Abstract
Nitrogen is the primary technical means responsible for food production increase, but on the other hand, wise management is needed because its excessive use can have a negative impact on the environment and on green leafy vegetable quality, such as that rocket. Rocket has the characteristics of accumulating nitrate in leaves with possible impacts on human health. In order to overcome this issue, researchers are focusing their attention on the use of alternative means, such as plant biostimulant application. The scope of this study was to assess the effect of legume-derived protein hydrolysate(LDPH) and tropical plant extract(TPE), combined with various doses of nitrogen (0 kg ha−1 non-fertilized; N0); 60 kg ha−1 (sub-optimal; N1); 80 kg ha−1 (optimal; N2); and 100 kg ha−1 (supra-optimal; N3)), in order to reduce nitrogen use, boost yield, and enhance the chemical and nutritional value of leaves without significantly accumulating nitrate. Both vegetal-based plant biostimulants enhanced plant growth, boosted the marketable yield (especially at N0 and N1 levels, by 38.2% and 28.2%, respectively, compared to the non-treated control), and increased the SPAD (Soil Plant Analysis Development) index and leaf pigments content, such as chlorophyll and carotenoids, especially in treated-LDPH rocket. The plant-based biostimulants also produced a major amplification in lipophilic antioxidant activity (+ 48%) and total ascorbic acid content (average + 95.6%), especially at low nitrogen fertilization levels, and maintained nitrate content under the legal European Comission limits.
Highlights
In the last decades, world food demand has been increasing due to global population growth.In order to satisfy this concern, growers around the globe are intensifying food crop production by increasing the use of resources, in particular, fertilizers [1]
legume-derived protein hydrolysate (LDPH)) on fresh yield of rocket were reported by Caruso et al [30] and by several authors on a wide range of fruit and leafy vegetables grown under greenhouse conditions, such as baby leaf lettuce [31], tomato [32], zucchini squash [33], and spinach [34]
Similar to the effects on rocket yield, the increase in leaf area index (LAI) recorded in the present work due to biostimulant application was more pronounced than those reported by Rouphael et al [34] and Caruso et al [30] on spinach and perennial wall rocket, showing a species-specific response [35], especially when the same two commercial plant biostimulants were tested
Summary
In order to satisfy this concern, growers around the globe are intensifying food crop production by increasing the use of resources, in particular, fertilizers [1]. A large number of crops, including leafy vegetables, require large quantities of nitrogen to reach maximal productivity, notwithstanding that high nitrogen availability is not correlated with higher quality of produce. Excessive nitrogen fertilization can trigger superfluous vegetative growth, making plants prone to pathogen. Uncurbed nitrogen presence usually induces nitrate accumulation in leafy vegetables to levels that exceeds the EU regulation limits [2,3]. Exorbitant nitrogen fertilizer rates can have deleterious impacts on human health [4,5,6] and on the environment through nitrate leaching into water resources and greenhouse gas emissions, such as nitrous oxide [7]. After intake into the human body, nitrate can be converted into nitrite, and the latter can cause methemoglobinemia or be used to produce the cancer-causing compounds nitrosamine and nitrosamide [8,9]
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