Micronutrient Indexing of Soils Located in Attock District of Pakistan: A Guide to Replenish the Nutrient Deficiency.

: The agricultural land of Attock district falls in Pothwar area of the Punjab Pakistan which is mostly rainfed ( barani ) and agriculture in the area depends on rainfall which is erratic and scanty. Therefore, soil health becomes more crucial for crop growth while application of micronutrients is negligible in this area. During the years from 2016 to2018, 15,337 soil samples were collected from the district Attock to determine micronutrient status of the soil. These soil samples were analyzed for Zinc (Zn), copper (Cu), Iron (Fe) and Manganse (Mn) using DTPA extraction method while dilute HCl method for Boron (B). The results indicated that nutrient index value of plant available Zn was in the marginal category (1.84) with 30.7% soil samples falling in low, 54.1% in marginal and 15.2% in adequate category. Nutrient index value of plant available Cu was in the adequate category (2.18) with 16.9 % soil samples in low, 47.9% in marginal and 35.2% in adequate category. Nutrient index value of plant available Fe was 1.46 (low) where 76.8% soil samples were found to be low and 23.2% adequate. Nutrient index value of plant available Mn was 1.11 (very low) where 89.3% soil samples were low, 9.9% marginal and only 0.8% adequate. Nutrient index value of plant available B was also in very low category (1.25) with 74.2% soil samples low and 25.8% marginal. The results indicated depletion and low concentration of micronutrient in most soil of Attock district which ultimately urges the use of balanced fertilizer for higher crop yield.


Introduction
The district of Attock lies between 33.46 o N latitude and 72.22 o E longitude comprising 692 thousand hectares of land area with 46 % under cultivation while 54 % is non cultivated. Major portion of area is comprised of plain agriculture land, mountains and barren land. Major crops grown in the district are wheat, maize and ground nut. The climate of the area varies from hot humid summers to dry cold winters. The maximum summer temperature is 50 0 C while minimum winter temperature is -2 0 C. Attock district falls in rainfed (barani) areas of Pakistan where rainfall pattern is erratic and unpredictable. Average annual rainfall is around 783 mm (Yunas et al., 2015). Thus, crop growth is dependent on rainfall and soil fertility status. Various nutrients, both macro and micro are required for achieving optimum yield potentional. However, micronutrient status of the soils is ignored in most of the cases which adversely affect quality and quantity of the produce. Microelements play a vital role in the growth and development of crops through regulating specific functions. Plants tend to maintain a balanced physiology by utilizing micronutrients as evident from various studies. The plants are prone to damage due to micronutrient deficiency. Key growth processes like cell development, protein synthesis, carbohydrate metabolism, chlorophyll synthesis, synthesis of growth hormones, respiration and redox reactions are regulated by micronutrients (Ahmed et al., 2017). There is widespread deficiency of micronutrients in plants and consequently in humans, specifically in developing countries like Pakistan. There are many reasons for micronutrient deficiency in soil including calcareousness, alkaline pH, low organic matter, and improper fertilizer usage (Malakouti, 2008). Micronutrient deficiency in plants results in symptoms like leaf chlorosis, de shaped leaves and stunted growth which ultimately deteriorate the fruit quality. Evaluation of micronutrient status of the soil can help in promoting balanced use of inputs and 4R nutrient stewardship i.e right nutrient, right rate, right time, right place (Soil Fertility Atlas of Pakistan, FAO 2017). The most prevalent micronutrient deficiency is of Zn in crops in the rain fed Pothowar plateau of Pakistan. It has been reported by Imtiaz et al., (2010) that most of the arable soils of Pakistan originated from alluvium and loess parent material and are naturally deficient in organic matter and most of the essential nutrients. It was ascertained through a research study by Malakouti, (2008) that keeping in view the vital role of micronutrients in elimination of hidden hunger and maintaining normal human health, more work is needed to evaluate the benefits of using their optimum level instead of viewing critical level as threshold with regard to crop yield and grain quality. Our farmers are still unaware about the role of micronutrient in crop production, micronutrient analysis and recommendation facilities. Hence, there is need to know the status of micronutrients in soils which will help to promote the use of micronutrient for crop production in rainfed areas.

