Plant biomass and water use efficiency of winter barley (Hordeum vulgare L.) under biosolid applications

Water scarcity is one of the most pressing issues and a limiting factor for agriculture, which consumes most of the water resources. Increased water use efficiency (WUE) will favorably improve agricultural crops' productivity (Manal & Aly 2008; Albrizio et al. 2010), and decide fodder and grain crop production. WUE as a parameter used to enhance plant conservation and production has been defined as the amount of carbon (C) assimilated as biomass or grain produced per unit of water used by the crop in a processes of controlling the gradients of CO₂ and H₂O (Hatfield & Dold 2019).

Perry et al. (2009) reported that WUE was calculated as a productivity term ‘output of crop per unit of water.’ To improve WUE in irrigation we need to raise the production per water unit (Howell 2001). As a result, numerous researchers investigate these items in many ways worldwide, focusing on the increase of WUE by the crops. To improve WUE, research should focus on selecting plants with high potential for utilizing available water and/or improving soil properties, particularly water-holding capacity.

Global biosolids production is predicted to be 100 million tons per year, with an annual rise of 175 million tons by 2050 (Wijesekara et al. 2017). Biosolids (Collivignarelli et al. 2019) are nutrient-rich organic compounds derived from waste water treatment plants that have processed residential wastewater. It is a slow-release organic fertilizer comprising vital plant nutrients and organic matter, providing not only improvements in soil fertility and physical properties but also leading to an improvement in biomass yield quantity and quality, as well as a means for its disposal methods. Recycling biosolids to agricultural land improves crop production economics. It has been shown that biosolid land application increases soil organic matter (Collivignarelli et al. 2019), as more than 75% of the total N in biosolids was in organic forms, and improve soil water-holding capacity as well as increase soil NO₃ leaching, and at the same time decreases soil bulk density (Khaleel et al. 1981; Binder et al. 2002; Arduini et al. 2018). The increasing demand for organic matter and the increasing amount of waste produced from municipal wastewater treatment plants lead many researchers to focus on biosolid application, and so publications show the potential of applying biosolid as a resource of organic matter for biomass production, adding organic matter, nitrogen (N), and phosphorus (P) (Silva-Leal et al. 2021) as well as adsorbent materials from non-traditional resources, especially biosolid land application, which improves crop productivity and increases the availability of ammonium, nitrites, and nitrates in the soil (Wang et al. 2017).

Biosolid application improves production (Tamimi et al. 2016), which enhances the plant vegetative growth pattern and significantly increase biomass production and improves soil fertility (Kumar et al. 2017; Wijesekara et al. 2017), and regulates and stimulates plant growth (Sigua et al. 2005; Guo et al. 2012). Biosolid applications were used for agriculture purposes as a soil amendment (Angin & Yağanoğlu 2009; Kumar et al. 2017; Wang et al. 2017; Dad et al. 2019; da Mota et al. 2019), and better soil aeration and water-holding capacity. Improvement of soil chemical properties as well as storing biosolids C in soils for a longer period and the enhancement of CO₂ emission (Wijesekara et al. 2017) was improved as it improves Carbon sequestration as a long-term storage of C in soil and greenhouse gas emission reduction. Further investigation is needed to evaluate its importance to quantify their potential for nutrient release properties or any other organic product. There is also the possibility of being a source that might contain pollutants, such as heavy metals, which indeed will limit their usage in croplands, so, it is necessary to consider environmental effects and their application in different agroecosystems (Sharma et al. 2017).

Barley grown under biosolid application was considered as a new fodder production resource, especially under poor soil and harsh environmental conditions. Barley as feedstock might be used in cereal farming production to get rid of this huge amount of waste as well as to increase income to farmers with low income. Barley (Hordeum vulgare L.) is a major cereal crop grown globally and considered the first crop that humans domesticated and as a very important resource for animal feed. It is grown throughout three seasons in a temperate climate and is known as being among the main field crops cultivated in the Mediterranean area, and it is well known for its better adaptation to diverse environmental conditions than most other cereals. Barley production was ranked globally as the fourth-most important crop among other grain crops. Therefore, this study aims to evaluate the significance and potential of barley to generate ultimate WUE and biomass production under different biosolid application rates.

Six levels (0, 2, 4, 6, 8, 10 ton/ha) of biosolid were distributed and mixed with the topsoil of 18 plots. Each plot was 10 m² in area (dimensions: 5*2 m). The experiment was organized based on a randomized completely block design with 3 replicates during three seasons (2014–2017). Data were statistically analyzed using analysis of variance (ANOVA) according to the statistical package MSTAT-C (Michigan State Univ., East Lansing, MI, USA). Probabilities of significance among treatments and LSD (p ≤ 0.05) were used to compare means among treatments. Multiple comparisons were made with SAS (SAS Institute 2011). Least significant differences (LSD) were used to separate means where treatments with LSD < 0.05 were considered significant. Biosolid rates were considered fixed effects, and replications were considered random effects.

