The purpose of this study is to determine the critical soil pH, exchangeable aluminum (Al), and Al saturation of the soils derived from different parent materials for maize.
Materials and methodsAn Alfisol derived from loess deposit and three Ultisols derived from Quaternary red earth, granite, and Tertiary red sandstone were used for pot experiment in greenhouse. Ca(OH)2 and Al2(SO4)3 were used to adjust soil pH to target values. The critical soil pH was obtained by two intersected linear lines of maize height, chlorophyll content, and yield of shoot and root dry matter changing with soil pH.
Results and discussionIn low soil pH, Al toxicity significantly decreased plant height, chlorophyll content, and shoot and root dry matter yields of maize crops. The critical values of soil pH, exchangeable Al, and Al saturation varied with soil types. Critical soil pH was 4.46, 4.73, 4.77, and 5.07 for the Alfisol derived from loess deposit and the Ultisol derived from Quaternary red earth, granite, and Tertiary red sandstone, respectively. Critical soil exchangeable Al was 2.74, 1.99, 1.93, and 1.04 cmolckg?1 for the corresponding soils, respectively. Critical Al saturation was 5.63, 12.51, 14.84, and 15.16% for the corresponding soils.
ConclusionsGreater soil cation exchange capacity and exchangeable base cations led to lower critical soil pH and higher critical soil exchangeable Al and Al saturation for maize.
相似文献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 methodsA 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 discussionAll 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.
ConclusionsThese results imply that crop straws rich in organic anions, especially oxalate, would have a higher potential to alleviate soil acidification.
相似文献Soil consists of various sizes of aggregates, and different soil aggregates vary in their abilities to adsorb or transport metals. This study aimed to investigate the distribution behaviors of Cu from different fungicides in soil aggregates after a 15-month incubation.
Materials and methodsBordeaux mixture (CuSO4/Ca(OH)2?=?1/1 by weight, BR), copper nitrate (Cu(NO3)2·4H2O, CN), and copper oxychloride (3Cu(OH)2·CuCl2, CO) were applied to a representative Chinese Mollisol to reach the Cu content 200 mg kg?1. Five soil aggregate fractions, i.e., >?2000 μm, 2000–1000 μm, 1000–500 μm, 500–250 μm, and <?250 μm, were obtained by the wet sieving method. The modified Bureau Communautaire de Références (BCR) sequential extraction was applied to assess the Cu distribution among the main soil fractions.
Results and discussionThe highest Cu mass loading was found for the >?2000-μm soil aggregate. The input Cu was mainly in stable fractions, and the highest proportion was found for the residual fraction. The bioavailability and mobility of Cu from different fungicides in soils varied from each other, and they presented an order of CO > CN > BR. High bioavailability and transferring coefficients were found in the <?250-μm and >?2000-μm soil aggregates.
ConclusionsThis study indicated that the input Cu from fungicides mainly distributed in the >?2000-μm soil aggregates. Moreover, the CO-derived Cu presented a higher availability than the BR- and CN-derived Cu in the soil.
相似文献Identification of phosphorus (P) species is essential to understand the transformation and availability of P in soil. However, P species as affected by land use change along with fertilization has received little attention in a sub-alpine humid soil of Tibet plateau.
Materials and methodsIn this study, we investigated the changes in P species using Hedley sequential fractionation and liquid-state 31P-NMR spectroscopy in soils under meadow (M) and under cropland with (CF) or without (CNF) long-term fertilization for 26 years in a sub-alpine cold-humid region in Qinghai–Tibet plateau.
