Using of Potassium Silicate to Alleviate Drought Stress Effect on Peanut as Grown in Sandy Soil

INTRODUCTION

Groundnut or peanut (Arachis hypogaea L.) is considered to be one of the most important edible legume crops in Egypt, due to its seeds has high nutritive value for human and the produced cake as well as the green leafy hay for livestock (Abdalla et al., 2009). Peanut is one of the most important cash crops, besides food crops and oil seed crops, in the world. However, most of the world’s peanut production is grown mostly under rain-fed conditions, where unpredicted and inadequate rainfall or drought seriously affects peanut production (Icrisat, 2011). Peanut is the world’s 4^th most essential edible oil crop and 3^rd most vital source of vegetable protein (CGIAR, 2005). Peanut is a vital legume crop grown in tropical and sub-tropical semi-arid regions of the world; the yield level is severely affected by deficiency of soil moisture. Peanut is a main seed legume in Egypt as compared with other oil crops (Arruda et al., 2015).

Drought is the most limiting factor, resulting in low yields in many parts of the world (Songsri et al., 2008). Drought during the pod filling phase of peanut is common and causes the greatest reduction in peanut pod yield (Ravindra et al., 1990). Also, Girdthai et al. (2010) stated that drought reduced pod yield up to 35% and biomass by 21%.Water deficit stress is one of the main environmental restraints limiting agricultural productivity and acts avital role in the distribution of plant species across different types of environments (Ashraf, 2010). Drought stress has been the major environmental factor responsible to yield losses in numerous crops worldwide. The losses are highly flexible reliant on timing, intensity, and period coupled with other location-specific environmental stress factors such as temperature and salinity (Kambiranda et al., 2012). Drought not only results in yield loss, but also is the chief reason for decrease innutritional quality of seed (Amir et al., 2005) and rises in aflatoxin contamination (Girdthai et al., 2010).

Silicon (Si) is one of the abundant elements in the lithosphere and it is the most abundant element in soil next to oxygen and comprises 28 percent of its weight and 3 - 7 percent in soil solution (Epstein, 1999). Si is most commonly found in soils in the form of solution as silicic acid and plants take up directly as silicic acid (Ma, et al., 2001). Application of silicon increased the shoot silicon concentration and dry matter production (Prakash, et al., 2011). Silicon can be enhanced plant resistance to manyabiotic stresses: salinity, drought, metal toxicity and ultra violet radiation (Balakhnina and Borkowska, 2013). Silicon spraying improved growth and physiological indices hence could increase the ability of plants to resistance water stress. Silicon application reduces transpiration leads to water stress tolerance (Asgharipour and Mosapour, 2016). The role of silicon in plant biology is to decrease various stresses such asbiotic and abiotic stresses. Si helps to protect crops from insect attack, disease and environmental stress. In organic farming system, the addition of silicon sources to crops may increase the yield and decreasing the use of chemical fertilizers, pesticides and fungicides (Patil, et al., 2017). Si can improve growth, biomass and yield of wide range of crops including monocotyledonous crops that have the capability to collect high amounts of Si in their organs (Shedeed,2018).

Foliar application of K- silicate has many benefits in enhancing leaf erectness and photosynthesis efficiency also decreasing capability to lodging in herbal crops (Ahmad et al., 2013). In addition, Si offers benefits in numerous agricultural applications e.g. increases growth and yield, improves strength, minimize climate stress and provides impedance to mineral stress. On this way Kandil et al. (2019) found that K- silicate increased yield, yield components and quality of soybean under environmental stress.Also, Gomaa et al. (2020) and Gomaa et al. (2021b) revealed that foliar application of  K-silicate three times resulted in the highest growth, yield and grain characters can increase WUE of maize. On the other hand, under water-deficit stress, irrigation every fifteen days combined with application of K-silicate spraying in three times recorded the highest values of growth and grain yield and its components. Also, El-Naggar et al. (2020) indicated that using Si in Nanoparticles increased yield and its components of maize. Gomaa et al. (2021a) showed that application of Si increased yield and its components of maize.

