PastAbstract
The effect of phosphorus (P) fertilizer on vegetative growth and yield components of two naked barley varieties, ‘Tombari’ and ‘Giza 130’, was studied at the National Agronomic Research Institute of Tunisia (INRAT) during the 2012 and 2013 growing seasons. Four rates of P (0; 50; 100; 150; 200 kg of P2O5/ha) were applied at sowing. Two trials were carried out: the first was done in pots to show the effect of P on plantlet root growth while the second was conducted in the field where experimental treatments were arranged in a split plot and in a complete randomized block design with three replications. All plots were fertilized with 25 kg/ha of ammonium nitrate at the elongation stage. No potassium (K) was used since the soil was naturally rich in K. P fertilizer positively affected root growth of the first trial and vegetative growth (plant height, flag leaf area, number of tillers/m2 and biomass product) of both barley varieties up to 100 kg/ha. However, both varieties exhibited contrasting behaviour: when P exceeded 100 kg/ha, all parameters of ‘Tombari’ decreased significantly while the same parameters showed no significant change in ‘Giza 130’, even at 200 kg/ha. Both varieties also responded differently with respect to yield: ‘Tombari’ showed a significant increase in the number of grains/spike and spike weight up until 100 kg/ha; even though there were no significant differences between ‘Tombari’ and ‘Giza 130’, ‘Giza 130’ produced significantly more fertile tillers/m2. P fertilizer benefits barley growth and yield up until 100 kg/ha in a genotype-independent manner.
Introduction
Nitrogen (N), phosphorous (P) and potassium (K) are considered to be the three most important nutrients for plant growth (Obidiebube et al., 2012). P promotes growth by stimulating root development and allows plants to better utilize nutrients and consequently improves flower production, fertilization and yield (Rahimi et al., 2012). P also plays a major role in photosynthesis, nutrient transport, and energy transfer. Plants that receive an adequate amount of P at an early stage will grow more vigorously due to the promotion of root growth, and they will be winter hardy and will reach maturity more rapidly than plants with an inadequate P supply (Teng et al., 2013). In wheat, plants will produce more fertile tillers/m2, more spikes per unit area and more biological yield in response to P fertilizer (Warraich et al., 2002). Insufficient P supply to a plant, however, makes it more vulnerable to stress and disease (Liaqat, 2003).
Many experiments have been conducted on the effect of N and/or P on yield and yield components of wheat (Gökmen and Sencar, 1999; Grant et al., 2001; Mckenzie, 2003; Kaleem et al., 2009; Ottman, 2011; Baraich et al., 2012; Sarker et al., 2015), rice (Bukvić et al., 2003; Chaturvedi, 2005; Alam et al., 2009; Sharma et al., 2011; Usman, 2013), and maize (Ibrikci et al., 2005; Rashid and Iqbal, 2012; Minapour et al., 2013). However, few papers have assessed the effect of P supply on barley (Hordeum vulgare L.) production (Jones et al., 2003; Turk et al., 2003; Eftekhari et al., 2012).
In Tunisia, even though barley is used as human food and animal feed, it is cultivated on marginal lands and often without fertilization and in these regions, low soil fertility is one of the most limiting production constraints. Despite being one of the major national food crops, its output average is about 0.8 T/ha, which is much lower than the world’s average (Slama et al., 2005). Thus, one way to ensure suitable barley production could be to apply organic and inorganic fertilizers as soil amendments.
Various crops have responded positively to the application of N and/or P fertilizer in different climates and at different levels. For example, Gurmani et al. (2006) showed the positive effect of P fertilizer on fodder and grain yield of vetch under rainfed conditions. They obtained the highest green fodder, dry matter and grain yields after applying 15 and 40 kg/ha of N and P fertilizer, respectively. Niri et al. (2010) studied the effect of N and P application on yield and protein content of lentil in dry land conditions. Optimal grain and protein yield was obtained with 25 and 40 kg/ha N and P, respectively. Zewide et al. (2012) showed that 165 and 60 kg/ha of N and P were optimum for potato ‘Jalen’ in Southwestern Ethiopia. Recommendations, however, depend on the crop and the climate. Gurmani et al. (2006) recommended 15 and 40 kg/ha of N and P for vetch ‘Cyprus local’ in rainfed conditions in Islamabad, Pakistan in order to produce the highest dry matter and highest grain yield. Baraich et al. (2012) found, also in Pakistan, that 90 kg/ha of P (as P2O5) combined with 30 kg/ha of K was most effective for field-irrigated wheat ‘Mehran-89’. When three combinations of common vetch-cereal (oat, barley and wheat) at a ratio of 75:25, 50:50 and 25:75 under rainfed conditions in the southern Marmara region of Turkey were tested, Carpici and Tunali (2012) found that 30 kg/ha of P2O5 and 30 kg N/ha was necessary for optimum dry matter and protein content. Turk et al. (2003) improved spike number/m2, number of grains/spike, spike length, plant height and optimum grain yield in rainfed barley ‘Roho’ growing in Jordan when 80 kg/ha P2O5 was applied.
