Effect of Phosphatic and Potassium Fertilization Rates on Some Faba Bean Cultivars

INTRODUCTION

Grain legumes, belonging to the family Fabaceae, are an important component of the food production systems in tropical agriculture for their mature seeds or immature green pods because of their protein content (20–26%)(Carangal et al.,1997and Metwally et al.,2011). These crops are very adaptable and fix atmospheric nitrogen through symbiosis (Wood and Myers, 1997).

Faba bean (Vicia fabaL.) is the most important legume crop in Egypt and many parts of the world (Metwally et al., 2011), where it is used for human consumption as a good source of vegetarian protein (Saad and El-Kholy, 2001 and Nawar et al.,2010) and animals (El-Gizawy and Mehasen,2009). Its seeds exhibit high levels of protein (28-36 % of seed dry matter). It is popular breakfast food which is also used as a green vegetable or fresh canned vegetable (Metwally et al., 2011). It is, also an important crop for soil improvement and used as a break crop in cereal rotation to keep the soil fertile and productive through nitrogen fixation (Metwally et al., 2011). Depending on the plant density and the field management, this plant is able to fix nitrogen up to 40kg ha^-1 annually (Hashemabadi, 2003).

The production of faba bean in Egypt is still limited and fails to face the increasing local consumption. Therefore, increasing crop productivity is one of the major targets of the agricultural policy and can be fulfilled through-increasing the cultivated area, using high productive varieties, and Supply of appropriate and balanced levels of essential plant nutrients and weed control (Ismail and Hagag, 2005 and El Habbasha et al.,2007). Faba bean productivity is low due to technological gaps in adoption of balanced fertilization (Rezk et al., 2013).

Phosphorus is a very important nutrient for crop growth and ensures high yield with good quality. It plays a key role in metabolic processes such as the conversion of sugar into starch and cellulose. As a result, phosphorus deficiency causes stunting, delayed maturity and shriveled seeds (Abou Hussien et al.,2002 and El Douby and Mouhamed, 2002). Several researchers reported that plant height, number of pods and seeds/plant as well as weight of pods and seeds/plant, straw and biological yield/feddan and seed protein content were increased due to phosphorus fertilizer applications (Mokhtar,2001 and Abdalla,2002).

Potassium is an essential element for all living organisms. In plants, it is an important cation involved in physiological pathways (Duke and Collins, 1995 and Sangakkara et al.,1996). In particular, the ability of ATPases in membranes to maintain active transport is highly dependent on adequate K supply. Thus efficient cell development and growth of plant tissues, translocation, storage of assimilates and other internal functions, which are based upon many physiological, biochemical and biophysical interactions, require adequate K in the cell sap (Marschner, 1995 and Lindhauer,1999). Potassium is an important nutrient for several physiological processes directly related to nodulation and N₂ fixation (Abdel Wahab and Abd-Alla, 1995 and People and Koch, 1999).The influence of K on growth and yield of food legumes has been demonstrated, to improve plant's resistance against environmental stress (Sangakkara,1990 and Hanway and Johnson,1995).

The present investigation aimed to evaluate some local and introduced faba bean varieties under varying levels of phosphorus and potassium fertilization to determine the appropriate level of the two macronutrients that would realize optimal growth and productivity of those varieties.

MATERIALS AND METHODS

The present study was carried out during the two successive winter seasons of 2013/2014 and 2014/2015 at Agriculture Research Station and Laboratories of Crop Science Department, Faculty of Agriculture, Alexandria University. This investigation aimed to evaluate some faba bean cultivars and determine the suitable phosphorus and potassium fertilizers levels to maximize plant growth and productivity of the studied varieties.

The soil of the experimental fields was silty loam and approximately homogenous. Soil of the experimental sites were analyzed in the two seasons as shown in  Table (1).