The overall objective of the present research was to study the role of foliar application of potassium silicate for alleviating drought stress effect on peanut grown in sandy soil.

MATERIALS AND METHODS

                        Two field Experiments were conducted at Abd El-Maneim Ryad, South Tahrir, Beheira, Governorate, Egypt, in the summer growing seasons of 2017 and 2018 to study the alleviating drought stress effect on peanut grown in sandy soil using foliar application of potassium silicate.

The preceding crop was Potato (Solanum tuberosum L.) in the two seasons. The physical and chemical properties of experimental soil are presented in Table (1) according to the method described by Page et al. (1982).

Table (1). The initial physical and chemical properties of the experimental soil seasons of 2017 and 2018

Experimental layout

The experiments were carried out in a split plot design with three replicates, where the irrigation treatment i.e. (irrigation after depletion of 40 %, 55%, 70% and 85% available soil water) was applied after ten days from planting were arranged in the main plots, then the four potassium silicate (control=spray tap water, 500, 1000 and 1500 mg/l silicate) as applied after 35, 45, 55 and 65 days from planting and were allocated in the subplots.

Peanut (Arachis hypogaea L.) variety Giza 6 were planted on 20^th April and harvested on 18^th of August in the two seasons 2017 and 2018.

Table (2). Field capacity (FC), permanent wilting point (PWP), available soil water (ASW), and bulk density (BD) of the experimental soil.

Determination of available water

AW(mm)  = (q_fc - q_pwp)Dr

AW(%)  = (q_fc - q_pwp)

Where:

AW = depth of water available

q_fc = volumetric field capacity

q_pwp = volumetric permanent wilting point

Dr = depth  of  root  zone

Determination of depletion (%)

Depletion of 40% available soil water = 0.40 x AW(%)   

Depletion of 55% available soil water = 0.55 x AW(%)   

Depletion of 70% available soil water = 0.70 x AW(%)   

Depletion of 85% available soil water = 0.85 x AW(%)

Soil moisture (%) was measured using the following equation:

Soil moisture (%) =  × 100

To convert into volumetric moisture content, the dry weight fraction is multiplied by the bulk density, g _b

Irrigation treatments

Irrigation after depletion of 40% available soil water

                                             = field capacity - depletion of 40% available soil water

Irrigation after depletion of 55% available soil water

                                             = field capacity - depletion of 55% available soil water

Irrigation after depletion of 70% available soil water

                                             = field capacity - depletion of 70% available soil water

Irrigation after depletion of 85% available soil water

                                                             = field capacity - depletion of 85% available soil water

Fertilizer application

Before sowing were applied 300 kg/fed super phosphate calcium and 100 kg sulphur/fed during soil preparation. After sowing all experimental units were received fertilizer as 40 and 25 kg/fed of N and K, respectively.  Sources of these fertilizers were ammonium nitrate (33.5% N) and potassium sulphate (50% K₂O), while, N fertilizer was added in four equal doses and K fertilizer were added in two equal doses during vegetative growth. The experimental units were hand hoed three times for controlling. Other agricultural practices were done as recommended by the Ministry of Agriculture and Land Reclamation.

Studied characters

Yield and yield components such as 100-pods weight (g), no. of pods/plant,  pods yield (kg/fed), straw yield (kg/fed), biological yield (kg/fed), and harvest index (%) as well as chemical composition such as proline (mg/g) and oil (%) in addition to water use efficiency (Kg/m³)  were studied.

3.5 Statistical analysis

The obtained data were subjected to the proper method of statistical analysis of variance as described by Gomez and Gomez (1984). The treatment means were compared using the least significant differences (L.S.D.) at 0.05 level of probability by SAS (Statistical Analysis System) version 9.1 (2002).