Therefore, investigating the response of barley to P2O5 fertilizer is essential to understanding the appropriate P level required for arid and semi-arid regions such as Tunisia. To achieve this, in this study, two naked barley varieties (‘Tombari’, a variety from Tunisia and ‘Giza 130’, a variety from Egypt) were selected. The predominant barley type is hulled, having a hard fibrous hull, and is mainly used for feed in Tunisia. The other type is the hulless or naked barley in which the hull is easily removed, being similar to wheat. This barley is rare both in Tunisia and around the world. Nevertheless, because of its high β-glucan content (Bhatty, 1999; Ben Naceur, 2013), naked barley is regaining interest for its use as human nutrition. β-Glucan, a major component of soluble fibre with many health benefits, is implicated in hypocholesterolemia, hypoglycemia, and in its ability to relieve constipation and reduce the incidence of chemically-induced colon cancer in experimental animals (Bhatty, 1999). It also has a natural nutritional fiber property which has many benefits. It acts as an anticoagulant or as an antioxidant, especially when extracted from bacterium and a mushroom (Vetvicka and Vetvickova, 2012). It can play an important role, not just in preventive medicine, but also in therapeutics of major illnesses such as infectious diseases and cancer (Vetvicka and Novak, 2011). β-Glucan stimulates the innate immune system against bacterial, viral, fungal and parasitic infections (Vetvicka and Vetvickova, 2012). Moreover, β-glucan can be used to treat cervical and prostate cancer (Fullerton et al., 2000), as well as breast cancer (Vetvicka and Yvin, 2004). These medicinal and nutritional qualities of β-glucan make naked barley an important plant resource, and thus optimized yield and productivity are keys to effective crop management.
This paper studied the optimum P level that could result in highest biomass production, grain yield, yield components and other relevant characteristics that are directly linked to the nutritional quality of naked barley. This is the first such study that examines the behaviour of naked barley in response to P fertilizer.
Materials and Methods
The experiment was conducted at the National Agronomic Research Institute of Tunisia during two growth seasons (2011-2012 and 2012-2013). The amount of precipitation in the growing period was 460 mm and 338 mm respectively, indicating a normal growth season for the first year and a dry season for the second year. The soil type of the test site was clay loam with 70 mg/kg of P, 284 mg/kg of K and a pH of 8.3. According to Ryan et al. (2012), soil is poor in P when the level is 51-100 mg/kg and average to rich in K when the level is 201-300 mg/kg. Consequently, K fertilizer was not applied in this study.
Two naked barley varieties were used: ‘Tombari’, originating from Tunisia (hereafter V1), and ‘Giza 130’, from Egypt (hereafter V2). V2 was supplied by Prof. M. Sarker from the National Research Centre (NRC) of Egypt in the frame of the New Partnership for African’s Development (NEPAD) project. The key characteristics of these two varieties also described by Ben Naceur et al. (2012), but are described next. V1, usually grown in 6 rows, was collected in 2000, is late and moderately productive in favourable conditions. V2 is also grown in 6 rows, is precocious, moderately productive in favourable conditions and is tolerant to drought and fungal diseases. V2 was selected from the crosses “Comp.cross” 229//Bco.Mr./DZ02391/3/ Deir Alla 106 using the bulk method (Ben Naceur et al., 2012).
Four levels of P (0; 50; 100; 150; and 200 kg of P2O5/ha) were applied at the time of sowing for both trials. The first one was carried out in a small pots (ɸ = 7 cm) to study the effect of P on root growth, 30 days after sowing (DAS). The second one was carried out in the field and at the elongation stage (70 DAS) in which all plots were fertilized with 25 kg/ha of ammonium nitrate. No K was applied since the soil is rich in K (284 mg/kg).
Each plot was 3 × 4.0 = 12 m2 in size and consisted of 15 lines (20 cm between each line) 4 m long for each variety. Seeds were sown 20 cm apart in rows with a density of 300 plants/m2. Seeds were sown by hand. The research was conducted in a randomized complete block design (RCBD) with three replications. The main factor was P2O5 fertilizer at four levels: 0, 50, 100, 150 and 200 kg P/ha (P-0, P-50, P-100, P-150, and P-200, respectively). The sub-factor was the variety (V1 and V2).
For the first trial only, root weight was quantified. For the second trial, the vegetative traits assessed were plant height, flag leaf area, number of tillers/m2 and the biological product. All these parameters were measured at the heading stage (120 DAS). The reproductive traits (number of grains/spike, spike weight and grain yield) were measured at the maturity stage (210 DAS).
Data for vegetative and reproductive traits were analysed using Statisca software (Statsoft.com, France). Following an analysis of variance (ANOVA), significant differences between treatments were determined using the Newman-Keul’s test at P ≤ 0.01 to compare differences among treatment as described by Ali et al. (2003).