Influence of Phosphorus Fertilizers Application on Phosphorus use Efficiency and Grain Protein of Winter Wheat in Alkaline-Calcareous Soil, Southern Algeria

Low soil phosphorus availability is a primary constraint for plant growth in many terrestrial ecosystems, as P is involved in several energy transformation and biochemical reactions of plant growth and development (Liao et al., 2008). Mineral fertilization, especially that of P significantly increased wheat grain yield and protein content (Gaj et al., 2013). Most of P accumulation by wheat occurs during pre-anthesis and consequently adequate P uptake during early vegetative stages that is critical for grain production (Grant et al., 2001). However, large amounts of P fertilizers are generally required for sustainable crop production, which can entails risks of environmental pollution (Liang et al., 2015), by phosphorus accumulation in the soil, which also increases the risk of aquatic eutrophication (White and Brown, 2010; Xu et al., 2014).
       
In relation to nitrogen and potassium, recovery of P fertilizers by crop plants is usually very low due to high capacity of soil to fix P (Manske et al., 2001; Lynch, 2007). High calcium carbonate contents, high pH, sandy texture and low organic matter coupled with low rainfall are the principal factors for low P availability in dry land of Southeastern of Algeria; consequently, phosphorus fertilizer efficiency remains low (Delgado et al., 2002; Al Harbi et al., 2013). The climatic factors such as high temperature can have a significant effect in reducing yield and quality of wheat and drought stress limits photosynthetic production because of stomatal closure (Li et al., 2000; Altenbach et al., 2003).
       
Nutrient utilization efficiency has long been concerned with several plant-related factors, in particular, rooting (density and length) (Sandana and Pinochet, 2014), mycorrhizal colonization (Li et al., 2006; Djadjaglo and Richter, 2008), root exudates (Dakora and Philips, 2002) and chemical forms of P in soil (Liao et al., 2008). In addition, P deficiency is often associated with changes in root morphology which induce changes in root functions that also increase PUE (Liao et al., 2008). For example in some species the release of protons, organic-acid anions, phosphatases and other compounds into the rhizosphere (Vance et al., 2003) can help release P from the fixed pools in the soil. However, increase in soil P level reduced the length of root hairs (Gahoonia et al., 1999).
        
Use of phosphorus fertilizers had a beneficial effect on phosphorus use efficiency (Ghafoor, 2016). However, the choice of phosphorus fertilizer type is essential because the reaction of added P after dissolution decides its availability to the crop growth and fertilizer use efficiency (Sushanta et al., 2014).
       
The management of phosphate fertilization is complex because of the various phosphorus transformations that occur in the soil-plant system, reducing the efficiency of fertilization and the productivity of durum wheat (Marshner, 1995; Liao et al., 2008).
       
In order to improve the productivity of cereals in general and wheat in particular, we studied the effects of different phosphate sources fertilizers and rates on phosphorus use efficiency of wheat crop in arid area conditions of southeastern Algeria.

Field trials
 
The research was performed in three different growing seasons(2008-09, 2009-10 and 2010-11) in El-Menia (southeastern Algeria, 30°57 N, 2°78 E, 397 m above sea level). The region is characterized by an arid climate, with very low and erratic rainfall (<100 mm) and warm dry summers with maximum air temperature exceeding 40°C. During the three cropping seasons, the maximum temperature average ranged between 25-35°C from February to May (Fig 1).
 

 
       
The main soil characteristics of the three plots of the same site used for experimental trials are presented in Table 1. Plots were laid out in hierarchical two-factor model design with three P source fertilizers applied at sowing time at four rates for the first season (30, 60, 90 and 120 kg P/ha) and at three rates during second and third growing seasons (30, 60 and 90 kg P/ha). The P fertilizer tested in 2008-09were Single Super Phosphate P 20 and Fosfactyl P 22, while, the third fertilizer, Mono-ammonium phosphate NP 12:52, was added in 2009-10 and 2010-11.Crop was irrigated with center pivot system and receives an amount of 750 mm water during its growth cycle. Water is pumped from the continental interlayer at 250 m deep and had a good quality with low salinity sodicity risks. For each treatment, plants were sown in1800 m² plots (24×75 m). The seedling rate was 200 kg/ha. The plots were fertilized with 212 kg N/ha as ammonium nitrate and urea (UAN 32), split into several provisions applied through fertigation.
 

 
Sampling and plant measurement
 
At harvest, seed samples were collected for chemical analysis of phosphorus and nitrogen. Phosphorus use efficiency (PUE) and their components were defined analogue to the definition of nitrogen use efficiency by Moll et al., (1982).Use efficiency of P or N was defined as grain weight Gw (kg ha^-1) per unit of available element (kg ha^-1) in the soil and expressed as absorption efficiency and the utilization efficiency. The Absorption efficiency (PAE, NAE) was calculated as P or N uptake (kg ha^-1) per P or N available in soil (kg ha^-1) and Utilization efficiency (PUTE, NUTE) was calculated as grain weight (kg ha^-1) per P or N uptake (kg ha^-1).Grain protein content was determined by kjeldahl nitrogen multiplied by 5.7. 

Statistical analysis
 
Experimental data were recorded and classified using Microsoft Office Excel 2010. The significance between the means was determined using analysis of variance (ANOVA) at the level P ≤ 0.05 with the software package Statistica 8.0.

Phosphorus and nitrogen use efficiency
 
Data in Table 2 showed that the phosphorus use efficiency (PUE) is strongly affected by phosphorus rates (P ≤ 0.001), while they were not affected by phosphorus sources in all experiments. The highest mean PUE was obtained in the year 2008-09, which was twice and six times higher than that of 2009-10 and 2010-11, consequently.
 

