Integrated Application of Composted Agricultural Wastes, Chemical Fertilizers and Biofertilizers as an Avenue to Promote Growth, Yield and Quality of Maize in an Arid Agro-Ecosystem

Formulating new integrated plant nutrient management (IPNM) strategies in order to sustain crop production and protect the environment has become an important issue in the present agricultural system. Therefore, a field study was carried out in the two seasons 2016 and 2017 to formulate the best IPNM strategies for improving the growth, yield, and quality of maize grown in an arid agro-ecosystem. The IPNM comprised full-dose NPK (T1); composted agricultural wastes based on cow manure (T2), poultry manure (T3), and a mixture of sheep and camel manure (T4) as activators at the rate of 5 t ha−1 for each; half-dose NPK was combined with the mixture of the three types of composted agricultural wastes at the rate of 5 t ha−1 (T5) or 10 t ha−1 (T6), and a mixture of the three types of composted agricultural wastes at the rate of 10 t ha−1 (T7), 15 t ha−1 (T8), or 20 t ha−1 (T9), either with or without biofertilizers. The results showed that, as compared to T1, T6 or T9 significantly increased different growth, yield, and quality parameters of maize by 11.4–27.3%, 0.8–31.8%, and 4.6–17.2%, while T2 significantly decreased these parameters by 2.2–17.8%, 3.5–16.7%, and 4.5–9.4%, respectively. Seed inoculation with biofertilizers significantly increased different parameters of maize by 1.8–12.9%, compared to that of the non-inoculation seed treatment. Principal component analysis showed a strong relationship between different parameters of maize and treatments T5, T6, T8, and T9 with seed inoculation. Further, a significant and linear relationship was observed between different parameters of maize and the amount of N (R2 = 0.65–0.77), P (R2 = 0.58–0.71), and K (R2 = 0.63–0.73). These results indicated that any IPNM strategies that manage the NPK status and dynamics in the soil are a promising avenue for improving the growth and productivity of maize grown in the arid agro-ecosystem.


Introduction
Maize (Zea mays L.) is one of the most important cereal crops worldwide after rice and wheat. It is grown annually on nearly 197 million hectares in about 160 countries with a wide range of environmental conditions and agronomic management practices. It contributes nearly 35% (1148 million metric tons) to the global grain production. This production is projected to grow to 1315 million metric tons over the next decade to feed the increasing population [1]. Moreover, maize is a multipurpose crop; besides serving as human food, poultry feed, and livestock fodder, it is also a vital source of raw material for several industrial purposes [2]. However, maize consumes mineral fertilizers voraciously and exhausts a considerably large amount of nutrients during the growing season as compared to other cereal crops [3]. For instance, in the high-yielding regions, rate of poultry manure increased. Rahimabadi et al. [23] also found that, as compared with non-composting treatment, the grain yield (GY) of rice increased by approximately 800 kg ha −1 by the application of 30 t ha −1 of cow manure, while TGW was decreased at both the application rates of 15 and 30 t ha −1 of cow manure. In contrast, Khan et al. [24] found that, as compared with the recommended dose of NPK for maize, the application of 20 ton ha −1 of dairy manure resulted in a decrease in the GY, biological yield (BY), and TGW of maize by 1. 5,18.1, and 4.6%, respectively, while the harvest index increased by 23.6%. Mahmood et al. [25] also found that the treated maize crop with full-dose NPK increased TGW by 5.3, 8.8, and 4.0%, GY by 8.8, 18.7, and 4.9%, and BY by 11.5, 13.7, and 5.9%, compared with the treatment treated with sheep manure at a rate of 15 t ha −1 , farmyard manure (FYM) at a rate of 16 t ha −1 , and poultry manure at a rate of 13 t ha −1 , respectively. Meanwhile, the highest values for the three plant parameters were obtained with the treatments that treated with a combination of a half dose of NPK and half application rate of any organic manure source. However, based on a meta-analysis of long-term trials in Europe, Edmeades [26] reported that when the FYM amendment was balanced with the chemical fertilizer to have the same NPK rates applied, the chemical fertilizer treatment gave slightly greater yields than the combination of chemical fertilizer with FYM manure treatments after 10 years. Considering the aforementioned facts, the key benefits of organic compost in an agricultural cropping system largely denuded on several complex factors, including the types of plant, the different characteristics of soil and organic compost, the source of organic compost and its application rates, timing, and methods, the composition of the organic compost, and environmental conditions.
It is well known that long-term application of chemical fertilizers will eventually lead to a significant decrease in soil biological properties and weaken the soil microbial communities. Therefore, the integrated use of chemical fertilizers and organic compost along with biofertilizers is also a promising approach to sustain crop production practically under intensive cropping cultivation and arid conditions [10,27,28]. Phosphorus solubilizing and nitrogen-fixing bacteria are examples of biofertilizers. When these bacteria are applied as seed or soil inoculants, they participate in nutrient cycling and enhance the availability of nutrients for plant growth, which ultimately show positive impacts on crop production [29]. It has been shown that the application of bio-inoculants containing P-solubilizing bacteria and N-fixing bacteria have been proven to increase crop yield by 20-30% and are able to minimize P fertilizer by 25% to 50% [27,30,31]. In this regard, microbial inoculants have paramount significance in the IPNM strategy by offering enormous economic and environmental advantages.
Given the potential agronomic, economic, and environmental benefits of the integrated use of chemical fertilizers, organic compost, and biofertilizers, it is important for researchers to continue seeking ways to establish quantitative benchmarks for IPNM strategies in intensive cropping cultivation under arid conditions. This can, thus, be a justification on whether to replace the chemical fertilizers that are somewhat detrimental to the environment with organic compost and biofertilizer in improving soil fertility and, hence, increase crop production. Within this context, the main objective of this study was to investigate the effect of different IPNM practices on the growth, grain yield, yield components, and quality of maize under arid conditions. In the IPNM practices, the full dose of NPK, different types of organic composts, and a mixture of different organic composts at different rates either alone or in combination with a half dose of NPK were investigated in a two-year field experiment.

