Heavy metal and nutrient concentrations in top- and sub-soils of greenhouses and arable fields in East China - Effects of cultivation years, management, and shelter.

Although greenhouse vegetable production in China is rapidly changing, consumers are concerned about food quality and safety. Studies have shown that greenhouse soils are highly eutrophicated and potentially contaminated by heavy metals. However, to date, no regional study has assessed whether greenhouse soils differ significantly in their heavy metal and nutrient loads compared to adjacent arable land. Our study was conducted in Shouguang County, a key region of greenhouse vegetable production in China. Soil samples down to soil depths of 3 m were taken from 60 greenhouse vegetable fields of three different ages (5, 10, and 20 years) and from 20 adjacent arable fields to analyze the concentrations of heavy metals, nutrients, and soil physio-chemical parameters. A comparison of greenhouse soils with adjacent arable fields revealed that for greenhouses, (a) micro (heavy metals: Cu, Zn, and Mn) and macronutrients (Nmin, Olsen-P, available K) were significantly higher by a factor of about five, (b) N:P:K ratios were significantly imbalanced towards P and K, and (c) topsoil (0-30 cm) concentrations of the above-mentioned micro- and macronutrients increased with years of vegetable cultivation. In contrast, the soil concentrations of the heavy metals Cr and Pb were lower in greenhouse soils. Heavy metal concentrations did not vary significantly with soil depth, except for the micronutrients Cu and Zn, which were between 1- and 3-fold higher in the topsoil (0-30 cm) than in the subsoil (30-300 cm). The Nemerow pollution index (PN) was 0.37, which was below the recommended environmental threshold value (PN < 1). Structural equation model analysis revealed that soil nutrient concentrations in greenhouse soils are directly related to the input of fertilizers and agrochemicals. Lower values of soil Pb and Cr concentrations in greenhouses were due to the sheltering effect of the greenhouse roof, which protected soils from atmospheric deposition due to emissions from nearby industrial complexes.

Impact of anaerobic soil disinfestation on seasonal N2O emissions and N leaching in greenhouse vegetable production system depends on amount and quality of organic matter additions.

Greenhouse vegetable production (GVP) systems in China receive excessive amounts of fertilizers (>1500 kg N ha-1 yr-1) and irrigation (>1200 mm yr-1), which results in severe soil degradation. Moreover, soil borne diseases are common as the same crop is planted continuously over years. Anaerobic soil disinfestation (ASD) is a method carried out every 3-4 years during the summer fallow period to combat soil-borne diseases and to improve soil health. The standard ASD practice, which is carried out before the cropping season, involves incorporation of organic matter (i.e. rice shells or straw) into the soil, covering of the soil with plastic films and soil irrigation until saturation. However, many farmers incorporate large amounts of organic nitrogen fertilizer for priming ASD. In this study, we investigated if incorporation of rice shells plus chicken manure (ASD+RM; farmers practice) provokes higher environmental N losses (N2O emissions and N leaching) during the ASD and the following tomato crop growing period as compared to the standard ASD practice (ASD+R: only rice shells) or a Control (fallow, but with incorporation of organic manure, standard in non-ASD years). Results showed that ASD+RM increased seasonal (ASD/fallow period plus tomato crop growing period) soil N2O emissions by a factor of 3 (ASD+RM: 14.1 kg N2O-N ha-1; ASD+R: 4.7 kg N2O-N ha-1), with 2/3 of emissions occurring during the 25 days long ASD period. Across all treatments, nitrate (NO3-) leaching dominated total N leaching (75%), with significantly lower rates observed for ASD+R as compared to ASD+RM. For both ASD treatments, total dissolved organic nitrogen (DON) leaching was a factor of two higher than for the Control. Crop productivity was not affected by ASD. Our findings imply that ASD+RM should be abandoned as the additional supply of manure N results in high environmental N losses without further increasing yields.

Anaerobic soil disinfestation with incorporation of straw and manure significantly increases greenhouse gases emission and reduces nitrate leaching while increasing leaching of dissolved organic N.

