Seed priming with iron and zinc improves growth and yield of groundnut ( Arachis hypogaea L . )

Seed priming is considered as an important component that results in early establishment of crop seedling. Thus, the effect of seed priming with iron (Fe) and zinc (Zn) on growth and yield components of groundnut (cv. BARI-2011) was evaluated by using different doses of Fe (0.1% and 0.3%) and Zn (0.5% and 1.0%) in RCBD design with two factors factorial arrangement having three replications. The crop was grown in April, 2016 at the Research Farm of PMASArid Agriculture University, Rawalpindi, (Pothowar Pleatue) Punjab, Pakistan. Data revealed that plant height and number of plants were highest at 0.3% Fe in combination with 1.0% Zn. Similarly, numerical values for all measured yield components i.e., number of pods plant, kernel weight (kg ha), 100 kernel weight (g), pod yield (kg ha), biological yield (kg ha), harvest index (HI) and shelling percentage were significantly higher at 0.3% Fe in combination with 1.0% Zn as compared to the control. The control plot resulted in the lowest values for all the parameters studied. It can be inferred from the results that seed priming at the rate of 0.3% Fe in combination with 1% Zn is recommended for obtaining higher yield of groundnut.


Introduction
Groundnut (Arachis hypogaea L.) is the fourth-largest oilseed crop in the world, cultivated in more than 100 countries [1].Worldwide, it is cultivated on 25.41 million hectares whereas the share of Pakistan is 0.0938 million hectares [2].Groundnut is used for direct consumption, in confectionary industry and as a vegetable oil for cooking.Moreover, groundnut restores nitrogen into the soil by fixing it without upsetting non-renewable resources or disturbing balance in the environment and thus is considered as one of the most important legume crop [3].In Pakistan, groundnut is grown mainly in rainfed areas.In 2011-12, out of total peanut cultivated area, about 91% lies in Punjab, 8% in Khyber Pakhtun khwa (KPK), and 1% in Sindh [4].About 85% of total area under groundnut cultivation in Punjab lies in the Pothowar tract, producing 71% of the country's total production [5].Among other factors, micronutrient deficiency is an important factor for low crop productivity of groundnut in these areas.Zinc plays a vital role in the germination and crop growth [6, 7] but overall Pakistani soils are deficient in micronutrients, especially in Zinc, Iron and Copper [8].
Due to the calcareous nature of soils, in many arid areas, alkaline pH, poor organic matter status, salinity, drought stress and improper utilization of fertilizer, deficiency of micronutrients is a common problem in plants, [9,10]  In the light of the importance of micronutrients, the main objective of the present study was to evaluate the effects of seed priming with micronutrients i.e. iron and zinc on the growth, yield and yield components of groundnut.

Materials and methods
The study was carried out to determine the effects of seed priming with Fe and Zn on the growth and yield of groundnut from April to October, 2016 at University Research Farm (33.11°N latitude to 73.01° E longitude), Chakwaal Road, PMAS-Arid Agriculture University, Rawalpindi (Pothwar pleatue), Punjab, Pakistan.The climate of the region is semi-arid with annual rainfall of 850 mm and soil of the farm varies from sandy loam to loam in texture with pH ranging from 7.7 to 7.8.An approved variety of groundnut (cv.BARI-2011) was used.The seeds of groundnut were obtained from National Agricultural Research Center, Islamabad, Pakistan.The seeds were sown using hand drill in rows at a depth of 2-3 cm from the soil surface.Row-row and plant-plant distance was maintained at 45 and 10 cm, respectively.The experiment was laid out in a Randomized Complete Block Design (RCBD) with two factors factorial arrangement (Fe and Zn) and replicated three times.The field was divided into 3 blocks, each containing 9 plots of size 3.15 m × 3 m with a total plot size of 330 m 2 .Three levels of iron, viz.[0 (control), 0.1% and 0.3% solution] and three levels of zinc, viz.[0 (control), 0.5% and 1% solution] were used to treat the groundnut seeds before sowing.Solutions of the required concentrations of Fe and Zn were prepared in 9 beakers and the seeds were soaked in these solutions for 8 hours.Treatment combinations were randomly allocated in each block.Basal dose of fertilizer was applied at the rate of 30-80-30 NPK kg ha -1 .The crop was sown only on rain water.No irrigation was given throughout the growing season of the crop.The studied growth parameters were: number of plants (m -2 ) at maturity, plant height (cm) and yield and yield contributing parameters were: number of pods plant -1 , kernel weight (kg ha -1 ), hundred kernel weight (g), pod yield (kg ha -1 ), biological yield (kg ha -1 ), harvest index (HI) and shelling percentage (SP).Harvest index for each plot was calculated by using the following formula: Harvest Index (HI) = (Grain Yield / Biological Yield) × 100 Shelling percentage for each plot was calculated by dividing the kernel weight (kg ha -1 ) with pod weight (kg ha -1 ) and then multiplied by 100.The formula used to calculate shelling percentage was as follows Shelling Percentage (SP) = (Kernel Weight / Pod Weight) × 100 Collected data was subjected to analysis of variance (ANOVA) by Statistics 8.1 and the differences among treatment means were compared by Tukey's honest significant difference test (HSD).