Site and Soil Descriptions
Field experiments were conducted during two consecutive summer seasons (2016 and 2017) at the experimental research farm of the College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia. The experimental farm is located at 24 • 25 N latitude, 46 • 34 E longitude at an altitude of 600 m above sea level. The climate condition was arid, with hot and dry summer seasons and an annual mean rainfall of 32.0 mm. During the period of experiments (from May to October), the minimum and maximum temperature ranged from 21.2 to 29.3 • C and 35.3 to 43.6 • C, respectively.
The different basic physical and chemical properties of the experimental soil were determined based on one composite soil sample collected before the start of the experiment from the soil layer approximately 0-30 cm deep [12]. These properties are presented in Table 1. The different physiochemical soil properties were determined using the method described by Okalebo et al. [32].

Land Preparation, Cultural Practices, Experimental Design, and Treatments
The experimental field was used for a wheat-faba bean/maize cropping system, while the preceding field crop was wheat during both seasons in this study. Additionally, chemical fertilizer has been a common practice for the last 25 years preceding this study. The residual of wheat crops was cleared manually, thrashed and removed from the experimental field before land preparation for sowing maize crop. In the first season, the land was prepared to achieve the normal seedbed by plowing the soil to a depth of 40 cm three times followed by disk harrowing once to the 10 cm depth shortly before sowing. After leveling the soil, the experimental field was divided into 3 main blocks with a size of 72 m × 4 m for each and a 1 m buffer zone between them. Thereafter, each block was divided into 18 subplots with a size of 3m × 4 m for each and a 1 m buffer zone between them. The different IPNM treatments were distributed randomly on the subplots in the first season. The experiment in the second season was carried out in the same place as the first season. As the IPNM treatments differ in their types of organic compost and amounts, they were applied to the same subplots of the first season. Therefore, the subplots in the second season were manually tilled to a depth of 20 cm when organic composts were incorporated into the soil. At 1 day before sowing in both seasons, the organic compost was spread evenly on the soil surface in each subplot and thoroughly mixed with the top 20 cm of the soil using a hand-held hoe.
In each subplot, the seeds of a hybrid maize cultivar (Pioneer SC 30N11) were sown manually in five rows spaced 60 cm apart, with two seeds sown per hill and 20 cm between hills. The seeds were sown on the fifth and tenth day of May 2016 and 2017, respectively.
After crop establishment, the plants were hand-thinned to one plant per hill, which gave a plant population of 83,333 plant ha −1 . The irrigation water was applied using a lowpressure surface irrigation system. The maize plants were irrigated about 12 times during the growing season, with the total amount of irrigation water applied being approximately 690.0 mm ha −1 . Weed control was carried out as needed with hand hoes.
The experiment was laid out in a randomized complete block design with a split-plot arrangement using three replications. The nine IPNM treatments were assigned in the main plots and the two biofertilizer treatments (seed inoculation and non-seed inoculation) were allocated in the subplots. The different IPNM strategies included the sole application of a full dose of NPK (T1); sole application of composted agricultural wastes based on cow manure (T2), poultry manure (T3), and the mixture of sheep and camel manure (T4) as activators at the rate of 5 t ha −1 for each; half-dose NPK combined with the mixture of the three types of composted agricultural wastes at the rate of 5 t ha −1 (T5) or 10 t ha −1 (T6); and the mixture of the three types of composted agricultural wastes at the rate of 10 t ha −1 (T7), 15 t ha −1 (T8), or 20 t ha −1 (T9).
The full recommended NPK dose was 150-90-60 kg ha −1 of N, P 2 O 5 , and K 2 O, respectively, which was selected based on recommendations from the Saudi Arabian Ministry of Environment, Water, and Agriculture. The NPK nutrients were applied through ammonium nitrate (33.5% N), calcium superphosphate (15.5% P 2 O 5 ), and potassium chloride (60% K 2 O), respectively. The entire amount of phosphorus and potassium fertilizers was applied to the soil prior to the planting of maize. The nitrogen fertilizer was applied in three equal doses, with one dose at sowing, at the knee-height stage, and at the pre-tasseling initiation stage.
The seeds of treatment treated with biofertilizer were coated with nitrogen-fixing bacteria (Azotobacter spp.) and phosphate-dissolving bacteria (Pseudomonas sp.). The seeds were first sterilized with 1% sodium hypochlorite for 5 min, washed many times with sterilized water, and then soaked for 30 min in the bacterial suspension containing the effective microorganisms of two bacterial strains at a concentration of 2 × 10 8 CFU mL -1 for each bacterial inoculant strain and Arabic gum as an adhesive agent. The bacterial suspension was used at a final concentration of 0.05 mL g −1 of seed. Then, the seeds were spread away from the direct sun for two hours prior to sowing.