RESULTS AND DISCUSSION

A)     Yield and yield components

Result tabulated in Table (3) showed irrigation after depletion of 55% available soil water recorded the heaviest 100 pods weight (209.36 and 198.80 g), maximum number of pods/plant (43.25 and 39.81) and pods yield (2910.74 and 2374.46 kg/fed) in two seasons, respectively, as compared to irrigation after depletion of 40% available soil water which recorded the lowest 100 pods weight (162.70 and 154.56 g), minimum number of pods/plant (28.66 and 26.45) and pods yield/fed (2514.17 and 2114.01 kg), during both seasons, respectively. Number of pods per plant was the most vulnerable item damaged by drought stress (Pandey et al., 1984). The effect of drought stress on the yield of three bean cultivars showed that stress at flowering stage reduced the number of pods per plant and seeds per pod in all three varieties (Fienebaum et al., 1991). The number of pods/plant reduced due to drought stress (Seyed et al., 2011). Also, Gomaa et al. (2020) and Gomaa et al. (2021b) reported the similar results, who found that water stress reduced growth and yield characters of maize.

The yield advantages due to moderate water deficit during the pre-flowering phase are associated with greater pod synchrony after the release of water stress, resulting in production of more mature pods (Nageswara et al., 1988). When stress is released, the plant try to set more fruiting sites with the existing assimilates as the vegetative site demanding assimilate supply are reduced. To improve the conventional irrigation management practices to enhance yield and water use efficiency in groundnut during summer seasons a field experiment was conducted by Nautiyal et al. (2002) where dry matter partitioning among various plant parts, and leaf area index (LAI) varied significantly under water deficit and more dry matter accumulated in petiole and stem under stress. The pod development are progressively inhibited by drought due to insufficient soil moisture and lack of assimilate (Reddy et al., 2003). Girdthai et al. (2010) found that peanut pod yield is decreased when subjected to drought stress due to reduction in the photosynthetic rate and disrupts the carbohydrate metabolism (Farooq et al., 2009). Moreover, most of stressed peanut genotypes had lower pod growth rate than peanut having Field capacity (FC) treatment, indicating that the assimilate portion may enhance to support the economic part. Prabawo et al. (1990) reported that re-watering after pod filling stages increased pod yields of Spanish type peanuts. Yield loss caused by moisture stress depends on genotype, plant developmental stage, severity and duration of water shortage (Korte et al., 1993).Under drought conditions, the peanut agronomic characteristics and grain yield of all cultivars decreased and a significant reaction of the genotypes was observed (Vorasoot et al., 2003).

In this respect, increasing the concentration of potassium silicate foliar application  increased 100 pods weight, number of pods/plant and pods yield/fed,whereas, foliar application of potassium silicate at 1500 mg/l silicate recorded the maximum 100 pods weight (214.75 and 204.01 g), number of pods/plant (42.17 and 38.79)and pods yield/fed (2965.97 and 2610.04 kg), as compared to control treatment which recorded the lowest mean values of 100-pods weight (156.55 and 147.42 g), number of pods/plant (30.74 and 28.35) and pods yield/ fed  (2420.99 and 1902.72 kg) during both seasons, respectively. These results are agreement with those results reported by Gomaa et al. (2020) and Gomaa et al. (2021a)

The interaction between irrigation treatments (A) and potassium silicate concentration (B) was significant on 100 pods weight, number of pods/plant and pods yield/fed during both seasons.The greatest values of these traits were recorded when peanut crop were irrigated after depletion of 55% available soil water under foliar application of potassium silicate at 1500 mg/l silicate, whereas the lowest values resulted from irrigation after depletion of 40% available soil water under tap water spray (control) during both seasons.

-          Irrigation level: irrigation after depletion of 40 %, 55%, 70% and 85% available soil water.

Means followed by the same letter within each column are not significant different at 0.05 level of probability.

*    Denotes significant at 0.05 level of probability.

