Effect of humic and calcareous substance amendments on the availability of cadmium in paddy soil and its accumulation in rice.

Humic substances (HS) are widely known as important components in soil and significantly affect the mobility of metals due to their large surface area and abundant organic functional groups. Calcareous substances (CSs) are also commonly used as robust and cost-effective amendments for increasing the pH of acidic soils and decreasing the mobility of metals in soils. In this study, we developed a new remediation scheme for cadmium (Cd)-contaminated soil remediation by coupling HS and CS. The results showed that regardless of the addition of fulvic acid (FA), all the CS-containing treatments significantly increased the soil pH by 0.32-0.60, and the concentration of bioavailable Cd decreased in the moderately (field experiment soil, maximum 62%) and highly (pot experiment soil, maximum 57%) Cd-contaminated soils. The Cd content in rice (Oryza sativa L.) tissues significantly decreased after all the treatments. The bioaccumulation factors (BAFs) decreased by over 50% in the roots, stems, leaves and husks in all treatments, while the translocation factors (TFs) only significantly decreased in the highly contaminated soil. Among all treatments, the two HS+CS treatments (FA+CaCO3 and FA+CaO) had the greatest effect on decreasing the concentration of bioavailable Cd in soil and Cd in brown rice grains. The suggested mechanism for the effectiveness of coupled HS and CS was that CS first mitigated the pH and precipitated Cd, followed by a complexation effect between HS and Cd. Although the Cd in rice grains in both cases was higher than the standard limit, HS+CS remediation can be advocated as a robust, simple and cost-effective scheme for Cd remediation if the additive dose is slightly increased, as this approach can simultaneously improve the pH of acidic soil and adsorb Cd in soil.

Dynamics of soil bacteria and fungi communities of dry land for 8 years with soil conservation management.

Microorganisms play an important role in nutrient cycling and ecosystem stability. This experiment studied the conservation management approaches [control without fertilizer (CK); fertilizer and different mulching based straw mulching (SM), plastic mulching (PM), ridge-furrow with plastic mulching (RFPFM), and green manure (GM)] effects on the soil microbial community structures in spring corn (Zea Mayis) dry land. The results showed that the bacterial phylum mainly included Proteobacteria (28.2%-36.8%), Acidobacteriota (9.1%-17.9%), Bacteroidota (5.6%-8.9%) and Actinobacteria (3.1-6.2%). The most richness fungal components were Ascomycota (35.2%-44.2%), Basidiomycota (3.3%-12%) and Mortierellomycota (3.4%-6.6%). Additionally, the highest Chao1 and abundance-based coverage estimator (ACE) indexes of bacteria (2931.9 and 2953.7) and fungi (1083.316 and 1100.650) were present in RFPFM that indicating the richest microbial abundance, the highest Shannon and Simpson indexes was exist in PM (9.332 and 0.996) for bacteria and RFPFM (6.753 and 0.974) for fungi. Therefore, this study reveals the conservation management of fertilizer addition and mulching management obviously promoted microbial diversity and altered the superior microbial distribution that provides a potential way for agricultural sustainable management approaches in production practice during circular economy.

Cadmium uptake in above-ground parts of lettuce (Lactuca sativa L.).

Because of its high Cd uptake and translocation, lettuce is often used in Cd contamination studies. However, there is a lack of information on Cd accumulation in the above-ground parts of lettuce during the entire growing season. In this study, a field experiment was carried out in a Cd-contaminated area. Above-ground lettuce parts were sampled, and the Cd content was measured using a flame atomic absorption spectrophotometer (AAS). The results showed that the Cd concentration in the above-ground parts of lettuce increased from 2.70 to 3.62mgkg(-1) during the seedling stage, but decreased from 3.62 to 2.40mgkg(-1) during organogenesis and from 2.40 to 1.64mgkg(-1) during bolting. The mean Cd concentration during the seedling stage was significantly higher than that during organogenesis (a=0.05) and bolting (a=0.01). The Cd accumulation in the above-ground parts of an individual lettuce plant could be described by a sigmoidal curve. Cadmium uptake during organogenesis was highest (80% of the total), whereas that during bolting was only 4.34%. This research further reveals that for Rome lettuce: (1) the highest Cd content of above-ground parts occurred at the end of the seedling phase; (2) the best harvest time with respect to Cd phytoaccumulation is at the end of the organogenesis stage; and (3) the organogenesis stage is the most suitable time to enhance phytoaccumulation efficiency by adjusting the root:shoot ratio.

A two-year field study of phytoremediation using Solanum nigrum L. in China.