Material and methods
During the period 2016-18, 15,337 soil samples were collected from the various location of Attock district to determine micronutrient status. The sampling depth was 0-15 cm. The samples were dried in the shade and were sieved using 2 mm sieve. The DTPA extractant was used to determine Fe, Cu, Zn and Mn in soil (Lindsay and Norvell, 1978) and diluted HCL was used for soil B extraction (Bingham, 1982). The micronutrient (Fe, Cu, Zn and Mn) contents were measured by Atomic Absorption Spectrometer and Boron by Spectrophotometer. The results were interpreted by statistical parameters like minimum, maximum, average and standard deviation etc. Nutrient index values: Nutrient index value was tabulated from the categorization of soil in low, medium and high nutrient levels as displayed by the following equation NIV = [(PH*3) + (PM*2) + (PL*1)] 100 Where, NIV = Nutrient index value PL, PM and PH are the %age of the soil samples found in the categories of low, medium and high nutrients status with numbering weightage of 1, 2 and 3 respectively (Ramamoorthy and Bajaj, 1969).

Classification of nutrient index value
Less than 1.33 = Very low 1.33 to 1.66 = Low 1.67 to 2.0 = Marginal 2.0 to 2.33 = Adequate 2.33 to 2.66 = High > 2.66 = Very high

Results
Micronutrient status of soil in district Attock on the basis of soil analysis for Fe, Cu, Zn, Mn, and B are presented in Table  Table 1 Soil analysis for Zn indicated > 80 % soil samples ranged between low (<0.5 mg kg -1 ) to marginal (0.5-1.0 mg kg -1 ) while <20 % of the soil samples were adequate (>1.0 mg kg -1 ). However, nutrient index value of plant available Zn was falling in the marginal category (1.84) as shown in Table 8.
The data analysis showed that up to 79 % soils were low in Fe and Fe content ranged 0.56-4.49 mgkg -1 . Around 25% soils were adequate in Fe with content ranging from 4.5 to12.30 mg kg -1 (Table 3). Nutrient Index Value of plant available Fe was 1.46 (low) as shown in Table 8.
Soil analysis of tehsil Attock revealed that 35% of soil samples had adequate level of Cu i.e. 2.01-4.63 mg kg -1 while almost 45% soils were marginal i.e. 0.2-0.49 mg kg -1 and almost 20% were low i.e. 0.04-0.19 mg kg -1 (Table 4). Nutrient index value of plant available Cu was in the adequate category (2.18) as shown in Table 8.
Nutrient index value of plant available Mn was 1.11 (very low) as shown in Table 8. The analytical results regarding Mn expressed that in tehsil Attock 86% soil samples had low Mn content ranging from 0.07 mg kg -1 to 0.99 mg kg -1 while 13% soil samples had marginal Mn between 1.0 mg kg -1 to 1.99 mg kg -1 .Only 1% soil samples had adequate iMn content varying from 2.0 mg kg -1 to 4.6 mg kg -1 ( Table 5).
The Nutrient index value of plant available B also fell in very low category (1.25). The analysis reflected that soil in tehsil Attock had low B in 75% soils containing B in range of 0.1 to 0.44 mg kg -1 while 25% soil samples had marginal level i.e. 0.45 to 0.91 mg kg-1. Boron status in tehsil Fateh Jang indicated that 74% soil samples had low B level ranging from 0.1 to 0.44 mg kg -1 while 26% soil samples had marginal level ranging from 0.45 to 0.90 mg kg -1 . In tehsil Hassan Abdal, 75% soil samples were low in B and ranged from0.11 to 0.44 mg kg-1 while 25% soil sample had marginal B ranging from 0.45 to 0.88 mg kg -1 . In tehsil Hazro, 75% soil samples had low B level falling in the range 0.1 to 0.44 mg kg -1 while 25% soil samples had marginal B status in the range of 0.45 to 0.90 mg kg -1 . In tehsil Jand, 73% soil samples were low in B ranging from 0.09 to 0.44 mg kg -1 while 27% soil samples had marginal B range from 0.45 to 0.88 mg kg -1 . In tehsil Pindi Gheb, 77% soil samples contained B in range of 010 to 0.44 mg kg -1 while 23% soil samples have marginal B content from 0.45 to 0.86 mg kg -1 (Table  6).  Dahar et al. (2014) also reported that all the soil series analyzed were found adequate in Mn  Attock  2216  329  24  2569  86  13  1  Fateh Jang  2746  316  29  3091  89  10  1  Hassan Abdal  1076  184  12  1272  85  14  1  Hazro  2111  155  08  2274  93  7  0  Jand  3904  312  27  4243  92  7  1  Pindi Gheb  1648  223  17  1888  87  12  1  Total  13701  1519  117  15337 89.3 9.9 0.8

