A preliminary assessment of growth regulators in agricultural: Innovation for sustainable vegetable nutrition

Agricultural Production today has to deal with different challenges. It has to increment production for a continuously increasing population, reducing the environmental burdens on the natural systems. In conventional agriculture, this is possible through the increase of inputs, especially nutrients, which, however, are responsible for the biggest part of emissions. It becomes more complicated though, adopting sustainable agricultural practices, to improve the quality and the quantity of agricultural production reducing the inputs use. Plant growth regulators are described in the literature for the significant role in securing crop management of modern agriculture. Therefore, this joint field experiment has been carried out on a pear orchard (Pyrus communis L. cv. Abate Fètel) in Emilia Romagna (Italy) by Fondazione Navarra and TIMAC AGRO Italia S.p.A., to test the “less for more” theory which consists in getting more and better agricultural produce using fewer inputs. Preliminary results of two consecutive years have confirmed our assumption as it was possible to substantially reduce the total fertilisation units applied, improving significantly quantitative and qualitative production indicators (i.e. flower and fruit density, fruit set (%), the average weight of fruits (g) and the total yield (t/ha)). Results have also shown a positive correlation between plant growth regulators and agronomic efficiency of pears.


Introduction
For decades plant nutrition has been under the scrutiny for the concerns of negative externalities generated from fertilisers' use in agriculture which emerged in the late 1960s [1]. Since a clear correlation has been found between plant nutrition, the eutrophication of surface water, the accumulation of nitrate in water bodies, and energy consumption. Even more recently, global studies have warned from unprecedented nitrate contamination of waters [2], which is creating irreversible direct damage to natural ecosystems and human health [3]. Further, the most universal forms of water quality deterioration in the world for the last decades is freshwater eutrophication from phosphorus loss [4,5].
Looking at the glass-half-full, the importance of fertilisers in agriculture has been extensively documented in the literature for over 150 years of research and experiments. The relevance of plant nutrition is fundamental for i) a normal growth and reproduction of the crops [6], ii) the average crop yield increase, and iii) to improve soil fertility [7]. However, the fertilisers' rates have reached the optimum in the developed world, and the new directions are to reduce them. This has been, for instance, one of the European Green Deal recommendations, expressed in the "Farm to fork strategy" 1 with the target to diminish by 2030 nutrients' losses by at least 50% and reduce fertilisers' use by at least 20% [8].
The focus of scientific innovation is currently on crop bio-stimulants to activate plant natural processes, which, according to the documented literature improve nutrient uptake and efficiency, crop quality and yields and build plants' tolerance to abiotic and biotic stressors [9]. A statutory definition of bio-stimulants has been provided in 2018 by the primary agricultural and food policy 3 rhizosphere, stimulates natural processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, or crop quality and yield".
Nevertheless, du Jardin [10] has identified in a review study seven different categories of biostimulants including i) humic and fulvic acids, ii) protein hydrolysates and other N-containing compounds, iii) seaweed extracts and botanicals, iv) chitosan and other biopolymers, v) inorganic compounds, vi) beneficial fungi and vii) beneficial bacteria. This emerging field of research is very promising and represents one of the fundamental management aspects of agro-systems to reach sustainable agriculture more resilient to climate change and able to feed the increasing population [11].
Therefore, the literature still needs to explore different research aspects related to the different bio-stimulants categories and their use in agriculture, to answer evolving enquiries arising with the technological advances in this field. In this context, this paper proposed to explore the category of seaweed extracts produced by TIMAC AGRO Italia, the Italian holding of the French multinational "Groupe Roullier" a world leader in the field of plant nutrition with the largest private research centre in Europe dedicated to plant physiology and nutrition and investing in these technologies.
The selection of the crop for trial has also its significance because pears constitute one of the major fruits of temperate climates, it is almost grown in the four corners of the world, reaching a total harvested area of 1.5 million hectares in 2018 and over 23.5 million tons of production [12].
The tree belongs to two species, the common pear cultivated mainly in Europe, the Near East, America and Australia and known as the European pear (Pyrus communis L.) given its European descendants; and the Nashi pear or Oriental pear (Pyrus pyrifolia) widely grown in Asia.

Material and Methods
The experiment was carried out in Emilia Romagna (Italy) on Abate Fetel orchard for the relevance of this cultivar in Italy, which happens to be the main producer of Pears in Europe [13] and the third world producer in terms of area harvest and second after China in terms of total production (Table 1a).
Despite the identified pear cultivars have superated 3,000 worldwide [14], in Italy, Abate Fetel (synonym Abbé Fetel) with other three cultivars (Conference, Beurrè Bosc, Doyenne du Comice), are the major cultivars commercially grown and producing more than 70% of the total annual production [15]. Further, the selection of Emilia Romagna has local importance given that this region is the first ranked in terms of harvest area, the production and the average size of fruit trees farms (Table 1b).