       
Increased phosphorus supply had a highly significant negative effect on the PUE regardless of the year, more so during last two growing seasons (2009-10 and 2010-11) for NUE (P £0.05) and the P levels 30 and 60 gave the best values (Table 2, Fig 2).
 

       
These results are identical to the observations by Sandana and Pinochet (2014), Balcha (2014) and Ghafoor (2016). They also reported that P sources had non-significant effect and the lower phosphorus use efficiency was observed at higher P application rates. In the case of nitrogen fertilization, Mandic et al., (2015), Zemichael et al., (2017) and Pandey et al., (2018) also reported that increased N level reduced NUE.
 
Phosphorus and nitrogen absorption efficiency
 
The efficiency of absorption reflects the ability of plant to extract phosphorus or nitrogen from the soil. PAE is strongly affected by phosphorus rates in the three experiments (Table 2). Differences between treatments are very highly significant (P ≤ 0.001), while fertilizer source had non-significant effect on PAE.
       
For all tests, the rate 30 kg ha^-1 soil supply had the best phosphorus absorption efficiency, whereas the highest rate gave the lowest PAE values. This efficiency was reduced due to increasing phosphorus inputs that did not result in an improvement of P uptake. In 2008-09, the PAE was twice as high as in 2009-10 and eight times higher than in 2010-11. This can be explained by high temperatures, above 30°C, occurred during anthesis for 2008-09 and during grain filling for 2009-10 and 2010-11; consequently the dry matter accumulation in grain was interrupted and grain weight decreased (Hunt et al., 1991; Wu et al., 2018; Erekul and Yigit, 2018). P uptake into shoots increased substantially with increased P supply as a result of increased dry weight and increased shoot P concentration (Osborne and Rengel, 2002).
       
Nitrogen absorption efficiency was influenced by P rates only in 2010-11. The lowest P level 30 kg ha^-1 recorded the best value, following by the two levels 60 kg ha^-1 and 90 kg ha^-1 respectively. Pierozan et al., (2015), in their study on nitrogen fertilization of soybean found that NUE was dependent on the phonological stage of the crop and climate conditions during crop growth, in addition to the timing of fertilizer application.
 
Phosphorus and nitrogen utilization efficiency
 
It expressed the efficiency with which the phosphorus absorbed is utilized to produce grain (Moll et al., 1982). In 2009-10 and 2010-11, significant results were obtained for P rates on PUTE, however, source of fertilizer had non-significant effect. The best values were obtained by the level 30 kg P/ha in 2009-10 and the 60 kg P/ha rate in 2010-11 (Table 2). The results were in confirmation with the findings of Osborne and Rengel (2002) and Fernándezet_al(2009), who concluded that phosphorus utilization efficiency decreased markedly with increasing P supply for all cereals studied.
       
NUTE was significantly affected by P fertilizers (P ≤0.05) and rates (P≤0.001) in 2008-09, where fertilizer fosfactyl and P level 90 kg ha^-1 gave the best results (Table 2).
 
Grain protein
 
The total protein content of durum wheat is a quality factor closely related to the grain nitrogen concentration. They vary under the influence of genetic as well as agro-climatic factors (Triboi et al., 2000). It resulted from a balance within the plant, between nitrogen nutrition and carbon nutrition (Jeuffroy and Oury, 2012).
       
In the present study, grain protein content was significantly influenced by source P fertilizer (P ≤ 0.05) and P rates (P ≤ 0.01) in the first growing season 2008-09, where SSP and 60 kg ha-1recorded the best values (Table 2). These results confirmed the findings of Zhu et al., (2012) and Zhang et al., (2017) who indicated that the increasing in P application decreased grain protein content of wheat. The optimum P fertilizer increased grain yield and improved grain quality with high P use efficiency, which improved leaf area index, increased chlorophyll content and photosynthetic rate, stable acid phosphatase activity to accumulate more dry matter after anthesis (Zhu et al., 2012). 
       
The correlations achieved between different parameters studied (Table 3) revealed that grain protein content was related positively to NAE and negatively to NUTE in the three seasons. While a positive relationship was established between protein content and PAE only in 2010-11. According to Crista et al., (2012), Phosphorus has no big influence like nitrogen on protein content, it supports in better assimilation and metabolism of nitrogen forms. Paunescu et al., (2009) indicated that environmental factors significantly influenced wheat grain yield and protein accumulation in grain, particularly affecting the quantity and quality of gluten. Dryness or high temperatures during grain filling induced a decrease in the protein and gluten content of grains (Daniel and Triboi, 2000). It also affects more carbonaceous nutrition than nitrogen, therefore, tending to increase protein content (Labuschange et al., 2009; Jeuffroy and Oury, 2012; Šukalovicet_al2013). These findings were in perfect agreement with our results obtained in 2009-10, where the Tmax during grain filling exceeded 30°C, resulting average protein content upper 17.6%.
 

Through the investigative study of the effect of phosphorus fertilizers application on phosphorus use efficiency in durum wheat, we conclude that the best results are recorded by Single super phosphate fertilizer and at an optimum P rate, 60 kg ha^-1, in Southeastern Algeria conditions.
 
The mechanisms of nutrients efficiency in general and phosphorus in particular will depend on many factors, including growth conditions and chemical forms of P fertilizer. The increase in the efficiency of fertilizer use can be achieved by a better supply of nutrients temporally and spatially corresponding to the crop requirements and the enhanced P efficiency of wheat will contribute to reducing the use of high amounts of phosphorus fertilizers, enables sustainable agriculture on soils with low phosphorus content in arid region of Algeria.