Preparing the Different Types of Organic Compost
The three types of organic compost were prepared by co-composting different plant residues (wheat straw and palm leaves) and household wastes with 10% of one of the three types of organic manure (poultry, cow, and mixed sheep and camel manures) as activators for 120 days. The different wastes were collected from agricultural residue and a local fruit and vegetable market, air-dried for several days, and then mechanically crushed into smaller size particles (15-40 mm). Next, the different crushed wastes were thoroughly mixed together, divided into three equal piles, and each pile was mixed with 2% CaCO 3 and 10% of one of the three types of selected organic manures. To speed up the decomposition process and enrich compost quality, each pile was inoculated with a mixture of 1 × 10 8 CFU/g bacteria of Streptomyces aurefaciens, Trichoderma viridie, T. harzianum, Bacillus subtilis, B. licheniformis (1 L ton −1 ). Each pile was prepared as static, triangular-shaped profiles with approximate dimensions of 10 m × 5 m × 1.50 m (length × width × height). During the composting period, each pile was mechanically turned upside down and watered weekly during the first month to ensure adequate aeration conditions, while subsequently, the process was performed two times each month. After 120 days of composting and for each composting pile, different samples were collected from places located at equal distances from each other being on the top, middle, and bottom of the pile and then the three samples were mixed together precisely to create one composite sample. This composite sample was dried at 105 • C for 12 h and then ground into a fine powder. This ground sample was used to determine organic matter (OM) and total organic carbon (TOC), N, P, and K. The loss-on-ignition procedure was used to determine OM [33]. TOC was assayed using a Vario Max CNS elemental analyzer. Total N was determined using the Kjeldahl digestion method, whereas P content was analyzed using the vanadium-molybdenum method. The content of K was analyzed using flame photometry. The total amount of OM and OC, and contents of N, P and K through the sole application of three different types of organic compost or mixture of three types of compost at the rate of 10 ton ha −1 is presented in Figure 1. Based on the analysis of organic compost, the amount of N, P, and K for each treatment of a different IPNM is shown in Figure 2.

Biometric Measurements
At the tasseling (VT) growth stage, five plants from each subplot were randomly selected and their height (PH), stem diameter (SD), dry weight (DW), and leaf area (LA) were measured. Plant height was measured as the distance from the soil surface to the end of the tassel. All the leaves from 5 plants were separated and run through an area meter (LI 3100; LI-COR Inc., Lincoln, NE, USA) to calculate the leaf area. All parts of the 5 plants were dried in an electrical oven at 70 • C for 72 h and then weighed to obtain the total dry weight.
At physiological maturity (R6) growth stages (about 140 days after sowing), ten ears from each subplot were randomly selected to determine the ear length (EL), the number of rows per ear (NRE), and the number of grains per ear (NGE). A hundred grains were selected from the seed lot of each subplot and weighted to determine the 100-grain weight (100-GW). The three internal rows in each subplot, each 4 m in length, were harvested and air-dried, and then weighed to record the biological yield (BY). Next, all cobs were separated, threshed manually, and grains were weighed to obtain the grain yield (GY) after adjusting the water content of grain to 15.5%. After the BY and GY were expressed as ton ha −1 , their values were used to calculate the harvest index (HI) = BY/GY.
A random sample was selected from the seed lot of each subplot and ground into a fine powder. The total N percentage was determined using the Kjeldahl digestion method and multiplied by 6.25 to calculate the grain protein (Pro) content, whereas the grain oil content (%) was determined using a Soxhlet apparatus according to the method described by the Association of Official Analytical Chemists [34].