Table (1). Some Physical and chemical properties of the experimental soil in 2013/2014 and 2014/2015 seasons

The experimental design was split-split plot with four replications, Phosphorus fertilization (as calcium monophosphate 15.5% P₂O₅)levels (0, 37 and  74 kg P₂O₅/ha) were randomly distributed in main plots, the potassium fertilization(as potassium sulphate 48% k₂O) levels(0, 57 and 114 kg k₂O/ha) occupied the sub-plots, whereas the cultivars(Libyan,Giza843,Nubariah3, Giza716 and Sakha1) were allocated to the sub-sub plots.

The sub-sub plot size was 6.3m²(3 ridges, 3m long and 70 cm apart).  Seeds were sown on one side of ridge in hills 20 cm apart and thinned to two plants per hill.  Seeds were obtained from the Agricultural Research Center in Giza, Department of  Legume Crops, except for seeds of Libyan variety which were obtained from the Agricultural Research Center in Tripoli.  seeding rate for all varieties was  144kg/ha. Planting dates were November 1^st and 10^th in 2013/2014 and 2014/ 2015 seasons, respectively. All other agricultural practices were carried out according to the recommended practices of this crop in the region.

Weed control was carried out using Stomp, as pre-emergence herbicide at the rate of 3.57 liter/ha. Fusilade super was applied at the rate of 3.57 liter/ha after germination of weeds, in the stage of four leaves, for weed control of narrow-leaved weeds. In both seasons, a 0.42 m² area, from each experimental unit, wastaken on l^st on February and March, to calculate the leaf area and dry weight of  plant. The leaf area was calculated using leaf area meter, model no. Li 3000c.andleaf area index for the March sample was calculated according to Gardner et al.(1985), as the following equation: leaf area index (LAI) = leaf area/feeding area.

Plants were oven-dried at 70C⁰ until constant weight and crop growth rate (CGR) was calculated according to Gardner et al.(1985) , for the period from l^st February to l^st March. At harvest, the following measurements were determined:

1-  Number of pods/plant, as an average of five plants.

2-  Number of seeds/plant, as an average of five plants.

3-  100-seed weight (g), as an average of three samples.

4-  Seed yield (ton/ha), as the weight of seed obtained from a guarded area of 1.75 m² and transformed to ton/ ha.

5-  Harvest index(%), was calculated as seed yield/biological yield X100.

Where P levels occupied the main plots, K levels were allocated to the sub-plots and faba bean verities were randomly assigned to the sub sub-plots.

Statistical analysis

Statistical analysis of the experimental data, in each season, was performed according to Gomez and Gomez (1984), using SAS (Statistical Analysis System) version: 9.1. Comparison between treatment means was carried out using least significant differences at 0.05 probability level (L.S.D_0.05).

RESULTS AND DISCUSSION

The present study aimed to investigate the effect of fertilization with varying levels of phosphorus and potassium on growth and yield characters of five faba bean cultivars. The obtained results are presented as follows:

A. Growth characters

These included leaf area index (LAI) and crop growth rate (CGR) measured at first of March for LAI and the period from February 1^st to March 1^st for CGR.

Phosphorus (P levels) affected both characters in the second season and LAI only in the first season, whereas potassium (K) levels had no significant effect on LAI but significantly affected CGR in the two seasons. Moreover, cultivars (C) and significant effect on both characters in the two seasons. LAI was significantly influenced by P×K interaction (2^nd season), P×C interaction (in the two seasons) and K×C interaction (2^nd season). On the other hand, CGR was affected by 2–factor and 3–factor interactions in the two seasons; hence the effect of P×K×C interaction will be discussed (Tables 2 and 3). Increasing P application level from 0 to 37 kg P₂O₅/ ha significantly increased LAI in the two seasons, whereas further increase to 74 kg P₂O₅/ha level resulted in insignificant increase in that character. Concerning CGR, increasing P level from 0 to 37 or 74 kg P₂O₅/ha showed progressive increase in CGR that was significant in the second season only. Phosphorus is an important macronutrient that plays an important role in biochemical processes in plants through its contribution in energy transformations. Agegnehu and Tsige (2006) reported that leaves dry weight of faba bean plants was positively influenced by increased P applications. Similarly, Saad and El-Kholy (2001) and Ahmed and El-Abagy (2007) concluded that the highest P application rate produced the most significant values of growth characters including LAI and CGR.

