By: Andrea Colantoni & Sara Rajabihamedani
Department of Agriculture and Forest Sciences, University of Tuscia, Italy

Biostimulants have outstanding potential for sustainable development of the agricultural sector due to their ability to manage productivity and increase nutrient use efficiency in crop productions. The environmental benefits derived from the application of biostimulant products can be a complementary advantage for the policy expansion in biostimulant development and boost their approval among agrochemical industries and farmers.

Among various environmental indices, carbon footprint is a controversial indicator not only for companies dealing with the production chain, but also for policymakers. The term ‘product carbon footprint’ denotes the GHG emissions of a product across its life cycle - from raw materials extraction through production phase, distribution, consumer use and disposal/recycling. It encompasses the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), together with families of gases including hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs).

In chapter 11 of the published book “Biostimolanti per un’agricoltura sostenibile” Colantoni and Rajabihamedani (2019) reported about the environmental performance of microbial and non-microbial biostimulants on the production systems of watermelon and maize under both optimal and stressful conditions. The overall environmental impact of the crop production chain, following a cradle to gate perspective (plant cultivation phases up to harvest), and considering both the direct emissions of the different phases of the process and the indirect emissions associated with the production of raw materials as inputs are assessed. Different ways of managing the production chains for 1 ton of watermelon and maize are compared to identify the most sustainable way from an environmental perspective.

In the referenced study, the field trial on watermelon (Kalinova et al., 2014) involves the comparison of four experimental treatments: (T1) standard irrigation without inoculation with the arbuscular mycorrhizal fungi; (M1) standard irrigation and inoculation with arbuscular mycorrhizal fungi; (T2) reduced irrigation without inoculation with arbuscular mycorrhizal fungi; (M2) reduced irrigation and inoculation with arbuscular mycorrhizal fungi. The arbuscular mycorrhizal fungi Glomus clarum had been previously multiplied on greenhouse-grown maize for 8 weeks on a substrate composed of perlite and vermiculite. Maize roots colonized by Glomus clarum are applied as inoculation of watermelon seedlings. Seasonal irrigation volumes are 7010 m3 ha-1 for standard irrigation treatments (T1 and M1) and 5670 m3 ha-1 for treatments subject to water stress (T2 and M2).

The field trial on maize (Kaya et al., 2003) involves various combinations of soil fertilizers and leaf applications of biostimulant and fertilizer containing micronutrients. Treatment C1 applies quantity of macronutrient per hectare equal to 300 kg of N, 150 kg of P and 150 kg of K; treatment B2 applies a quantity of macronutrient per hectare equal to 200 kg of N, 150 kg of P and 150 kg of K and a foliar application of biostimulant based on vegetable oils and algae extracts at a dose of 5 L ha-1 mixed with a fertilizer containing 300 g of Mn, 200 g of Zn and 84 g of Cu per litre of the product and treatment C2 applies a quantity of macronutrient per hectare equal to 200 kg of N, 150 kg of P and 150 kg of K. In all three treatments, the foliar treatment of biostimulant and micronutrient-based fertilizer are carried out on the vegetative stage of 4-6 leaves.

The results show that the mycorrhization increases watermelon yield under standard irrigation (M1=176.4 t/ha), followed by un-mycorrhized plants under standard irrigation (T1=139.8 t/ha), and mycorrhized plants under reduced irrigation (M2=130.6 t/ha), and finally by un-mycorrhized plants under reduced irrigation (T2=88.0 t/ha). Water use efficiency (cubic meters of irrigation water for producing 1 ton of watermelon fruits) is highest in mycorrhized plants under standard and reduced irrigation (M1 = 39.8 m3 per 1 ton of fruits; M2 = 43.4 m3 per 1 ton of fruits) whereas in un-mycorrhized plants under standard (T1) and reduced irrigation (T2) are necessary 50.1 and 64.4 m3 per 1 ton of fruits, respectively. Moreover, mycorrhization reduces the total emissions of carbon dioxide equivalent per ton of marketable watermelon collected, in correspondence with both irrigation regimes. Figure 1 indicates the effect of the mycorrhization on CO2 saving concerning the witness (T1, T2) is more considerable in plants subject to water stress (27%) compared to those grown in conditions of optimal water availability (19%). The lowest absolute values ​​of CO2 equivalent emissions are obtained in the treatment that involves the mycorrhization of irrigated plants with standard irrigation (M1). The mycorrhization reduces the emissions of all inputs used due to an effect on increasing the production of marketable watermelon with the same input consumption. On the contrary, water stress increases emissions of carbon dioxide equivalent per ton of marketable watermelon due to a reduction in production compared to standard irrigation treatments.

Figure 1: Comparative results of carbon footprint in watermelon production

The results show that biostimulant treatment plus micronutrients increases maize yield (B2 =10.3 t/ha) while plants fertilized with the same amount of NPK of B2 treatment provide a grain yield of 8.98 t/ha (C2). Plants fertilized with the highest rate of nitrogen (300 kg/ha) without the biostimulant and micronutrients application give an intermediate yield (C1=9.87 t/ha). Nitrogen use efficiency is higher in plants treated with biostimulant and micronutrients (B2=19.4 kg of N for producing 1 ton of maize grains) in comparison with plants treated with mineral fertilizers without biostimulants and micronutrients (C1 = 30.4 kg of N for producing 1 ton of grain; C2 = 22.3 kg of N for producing 1 ton of grain). The results of greenhouse gas calculation in maize production under defined treatments reveal that the foliar supply of biostimulant and microelements (B2) reduces total emissions of carbon dioxide equivalent per ton of grain harvested compared to the treatment that provides the same contribution of fertilizer, but without foliar application of biostimulant and microelements (C2). Figure 2 shows the increase in the contribution of nitrogen fertilizer (C1) increases the total equivalent carbon dioxide emissions per ton of maize crop by 33% compared to the treatment that involves lower nitrogen inputs along with biostimulant and microelement-based fertilizer (B2); this increase is 15% compared to the treatment with a reduction in nitrogen quantity and without application of biostimulant and microelement-based fertilizer (C2).

Figure 2: Comparative results of carbon footprint in maize production

The findings confirm that the application of microbial and non-microbial biostimulants can entail a substantial reduction in greenhouse gas emissions. Therefore, prioritizing biostimulant application in farm management enables farmers to mitigate corresponding greenhouse gas emissions. This achievement indicated as the label of the carbon footprint is certainly a distinctive element to signify quality improvement of a product. Indeed, regarding existing marketing strategies focused on the environmental protection which affect consumptions of products considering environmental impact associated with the products, mitigation of carbon footprint corresponding to a product creates a considerable commercial opportunity.

Colantoni A., Rajabihamedani S., 2019. Biostimolanti e sostenibilità ambientale delle colture. In: Colla G. & Rouphael Y., editors. Biostimolanti per un’agricoltura sostenibile. 1st ed., Verona: L’informatore agrario; p. 143–153.

Kalinova St., Kostadinova S., Hristoskov A., 2014. Nitrogen use efficiency and maize yield response to nitrogen rate and foliar fertilizing. Bulgarian Journal of Agricultural Science, 20 (1): 178-181.

Kaya C., Higgs D., Kirnak H., Tas I., 2003.  Mycorrhizal colonisation improves fruit yield and water use efficiency in watermelon (Citrullus lanatus Thunb.) grown under well-watered and water-stressed conditions Plant and Soil 253: 287–292.