Data Analyses
The impacts of different IPNM and seed inoculation treatments, as well as their interaction on the different growth, yield, and quality parameters of maize, were examined based on analysis of variance (ANOVA) that is appropriate for a randomized complete block design in time with split-plot design arrangement and three replications. The IPNM treatments were assigned as the whole plot, seed inoculation with biofertilizer as subplots, and replicates as blocks. Prior to statistical analysis, data were tested for homogeneity of variance and normality using Bartlett's and Shapiro-Wilk tests, respectively. As there is a homogeneity of error variance for different parameters, the data were analyzed for each season and over two seasons. The IPNM, seed inoculation, and their interaction were kept as fixed effects, whereas replication, season, and their interaction were random effects. A Duncan's multiple range test at the 0.05 level of probability was used to separate the significant differences between the mean values of different treatments. Pearson s correlation coefficient (r) matrix was used to test the relationship between all growth, yield, and quality parameters of maize. To provide a comprehensive picture of the relationships between all parameters of maize and different IPNM treatments, principal component analysis (PCA) was performed to more easily visualize this relationship. Linear regression analysis was performed to develop the production functions of the relationship between different parameters of maize and the amount of N, P, and K. Statistical analyses and correlations were performed using SPSS20.0 software (IBM Inc., Chicago, IL, USA). The Sigma Plot (v. 11.0; SPSS, Chicago, IL, USA) was used to analyze and draw the relationship between different parameters of maize and the amount of N, P, and K. The PCA was analyzed and the biplot was drawn using the XLSTAT statistical package software (vers. 2019.1, Excel Add-ins soft SARL, New York, NY, USA).

Analysis of Variance (ANOVA)
The ANOVA analysis (Table 2) showed that the IPNM fertilizer (IPNM) and seed inoculation (In) had a significant main effect on all growth, yield, and quality parameters of maize in the first and second seasons as well as in the combined two seasons. The In by IPNM interaction had significant effects on LA, NGE, GY, HI, and Pro content in the two seasons and combined two seasons as well as on SD and BY in the second season (Table 2). Seasons (S) had a significant main effect on all parameters except SD. The PH, SD, LA, BY, GY, and HI were significantly affected by the interaction of IPNM and S; however, In by S interaction effects were not found for any parameter (Table 2). Furthermore, the three-way interaction effects of IPNM, In, and S were only found for SD, LA, NGE, and GY (Table 2). Table 3 shows the effect of different IPNM treatments on different parameters of maize in each growing season and combined two seasons. In general, T6 (a combination of 50% recommended NPK dose with the mixture of the three types of organic compost at a rate of 10 t ha −1 ) and T9 (mixture of the three types of organic compost at a rate of 20 t ha −1 ) had the highest values for the different parameters, whereas the T2 treatment (composted agricultural wastes based on cow manure at 5 t ha −1 ) had the lowest ones. Compared with the full recommended NPK dose (T1), the values of different growth, yield, and quality parameters of maize for T6 and T9 significantly increased by 11.4-27.3%, 0.8-31.8%, and 4.6-17.2%, while these values for T2 treatment significantly decreased by 2.2-17.8%, 3.5-16.7%, and 4.5-9.4%, respectively ( Table 3). The T5 (a combination of 50% recommended NPK dose with the mixture of the three types of organic compost at a rate of 5 t ha −1 ) and T8 (mixture of the three types of organic compost at a rate of 15 t ha −1 ) had comparable values for almost all parameters and the values of both treatments were still significantly higher than that of the T1. The values of most parameters for T7 treatment (mixture of the three types of organic compost at a rate of 10 t ha −1 ) were occasionally comparable to those of the T1 (Table 3). The treatments that received the sole application of organic compost (T2, T3, and T4) always exhibited the lowest values for all parameters, with the Duncan groupings in decreasing order of these parameters were T2 < T3 (composted agricultural wastes based on poultry manure at 5 t ha −1 ) ≈ T4 (composted agricultural wastes based on the mixture of sheep and camel manure at 5 t ha −1 ) ( Table 3).

Impacts of Biofertilizer Treatments on Growth, Yield, and Quality Parameters of Maize
The data regarding seed inoculation with biofertilizers' effects on the growth, yield, and quality parameters of maize in each growing season and combined two seasons are shown in Table 4. The results reveal that seed inoculation with biofertilizers always significantly increased all different parameters of maize more than non-seed inoculation treatments. Regardless of the different IPNM treatments, seed inoculation with biofertilizers increased different parameters of growth, yield, and quality of maize by 4.4-10.9%, 1.8-12.9%, and 5.7-7.9%, respectively, compared to that of the non-seed inoculation (Table 4).