Case study
The experiment took place at the experimental field of "Navarra Foundation", a reference in agricultural knowledge for the Navarra agricultural technical institute and all farmers of the North-East of Italy, given its contribution in the development of the agro-food sector of the region through research, experiments, innovation and knowledge transfer.
The experimental field has a total area of ≈ 2.5 ha similar to the average size of fruit trees farms in the area and is located in Ferrara ( measured in a weather station in Ferrara ( Table 2) between 1961 and 1990 revealed a yearly average temperature of 13.1°C and rainfall around 689.5 mm [17], with considerable rain at high temperatures in the driest months (Figure 1).

Statistical analysis
The adopted experimental design was the randomised block design to minimise the effects of systematic errors. This design consisted of dividing the experimental block into three fertilisation treatments randomly selected within the block, with two replicated each made of 5 trees for each treatment. In total 60 trees were used for data collection and statistical analysis to determine whether mean scores differed significantly across the treatments. The measurements performed are divided into three pillars as follows: ➢ Flower density; ➢ Fruit density; ➢ Fruit Set; ➢ Total harvest (t ha -1 ) The field data collected have been statistically examined adopting the analysis of variance (oneway ANOVA) with a statistical probability ( − ≤ 0.05), and Tukey's HSD test which is a single-step multiple comparison procedure to find significantly different means.

Plants within a population often vary in the numbers of open flowers (flower density= =
) and the number of fruits (fruit density = = ). The correlation between those two indicators is calculated by the fruit set, a ratio defined as the transition from flower to young fruit (Fruit Set = = ( ⁄ ) × 100). These quantitative indicators, in the development process of any plant, are correlated to the rate of pollination [19] and they determine the final yield quantities (or the total harvest).

Field data for two consecutive years have demonstrated an increase of all quantitative indicators
under the TIMAC treatment compared to the conventional treatment and the control which generated the highest harvest for TIMAC treatment (Figure 2). Even though the numerical difference is considerable, the statistical significance is present only between the Control and TIMAC treatment. Complete statistical results are listed in a final table (Table 4).  8 22]. The role of plant regulators has been retained fundamental at this growth stage of plants to control fruit set [23] and to boost simultaneously the quantity and the quality of yields [24].
While the average fruit weight of different pear cultivars could vary according to the genetic characteristics [25], within the same variety, the fruit fresh weight is considered one of the most important quality indicators [26] which determines the value of the harvest on the market. The averaged results of this experiment confirm the results of An et al [23] and Bons and Kaur [24] and the next figure shows the qualitative and quantitative improvement of yields in the TIMAC treatment (Figure 3).  Nutrients agronomic efficiency (AE in kg kg -1 ) measures the technical performance of a crop.
Specifically, it estimates productivity improvement gained by the use of nutrient input. First, it has been used to evaluate nitrogen performance [27,28], to improve the environmental and economic performance of agriculture, after that it has been extended to include the performance of phosphorus nutrition [29], to reach a broader meaning and agronomic efficiency correlated inputs use to agro-system performance as an indicator for a transition to sustainable agriculture [30].
In this study, we calculated nitrogen efficiency, phosphorus efficiency and total nutrients' efficiency for the conventional fertilisation treatment and TIMAC treatment ( Table 5).

Results
showed that the efficiency of TIMAC treatment varied between 5.18 and 9.37 time higher compared to the conventional treatment (CF). The averaged results over two consecutive years of experiments have shown the role of plant growth regulators in the reduction of fertilisation units (FU) around 13%, which is an encouraging outcome towards the reduction of fertilisers according to the European "Farm to fork strategy" .
Results have also revealed a substantial reduction in P2O5 use (over 45%) which is a significant result impacting the AE of phosphorus, and participating in the global efforts to reduce and/or substitute the use of phosphate rock, a mineral fundamental for food security expected to end in a short lifetime [31,32].
The field experiment has confirmed the reviewed literature in Bons and Kaur [24] which assessed the positive correlation between plant growth regulators, quality and quantity of harvests, as the TIMAC treatment has improved both quality and quantity of the pears. Therefore, these results have disproved though results of Dicenta et al [33], which could not find a correlation between fruit set and the total harvest. Some questions that the research has raised and some future recommendations are mainly related to the importance of the balanced nutrition programme for sustainable management of crops. This has been defined by Liebig's law of the minimum which is a fundamental principle in plant nutrition, this research has partially demonstrated the importance of this law on the overall agronomic efficiency of the crop (AE has not been assessed in this study. Furthermore, it would be recommended to follow the framework suggested by El Chami et al [11] who proposed a methodology to reached sustainable agro-systems based on a life cycle study [34]. Therefore, future studies will be intensified and will address these questions and will implement the methodology suggested by El Chami et al [11], towards the European "Farm to fork strategy" and the United Nations sustainable development goals.