Results and discussionLand-use change and long-term fertilization affected the status and fractions of P. A strong mineralization of organic P (OP) was induced by losing protection of soil organic matter (SOM) and Fe and Al oxides during land-use change and resulted in an increase of orthophosphate (from 56.49 mg kg?1 in M soils to 130.07 mg kg?1 in CNF soils) and great decreases of orthophosphate diesters (diester-P, from 23.35 mg kg?1 in M soils to 10.68 mg kg?1 in CNF soils) and monoesters (from 336.04 mg kg?1 in M soils to 73.26 mg kg?1 in CNF soils). Long-term fertilization boosted P supply but failed to reclaim soil diester-P (from 10.68 mg kg?1 in CNF soils to 7.79 mg kg?1 in CF soils). This may be due to the fragile protection from the combination of SOM with diester-P when long-term fertilization had only improved SOM in a slight extent.
ConclusionsThese results suggest that SOM plays an important role in the soil P cycling and prevents OP mineralization and losses from soil. It is recommended that optimization of soil nutrient management integrated with SOM was required to improve the P use efficiency for the development of sustainable agriculture.
相似文献Imidacloprid is a widely used seed dressing insecticide in Brazil. However, the effects of this pesticide on non-target organisms such as soil fauna still present some knowledge gaps in tropical soils. This study aimed to assess the toxicity and risk of imidacloprid to earthworms Eisenia andrei and collembolans Folsomia candida in three contrasting Brazilian tropical soils.
Materials and methodsAcute and chronic toxicity assays were performed in the laboratory with both species in a tropical artificial soil (TAS) and in two natural soils (Oxisol and Entisol), at room temperature of 25 °C. The ecological risk was calculated for each species and soil by using the toxicity exposure ratio (TER) and hazard quotient (HQ) approaches.
Results and discussionAcute toxicity for collembolans and earthworms was higher in Entisol (LC50?=?4.68 and 0.55 mg kg?1, respectively) when compared with TAS (LC50?=?10.8 and 9.18 mg kg?1, respectively) and Oxisol (LC50collembolans?=?25.1 mg kg?1). Chronic toxicity for collembolans was similar in TAS and Oxisol (EC50 TAS?=?0.80 mg kg?1; EC50 OXISOL?=?0.83 mg kg?1), whereas higher toxicity was observed in Entisol (EC50?=?0.09 mg kg?1). In chronic assays with earthworms, imidacloprid was also more toxic in Entisol (EC50?=?0.21 mg kg?1) when compared to TAS (EC50?=?1.89 mg kg?1). TER and HQ values indicated a significant risk of exposure of the species to imidacloprid in all soils tested, and the risk in Entisol was at least six times higher than in Oxisol or TAS.
ConclusionsThe toxicity and risk of imidacloprid varied significantly between tropical soils, being the species exposure to this pesticide particularly hazardous in very sandy natural soils such as Entisol.
相似文献Serious soil salinization, including excessive exchangeable sodium and high pH, significantly decreases land productivity. Reducing salinity and preventing alkalization in saline-sodic soils by comprehensive improvement practices are urgently required. The combinations of aluminum sulfate with different types of fertilizer at different rates were applied on rice paddy with saline-sodic soils of the Songnen Plain in Northeast China to improve soil quality and its future utilization.
Materials and methodsExperiments were carried out in a completely randomized block design. Twelve treatments with aluminum sulfate at the rates of 0, 250, 500, and 750 kg hm?2 with inorganic, bio-organic, and organic-inorganic compound fertilizers were performed. Soil pH, electronic conductivity (EC), cation exchangeable capacity (CEC), exchangeable sodium percentage (ESP), total alkalinity, sodium adsorption ratio (SAR), soil organic carbon (SOC), available nutrients, soluble ions, rice growth, and yield in the saline-sodic soils were measured across all treatments. The relationships among the measured soil attributes were determined using one-way analysis of variance, correlation analysis, and systematic cluster analysis.