Greenhouse vegetable production in China mostly involves excessive N fertilization and flood irrigation. This causes serious soil degradation and spreading of soil borne diseases. As a countermeasure against soil borne diseases anaerobic soil disinfestation (ASD) is applied during the summer fallow period. Current practices involve the incorporation of organic C sources, covering of the soil with plastic film and flood irrigation. However, farmers not only apply straw but also organic manure in ASD which may result in significant greenhouse gas emissions and N leaching. A field experiment was conducted in a greenhouse during the summer fallow period to test the impact of three ASD practices on soil GHG (N2O, CO2 and CH4) emissions and N leaching: 1) control (CK), bare soil, no ASD; 2) ASD without straw incorporation (ASD-S); 3) ASD plus straw incorporation (ASD+S) and 4) ASD plus straw and chicken manure incorporation (ASD+SM). Applying any form of ASD resulted in an increase in N2O emissions from approximately 1 kg N ha-1 month-1 to 10.7 (ASD)-47.0 (ASD+SM) kg N ha-1 month-1. Furthermore, N leaching from treatments of ASD ranged from 24.1-54.2 kg N ha-1 month-1, with highest values in ASD-S. However, while N leaching in ASD-S was solely in the form of NO3-, DON leaching was with approximately 12-20% a significant component of total N leaching in ASD+S and ASD+SM. Overall, ASD+SM showed the highest environmental N losses, which were dominated by N2O emissions. This highlights the need to advise farmers and policy makers to ban the incorporation of chicken manure instead of straw only during the ASD period and to optimize irrigation schemes instead of flood irrigation to reduce environmental N losses. Putting in more environmental sound ASD practices will certainly help to improve the sustainability of greenhouse vegetable production.

Drip fertigation with straw incorporation significantly reduces N2O emission and N leaching while maintaining high vegetable yields in solar greenhouse production.

Approximately 1/3 of vegetables in China are produced in solar greenhouses. Most farmers use conventional irrigation with over fertilisation (CIF), thereby applying approximately 2000 kg N ha-1 fertiliser over two cropping seasons per year. Here, we tested the effect of drip irrigation with reduced fertilisation (DIF) combined with straw incorporation on reducing N2O emissions and nitrogen leaching from solar greenhouse vegetable production systems. Over three consecutive tomato cropping seasons, N2O emissions and nitrogen leaching were monitored in high temporal resolution, thereby producing a unique dataset. Compared to CIF, the realised drip fertigation scheme reduces N2O emission and nitrogen leaching of nitrate and dissolved organic nitrogen by approximately a factor of 5-10 (N2O-DIF: 10.3, CIF: 47.5 kg N ha-1 yr-1; N leaching-DIF: 83.6, CIF: 863 kg N ha-1 yr-1). Straw incorporation in CIF, though advantageous for soil health, resulted in pollution swapping as soil N2O emissions increased while NO3- leaching losses decreased. On the contrary, no significant negative environmental N effects of straw incorporation were found for DIF. As crop productivity was not affected by straw incorporation, neither for CIF nor for DIF, our study provides a sound basis for policy advice to recommend farmers to adopt drip fertigation combined with straw application. Wide scale adoption of this technique will result in reductions of environment N losses, alleviate major soil degradation signs, including soil acidity, nutrient imbalance and deterioration of soil microbial community structure, while allowing to maintaining high yields of vegetables in solar greenhouse production systems.

Global greenhouse vegetable production systems are hotspots of soil N2O emissions and nitrogen leaching: A meta-analysis.

