Effect of municipal biowaste derived biostimulant on nitrogen fate in the plant-soil system during lettuce cultivation

Abstract

A main concern of agriculture is to improve plant nutrient efficiency to enhance crop yield and quality, and at the same time to decrease the environmental impact caused by the lixiviation of excess N fertilizer application. The aim of this study was to evaluate the potential use of biopolymers (BPs), obtained by alkaline hydrolysis of the solid anaerobic digestate of municipal biowastes, in order to face up these main concerns of agriculture. The experimental trials involved the application of BPs (at 50 and 150 kg/ha) alone or mixed with different amounts (100%, 60% and 0%) of mineral fertilizer (MF). Three different controls were routinely included in the experimental trials (MF 100%, 60% and 0%). The effect of BPs on lettuce was evaluated by monitoring growth parameters (fresh and dry weights of shoot and root, nitrogen use efficiency), and the N-flux in plant-soil system, taking into account the nitrate leached due to over irrigation events. The activities of enzymes involved in the nitrogen uptake (nitrate reductase, glutamate synthase and glutamine synthase), and the nitrogen form accumulated in the plant tissues (total N, protein and NO3−) were evaluated. The results show that the application to the soil of 150 kg/ha BPs allows to increase lettuce growth and nitrogen use efficiency, trough stimulation of N-metabolism and accumulation of proteins, and hence to reduce the use of MF by 40%, thus decreasing the nitrate leaching. These findings suggest that the use of BPs as biostimulant greatly contributes to reduce the consumption of mineral fertilizers, and to mitigate the environmental impact caused by nutrients leaching, according to European common agricultural policy, that encourages R&D of new bioproducts for sustainable eco-friendly agriculture.

Enhancing Lettuce Yield through Innovative Foliar Spray of Biopolymers Derived from Municipal Biowastes

“…Prior to the present work, the biostimulant effect of BPs applied to soil in solid form was proven in different plant species [ 14 ], including also lettuce [ 7 , 12 ]. However, the foliar spray application of BPs in solution form had never been tested with food crops.…”

“…Fragalà et al [ 7 ] also showed that the application to the soil of solid BPs at a rate of 50 and 150 kg/ha greatly contributed to the ecofriendly sustainability of lettuce production by reducing the consumption of mineral fertilizers during lettuce cultivation, and by the consequent expected mitigation of the environmental impact caused by the mineral nutrient leaching. Although comparing the quantity of solid BPs used by Fragalà et al [ 7 ] and the spray application used in the present study for each plant may result in a very challenging calculation, some speculation suggests that the spray application allows the consumption of BPs to be reduced.…”

“…In broad terms, following the lettuce production guideline provided by Buturi et al [ 15 ], in order to achieve a good growth and maximize lettuce yields, farmers are used to cultivating around 50,000–60,000 plants per hectare, with a space between rows of 27–60 cm and space between lettuces in the rows of 18–30 cm. Considering the highest value of 60.000 lettuce plants/ha, the treatments with 50 kg/ha and 150 kg/ha [ 7 ] consume 0.83 g and 2.5 g of BPs powder per plant, respectively. In the spray application adopted in the present work, each lettuce was sprayed three times until the whole surface was wet, resulting in a consumption of 0.1 L of solution per plant.…”

“…MBW may be processed by anaerobic fermentation, yielding the production of biogas, anaerobic digestate and compost. Furthermore, digestate and compost may be converted into ecofriendly and value-added biobased products for multipurpose applications in various fields, including the agricultural area [ 7 ]. The agricultural applications of these biobased products to develop new sustainable products able to improve crop yields by acting as biostimulants and soil conditioners are attracting the interest of researchers and industry.…”

“…In this state-of-the-art context, the BPs were proven to exert a plausible biostimulant effect on the seed germination process at concentrations ranging from 1 to 5000 mg L −1 in cress and lettuce but showed no effect on tomato seeds [ 12 ]. Also, Fragalà et al [ 7 ] showed that the application of 150 kg/ha BPs to the soil allows the lettuce growth to increase, the nutrient use efficiency to be enhanced and the nitrogen lixiviation to be reduced by improving the nitrogen adsorption through the stimulation of the N metabolism and the protein accumulation, thus allowing a 40% reduction in the consumption of mineral fertilizers. The BPs OX were also tested for the seed germination of different species, showing a quite different behavior with respect to BPs as, at low concentrations (1–100 mg L −1 ), a positive effect on cress and lettuce was detected, while, at the highest concentration (5000 mg L −1 ), a phytotoxic effect was observed [ 12 ].…”