Boron status in soil:
Boron is found in soil solution as BO3 -3 anion and taken up by plants in the same form. After Zn, boron is most vital microelement supporting membrane and structural stability in plants. Boron deficiency symptoms at first appear at young leaves and also depends on soil texture as sandy soils tend to have more B deficiency. Zia et al., 2006 described that B deficiency in Banana and apple orchards is widespread. It may be due to monsoon as B is highly soluble. Boron application offers resistance to premature fruit drop and improves fruit quality through its impact on Ca nutrition of fruits.

Discussion
The data revealed that the soils in the Attock district are low in Zn, Fe, Mn and B, Therefore, the quality of crops grown in micronutrient deficient soils may be affected and there is need for application of nutrient supplement. Zia et al., 2006 reported a largescale deficiency of soil Zn followed by Fe in Pakistan while there was occasional deficiency of Cu and Mn. The soils deficient in micronutrients not only result in rediced crop productivity but also grain quality is deteriorated (Imtiaz et al, 2010). The soils currently falling under marginal category regarding macro and micro nutrients would further degrade into low category in the coming years, hence the sustainable crop production techniques should be adopted (Ahmed et al, 2017). A study showed an increment of 4 to 11 % in wheat grain yields grown at 815 irrigated sites in Iran by the application of micronutrients (Fe, Zn, Cu and B) alone and in combination with NPK fertilizers (Malakouti, 2000). Zinc status in soil: Zinc plays a key role in synthesis of auxin from tryptophane, its solubility is related with pH, as the pH increases, Zn solubility decreases. The low status of zinc in all tehsils may be the result of alkaline nature of soils. Most of the samples fell under alkaline range of pH and 75% samples were found to be in low to marginal category of soil Zn as narrated by Ahmed et al, 2017. As the soil has inadequate zinc content to be available for crop plants, there is a dire need for ample provision of Zn fertilization to enhance soil nutrient pool in order to ensure optimum crop production (Dahar et al, 2014). As zinc was the first element in micronutrients which was categorized as essential nutrients for plant growth and it is impossible to get higher crop yields without its application. Harvest Plus project suggests that Zn and Fe contents in cereals grains must be in the range of 50-60 mg kg -1 to cope with malnutrition in human beings (Imtiaz et al, 2010). There was no zinc toxicity detected in plants as well as in soil in spite of some higher Zn concentrations (Malakouti, 2008). The results are in coincidence with Dahar et al, 2014 who indicated that 40 % of the soil samples were low in available Zn content.

Recommendations
It is critical that the available micronutrients status of cultivated soil should be known on a sustained basis to make sure its application as and when required so as to avoid decline in crop productivity and food quality. The status of micronutrient in the district Attock compel the farming community for following actions: 1. Organic matter improves micronutrient uptake to plants through metal organic chelation process occurring naturally in presence of it. Therefore, application of organic matter will help to improve micronutrient status of soils 2. The regular application of micronutrients to plants will ensure high productivity and quality. 3. Biofortification or more precisely Fertifortification will enrich edible part of the plants with micronutrients through fertilization. This strategy needed to be adopted in order to reduce human malnutrition. 4. Use of chelates to cope with the deficiency of micronutrients. 5. The calcareous soils are the other hindrance in availability of micronutrients to plants because theses soils have high pH. It is very important to apply micronutrients to crops on regular basis to improve crop health.