation potential with respect to soil contaminated with cadmium. Cellulose introduced to the soil and fertilisation with urea alleviated the negative impact of cadmium on the growth and development of plants.

     

Long-term straw mulch effects on crop yields and soil organic carbon fractions at different depths under a no-till system on the Chengdu Plain,China

Proposal

A 12-year field experiment was conducted to assess straw mulch effects on soil organic carbon fractions, the carbon pool management index (CPMI) at different depths, and crop yield under a no-till rice-wheat rotation system on the Chengdu Plain, southwestern China.

Materials and methods

There were two treatments in the experiment: no-till without straw mulch (CK) and no-till with straw mulch (SM). The soil was sampled at 0–5, 5–10, 10–20, and 20–30-cm depths. Soil total organic carbon (TOC), the labile organic carbon fractions, including particulate organic carbon (POC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and permanganate-oxidizable carbon (KMnO₄-C), and the CPMI were analyzed. The crop grains were measured between September 2013 and May 2018.

Results and discussion

Between 2013 and 2018, rice and wheat grain yields under SM were comparable to CK, except there were higher rice yields in 2016 and higher wheat yields in 2017 under SM. The soil organic carbon decreased as soil depth increased in both treatments. Soil TOC, POC, and KMnO₄-C concentrations at 0–5 and 5–10 cm, CPMI at 0–5 and 5–10 cm, and DOC at 0–5, 5–10, and 10–20-cm soil depths were significantly greater under SM than under CK, whereas the MBC at 0–5 and 5–10 cm under SM was lower than CK. The POC/TOC, KMnO₄-C/TOC, and DOC/TOC ratios were greater under SM in the 0–5 and 5–10 cm, 0–5 cm, and 5–10 and 10–20-cm layers than CK, respectively, whereas the MBC/TOC ratio decreased under SM at 0–5, 5–10, and 10–20-cm depths.

Conclusions

The results showed that straw mulching should be adopted when a no-till rice-wheat cropping system is used in southwestern China because it leads to effective improvements in SOC sequestration while still maintaining normal crop yields.

     

Biochar amendment of chromium-polluted paddy soil suppresses greenhouse gas emissions and decreases chromium uptake by rice grain

Purpose

Soil chromium (Cr) pollution has received substantial attention owing to related food chain health risks and possible promotion of greenhouse gas (GHG) emissions. The aim of the present study was to develop a promising remediation technology to alleviate Cr bioavailability and decrease GHG emissions in Cr-polluted paddy soil.

Materials and methods

We investigated the potential role of biochar amendment in decreasing soil CO₂, CH₄, and N₂O emissions, as well in reducing Cr uptake by rice grains at application rates of 0 t ha^?1 (CK), 20 t ha^?1 (BC20), and 40 t ha^?1 (BC40) in Cr-polluted paddy soil in southeastern China. In addition, the soil aggregate size distribution, soil organic carbon (SOC) concentration of soil aggregates, soil available Cr concentration, and rice yield were analyzed after harvesting.

Results and discussion

Biochar amendment significantly reduced CO₂, CH₄, and N₂O emission fluxes. Compared to CK, total C emissions in the BC20 and BC40 treatments decreased by 9.94% and 17.13% for CO₂-C, by 30.46% and 37.10% for CH₄-C, and by 34.24% and 37.49% for N₂O-N, respectively. Biochar amendment increased the proportion of both the 2000–200 μm and 200–20 μm size fractions in the soil aggregate distribution. Accordingly, the organic carbon concentration of these fractions increased, which increased the total SOC. Moreover, biochar amendment significantly decreased soil available Cr concentration and total Cr content of the rice grains by 33.6% and 14.81% in BC20 and 48.1% and 33.33% in BC40, respectively. Rice yield did not differ significantly between biochar amendment treatment and that of CK.

Conclusions

Biochar application reduced GHG emissions in paddy soil, which was attributed to its comprehensive effect on the soil properties, soil microbial community, and soil aggregates, as well as on the mobility of Cr. Overall, the present study demonstrates that biochar has a great potential to enhance soil carbon sequestration while reducing Cr accumulation in rice grains from Cr-polluted rice paddies.

     

Coupled effects of biochar use and farming practice on physical properties of a salt-affected soil with wheat–maize rotation

Purpose

Being carbon-rich and porous, biochar has the potential to improve soil physical properties, so does conventional farming practice. Here, a field trial was conducted to investigate the combined effects of biochar use and farming practice on the physical properties of a salt-affected compact soil for wheat–maize rotation in the Yellow River Delta region.