Anaerobically digested biosolids (Collivignarelli et al. 2019) were pasteurized and dewatered in a process in which pathogens were treated. Biosolids were treated to reduce vector attraction through drying (National Research Council 2002; Gerba & Smith 2005). Treatment of biosolids involved keeping it under black plastic mulch after grinding. Biosolid was kept at 10% in moisture content C. Biosolid application rates were estimated to be 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 ton/ha. Control plots received no biosolids (0.0 ton/ha). Biosolids were weighed, distributed manually and evenly across the plot surfaces one week before sowing seeds with different rates depending on the treatments and the plot assigned to each treatment within the blocks. Biosolid quantities were mixed and incorporated in the upper soil surface layer (20 cm in depth). Field preparations for plant growth were applied for all plots, as pre-sowing treatments, soil preparation for seed germination and plant growth, and total amount of water was applied as scheduled by rainfall and supplementary irrigation, as needed and other land preparation practices were applied equally for both crops with the different treatments. A drip irrigation system was used to irrigate these crops with treated wastewater effluent as supplementary irrigation. Inline emitters (4 L h⁻¹) spaced 0.40 meters and 0.30 meters between laterals were used. Water meters were used to measure the quantity of water discharged to monitor the amount of water applied. Control plots were planted without biosolid application for both crops, and the same water quantity was applied.

The seeding rate for barley was 150 kg/ha. During the growing season and based on the total plant water requirement, we fixed the amount of water to be 350 mm, whereas an average value of 70 mm treated wastewater for all treatments was added as supplementary irrigation to fulfill the needed amount each year. Class A pan evaporation was used to account for the evaporated water. Barley was harvested as green forage at an age of 120 days.

Initial composite soil samples from the experiment site were taken before planting barley in a depth of 0–20 cm. Anaerobic digestion of biosolid involves biologically stabilizing sludge in a closed vessel to reduce the organic content, mass, odor, and pathogens under mesophilic temperatures (35 °C). Three years' fermented dewatered biosolid and treated wastewater sample were analyzed (Table 1). Chemical analysis results showed that trace elements and heavy metals in biosolid were found to be within norms.

Biosolid rates were fixed, and replications were random. Crop production was measured mainly by harvested above-ground biomass. Data were collected every season by the recurrent harvest of the total biomass produced, and then weighed in an accurate scale using the air-dry method to homogenize water quantity in the biomass obtained. Climatic conditions of the area follow the typical Mediterranean form with hot dry summers and humid winters. The daily values of temperatures and precipitation were not taken because all treatments were exposed to the same environmental stress. Precipitation and temperature did not significantly deviate from 25-year average records.

The provision of micronutrients and the improvement of soil microbiological activities were explained and ascribed to the clear beneficial effect of biosolids application to barley development and biomass yield (Elbl et al. 2014; Esperschuetz et al. 2016; Plošek et al. 2017). It was indicated that biosolid application increased the accumulated above ground dry matter of barley (Bouzerzour et al. 2002), and for sorghum (Akdeniz et al. 2006) as well as wheat (Khan et al. 2007). Thus, biosolids provide more benefits than mineral fertilizers (Silva-Leal et al. 2021), especially in semiarid conditions and in soils that are low in organic matter, which is a common feature of Mediterranean soil (Antoniadis et al. 2015).

Chemical analysis of biosolid obtained from the treatment plant shows that all heavy metals analyzed were within norms and are controlled (Table 1). Results showed that no concentration of nickel was recorded in water samples while the concentrations of cadmium, chromium, iron, and lead in water were recorded below the permissible limits set by WHO, while zinc and copper were recorded above the permissible limits and. pH of all water samples was recorded below the normal range while hardness and electrical conductivity of all water samples were recorded above the normal range set by WHO. Soil evaporation estimates showed that barley has the same rates of soil evaporation as usual in the cultivated area. Total evaporation during the growing season from December to the end of March was 223 mm.

The biomass production increased from 5.2 ton per ha for control plots (no biosolid) to 21.2 ton per ha at 10 ton per ha biosolid, which means that, barley biomass production was increased fourfold by adding biosolid to the soil, which was attributed to improved soil physical properties and increased soil fertility (Figure 1). Statistical analysis showed that the maximum dry biomass of harvested barley was attained at T5 (8 ton/ha of biosolid) with a dry biomass quantity of 21 ton/ha biomass yield as a mean value, and to be a significant production compared with 0, 2, 4, and 6 ton/ha biosolid. This increase was associated with the increase in leaf area development and improved light interception and biomass yield, especially with the application of biosolids as a natural fertilizer. While the highest biomass yield was obtained in T6 at a rate of 10 ton/ha of biosolids with a difference of 0.2 ton/ha biomass yield (21.2 ton/ha), which was not significant when compared with T5 (8 ton/ha biosolid) (Figure 1).