Impacts of Interaction between IPNM Treatments and Biofertilizer on Growth, Yield, and Quality Parameters of Maize
The combination of IPNM treatments and seed inoculation had a significant effect on LA, NGE, GY, HI, and Pro content in both seasons and combined analysis of two seasons, as well as SD and BY in the second season (Table 2). Generally, under each IPNM treatment, seed inoculation with biofertilizers always exhibited a more considerable improvement in these parameters than those the non-seed inoculation, with a few exceptions (Figure 3). The highest values for these parameters were obtained when the seed inoculation treatment was combined with T6 and T9 treatments, followed by T5 and T8 treatments, while the lowest values were recorded when the non-seed inoculation treatment was combined with T2, T3, and T4. Additionally, the combination of non-seed inoculation with T6, T8, and T9 treatments resulted in a remarkable increase in these parameters or at least achieved comparable values to that of the combination of seed inoculation with T1 treatment (Figure 3). The interaction between IPNM treatment and season had considerable effects on three growth parameters (PH, SD, and LA) and three yield parameters (BY, GY, and HI) (Table 1 and Figure 4). In general, all IPNM treatments exhibited higher values for these parameters in the second season than those of the first season. Compared with the first season, the values of PH, SD, LA, BY, GY, and HI for IPNM treatments in the second season increased by 2.9-15.1%, 1.8-21.6%, 5.6-13.1%, 1.5-7.3%, 5.6-21.1%, and 0.1-15.5%, respectively ( Figure 4). The three-way interaction between season, IPNM, and seed inoculation was significant for two growth parameters (SD and LA) and two yield parameters (NGE and GY) ( Table 2 and Supplementary File S1). Generally, the interaction of T6 or T9 with and without seed inoculation gave the highest values for these parameters in both seasons, followed by T5 and T8. However, the lowest values for these parameters were achieved when T2, T3, T4 interacted with non-seed inoculation, especially in the first season (Supplementary File S1).

Correlation Analysis
Pearson's correlation coefficients between all parameters over two seasons are summarized in Table 5. All parameters showed strong and positive correlations with each other (r = 0.79-0.98). Furthermore, all parameters also showed the highest significant positive correlation (r = 0.88-0.99) with GY and BY. The contents of Pro and oil were strongly and positively correlated with growth (r = 0.90-0.98) and yield (r = 0.82-0.98) parameters (Table 5).

Comprehensive Evaluation of the Relationship between IPNM Strategies and Different Parameters of Maize by Principal Component Analysis (PCA)
The results of PCA, including factor loading matrix, eigenvalues, variance percentage, and cumulative percentage for all parameters are presented in Table 6. The PCA generated two main factors (eigenvalue > 1) which explained 96.54 of the total variance of the parameters of maize under different IPNM treatments. The first and second factors accounted for 49.34% and 47.20% of the total variability, respectively. The first factor had a strong positive loading for all parameters (factor loadings > 0.75), with the exception of NGE, HI, and NGR, where the first factor had a moderate positive loading for the first two parameters and a weak loading for the third parameter ( Table 6). The second factor had a moderate positive loading for all parameters, with the exception of NGR, HI, and Pro contentment, where the second factor had a strong positive loading for the first two parameters and a weak loading for the third parameter (Table 6). Figure 5 illustrates the relationships between maize parameters and different IPNM treatments through the biplot of PCA. The first two components (PCAs) explained 49.34% and 47.20% of the total variability between all parameters, respectively ( Figure 5).
Based on the biplot of the PCA, the different IPNM treatments were divided into four groups. The first group included T5, T6, T8, and T9 with seed inoculation and leaned toward the positive region of PC1 and PC2. The different parameters of maize were significantly correlated with this group. The second group included T5, T6, T7, T8, and T9 with non-seed inoculation and was situated along the negative region of PC1 and positive region of PC2. The third group included T1, T2, T3, T4, and T7 with seed inoculation and was situated along the positive region of PC1 and negative region of PC2. The last group, which leaned toward the negative region of PC1 and PC2, included treatments T1, T2, T3, and T4 with non-seed inoculation. The last three groups of IPNM do not show any relationship with the different parameters of maize ( Figure 5).

Production Function
Based on the amount of N, P, and K that was calculated for each IPNM treatment, which shown in Figure 2, various equations were evaluated to determine the relationship between the amount of N, P, and K and the different measured parameters of maize. The