The results in Table (4) illustrated that irrigation after depletion of 55% available soil water recorded the highest straw yield/fed (2598.52 and 2858.34 kg) and biological yield/fed (5509.26 and 5232.80 kg) during the two seasons, respectively, as compared to irrigation after  depletion of 40% available soil water which recorded the minimum straw yield/ fed (1330.38 and 1463.33 kg) and biological yield/fed (3844.56 and 3577.34 kg), while, irrigation after depletion of 40% available soil water recorded the highest percentage of harvest index (48.50 and 49.05 %), respectively, as compared to irrigation after depletion of 55% available soil water which recorded the minimum harvest index (40.37 and 40.70%), during both seasons, respectively.

Toprope et al. (2004) reported that Harvest index (HI) was the critical measure of water use efficiency under water deficit stress conditions. Greater HI was observed at pegging and pod development stage under drought conditions. Yield loss caused by moisture stress depends on genotype, plant developmental stage, severity and duration of water shortage (Korte et al., 1993).Under drought conditions, the peanut agronomic characteristics and grain yield of all cultivars decreased, and a significant reaction of the genotypes was observed (Vorasoot et al., 2003).

Also, data in Table (4) indicated that all potassium silicate concentration significantly increased straw yield/fed and biological yield/fed, generally, potassium silicate concentration at 1500 mg/l silicate recorded the highest straw yield/fed (2230.47 and 2453.51 kg) and biological yield/ fed (5196.44 and 5063.55 kg), while, potassium silicate at control recorded the highest harvest index percentage (44.77 and 46.85%), respectively, as compared with all treatments during both seasons.

The interaction between irrigation treatments and potassium silicate concentration was highly significant for straw yield/fed, biological yield and not significant for harvest index percentage during both seasons. The maximum values of the straw yield/fed and biological yield/fed were recorded when peanut crop were irrigated after depletion of 55% available soil water under foliar application of potassium silicate at 1500 mg/l silicate in both seasons, whereas the lowest ones were given with irrigation after depletion of 40% available soil water under tap water spray (control) in both cropping seasons. Harvest index (%) under irrigation after depletion of 40% available soil water and tap water spray (control) recorded the maximum values, while, the minimum values recorded under irrigation after depletion of 55% available soil water  and foliar application of potassium silicate at 1500 mg/l silicate during both cropping seasons.

Table (4). Effect of irrigation levels (A) potassium silicate (B) and their interaction (A * B) for straw, biological yield and harvest index during 2017 and 2018 seasons.

-          Irrigation level: irrigation after depletion of 40 %, 55%, 70% and 85% available soil water.

Means followed by the same letter within each column are not significant different at 0.05 level of probability.

** Denotes significant at 0.01 level of probability.

ns, Denotes not significant.

  B ) Chemical composition

The perusal of results in Table (5) indicated that irrigation after  depletion of 85% available soil water recorded the highest proline content (236.08 and 219.55 mg/g) in two seasons, respectively, as compared to irrigation after depletion of 40% available soil water which recorded the minimum proline content (187.19 and 174.09 mg/g), during both seasons, respectively. The proline content enhances the drought stress progressed and reached a peak as obtained after 10 days stress, and then decreased under severe water stress as observed after 15 days of stress (Anjum et al., 2011). Proline can act as a signaling molecule to modulate mitochondrial functions, influence cell proliferation or cell death and trigger specific gene expression, which can be essential for plant recovery from stress (Szabados and Savoure, 2010). Accumulation of proline under stress in many plants has been related with stress tolerance, and its concentration has been revealed to be generally higher in stress-tolerant than in stress-sensitive plants  (Demiral and Turkan, 2005).

