The effect of chemical and organic N inputs on N2O emission from rain-fed crops in Eastern Mediterranean

N-Source Determines Barley Productivity, Nutrient Accumulation, and Grain Quality in Cyprus Rainfed Agricultural Systems

The Eastern Mediterranean and Middle East (EMME) region is already experiencing the negative effects of increased temperatures and the increase in prolonged drought periods. The use of organic fertilization could be a valuable tool to meet the main challenges of climate change and maintain the productivity, quality, and sustainability of rainfed agricultural ecosystems. In the current study, we compare the effect of manure, compost, and chemical fertilization (NH₄NO₃) on barley grain and straw yield in a field study for three consecutive growing seasons. The hypothesis that the barley productivity, nutrient accumulation, and grain quality remain similar among the different nutrient management strategies was tested. The results showed that both growing season and type of nutrient source significantly affected barley grain and straw yield (F_6,96 = 13.57, p < 0.01). The lowest productivity was noticed in the non-fertilized plots while chemical and organic fertilization exhibited similar grain yield, ranging from 2 to 3.4 t/ha throughout the growing seasons. For straw, the use of compost had no effect on the yield in any of the growing seasons examined. The use of manure and compost had a significant effect on grain macro- and micronutrient content but this was highly related to growing season. Principal component analysis (PCA) clearly demonstrated the discrimination of the different type of fertilization on barley performance during the course of the study, while the application of compost was highly associated with an increase in micronutrients in grain samples. Furthermore, structural equational modeling (SEM) showed that both chemical and organic fertilization had a direct positive effect on macro- (r = 0.44, p < 0.01) and micronutrient (r = 0.88, p < 0.01) content of barley grain and a positive indirect effect on barley productivity through N accumulation in grain (β = 0.15, p = 0.007). The current study showed that barley grain and straw yield was similar between manure and NH₄NO₃ treatments, while compost exhibited a residual positive effect causing an increase in grain yield during the growing season. The results highlight that N fertilization under rainfed conditions is beneficial to barley productivity through its indirect effects on N accumulation in grain and straw, while it improves grain quality through the increased accumulation of micronutrients.

LCA of Barley Production: A Case Study from Cyprus

Greenhouse gas emissions (i.e., carbon dioxide, methane, nitrous oxide) produced by agriculture contribute to global warming and climate change. Various practices followed by farmers in different environmental conditions contribute to the increase in the phenomena, and there is a need for immediate measures. The current study examines the environmental impact of barley production under rain-fed conditions in Cyprus. For this, four different nutrient management scenarios were investigated in order to evaluate the environmental performance of crop production, namely: (1) Nitrogen (20%), Phosphorous (20%), Potassium (10%); (2) Nitrogen (20%), Phosphorous (20%), Potassium (10%) and manure; (3) Nitrogen (25%), Phosphorous (10%), Potassium (0%); and (4) Nitrogen (25%), Phosphorous (10%), Potassium (0%) and manure. Data were collected from two different areas of Cyprus (Nicosia and Larnaca) through on-site visits and questionnaires. Life Cycle Assessment (LCA) was used as a method to quantify environmental impacts which were categorized into six impact categories: (i) acidification potential (AP), (ii) eutrophication potential (EP), (iii) global warming potential (GWP), (iv) ozone depletion potential (ODP), (v) photochemical, ozone creation potential (POCP), and (vi) terrestrial ecotoxicity (TAETP). LCA was used with system boundaries from field to harvest and a functional unit (FU) of one bale of hay. Research results showed that the addition of manure increased values in all impact categories. Comparing scenarios without manure (1 and 3) and with manure (2 and 4), the main process which contributed to GWP was field preparation, which resulted in 3 t CO₂-Eq∙FU^-1 and 46.96 t CO₂-Eq∙FU^-1, respectively. Furthermore, the highest contribution of sub-processes to GWP (kg CO₂-Eq∙FU^-1) was machinery maintenance (scenarios 2 and 4). The potential to reduce environmental impacts from barley and moreover, to mitigate the footprint of the agriculture sector in Cyprus is proposed by changing existing practices such as decreasing fuel consumption by agricultural machinery, and monitoring fertilizing and seeding. Conclusively, the carbon footprint of barley can be decreased through the improvement of nutrient management and cropping practices.

Soil surface management of legume cover has the potential to mitigate nitrous oxide emissions from the fallow season during wheat production

Soil surface management, i.e., mulch by film, straw or cover crop, is very important to water availability in soil on drylands worldwide, especially during the fallow season, when there is a high concentration of soil nitrate nitrogen (N) to produce nitrous oxide (N₂O). To determine whether soil surface management affects N₂O emissions during the fallow season, we conducted an experiment to compare N₂O emissions from a wheat field that received different surface soil management strategies: control (CK), straw mulch and incorporation (SR), planting legume green manure and incorporation (GM), SR plus GM (SR + GM), and plastic film mulch (FM). The results showed that the average hourly N₂O emissions during the fallow season were in the order SR (7.4 μg N m^-2 h^-1), GM (10.7 μg N m^-2 h^-1), SR + GM (11.7 μg N m^-2 h^-1), FM (15.5 μg N m^-2 h^-1), and CK (16.4 μg N m^-2 h^-1). Correspondingly, reduced total N₂O emissions were observed in the SR, GM and SR + GM treatments, with an average reduction of 39.0% (from 302 to 184 g N ha^-1) while increased N₂O emissions were from the GM and SR + GM treatments in the wheat growing season. Additionally, N₂O emissions were related to soil nitrate N content, microbial biomass and moisture. Overall, considering N₂O emissions, C and N inputs by plant residues and grain yield, the management of GM has the potential to reduce greenhouse gas emissions and improve soil C sequestration and soil fertility. These results emphasized the importance of legume green manure to wheat-fallow cropping systems.