Soil sampling
Soil sampling was done with the help of agar for soil fertility determination before sowing and after harvesting.The samples were collected from 5 randomly selected points from the field at the depth of 15 cm and composite sample was prepared.The analysis was carried out at the Laboratory, Department of Soil Fertility Analysis and Water Status, Rawalpindi, Pakistan for the determination of soil iron and zinc status.
The soil analysis showed that the soil was low in both micronutrients.The levels of iron and zinc in the soil before sowing were 0.83 and 0.56 ppm, respectively.After harvesting, it was observed that the levels of iron and zinc were considerably low i.e., 0.27 and 0.35 ppm, respectively.

Growth parameters
The number of plants and plant height calculated at maturity was significantly affected by the levels of iron while in case of zinc, the effect was significant for number of plants and non-significant for plant height (Figure 1 and 2).It was noticed that the number of plants increased with increase in iron and zinc concentrations.Maximum number of plants (m -2 ) of groundnut was recorded at the highest tested concentrations for both the micronutrients (0.3% Fe and 1% Zn) and the lowest number of plants was found in the control.The data presented in Figure 1 depicted that the plant height responded positively to iron application.The plant height of groundnut was increased with the increase in iron concentrations where taller plants (41.50 cm) of groundnut were recorded at 0.3% Fe and shorter plant height were found in the control i.e., 35.46 cm.The interaction (Fe × Zn) was significant for number of plants and plant height of groundnut (Table 1).The interaction 0.3% Fe × 1% Zn produced 20 plants m -2 of groundnut but the effect of Fe was more visible as compared to Zn.Because seed priming with 0.3% Fe resulted in significantly higher number of plants (18.8 m -2 ), compared to seed priming with 1% Zn where number of plants (15.6 m -2 ) was found which was non-significantly higher than the control.The interaction effect of the highest levels of micronutrients (0.3% Fe × 1% Zn) produced the maximum plant height of groundnut, i.e., 42.3 cm that was statistically at par with the interactions 0.3% Fe, 0.3% Fe × 0.5% Zn and 0.1% Fe × 1% Zn (Table 1).The minimum (34.5 cm) plant height of groundnut was recorded in the control.

Yield components
The number of pods plant -1 , kernel weight, 100 kernel weight, pod yield, biological yield, harvest index and shelling percentage were significantly affected by the levels of iron and zinc (Table 2).It was noticed that yield and all yield components increased by using higher doses of iron and zinc.Maximum values for number of pods (42.7), kernel weight (1715.6 kg ha -1 ), 100 kernel weight (60.4 g), pod yield (2537.2 kg ha -1 ), biological yield (7623.9 kg ha -1 ), harvest index (22.5 %) and shelling % (67.6) were recorded at 0.3 % Fe level.As compared to the treated plots, control resulted in lower values for all the variables.The interaction effect of Fe and Zn on the yield and yield components of groundnut was also significant (Table 3).The interaction (0.3% Fe × 1.0% Zn) produced significantly higher pod yield (2603.8 kg ha - 1 ) of groundnut followed by 0.3% Fe × 0.5% Zn.The other interaction was found to be non-significant with each other.

Table 3 . Interaction effect of various levels of Fe and Zn on the yield and yield components of groundnut Interactions No. of Pods plant -1 Kernel Weight (kg ha -1 ) 100 Kernel weight (g) Pod Yield (kg ha -1 ) Biological Yield (kg ha -1 )
These research findings have an implication for enhancement of yield of groundnut which can be further implied on other leguminous crops.Moreover, further investigation on higher levels above 0.3% and 1% of Fe and Zn, respectively can be a step forward to identify the highest beneficial levels of Fe and Zn.Finally, these findings will help motivate our farmer to adopt seed priming technique to apply micronutrients like Fe and Zn in more efficient and effective way.