A two-year in-situ phytoremediation trial was launched in Shenyang Zhangshi (Sewage) Irrigation Area (SZIA). The phytoremediation efficiency of Solanum nigrum L. was determined, by both monitoring the change of soil Cadmium level in the upper 20 cm of soil, and calculating the plant uptake of soil Cd. After two years experimental, by monitoring the soil Cd concentrations, The Cd concentrations decreased on average from 2.75 mg kg(-1)to 2.45 mg kg(-1) in the first year and from 2.33 mg kg(-1) to 1.53 mg kg(-1) in the second year, amounting to a decrease by a factor of 10.6% in the first year and 12% in the second year. After two years phytoremediation by S. nigrum, Cd concentrations of the seven experimental plots with S. nigrum growth decreased from 2.75 mg kg(-1) to 1.53 mg kg(-1), a decrease by a factor of 24.9%. And the soil Cd concentration decreased only 2.1% and 1.7% in the bared experimental plot. And the calculating of Cd uptake by S. nigrum shown that, the plants uptake 4.46% and 5.18% of the total soil Cd in 2008 and 2009, while the soil Cd concentrations decreased by a factor of 10.6% in 2008 and 12.1% in 2009.

Potential of Gibberellic Acid 3 (GA3) for Enhancing the Phytoremediation Efficiency of Solanum nigrum L.

A microcosm experiment with artificially contaminated soils was conducted in a greenhouse to evaluate the effect of gibberellic acid 3 (GA3) on phytoremediation efficiency of Solanum nigrum L. The GA3 was applied at three different concentrations (10, 100, 1000 mg L(-1)) to S. nigrum. Results indicated that GA3 can significantly (p < 0.05) increase the biomass of S. nigrum by 56 % at 1000 mg L(-1). Concurrently, GA3 application increased Cd concentrations in the shoot of S. nigrum by 16 %. The combined effects resulted in an increase in the amount of Cd extracted by a single plant by up to 124 %. Therefore, it is possible to use GA3 to promote the Cd phytoremediation efficiency of S. nigrum.

Phytoremediation potential of Solanum nigrum L. under different cultivation protocols.

In this study, Solanum nigrum L. was used as a hyperaccumulator for remediation of cadmium contaminated soil, and 3 different cultivation protocols were investigated. The results showed that a double cropping treatment enhanced the phytoremediation efficiency significantly, since it increased the amount of Cd extracted in one growing season by a factor of 1.62 compared to single cropping. However, the labor cost for double cropping was twice that of single cropping. If the time consumed is considered as a cost of phytoremediation, the double cropping treatment might be considered as an effective and economic cultivation protocol by reducing the overall time required to reach the targeted soil quality.

Evaluation of N2O emission from rainfed wheat field in northwest agricultural land in China.

The net greenhouse gas (NGHG) emissions and net greenhouse gas intensity (NGHGI) were investigated via the determination of nitrous oxide (N2O) emission in loess soil under rainfed winter wheat monocropping system during 3 years of field study in Northwest China. Five treatments were carried out: control (N0), conventional nitrogen (N) application (NCon), optimized N application with straw (SNOpt), optimized N application with straw and 5% of dicyanodiamide (SNOpt + DCD), and optimized N rate of slow release fertilizer with straw (SSRFOpt). Over a 3-year period, the NGHG emissions were achieved 953, 1322, 564, and 1162 kg CO2-eq ha-1, simultaneously, and the NGHGI arrived 158, 223, 86, and 191 kg CO2-eq t-1 grain in NCon, SNOpt, SNOpt + DCD, and SSROpt grain, respectively. Contrasted with conventional farming system, optimized farming methods reduced 32% of N fertilizer use without significant decrease in grain yield, but brought about 38% increase in N2O emissions, up to 28% gained in soil CH4 uptake. Thus, it was observed that the straw incorporation performs noticeable increased in N2O emissions in the winter wheat cropping season. Among the optimized N fertilizer rates compared with the SNOpt treatment, the SNOpt +DCD and SSROpt treatments decreased in N2O emissions by approximately 55% and 13%, respectively. Additionally, the N2O emission factor across over a 3-year period was 0.41 ± 0.08% derived from N fertilizer, and it was half of IPCC default values for upland corps. It is expected possibly due to low precipitation and soil moisture with the monocropping system. The 25% higher in the amount of rainfall (almost 300 mm in 2013-2014) during a cropping season underwent into 1-2-fold increase in N2O emissions from N-fertilized plots. As the statistical differences among annual cumulative emissions coincided with that during winter wheat growing season, it can be concluded that crop growing season is a vital important period for the determination of N2O emissions from under rainfed monocropping system.