Short-Term Assessment of Nitrous Oxide and Methane Emissions on a Crop Yield Basis in Response to Different Organic Amendment Types in Sichuan Basin

Agriculture’s goal to meet the needs of the increasing world population while reducing the environmental impacts of nitrogen (N) fertilizer use without compromising output has proven to be a challenge. Manure and composts have displayed the potential to increase soil fertility. However, their potential effects on nitrous oxide (N2O) and methane (CH4) emissions have not been properly understood. Using field-scaled lysimeter experiments, we conducted a one-year study to investigate N2O and CH4 emissions, their combined global warming potential (GWP: N2O + CH4) and yield-scaled GWP in a wheat-maize system. One control and six different organic fertilizer treatments receiving different types but equal amounts of N fertilization were used: synthetic N fertilizer (NPK), 30% pig manure + 70% synthetic N fertilizer (PM30), 50% pig manure + 50% synthetic N fertilizer (PM50), 70% pig manure + 30% synthetic N fertilizer (PM70), 100% pig manure (PM100), 50% cow manure-crop residue compost + 50% synthetic N fertilizer (CMRC), and 50% pig manure-crop residue compost + 50% synthetic N fertilizer (PMRC). Seasonal cumulative N2O emissions ranged from 0.39 kg N ha−1 for the PMRC treatment to 0.93 kg N ha−1 for the NPK treatment. Similar CH4 uptakes were recorded across all treatments, with values ranging from −0.68 kg C ha−1 for the PM50 treatment to −0.52 kg C ha−1 for the PM30 treatment. Compared to the NPK treatment, all the organic-amended treatments significantly decreased N2O emission by 32–58% and GWP by 30–61%. However, among the manure-amended treatments, only treatments that consisted of inorganic N with lower or equal proportions of organic manure N treatments were found to reduce N2O emissions while maintaining crop yields at high levels. Moreover, of all the organic-amended treatments, PMRC had the lowest yield-scaled GWP, owing to its ability to significantly reduce N2O emissions while maintaining high crop yields, highlighting it as the most suitable organic fertilization treatment in Sichuan basin wheat-maize systems.

K fertilizer alleviates N2O emissions by regulating the abundance of nitrifying and denitrifying microbial communities in the soil-plant system

Potassium (K) fertilizer additions can result in high crop yields of good quality and low nitrogen (N) loss; however, the interaction between K and N fertilizer and its effect on N₂O emissions and associated microbes remain unclear. We investigated this in a pot experiment with six fertilizer treatments involving K and two sources of N, using agricultural soil from the suburbs of Wuhan, central China. The aim was to determine the effects of the interaction between K and different forms of N on the N₂O flux and the abundance of nitrifying and denitrifying microbial communities, using static chamber-gas chromatography and high-throughput sequencing methods. Compared with no fertilizer control (CK), the addition of nitrate fertilizer (NN) or ammonia fertilizer (AN) or K fertilizer significantly increased N₂O emissions. However, the combined application (NNK) of K and NN significantly reduced the average N₂O emissions by 28.3%, while the combined application (ANK) of K and AN increased N₂O emissions by 22.7%. The abundance of nitrifying genes amoA in ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) changed in response to N and/or K fertilization, but the denitrifying genes narG, nirK and norl were strongly correlated with N₂O emissions. This suggests that N or K fertilizer and their interaction affect N₂O emissions mainly by altering the abundance of functional genes of denitrifying microbes in the soil-plant system. The genera Paracoccus, Rubrivivax and Geobacter as well as Streptomyces and Hyphomicrobium play an important role in N₂O emissions during denitrification with the combined application of N and K.

The Importance of Microbial Inoculants in a Climate-Changing Agriculture in Eastern Mediterranean Region

Climate change has gained importance due to its severe consequences for many aspects of life. Increasing temperature, drought and greenhouse gases affect directly or indirectly the productivity of agricultural and natural ecosystems as well as human health. The nutrient supply capacity of the soil is diminishing, while food requirements for the growing population are increasing. The ongoing application of agrochemicals results in adverse effects on ecosystem functioning and food chain. Now, more than ever, there is a need to mitigate the effects of agricultural activities on climate change using environmentally friendly techniques. The role of plant beneficial microorganisms on this global challenge is increasingly being explored, and there is strong evidence that could be important. The use of functional microbial guilds forms an alternative or even a supplementary approach to common agricultural practices, due to their ability to act as biofertilizers and promote plant growth. Application of microbial inocula has a significantly lower impact on the environment compared to chemical inputs, while the agricultural sector will financially benefit, and consumers will have access to quality products. Microbial inoculants could play an important role in agricultural stress management and ameliorate the negative impacts of climate change. This short review highlights the role of microbes in benefiting agricultural practices against climate-changing conditions. In particular, the main microbial plant growth-promoting functional traits that are related to climate change are presented and discussed. The importance of microbial inoculants’ multifunctionality is debated, while future needs and challenges are also highlighted.