The present study shows the same trend for WUE, which was increased from 1.5 to 6.1 kg/m³ at (0 and 10 ton per ha biosolid respectively) applied to soil (Figure 2). Results show that the plant's production and dry biomass at a high biosolid application rate were high, whereas at a low application rate and with the control soil were relatively low. It was found that the performance of barley was improved as the rate of application of biosolids increased. Barley does not show a significant difference with the biosolid rate at 8 and 10 ton/ha, as it was for WUE (6% (A) and 6.04% (A) respectively), and for dry biomass was 21(A) and 21.2 (A) respectively. In conclusion, WUE as well as biomass production can be used as an indicator of plant growth and can be improved with an intermediate level of fermented biosolids.

There was a significant difference at p ≤ p0.05, according to ANOVA (Tables 2 and 4). It is well noticed that the addition of biosolid improves soil fertility due to increased availability of N and P. Statistical analysis shows that WUE (Tables 4 and 5) was more significant at T5 with 8 ton/ha of applied biosolid with the highest WUE rate with a mean of 6.003 and starts to be non-significant for T6 with 10 ton/ha applied biosolid with a mean of 6.04. From statistical analysis and to economically increase the productivity of barley (1 ton), the optimum amount of biosolid rate raises the biosolid concentration with a standardized b-coefficient of 0.556 using

Our results showed a potential application of biosolids to barley to improve agricultural performance. Results were compatible with what was reported by Azam & Lodhi (2001), in which they reported that the aboveground wheat crop components were responded positively to the addition of biosolid. This reflects an increment in the dry biomass by six times (5.98%). There were significant differences among different treatments in terms of the biomass dry weight, which has an implication on selection of the best crop production needed relative to the better biosolid application rate. Similarly, it was reported that, cowpea plant shows a significant effect of biosolid application through the increase in shoot dry weight (Karem et al. 2000).

Table 2's biomass ANOVA analysis shows it is scientifically different and the variation in biomass production values obtained of barley at different biosolid application rates [mean standard deviation (σ)] throughout the cultivation period. All biosolid treatments increased the biomass of barley by the addition of biosolid to the soil from 1.48 at 0.0 to 6.04 ton/ha at 8 and 10 ton/ha biosolid rate by 406%. Results of this study indicated that the biomass production in barley increased, which agreed with the findings of Weggler-Beaton et al. (2003), who reported that biosolid serves as a resource for essential nutrients. Increasing biosolid application rate significantly increases the total biomass production and WUE of barley. In our experiments, there was an increase in WUE, which was synchronized with the increase in biomass production in all treatments as an effect of biosolid application to the soil surface before cultivation. This was consistent with Blum (2005), who indicated that WUE can be improved if the biomass production is increased.

Table 4's ANOVA for WUE analysis shows it is scientifically different and the variation in WUE values obtained of barley at different biosolid application rates [mean standard deviation (σ)] throughout the cultivation period. All biosolid treatments increased the WUE of barley by the addition of biosolid to the soil from 1.48 at 0.0 biosolid rate to 6.04 ton/ha at 8 and 10 ton/ha of biosolid by 408%. The obtained results indicated an improvement in the WUE in response to biosolid application where positive effects were shown in all advance treatments.

Finally, from field observations we can say that there were no symptoms of chlorosis, necrosis, and toxicity in these crops during cultivation, especially in the above-ground plant parts. Plants grown under biosolid applications, especially with the increased application rates, showed healthier shape. Furthermore, we suggest performing additional studies to investigate the potential toxicity levels and heavy metal accumulation effects as well as the increase in nutrient availability (particularly phosphorus) and the effects on microbial content through extended and successive rounds of biosolid applications.

At T1–T5, there was a proportional link between biosolid application rates and biomass production and WUE, indicating this outcome. As a result, biosolid application rates will be insufficient to apply this quantity in our research area conditions.

After recalculating the application rate of biosolids based on the results obtained, we conclude that the significant amount of biosolid was obtained at 8 ton/ha for significant yield in terms of WUE and biomass production. On the other hand there is no significant differences seen in either WUE and biomass production at 10 ton/ha of applied biosolid.

Therefore, barley (H. vulgare L) can be economically cultivated using biosolid at 8 ton/ha as it can be harvested as feed and hay as a valuable source of forage for livestock production in most arid and semiarid regions because it can be an inexpensive and readily available feed source.

This work has been funded by the National Center for Agriculture Research and Extension, Jordan.

We have no pecuniary or other personal interest, direct or indirect, in any matter that raises or may raise a conflict with our duties as authors.

All authors listed have made a substantial, direct, and intellectual contribution to the work, and approved it for publication.

All relevant data are included in the paper or its Supplementary Information.