Materials and methods

Salix fragilis L. was used as feedstock to produce biochar in the field via aerobic carbonization at an average temperature of 502 °C, terminated by a water mist spray, for use as a soil amendment at 0, 1, 2, and 4 g kg^?1 doses (CK, T1, T2, and T3, respectively). Farming practices included rotary tillage/straw returning for wheat sowing, spring irrigation, no-tillage seeding of maize, and autumn irrigation. Both cutting ring and composite samples of the soil were collected at four stages of wheat–maize rotation (22, 238, 321, and 382 d after the benchmark date of land preparation for wheat sowing) for the determination of soil properties by established methods.

Results and discussion

Rotary tillage/straw returning reduced soil bulk density (BD) from 1.48 to 1.27 g cm^?3 (CK) and 1.14 g cm^?3 (T3) and increased saturated hydraulic conductivity (Ks) from 0.05?×?10^?5 to 0.75?× 10^?5 cm s^?1 (CK) and 1.25?× 10^?5 cm s^?1 (T3). This tillage effect on BD and Ks gradually disappeared due to the disturbance from the subsequent farming practice. Biochar use lessened the disturbance. At maize harvest, BD was 1.47 (CK) vs. 1.34 g cm^?3 (T3), and Ks was 0.06?×?10^?5 (CK) vs. 0.28?×?10^?5 cm s^?1(T3); in comparison with CK, T3 increased Na⁺ leaching by 65%, Cl^? leaching by 98%, organic carbon content by 40.3%, and water-stable aggregates (0.25–2 mm) by 38%, indicating an improvement in soil properties.

Conclusions

Biochar use and rotary tillage improved soil physical properties (BD, Ks) and favored soil aeration, water filtration, and salt leaching, which further helped the accumulation of soil organic carbon, the formation of water-stable aggregates, and the amelioration of salt-affected compact soil.

     

Effect of plantain on nitrous oxide emissions and soil nitrification rate in pasture soil under a simulated urine patch in Canterbury,New Zealand

Purpose

The aim of this research was to quantify the effect of plantain (Plantago lanceolata L.) on soil nitrification rate, functional gene abundance of soil ammonia oxidisers, and the concomitant effect on nitrous oxide emissions from urine patches in a shallow, free-draining soil in Canterbury during late autumn/winter season.

Materials and methods

Urine was collected from dairy cows grazing either ryegrass/white clover (RGWC), 30% plantain (P30) mixed in with RGWC or 100% plantain (P100) pasture, and applied at two rates (700 or 450 kg N ha^?1) to intact soil blocks growing either RGWC, P30 or P100 pasture.

Results and discussion

Results showed that increased plantain content reduced N-concentration in urine from 7.2 in RGWC urine to 4.5 and 3.7 g N L^?1 in P30 and P100 urine, respectively. Total N₂O emissions and emission factors (EF₃) from urine-treated pastures were low, <?2 kg N ha^?1 and <?0.22%, respectively. Urine application at the lower urine N-loading rate of 450 kg N ha^?1 (i.e. representative of that in a P30 urine patch) resulted in 30% lower N₂O emissions (P?<?0.01) and 35% lower soil nitrate concentrations (P?<?0.001) compared to those at the higher urine loading rate of 700 kg N ha^?1 (i.e. representative of that in a RGWC urine patch). Increasing plantain content in the pasture sward from 0 to 30% and 100% with urine N applied at the same loading rate did not reduce N₂O emissions or nitrification compared to the standard ryegrass-white clover pasture. Cow urine derived from the different pasture diets had no effect on N₂O emissions, N transformation or ammonia-oxidiser abundance in soil compared to the RGWC urine applied at the same rate.

Conclusions

The main effect of plantain in this study appears to be related to the reduction in urine N-loading rate, rather than factors related to urine properties or plantain-soil interactions.

     

Effect of split application of zinc on yield of rice (Oryza sativa L.) in an inceptisol

Abstract

Rice is mostly transplanted under puddled low land soil conditions in India, where Zinc (Zn) deficiency is a common problem. The objective of this study was to find out the efficacy of split application of Zn on growth and yield of rice in an inceptisol. The split application of Zn as ZnSO₄ · 7H₂O performed better than its single basal application, while the split application of Zn-EDTA did not show any significant difference on yield and yield components of rice over its single basal application. Zn-EDTA was found to be better for growth and yield of rice among the two sources of Zn. The soil application of Zn at 1.0 kg ha^?1 as Zn-EDTA (T₇) recorded highest grain yield of 5.42 t ha^?1, filled grain percentage of 90.2%, 1000-grain weight of 25.41 g and number of panicles m^?2 of 452. The Zn content of grain and straw were found to be maximum in the treatment T₇ i.e. 38.19 and 18.27 mg kg^?1, respectively. Linear regression studies indicated that grain yield of rice is significantly influenced by Zn content of grain, Zn content of straw and DTPA extractable Zn content of soil at the level of 95.96, 96.74 and 95.57%, respectively.