Production Function
Based on the amount of N, P, and K that was calculated for each IPNM treatment, which shown in Figure 2, various equations were evaluated to determine the relationship between the amount of N, P, and K and the different measured parameters of maize. The response function between the different maize parameters (growth, yield, and quality parameters) and the amount of N, P, and K was linear and positive except for HI, where the function was quadratic ( Figure 6). Generally, different parameters exhibited a higher relationship with amount of N and K than the amount of P. The amount of N and K exhibited strong relationships with the four growth parameters (R 2 ranged from 0.70 to 0.75), BY and GY (R 2 ranged from 0.70 to 0.75), and quality parameters (R 2 = 0.75), while they exhibited weak to moderate relationships with yield components (EL, NRE, NGE, NGR, and 100-GW) and HI (R 2 ranged from 0.47 to 0.68). A weak to moderate relationship was found between the amount of P and different maize parameters (R 2 ranged from 0.44 to 0.66), with the exception of DW (R 2 = 0.69) and Pro content (R 2 = 0.71), which had a strong relationship with the P amount ( Figure 6).
The linear regression equations, which represent the increase in each parameter for each unit increase in the amount of N, P, or K, are presented in Table 7. Based on these equations, the increment in LA, DW, BY, GY, Pro content, and oil content were 5.22 cm 2 , 0.17 g, 17.2 kg, 10.8 kg, 0.005%, and 0.010% for each unit increase in N amount, 11.61 cm 2 , 0.38 g, 38.2 kg, 24.1 kg, 0.011%, and 0.022% for each unit increase in P amount, and 17.09 cm 2 , 0.55 g, 55.5 kg, 25.3 kg, 0.016%, and 0.032% for each unit increase in K amount, respectively (Table 7). The linear regression equations, which represent the increase in each parameter for each unit increase in the amount of N, P, or K, are presented in Table 7. Based on these equations, the increment in LA, DW, BY, GY, Pro content, and oil content were 5.22 cm 2 ,  Table 7. Regression equations between selected maize parameters (Y) and amount of N, P, and K.

Parameters Equation Increase in Each Parameters for Each Unit Increase in Amount of N, P, and K
Leaf area (cm 2 plant −1 ) Y = 6.531 N + 5471.