Vegetable production in greenhouses is often associated with the use of excessive amounts of nitrogen (N) fertilizers, low NUE (15-35%), and high N losses along gaseous and hydrological pathways. In this meta-analysis, we assess the effects of application rate, fertilizer type, irrigation, and soil properties on soil N2O emissions and nitrogen leaching from greenhouse vegetable systems on the basis of 75 studies. Mean ± standard error (SE) N2O emissions from unfertilized control plots (N2Ocontrol) and N leaching (NLcontrol) of greenhouse vegetable systems were 3.2 ± 0.4 and 91 ± 20 kg N ha-1 yr-1, respectively, indicating legacy effects due to fertilization in preceding crop seasons. Soil organic carbon concentrations (SOC) and irrigation were significantly positively correlated with NLcontrol losses, while other soil properties did not significantly affect N2Ocontrol or NLcontrol. The annual mean soil N2O emission from fertilized greenhouse vegetable systems was 12.0 ± 1.0 kg N2O-N ha-1 yr-1 (global: 0.067 Tg N2O-N yr-1), with N2O emissions increasing exponentially with fertilization. The mean EFN2O was 0.85%. The mean annual nitrogen leaching (NL) was 297 ± 22 kg N ha-1 yr-1 (global: 1.66 Tg N yr-1), with fertilization, irrigation, and SOC explaining 65% of the observed variation. The mean leaching factor across all fertilizer types was 11.9%, but 18.7% for chemical fertilizer. Crop NUE was highest, while N2O emissions and N leaching were lowest, at fertilizer rates <500 kg N ha-1 year-1. Yield-scaled N2O emissions (0.05 ± 0.01 kg N2O-N Mg-1 yr-1) and nitrogen leaching (0.79 ± 0.08 kg N Mg-1 yr-1) were lowest at fertilizer rates <1000 kg N ha-1 yr-1. Vegetables are increasingly produced in greenhouses, often under management schemes of extreme fertilization (>1500 kg N ha-1 yr-1) and irrigation (>1200 mm yr-1). Our study indicates that high environmental N2O and N leaching losses can be mitigated by reducing fertilization rates to 500-1000 kg N ha-1 yr-1 (mean: ∼762 kg N ha-1 yr-1) without jeopardizing yields.

Influence of aeration rate and reactor shape on the composting of poultry manure and sawdust.

To achieve successful composting, all the biological, chemical, and physical characteristics need to be considered. The investigation of our study was based on various physicochemical properties, i.e., temperature, ammonia concentration, carbon dioxide concentration, pH, electrical conductivity (EC), carbon/nitrogen (C/N) ratio, organic matter (OM) content, moisture content, bacterial population, and seed germination index (GI), during the composting of poultry manure and sawdust for different aeration rates and reactor shapes. Three cylindrical-shaped and three rectangular-shaped pilot-scale 60-L composting reactors were used in this study, with aeration rates of 0.3 (low), 0.6 (medium), and 0.9 (high) L min-1 kg-1 DM (dry matter). All parameters were monitored over 21 days of composting. Results showed that the low aeration rate (0.3 L min-1 kg-1 DM) corresponded to a higher and longer thermophilic phase than did the high aeration rate (0.9 L min-1 kg-1 DM). Ammonia and carbon dioxide volatilization were directly related to the temperature profile of the substrate, with significant differences between the low and high aeration rates during weeks 2 and 3 of composting but no significant difference observed during week 1. At the end of our study, the final values of pH, EC, moisture content, C/N ratio, and organic matter in all compost reactors were lower than those at the start. The growth rates of mesophilic and thermophilic bacteria were directly correlated with mesophilic and thermophilic conditions of the compost. The final GI of the cylindrical reactor with an airflow rate of 0.3 L min-1 kg-1 DM was 82.3%, whereas the GIs of the other compost reactors were below 80%. In this study, compost of a cylindrical reactor with a low aeration rate (0.3 L min-1 kg-1 DM) was more stable and mature than the other reactors. Implications: The poultry industry is growing in South Korea, but there are problems associated with the management of poultry manure, and composting is one solution that could be valuable for crops and forage if managed properly. For high-quality composting, the aeration rate in different reactor shapes must be considered. The objective of this study was to investigate various physicochemical properties with different aeration rates and rector shapes. Results showed that aeration rate of 0.3 L min-1 kg-1 DM in a cylindrical reactor provides better condition for maturation of compost.