Introduction

Increasing global population and their subsequent dietary requirements have put a lot of onus on agriculture, whose output is significantly influenced by numerous factors i.e., land holdings, lack of proper mechanization and prevalence of various biotic and abiotic stresses [1-3]. Water stress causes significant setbacks to agricultural production every year [4, 5]. Water scarcity due to reduced rainfall and enhanced dry spells have given rise to drought stress, which is stimulated and prolonged for a relatively longer time period due to inadequate rainfall, and is not generally restricted to a specific region or time period [6, 7]. It is a multi-dimensional abiotic stress that chiefly occurs due to depreciated rainfall and long-term drying conditions [8]. About 33% population of human beings in developing countries are living in water deficit zones [9]. Pakistan also lies in the arid to semi-arid region, with low precipitation and high evapotranspiration, and as a result, more water is lost to the environment. Water is an essential factor for key plant physiological processes, such as photosynthesis, enzymatic activity, metabolism, protein synthesis and transpiration [10]. Water use efficiency (WUE) can be improved by the irrigation scheduling at different crop growth stages [11]. WUE decreases by over irrigation while deficit irrigation increases water use efficiency as well as crop production [12]. Kang et al. [13] revealed that the yield and WUE are strongly affected by the irrigation scheduling and soil water contents.

Maize (Zea mays L.) is the third most important feed and food cereal crop worldwide, after wheat and rice. It is an important cereal crop, which supplies diet to millions of people worldwide. Maize seeds contain ash (1.2%), protein (10.5%), fiber (2.8%), starch (80.8%), sugar (2%) and oil (2.7%) [14]. Maize is used as forage and feed for livestock and poultry and used as the raw material for almost 4000 products created by agro-based chemical industries. Its cultivated area in Pakistan is about 1.720 million hectares (Mha) that contributes to 0.7% in gross domestic product and 3.0% to value addition in agriculture [15]. Maize seeds are composed of 2%, 65% and 33%, amino acids, sugars and organic acids respectively [16]. Un-even spatiotemporal distribution and limited water resources have restricted its production as insufficient water halts the metabolic activities of maize and decreases its biomass production and metabolic photosynthetic rates by reducing the chlorophyll contents and subsequently, its yield [17]. Water stress to any stage of growth can decrease the maize yield due to the modification in the physiological processes of the plant [18].

Phosphorus (P) is an important primary macronutrient among all essential nutrients required by plants. It serves as a major element for improved root growth, energy carrier in the form of adenosine triphosphate (ATP), and in genetics owing to its role in the composition of deoxyribonucleic acid (DNA). Its application via different organic and inorganic sources is inevitable to proper crop growth, and that is why its deficiency cannot be ignored. The main function of the inorganic fertilizer is to enhance the crop production, but low use of P fertilizers is a major concern in obtaining the proven maximum crop yield, by comparison to nitrogen [19]. For maximum crop production, crop requires adequate supply of P during early stages of growth [20]. P is required by the crop in larger quantities after nitrogen (N), and application of phosphatic fertilizers is needed in order to maintain the fertility of soil. Agriculture sector depends largely upon phosphatic fertilizers, which are manufactured from rock phosphate, a non-renewable resource. It should be well managed to avoid its over exploitation. Availability of P depends upon the water contents in soil, where higher moisture contents results in higher mobility and P availability to the crop [21] and increased water contents also enhance the utilization efficiencies of P in plants by improving the root length as well as root shoot ratio, releasing organic acids and protons [22], and phosphatases [22].

Combined effect of P fertilizer and soil available water plays an essential role for growth and development of crops [23]. In order to increase the production, a suitable method of irrigation and application of fertilizer should be adopted. Malik and Khan, [24] suggested the recommended method of the application of P fertilizer is broadcasting in Pakistan, followed by incorporation in the soil, before crop sowing. This method resulted in the formation of insoluble P. Some studies have also revealed that split applications of N and P fertilizers by side -dressing or with irrigation can produce equal grain yield or sometimes more P uptake and higher grain yield [25, 26].

Hence, our hypothesis aimed to test whether applying P via chemical fertilizer, combined with an optimal irrigation scheme, could enhance P use efficiency, soil P availability, and consequently, improve maize growth and yield attributes. This field trial aimed to assess the influence of varying P levels (0, 90, 120, and 150 kg ha^-1) on growth, yield, physiological aspects, and soil fertility under diverse irrigation management approaches.