Results and discussionThe pH, EC, ESP, total alkalinity, SAR, Na+, CO32?, and HCO3? in saline-sodic soil were significantly decreased, while CEC, SOC, available nitrogen (AN), available phosphorus (AP), available potassium (AK), K+, and SO42? were significantly increased due to the combined application of aluminum sulfate with fertilizer compared with the fertilizer alone. The most effective treatment in reducing salinity and preventing alkalization was aluminum sulfate at a rate of 500 kg hm?2 with organic-inorganic compound fertilizer. This treatment significantly decreased the soil pH, EC, ESP, total alkalinity, SAR, Na+, and HCO3? by 5.3%, 28.9%, 41.1%, 39.3%, 22.4%, 23.5%, and 35.9%, but increased CEC, SOC, AN, AP, AK, K+, SO42?, rice height, seed setting rate, 1000-grain weight, and yield by 77.5%, 115.5%, 106.3%, 47.1%, 43.3%, 200%, 40%, 6.2%, 43.9%, 20.3%, and 42.2%, respectively, compared with CK treatment in the leaching layer.
ConclusionsThe combined application by aluminum sulfate at a rate of 500 kg hm?2 with organic-inorganic compound fertilizer is an effective amendment of saline-sodic soils in Songnen Plain, Northeast China. These results are likely related to the leaching of Na+ from the soil leaching layer to the salt accumulation layer and desalination in the surface soil, and the increase of SOC improved the colloidal properties and increased fertilizer retention in soil. In addition, the environmental impact of aluminum sulfate applied to soil needs to be further studied.
相似文献Elevated CO2 and nitrogen (N) addition both affect soil microbial communities, which significantly influence soil processes and plant growth. Here, we evaluated the combined effects of elevated CO2 and N addition on the soil–microbe–plant system of the Chinese Loess Plateau.
Materials and methodsA pot cultivation experiment with two CO2 treatment levels (400 and 800 μmol mol?1) and three N addition levels (0, 2.5, and 5 g N m?2 year?1) was conducted in climate-controlled chambers to evaluate the effects of elevated CO2 and N addition on microbial community structure in the rhizosphere of Bothriochloa ischaemum using phospholipid fatty acid (PLFA) profiles and associated soil and plant properties. Structural equation modeling (SEM) was used to identify the direct and indirect effects of the experimental treatments on the structure of microbial communities.
Results and discussionElevated CO2 and N addition both increased total and fungal PLFAs. N addition alone increased bacterial, Gram-positive, and Gram-negative PLFAs. However, elevated CO2 interacting with N addition had no significant effects on the microbial community. The SEM indicated that N addition directly affected the soil microbial community structure. Elevated CO2 and N addition both indirectly affected the microbial communities by affecting plant and soil variables. N addition exerted a stronger total effect than elevated CO2.
ConclusionsThe results highlighted the importance of comprehensively studying soil–microbe–plant systems to deeply reveal how characteristics of terrestrial ecosystems may respond under global change.
相似文献Calcareous soils are characterized by high pH and phosphorus (P) fixation capacity. Increasing application of P fertilizer recently has significantly improved soil P concentration, especially available P (Olsen-P) and inorganic phosphate (Pi) fractions. However, there are few data available on the ability of soils with different initial Olsen-P levels to continuously supply P (i.e., P desorption capacity) to crops without additional P fertilization and on which Pi fraction exerts the greatest influence on P desorption capacity.
Materials and methodsFive soils with different initial Olsen-P levels (0.5, 14.3, 38.4, 55.4, 72.3 mg kg?1, hereafter refer as OP1, OP2, OP3, OP4, and OP5) but similar other soil properties were selected to evaluate the capacity of P desorption and its relationship with Pi fractions. Soil P was sequentially extracted once daily for 16 consecutive days using Olsen solution.
Results and discussionThe content and proportions of dicalcium phosphate fraction (Ca2-P), octacalcium phosphate fraction (Ca8-P), aluminum phosphorus fraction (Al-P), and iron phosphorus fraction (Fe-P) in Pi increased significantly with the increase of initial Olsen-P (P?<?0.01). Applied P fertilizer was mostly stored as Ca8-P in the soil. Soil P desorbed reached an equilibrium after 16 extractions for all soils, and P desorption capacity (12–358 mg kg?1) showed a significant linear relationship with initial Olsen-P (P?<?0.01), with an increase of 4.2 mg kg?1 desorbed P per 1 mg kg?1 increase of initial Olsen-P. Ca2-P exerted the conclusive effect on P desorption in the first four extractions, but Ca8-P played a more important role in the 16 extractions.