Discussion
The results from the analysis of variance (Tables 2 and 3) revealed that the different growth, yield, and quality parameters of maize were significantly affected by different IPNM treatments, with the treatments T6 and T9 induced a considerable increase in different parameters of maize over the treatments T1 or T2, T3, and T4. The treatments T5 and T8 also improved the most measured parameters of maize compared to the T1, T2, T3, and T4 treatments (Table 3). These results indicate that the integrated use of a mixture of different organic composts with a high application rate (as shown with T8 and T9) or the integrated use of a half dose of NPK with half the application rate of organic compost (as shown with T6) could be a better IPNM strategy for maintaining the growth, production, and quality of maize crop at an acceptable level, especially in poor soil quality under arid conditions. These results are also supported by other previous studies, who reported that the highlevel application amount of organic composts or combined use of organic composts and chemical fertilizers is an effective IPNM strategy and is being promoted as an alternative to the intensified use of chemical fertilizers to enhance the growth, production, and quality of several field crops, particularly under arid conditions [8,12,21,[35][36][37][38][39]. The significant increase in different parameters of maize in response to the high application rates of organic composts or to the combined application of organic and chemical fertilizers over the sole application of chemical fertilizer may be attributed to several reasons, including the fact that the organic matter in organic composts have been reported to have multiple positive effects on soil fertility by improving several biological and physiochemical soil characteristics [12,22,40,41]; the different nutrients of organic composts are released slowly into the soil at a consistent rate, which gradual and continuous supply of available nutrients for plants, along with a reduction in nutrient losses through leaching, volatilization, and denitrification [36,[41][42][43]; organic composts stimulate the soil organism community structure, which not only enhance the availability of different nutrients for plant, but also produces different phytohormones, which further augment plant growth and health [21,40,44]; organic composts have the ability to reduce the pH of calcareous soil, which has a positive indirect effect on phosphorus availability [45,46]. In addition, the combined application of organic and chemical fertilizers appears to be good a IPNM practice, which may be due to the fact that this combination improves the synchronization and synergism between nutrients provided by both sources and plant nutrient requirements during the full growth cycle. The chemical fertilizer is known to be taken up by plants immediately after application and, therefore, provide nutrients for the plant for a short period and rapidly enhance crop growth, but on the other hand, the slower release of nutrients from organic fertilizers leads the fertilizer to provide the plants with its nutrient requirements in the long run and in the critical yield-forming period [10,47]. However, applying chemical fertilizers alone results in the rapid loss of soil organic carbon, which causes a considerable deterioration in soil fertility and quality in the long term [48]. Therefore, the IPNM practices that included the combined use of chemical and organic compost fertilization or high application rates of organic composts gave the best results for plant growth and final yield in this study over NPK (Table 3). In a study where the effect of the combined application of chemical and organic fertilizers on maize performance was evaluated, Negassa et al. [49] found that, relative to the chemical fertilizer alone, the integrated use of organic composts along with chemical fertilizers increased the GY by 35%. Adeyemo et al. [22] also reported that the different yield attributes of maize were gradually increased by increasing the application rates of organic composts. The findings of these studies and our results are confirmed by a biplot of the PCA that revealed the relationships between maize parameters and different IPNM treatments ( Figure 5). Interestingly, all measured parameters of maize were closely related to T5, T6, T8, and T9 treatments, wherein these IPNM treatments were treated with the combined application of chemical fertilizers and organic compost (T5 and T6) or treated with the high application rate of organic composts (T8 and T9) with seed inoculation. These results confirm that organic fertilization is an important IPNM practice in the maize production system, particularly in arid and semiarid conditions, where the scarce rainfall, high temperature, and intensive cultivation systems are the most dominant factors that usually led to progressively deteriorated soil fertility and crop production. Organic composts have been shown to have noticeable qualitative and quantitative positive effects on several soil characteristics, and therefore enhance the growth and production of maize.
The analysis of variance also revealed that the interaction of IPNM and S had significant effects on some plant parameters such as PH, SD, LA, BY, GY, and HI (Table 2). Averaged over all IPNM treatments, the values of these parameters in the second season were increased by 4.5-10.7%, when compared with their values in the first season ( Figure 3). Interestingly, the treatments treated with a mixture of the three types of organic composts alone at the high application rates (T7, T8, and T9) or in conjunction with 50% NPK (T6) increased the GY in the second season by 15.5, 12.1, 17.5, and 13.3%, respectively, compared with those of GY in the first season. However, the GY of T1 treatment in the second season increased by 7.6%, compared with those of GY in the first season (Table 3 and Figure 4). This result indicates that the high application rate of organic composts alone or in combination with chemical fertilizers could be effective to increase maize yield in the short term. These findings may be due to the organic composts not only providing longer lasting supplies of nutrients for plants and leading to good synchrony between nutrient crop demands and nutrient release from composts during the full growth cycle of maize, but also having the potential to improve several soil properties, particularly soil organic carbon (SOC), which is the key to restoring and maintaining soil fertility and health [12,36,50]. Similarly, Hui et al. [36] also reported that, over time, chemical fertilizer was not as effective as organic compost for enhanced maize yield, with the rate of increase in maize yield being higher for treatments treated with a high-level application amount of organic composts alone or in conjunction with chemical fertilizer than for treatment treated with NPK alone. Furthermore, they also found that, over time, the rate of increase in maize yield with NPK treatment was reduced to zero when SOC stock reached 41.96 Mg C ha -1 and therefore, NPK fertilizer could be partially replaced by organic compost until the SOC reached this value.
Biofertilizers represent a cost-effective approach to enhance plant growth and crop yield through increasing the number and biological activity of beneficial microbe communities in the rhizosphere zone. This approach is able to enrich the rhizosphere with different kinds of macro-and micronutrients and provide plants with sufficient quantities of plant growth-promoting substances that lead to the enhancement of several plant physiological properties. [29,[51][52][53][54][55][56]. The results of the current study reported that, regardless of the different IPNM treatments, the seed inoculation with biofertilizers increased different growth, yield, and quality parameters of maize by 4.4-10.9%, 1.8-12.9%, and 6.2-7.9%, respectively, as compared to that of the non-seed inoculation (Table 4). Additionally, as shown by a biplot of the PCA, all measured parameters were largely associated with the treatment of seed inoculation with biofertilizers ( Figure 5). The findings of Kawalekar [57] showed that inoculation seed by biofertilizers significantly improves the growth and yield of many crops by 10-40%. Asante et al. [58] also reported that inoculated peanut seeds with biofertilizers had 13-40% higher yields than treatments without seed inoculation. The observed increase in the different parameters of maize in response to seed inoculation may be attributable to the fact that the biofertilizers not only improve soil fertility by effectively increasing the availability of essential plant nutrients, but also can bring several positive impacts to different plant functions, such as increasing the cell membrane permeability and stability, root cell elongation, the photosynthetic process, and the synthesis of several plant enzymes and hormones as well as increasing the tolerance of plants to different biotic and abiotic stress [56,[59][60][61].
The results of the analysis of variance also revealed that a significant interaction effect was detected between seed inoculation and IPNM treatments in terms of SD, LA, NGE, GY, HI, and Pro content (Table 2 and Figure 3). Generally, under each IPNM treatment, seed inoculation with biofertilizers always exhibited a considerable improvement in these parameters compared to those in the non-seed inoculation, with a few exceptions (Figure 3). These findings indicate that the biofertilizers do not merely play a key role in enhancing the growth, yield, and quality of maize when combined with IPNM treatments that including organic composts, but also with those treatments that include a full chemical fertilizer, such as T1. This could be due to the fact that biofertilizers have further notable advantages over organic and chemical fertilizers. The biologically active substances that are produced by the microorganisms stimulate the growth of the root system, which in turn enhance the mineral solubilization and nutrient and water uptake by plants, as well as stimulate several physiological metabolisms, which in turn enhance plant growth and plant tolerance to environmental stresses [56]. All of these additional advantages of biofertilizers consequently improve the growth, yield, and quality of maize under either organic or non-organic fertilizers. Similar findings were also reported with different field crops [40,[52][53][54][62][63][64].
The different growth, yield, and quality parameters of maize showed very strong and positive correlations with each other (r ranged from 0.79 *** to 0.98 ***, Table 5). Additionally, the first factor of PCA, which explained 49.34% of the total variability of all parameters, had strong loadings for all parameters (loading values greater than 0.75), except NGR and HI, which both showed strong loadings in the second factor that accounted for 47.20% of the total variability (Table 6). These findings indicate that most of the parameters examined in this study were significantly affected by different IPNM practices and therefore, are good candidates to predict the optimal and effective fertilization scheme for adequate plant growth and the sustainable production of maize under similar agro-ecosystem conditions. In this study, the treatments T6 and T9 had the highest values for all parameters of maize followed by treatments T5 and T8 (Table 3). This confirms that the application of high rates of organic compost alone or in combination with 50% of synthetic fertilization seems to be better IPNM practices for the optimal performance of maize under arid conditions. The improvements in all parameters of maize could be correlated with the ability of these treatments to provide sufficient nutrients for plants gradually throughout their growth period, which ultimately improved several fundamental physiological activities in leaves, such as the chlorophyll biosynthesis process and photosynthetic capacity [6,8,43].
To confirm this finding, the relationship between different parameters of maize (y) and the amount of N, P, and K (x) that was calculated for each IPNM treatment were tested. The results of these relationships revealed that the different parameters of maize exhibited strong relationships with the amount of N (R 2 ranged from 0.65 ** to 0.77 ***), P (R 2 ranged from 0.58 ** to 0.71 ***), and K (R 2 ranged from 0.63 ** to 0.73 ***), with the exception of EL and NGR, which showed a weak relationship with the amount of three nutrients ( Figure 6). These results indicate that increments in the growth, yield, and quality of maize directly depend on the sufficient availability of N, P, and K for the plant and the changes in the availability of these nutrients in soil could result in corresponding linear changes in the performance of maize under different IPNM practices. Therefore, the amount of N, P, and K have been considered to be the most growth and yield-limiting nutrients in any crop production system because the availability and uptake of these nutrients depend on several factors, such as climatic conditions, crop and soil characteristics, and culture and IPNM practices. Furthermore, these elements have direct influences on the growth and yield of plant. For example, N plays a hugely important role in several biochemical activities of plants, and its substantial losses are ascribed with the interaction in soil-plant systems [65]. It directly influences the growth, yield, and quality of a plant by enhancing enzymatic activities, chlorophyll formation, cell division and elongation, leaf area expansion, and photosynthetic and sink capacities [43,[66][67][68][69]. P is the second most important element after N that directly influences the growth, yield, and quality of a plant by stimulating root growth and promoting flower initiation and seed development; however, it is one of the least available nutrients to plants, especially in soils with high in CaCO 3 and pH [70,71]. K is also an important nutrient that plays a key role in enhancing crop growth and production, where various physiological mechanisms, such as photosynthesis, stomatal regulation, water storage control, and partitioning of dry matter, depend on this element [40,72,73]. This suggests that any IPNM practices that manage the NPK status and dynamics in the soil and also improve their availability and uptake are highly required and important for the optimum performance of maize and to gain higher crop yields.