[Effect of planting white clover on nutrients and biological properties of soils in persimmon orchard of Weibei, Shaanxi Province, China]. / é™•è¥¿æ¸­åŒ—æŸ¿å­å›­ç§æ¤ç™½ä¸‰å¶è‰å¯¹åœŸå£¤å »åˆ†å’Œç”Ÿç‰©å­¦æ€§è´¨çš„å½±å“.

Leguminous crop planting is one of the most important managements in sustainable agriculture, which has the potential to improve soil quality and environmental health by increasing N input and facilitating soil and water conservation. In this study, effects of white clover planting on soil nutrients and biological properties in persimmon orchard was investigated to understand its potential effects on improvement of soil fertility and economic performance. Soil samples were collected on September 14th, 2017 at 0-10 cm, 10-20 cm, 20-30 cm and 30-40 cm soil depth in two treatments (i.e. ploughing with no grass and planting white clover) in persimmon orchard, and were analyzed for soil available nitrogen, organic matter, microbial biomass carbon and nitrogen, and enzyme activity. Compared to the control, soil available nitrogen, organic matter, microbial biomass carbon and nitrogen, and the activities of urease, sucrase, catalase and alkaline phosphatase all increased in grass treatment. Specifically, in grass planting treatment, soil organic matter and microbial biomass carbon were significantly increased at 0-10 cm soil, and increased soil avai-lable nitrogen was found at 10-20 cm soil. For enzyme activity, significantly elevated urease activity exhibited at surface depth (0-20 cm), while catalase, sucrase activity and geometric mean (GME) of enzyme activity were higher within entire tested soil profile (0-40 cm). Overall, our results indicated white clover planting in orchard could not only facilitate soil fertility, but also reduce chemical fertilizer input and improve economic benefit, which could be considered as a good orchard cultivation mode.

Ridge-furrow with plastic film and straw mulch increases water availability and wheat production on the Loess Plateau.

Mulching is critical for increasing water availability and hence winter wheat production in dryland farming systems. A two-year study was conducted to assess the effects of mulches on soil water storage (SWS), temperature, water use efficiency (WUE) and yields of winter wheat on the Loess Plateau. Four treatments were examined: conventional flat planting (CK), straw mulch (FPS), transparent plastic film mulch (FPP) and ridge-furrow with plastic film-mulched ridge and straw-mulched furrow (RFPS). Compared with CK, RFPS greatly increased SWS from 0-60 cm, FPP increased SWS from 0-40 cm, and FPS slightly increased SWS from 0-60 cm; however, FPP significantly (P < 0.05) decreased SWS from 61-100 cm. RFPS and FPP increased soil temperatures in cold seasons relative to CK, especially in RFPS (2.0-2.3 °C). Meanwhile, the rate of soil temperature increase was greater in RFPS and FPP than in CK but was lower in FPS. Mean yields were significantly increased in RFPS (56.78%), FPP (44.72%) and FPS (9.57%), and WUE was significantly increased in RFPS (44.04%) and in FPP (37.50%) compared with CK (P < 0.05). We conclude that ridge-furrow planting with plastic film-mulched ridge and straw-mulched furrow has a good potential for raising winter wheat production on the Loess Plateau.

[Effects of reducing N, straw returning and dicyandiamide application on winter wheat yield and nitrogen budgets in rain-fed region.] / 减氮-ç§¸ç§†è¿˜ç”°åŠåŒæ°°èƒºæ–½ç”¨å¯¹æ—±åœ°é›¨å »åŒºå†¬å°éº¦äº§é‡å’Œæ°®å¹³è¡¡çš„å½±å“.

In a 3-year field experiment, effects of reducing N fertilizer, straw returning and dicyandiamide (DCD) application on wheat yield and nitrogen budgets under wheat-fallow system were studied in rain-fed region. The experiment was carried out in Yangling of Shaanxi Province, and 4 treatments were installed including no nitrogen (CK), 220 kg N·hm-2 and no straw returning (FP), 150 kg N·hm-2 and straw returning (OPT), 150 kg N·hm-2, 7.5 kg·hm-2 DCD and straw returning (OPT+DCD). The results showed there was no remarkable difference for wheat yield between OPT and FP, but the N use efficiency of the former was 6.1% more than that of the latter, and the apparent N loss ratio was 7.2% less. OPT+DCD increased the average yield of winter wheat by 10.4% and 7.9% respectively compared to OPT and FP, the N use efficiency of winter wheat increased by 20.8% and 28.1%, and the apparent N loss ratio decreased by 8.5% and 15.1%, respectively. NH4+-N content in 0-20 cm of soil increased, accordingly the NO3--N content decreased in 40 to 45 days when DCD was applied.