ConclusionsCa8-P was the greatest potential pool for P desorption after Ca2-P was depleted. P desorption capacity was significantly linearly related to initial Olsen-P (P?<?0.01). Different fertilizer use strategies were developed based on P desorption capacity for soils with different initial Olsen-P levels. The present study provided basic data on how to reduce effectively the application amount of chemical P fertilizer.
相似文献Although litter decomposition and nutrient release patterns have been studied in cocoa agroforestry systems in general, studies focusing on organic and conventional cocoa systems are lacking which is critical as organic farms are particularly dependent on nutrient returns from decomposing litter.
Materials and methodsDynamics in leaf litter decomposition and the mineralisation of macro- and micro-nutrients in organic and conventional cocoa agroforestry systems were studied using the litterbag technique for 12 months.
ResultsThe average monthly mass loss was more than two times higher on organic farms (9.2–14.4 g month?1) compared to conventional farms (4.2–7.3 g month?1) in the first five months. The annual rate of decomposition (k) was higher on organic farms (1.9) compared to conventional systems (1.4). The time required for 50% (t50) and 99% (t99) decomposition of leaf litter was both lower on organic farms (t50?=?0.4 years, t99?=?2.6 years) than conventional farms (t50?=?0.5 years, t99?=?3.5 years). The estimated k values for macro- and micro-nutrients on organic cocoa systems ranged from 2.3 for calcium to 4.5 for potassium compared to 1.6 (Ca) to 2.8 (K) on conventional farms. The k values of all nutrients (except nitrogen and phosphorus) were significantly greater on organic farms than conventional systems. The estimated k values for both litter decomposition and nutrient mineralisation correlated with soil pH and moisture content, but not initial litter chemistry.
ConclusionsOrganic management of smallholder cocoa agroforestry systems enhanced leaf litter decomposition and nutrient mineralisation through improved soil conditions. Thus, organic management of cocoa agroforestry systems may contribute to sustainable cocoa production in smallholder systems through enhanced nutrient return from litter decomposition.
相似文献Humic substances, which are integral components of total organic carbon (TOC), influence soil quality. The study aimed to investigate whether humic and non-humic fractions exhibit early, consistent, and measurable changes and affect TOC sensitivity and storage in a tropical sandy loam soils amended with corn cob biochar.
Materials and methodsThere were four treatments with four replicates established in a randomized complete block design. Composite soil samples were taken from plots without biochar (CT), from plots incorporated with 15 t biochar ha?1 (BC-15), and 30 t biochar ha?1 without or with phosphate fertilizer (BC-30 and BC-30+P). The TOC, and humin, humic acid (HA), and fulvic acid (HA) fractions of soil organic carbon were determined for each treatment. The optical densities (400–700 nm) were measured on the soil-free extracts by spectrophotometry; the densities measured at 465 and 665 nm were used to calculate the E465/E665 ratios.
Results and discussionThe BC-30 and BC-30+P plots recorded the highest TOC, humin, humic acid (HA), and fulvic acid (FA) contents with respect to the lowest in the CT. The total exchangeable carbon stratification was significantly higher in all the biochar-treated plots relative to the CT. Spectral analysis showed higher values of E465/E665 (5.02 and 5.15) in the CT and BC-15-treated soils, respectively, compared with the BC-30 and BC-30+P-amended soils with E465/E665 ratios of 2.76 and 2.98, respectively.
ConclusionsCorn cob biochar applied to a tropical sandy loam:
? increased the concentrations of HA and FA and led to increased stratification of TOC, with a stronger effect on HA compared with FA;
? significantly lowered E465/E665 at the high biochar application rate of 30 t ha?1, implying the dominance of high molecular weight humic acid-like substances, and increased degree of aromaticity of the TOC.
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