Conclusions
The results of the two-year field experiments revealed that the various IPNM and biofertilizer treatments had significant impacts on the growth, yield, and quality parameters of maize in an arid agro-ecosystem. The treatments that received a mixture of different organic composts at 20 t ha −1 (T9) or a combination of 10 t ha −1 with a half dose of NPK (T6) were found the most promising IPNM practices that had considerable beneficial impacts on the performance and production of maize crops. These treatments increased the different growth, yield, and quality parameters of maize by 11.4-27.3%, 0.8-31.8%, and 4.6-17.2%, respectively, compared with the treatment receiving the full dose of NPK only. The addition of biofertilizer through seed inoculation with IPNM treatments also enhanced the different growth, yield, and quality parameters of maize by 4.4-10.9%, 1.8-12.9%, and 5.7-7.9%, respectively, compared with the treatment not receiving biofertilizer. The biplot of PCA confirmed the importance of treatments T6 and T9 with biofertilizer for maize production, where all parameters of maize showed a strong relationship with such treatments, as well as a linear relationship with the amount of N, P, and K of IPNM treatments. Therefore, any IPNM practices that had the ability to improve the availability of nutrients for plants and showed a strong relationship with the different measured parameters of plants can serve as a beneficial and effective avenue for sustainable maize production under the same conditions of this study.
Supplementary Materials: The following are available online at https://www.mdpi.com/article /10.3390/su13137439/s1, Supplementary File S1: effects of the 3-way interaction between season, integrated plant nutrient management (IPNM), and seed inoculation on stem diameter, leaf area per plant, number of grains per ear, and grain yield per ha.