Materials and Methods

A field trial was performed to study the effect of different levels of irrigation and phosphorus (P) on water and P use efficiency in maize at the research farm of Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad. The experimental site is situated at 31.25°N latitude, 73.04°E longitude, with an altitude of 184 meters, characterized by a semi-arid climate. The experiment was laid out in randomized complete block design (RCBD) with factorial arrangements. Composite samples of soil were randomly collected before the crop sowing from the field. Air dried soil samples were ground and homogenized by passing through 2 mm sieve, and analyzed for different soil properties (Table 1). Four different phosphorus levels (0, 90, 120 and 150 kg ha^-1) were used and three different irrigation levels (recommended, irrigation skipped at flowering stages and irrigation skipped at flowering and milking stages) were used for this purpose. Single super phosphate (SSP) was used as a source of P, and each treatment was replicated thrice. Maize (Syngenta-8611) was sown at 10 kg acre^-1 with a single row hand drill. At crop harvest, different soil physical parameters (bulk density and water contents at field capacity) were measured. Furthermore, different growth and yield attributes were noted upon harvest. At maturity, plant samples were collected and analyzed for P concentration. Soil samples were collected after harvesting of maize crop from 0-15 cm and 15-30 cm and were analyzed for available P and extractable K.

Results

Phosphorus is an essential plant nutrient, and is required for major plant functions ranging from root growth to biochemical and metabolic functions. However, its soil availability is limited on account of different factors, which lessen its plant use efficiency along with restriction of other important plant functions. Soil moisture contents offer a critical role in improving the soil P availability and are, therefore, of crucial importance in lieu of increased plant P availability and improved growth. We checked the impact of different P levels (0, 90, 120 and 150 kg ha^-1) in improving the P use efficiency in maize and its impact on improving maize growth and yield in association with different irrigation management schemes. Irrigation was provided at recommended levels, skipped at flowering and milking stages. Results of different plant attributes are given below.

Soil Fertility Attributes and Physical Attributes

Data in terms of different soil fertility attributes (Fig. 4) depicted that application of P at 90 kg ha^-1 along with recommended irrigation levels significantly improved soil fertility status as evident in terms of different fertility related attributes such as soil organic matter contents (17%), soil active carbon (23%), soil available P (122%) and soil extractable K (37%) as compared to control treatment followed by P at 120 kg ha^-1, which also led to a significant increment in these attributes than control treatment. Furthermore, P application at 90 kg ha^-1 also increased soil organic matter contents (47 and 49%), soil active carbon (46 and 55%), soil available P (279 and 248%) and soil extractable K (46 and 80%) when irrigation was skipped at flowering and flowering plus milking stages as compared to control treatment. Similarly, soil physical attributes (Fig. 5) as measured in terms of soil bulk density and P-use efficiency also explained the beneficial role of P application at 90 kg ha^-1 at recommended irrigation levels. We observed a non-significant impact of P application on the soil bulk density at all the irrigation management schemes at both depths. However, at 15-30 cm soil depth, more bulk density in all the treatments was observed as compared to 0-15 cm soil depth. In addition, results of P use efficiency again confirmed the advantageous role played by P against all the irrigation schemes, where maximum outcomes were visible in P application at 90 kg ha^-1 along with recommended irrigation levels. It was observed that application of P at 90 kg ha^-1 enhanced the P use efficiency by 255, 531 and 887% respectively at recommended irrigation level, skipped irrigation at flowering and skipped irrigation at flowering plus milking stages respectively.

Fig. 1.

Effect of different phosphorus levels and irrigation schemes on the growth attributes of maize under field conditions.

Fig. 2.

Effect of different phosphorus levels and irrigation schemes on the yield attributes of maize under field conditions.

Fig. 3.

Effect of different phosphorus levels and irrigation schemes on the physiological attributes of maize under field conditions.

Fig. 4.

Effect of different phosphorus levels and irrigation schemes on the soil nutrient contents in maize field.

