The experiment was developed in the agricultural plot B4-60 of the Majes Irrigation, Arequipa, Peru (16°21'11" S, 72°11'27" W), 1,410 meters above sea level (masl) during May and June 2022. The average temperature was 18.3 °C (maximum 27.2 °C and minimum 9.4 °C), with a relative humidity of 29% and no precipitation. The area's climate is classified as desert, characterized by extreme aridity. The soils in the area are classified as Entisols (MINAG 1975; Wei et al. 2021), with low organic matter (OM) (1.12%) and sandy-loam texture (88.14% sand, 6.61% silt and 5.25% clay).

Agro-industrial waste is currently perceived as an opportunity to reuse nutrients (Cantão et al. 2021), with benefits that were evidenced in this study. Analysis of the evaluated soil characteristics at the main effects and interaction levels revealed that the differences were significant for all the variables evaluated (Table 1). At the level of main effects, PGP applications significantly favored the content of OM, N, P, K, and CEC, increased pH, and significantly decreased EC compared to the absolute control. It has been described that in arid and semi-arid climates, the incorporation of biofertilizers improves soil physical, chemical and biological properties (Celestina et al. 2019; Lu et al. 2020; Liu et al. 2021) with environmental benefits, such as increased soil carbon, soil water holding capacity, net primary productivity and N content in plant tissues and decreased amount of surface runoff (Gupta et al. 2018; Gravuer et al. 2019; Hafez et al. 2020). In this trial, the initial OM content is typical of an arid zone, probably due to limited plant cover, lack of moisture and microorganisms (Wei et al. 2021); this initial condition made it possible for soil improvements to be significant despite the fact that bio-fertilizer applications were spotty.

Table 1

Regarding WB, the application of 100 mL L^-1 showed the highest values of EC with a significant difference from 50 mL L^-1 and the absolute control (Table 2), evidencing one of the most important limitations of the use of bio-ferments and organic fertilizers in arid and semi-arid zones: the high salt content (Lu et al. 2020).

Table 2

At the interaction level, it was observed that combined applications of PGP and WB decreased EC by 0.99 dS m^-1 concerning individual applications. The negative relationship of K with EC (R² -0.45; P=0.02) (Table 3) could explain why joint applications of PGP and WB caused less salinity than applying separately; the K contained in PGP may have a buffering effect on the elevated salinity of WB. Hafez et al. (2020) reported a similar result when applying vermicompost and biochar, which generated a combined effect by decreasing the detrimental effects of soil salinity and water stress in wheat plants.

Table 3

The results obtained in the crop evaluations showed significant differences in the effects of the treatments applied, both at the level of the main effects and interaction levels (Table 4). To analyze the effects of PGP and WB, the results are shown at the main effects level. The application of biofertilizers was found to improve crop features in comparison to absolute control, based on the benefits identified in the soil characteristics. (0 g PGP, 0 mL WB) (Figure 1). Regarding PGP doses, a strong directly proportional relationship was found with the variables leaf length (P<0.0001), chlorophyll (P<0.05), length (P<0.05), diameter (P<0.05), weight (P<0.05), DM (P<0.05), and TSS (P<0.05) of the root. In the case of WB, although correlations were positive in all cases (minimum R² 0.25 and maximum 0.38), they were not significant (Table 3). These results correlate fairly well with Ramírez and Pérez (2006) and Mali et al. (2018), who concluded that applying organic fertilizers and biofertilizers affects crop growth directly, development, and production.

Figure 1

Table 4

Plant size was significantly increased by the application of PGP (25 g kg^-1), with a difference of 6.53 cm in leaf length (Figure 1A), 24.45 g in fresh weight (Figure 1E), 1.77 cm in root length and 1.6 cm in root diameter (Figure 1D) over the control. Chlorophyll and TSS measurements showed the same trend: higher PGP concentration, higher chlorophyll (Figure 1B), and TSS (Figure 1F). These improvements would be related to the nutritional supply of MO, N, P, K, Ca, and Mg from the PGP.

For WB, the highest values were obtained with the 50 mL L^-1 dose, but when increasing to 100 mL L^-1, the leaf length (Figure 1A), chlorophyll index (Figure 1B), DM (Figure 1C), root length (Figure 1D), root weight (Figure 1E) and root TSS content (Figure 1F) decreased significantly (P<0.05). This could be attributed to the high salinity (EC) of WB impacting nutrient imbalance, uptake blockage, and even phytotoxicity (Lu et al. 2020), which is reflected in the negative correlation of crop variables and soil EC (Table 3). Ghosh et al. (2014) found that salinity adversely affected the growth of three radish varieties, an EC of 12 dS m^-1 limited root growth relative to an EC of 4 dS m^-1.

Plant growth had a strong positive correlation with the final edaphic content of OM (average R² 0.89; P<0.0001), P (average R² 0.96; P<0.0001), K (average R² 0.95; P<0.0001), pH (average R² 0.95; P<0.0001) and CEC (average R² 0.94; P<0.0001), characteristics that are beneficial to achieve better yields (Table 3). Fertilizers from agro-industrial waste are characterized by their contribution of OM, microorganisms, amino acids, macro and micronutrients, structural compounds, and biostimulants that accelerate plant metabolism (Saval 2012; López-Barreto et al. 2018; Lu et al. 2020), increasing photosynthetic rate, leaf area development, fresh and dry biomass, TSS (Ramírez and Pérez 2006; Liriano et al. 2020). In the case of PGP, it mainly provides N, which acts directly on growth, production of reserve substances, and their maturation; on the other hand, WB mainly provides K, which participates in protein synthesis, assimilation, and transport of substances from the leaves to the radish reserve organs (De Sousa et al. 2018; Rattin et al. 2022).

WB applications have been reported to range from 26,000 L ha^-1 (Canada) to 60,000 L ha^-1 (Wisconsin, USA) (Felli et al. 2012); however, under the arid climate conditions of this study, the 50 mL WB L^-1 dose presented the best results at the soil level and on radish characteristics. In the case of PGP, the results indicate that the higher the dose, the greater the benefits on the soil and on the agronomic yield of the crop (Table 2).

The results of this study underscore the potential for enhancing the agronomic performance of radish crops through the utilization of processed grape pomace and whey bio ferment. These have demonstrated efficacy in augmenting the availability of crucial macronutrients, including nitrogen, potassium, phosphorus, calcium, and organic matter. Such innovative approaches hold promise for optimizing crop productivity and sustainability in agricultural systems.