In another side, increasing potassium silicate concentration decreased proline content, during both seasons. However, potassium silicate at 1500   mg/lsilicate   gave the lowest mean values of proline content (181.18and 168.96 mg/g), as compared to control treatment which recorded the highest mean values of proline content (249.22 and 231.77 mg/g), during both seasons, respectively. These findings may be related to the synergistic effect of the two studied factors on the different biochemical pathways in the plant cell. Silicon moderately offset the negative effects of drought stress by accumulation of proline and soluble protein content, thereby conferring stress tolerance (Sapre and Vakharia, 2016). In contrast, Crusciol et al. (2009) and Pilon et al. (2014) stated that proline (%) in leaves increased under water-deficit stress and higher silicon availability, which shows that silicon may be helpwith plant osmotic adjustment. Mauad et al. (2016) indicates that under water stress conditions, silicon application the proline content in the vegetative and reproductive phases of rice plants, which could be an indicator of stress tolerance.

The interaction between irrigation treatments and potassium silicate concentration was highly significant on proline content during both seasons. Irrigation after  depletion of 85% available soil water recorded the highest proline content under the foliar spraying of tap water.

Results resented in Table (5) showed that irrigation after depletion of 40% available soil water recorded the highest oil percentage (45.31 and 42.14 %), as compared to irrigation after  depletion of 85% available soil water which recorded the lowest oil percentage (34.36 and 31.95 %), during both seasons, respectively.

With regards to the effect of foliar application of different concentrations of potassium silicate increased oil percentage, during 2017 and 2018 seasons. Whereas, foliar application of potassium silicate at 1500 mg/l silicate recorded the best content of oil percentage (45.51 and 42.32 %), followed by potassium silicate at 1000 mg/l silicate (40.95 and 38.09 %), as compared to control treatment which recorded the lowest mean values of oil percentage (33.17 and 30.85 %), during both seasons, respectively.

The interaction between irrigation treatments and potassium silicate concentration was highly significant on oil percentage during both seasons. Oil content recorded the best results under irrigation after depletion of 40% available soil water with foliar spraying of potassium silicate at 1500 mg/l silicate in both seasons.

C) Water use efficiency

Results in Table (6) showed that increasing drought levels increased water use efficiency during both seasons. However, irrigation after depletion of 85% available soil water recorded the highest water use efficiency (0.835 and 0.706 Kg/m³),followed by irrigation after depletion of 70% available soil water(0.779 and 0.655 Kg/m³), as compared to irrigation after depletion of 40% available soil water which recorded the lowest mean value of water use efficiency (0.492 and 0.414 Kg/m³), during both seasons.

Where water is the limiting factor to crop production, deficit irrigation can enhance WUE, so that the available water is better allocated. Water use efficiency (WUE) calculated as the harvested yield (kg) per volume of irrigation water (m³) according to FAO recommendations (Doorenbos and Kassam, 1979). Out of several biotic and abiotic factors responsible, optimum water management is one of the most important factors that significantly influence productivity as well as the quality of the production (Bhriguvanshi et al., 2012).

In another side, increasing potassium silicate concentration increased water use efficiency (WUE), during 2017 and 2018 seasons. However, potassium silicate at 1500   mg/l silicate   gave the highest mean values of water use efficiency (0.782 and 0.688 kg/m³), as compared to control treatment which recorded the lowest mean values of water use efficiency (0.637 and 0.501 kg/m³),  during both seasons, respectively.

WUE under water stress may be due to the vital role of K-silicate in reducing water-deficit stress on plant growth and yield (Gomaa et al. 2021b).

The interaction between irrigation treatments and potassium silicate concentration was highly significant on water use efficiency during both seasons. WUE under irrigation after  depletion of 85% available soil water and foliar spraying with K-silicate at 1500 mg/l silicate gave the highest values followed by irrigation after depletion of 70% available soil water under the same foliar spray of  K-silicate.

-          Irrigation level: irrigation after depletion of 40 %, 55%, 70% and 85% available soil water.

Means followed by the same letter within each column are not significant different at 0.05 level

of probability.

** Denotes significant at 0.01 level of probability.