Discussion

Phosphorus (P) stands as an essential nutrient element, playing a pivotal role in carbohydrate metabolism and the energy transfer system within plants. It serves as a crucial component of DNA, RNA, ATP, and phospholipids. Deficiency in P can significantly diminish various metabolic processes, affecting cell division, development, respiration, and photosynthesis [30]. Chemical fertilizers generally provided the plants P requirements. However, a large amount of P in fertilizers may become insoluble and lose their plant availability after entrance into the soil [31]. In calcareous soils developed under arid and semi-arid climates, the combination of factors such as the presence of calcium carbonate, high pH levels, limited organic matter, and soil dryness often results in insufficient available P for the optimal growth of most crops. Using chemical P fertilizers to address this deficiency is not notably effective in calcareous and alkaline soils, with the efficiency of P fertilizers in these conditions typically not exceeding 20% [32, 33]. We explored the individual and combined effects of P application and different irrigation management patterns in improving the P use efficiency of maize, soil P availability, maize growth and yield attributes. Based on the results, it was concluded that P application in combination with recommended irrigation level can significantly improve maize growth, yield and physiology along with improved soil fertility status.

Fig. 5.

Effect of different phosphorus levels and irrigation schemes on the soil bulk density and P use efficiency in maize field.

In terms of growth attributes, P application at all the levels resulted in improved growth and yield attributes. This observed increment in plant growth and yield traits have been earlier reported by Zhang et al. [34] and Izhar Shafi et al. [35] Phosphorus offers a keen role in various plant functions such as energy transfer [36], respiration [37], photosynthesis [38] and root growth [39, 40]. In our current study, we noted a notable enhancement in photosynthetic and root attributes due to P application, illustrating the advantageous impact of P in augmenting plant growth and yield in our experiment. However, under water-stressed conditions, we observed a negative influence on all growth attributes, likely linked to reduced P uptake in lower moisture conditions. Similar findings were reported by Attarzadeh et al. [33], suggesting that heightened moisture stress diminishes P availability for plants, subsequently lowering uptake. Regarding maize yield attributes, P application across all irrigation schemes increased plant yield compared to their respective controls. Nonetheless, in cases where irrigation was withheld, diminished P uptake resulted in a significant decline in maize yield attributes. Similar outcomes were reported earlier by Zheng et al. [41], who observed that under alternative wetting and drying irrigation schemes, P uptake was reduced as compared to recommended irrigation continuous and recommended irrigation pattern, which caused a significant decrement in plant yield. In the current study, we also observed that P application at continuous and recommended irrigation level resulted in a considerable improvement in maize yield attributes; however, this increment was reduced at skipped irrigation systems, which not only decreased the P use efficiency, and hence, interfered with its functions and subsequently, decreased maize yield.

Results regarding the role of P application in improving plant physiological attributes revealed a significant correlation between P uptake, its used efficiency and plant physiology, which are also in line with the findings of Neocleous and Savvas, [42]. Phosphorus (P) is crucial for plant metabolic functions, notably in ATP formation, the body’s primary energy carrier. In conditions with limited P, the efficiency of the photosynthetic apparatus is significantly impacted. This limitation interferes with phosphorylation activities, Rubisco function, and Calvin cycle reactions, ultimately reducing carbon fixation and constraining photosynthetic processes. In our current study, the observed decrease in P uptake under skipped irrigation schemes resulted in reduced P use efficiency, leading to a decline in photosynthesis. This reduction in photosynthesis due to P deficiency has been documented in various crops like lettuce, wheat, maize, rice, and tomato by previous researchers [42-46].

Conclusion

Phosphorus stands as a vital macronutrient crucial for sustaining key plant functions. Its limited availability due to soil fixation restricts its accessibility for plants. The role of soil moisture content in enhancing soil P availability and subsequent plant uptake is evident. Our experiment explored the impact of various P application levels on maize growth, yield, physiology, and P use efficiency under diverse irrigation management schemes. We observed significant improvements across all measured maize attributes with the application of P at 90 kg ha^-1 under recommended irrigation levels. Conversely, skipping irrigation at milking and flowering stages had detrimental effects, particularly evident in combined milking and flowering stage omissions. Furthermore, the combined application of P and recommended irrigation levels notably enhanced soil fertility status, augmenting available P and K contents along with organic matter levels. Looking ahead, this study opens avenues for further research. Future investigations could delve deeper into optimizing P application strategies under varying moisture and climatic and soil conditions to maximize crop productivity sustainably. Understanding these interactions can pave the way for more precise recommendations, fostering enhanced P use efficiency and overall plant growth and yield.