Potassium had insignificant effect on LAI, in the two seasons, but showed a trend of progressive increase in that character with increasing K level up to 114 kg K₂O/ha. On the other hand, K levels had significant influence on CGR in the two seasons. Increasing K level resulted in significant progressive increment in CGR up to 114 kg K₂O/ha.

The P×K interaction, in the second season, showed that increasing P application to 37 kg P₂O₅/ ha and K fertilization rate to 57 kg K₂O/ha resulted in a significant increase in LAI. Further increase of P to 74 kg P₂O₅/ha and K to 114 kg K₂O/ha gave insignificant increase in LAI compared to the two intermediate levels. Hence, the value of P×K interaction for intermediate levels (4.52) wastatistically similar to that of the highest levels of both macronutrients (4.74). Ebrahem and Abd El-Mohsen (2010) reported that growth parameters of faba bean plants, including LAI, increased with balanced applications of both phosphorus and potassium fertilizers. Significant differences between cultivars and P× cultivars interaction in the two seasons, and K×cultivars in the second season, may be explained by the differences in genetic constitution of cultivars and the response of genetic makeup to the applied levels of P and K. Means in (Table 2) revealed that Libyanl, Nubariah 3 and Giza 716 had significantly higher LAI values compared to Giza 843 and Sakha 1. The data, also, showed that Libyan 1 with 74.0 kg P₂O₅/ha, or 114 kg K₂O/ha, gave the highest values for LAI, whereas Sakha 1 with P or K fertilization gave the lowest values for LAI. Application of phosphorus, or potassium, enhances plant growth through activation of various biochemical processes, uptake N₂ fixation and nodules activity and increases nutrients uptake from the soil, leading to more vigorous plant growth and higher leaf area. Similar findings were reported by El-Hadidy and Sweelam (2000), Abdallah (2002), Weldua et al. (2012) and Mohammad (2014), who confirmed the positive effect of increasing P and/or K levels on faba bean growth, and the variation of cultivars response to applied P and/or K fertilization levels.

The significant three-factor interaction, in the two seasons, indicated that CGR manifestation was a result for the combined effects of the three studied factors (Table 3).  The highest values for CGR were obtained for Giza 843 with 74 kg P₂O₅/ha and 114 kg K₂O/ha in the first season (6.55 g/m²/day), whereas in the second season, both Libyanl and Nubariah 3 exhibited the highest values for CGR (6.33 g/m²/day for both genotypes) at the same levels of P and K. On the other hand, Sakha 1 gave the lowest values for CGR when neither phosphorus nor potassium were applied (1.25and 0.08 g/m²/dayin the first and second season, respectively). These results emphasize the importance of application of both P and K fertilizers, in balanced proportion, for proper growth of faba bean plants. El-Habbasha et al. (2007), Osman and Elaziz (2010) and Farhan (2012) reported positive influence of P and K application on dry matter production, leading to increased dry weights of both shoots and roots, in faba bean plants and differential varietal response to applied levels of both macronutrients. It should be noted that faba bean varieties with higher LAI values produced higher CGR values, in the two season. That implies a close relationship between functional leaf area and accumulation of dry matter in plants. Kurdali et al. (2002) and Abd El-Latif and Moursi (2006) reported a positive relationship between the two growth parameters.

B. Yield characters

This group of characters included number of pods/ plant, number of seeds/ plant, 100-seed weight, seed yield/ ha and harvest index P levels significantly affected number of pods/ plant in the two seasons, number of seeds/ plant and 100-seed weight in the second season. K fertilization levels significantly influenced all studied characters, in the two seasons, except number of pods/plant in the second season. Cultivars varied significantly in all studied characters, in the two seasons, except seed yield/ ha in the second season. The 3– factors interaction had significant effect on all studied characters, in the two seasons, except harvest index in the second season (Tables 4 to 8).

Increasing P application from 0 to 37 then 74 kg P₂O₅/ha resulted in significant increase in number of pods/ plant in the two seasons,number of seeds/ pod and 100-seeds weight in the second season. Seed yield/ ha and HI showed the same trend but did not reach the level of significance in the two seasons. Bolland et al. (2001) concluded that P is a major nutrient element for seed production of faba bean in neutral and alkaline soils. Ahmed et al. (2005) and Agegnehu and Fessehaie (2006) reported that the highest P level resulted in highest number of pods and seeds/ plant. Similarly, Ahmed and El-Abagy (2007) found that seed yield and yield components increased with foliar application of P.

Concerning K levels, increasing application from 0 to 57 then to 114 K₂O/ ha significantly increased number of pod/ plant in the first season, number of seeds/ plant and 100-seed weight in the two seasons, seed yield/ha and HI up to 57 kg K₂O/ha in the first season and up to 114 kg K₂O/ ha in the second season. Several researchers reported the beneficial effects of increasing K application level on seed yield and yield components of faba bean (Metwally et al., 2011, Shaban et al., 2012, Jasimand Obaid, 2014 and Sadeghi et al., (2014). They all concluded that the enhancement effect of K, as a major nutrient, on growth, dry matter production and translation positively affected yield components and finally increased seed yield.

Cultivars varied significantly for yield components and harvest index, in the two seasons, and in seed yield in the first season only. Libyanl exhibited the highest values for number of pods/ plant, 100-seed weight and harvest index in the two seasons, while Sakhal gave the lowest value for the same characters in the two seasons. Concerning number of seeds/plant, Giza 843 gave the highest values, whereas Giza 716 exhibited the lowest values in the two seasons. Regarding seed yield/ ha, Nubariah 3 gave the significantly highest value (2.54 t/ha) while Sakhal gave the lowest value (2.18 t/ ha) in the first season. The same trend was obtained in the second season but did not reach the statistical level of significance. Similar variations between yield and yield components of faba bean cultivars were reported by Saad and El-Kholy (2001) and Talaat and Abdallah (2008), who concluded that these variations may be attributed to differences in genetic constitution of the varieties which affects their response to environment. Its worth mentioning the noticeable variation in seed yield and yield components between the two seasons, where the recorded values for those characters varied from one season to another. That variation is a natural phenomenon in faba bean and is, principally, influenced by the percentage of flower shedding caused by environmental conditions such as win and amount of rainfall druing flowering stage. Similar findings were reported by Masri (2001) and Khalil et al. (2004).

The three factor interaction revealed that varieties differed in their performance, under the influence of applied phosphorus and potassium levels, for seed yield and yield components characters. Application of the highest levels of P (74 kg P₂O₅/ ha) and K (114 kg K₂O/ ha) gave the highest values in the two seasons, for number of pods/ plant with Libyanl, for number of seeds/ plant with Sakhal, for 100-seed weight with Libyanl, for seed yield/ ha with Giza 716 in the first season and Giza 843 in the second season, and for harvest index with Giza 843 in the first season. On the other hand, the lowest values were obtained with zero application of both macronutrients with Sakhal for number of pods/ plant, 100-seed weight, seed yield/ha and harvest index in the two seasons, and number of seeds/ plant in the second season, whereas Nubariah 3 gave the lowest number of seeds/ plant in the first season. Interaction between cultivars and P and/or K level were reported by Khalil et al. (2004), Ahmed and El-Abagy (2007), Ahmed et al. (2010) and El-Aal(2015).

The present investigation revealed the importance of appropriate fertilization with phosphorus and potassium for obtaining enhanced vegetative growth, higher seed yield and yield components. Fertilization with 74 kg P₂O₅ and 114kg K₂O /ha gave the highest seed yield indicating the importance of both macronutrients in acheiving high seed yield from faba bean.  The results also indicated  the importance of growing of faba been variety that performs well under the applied  phosphorus and potassium levels, in addition to its stable response to changing seasonal environmental conditions.