Micronutrient availability in soils of Northwest Bosnia and Herzegovina in relation to silage maize production

ABSTRACT

Maize (Zea mays L.) is the most widely grown crop in Bosnia and Herzegovina especially in Northwest part of the country. Considering that, the maize is extremely sensitive to micronutrient deficiency the main aim of this study was to asses: (1) micronutrient availability in soil, (2) micronutrient status in silage maize; and (3) the relationship between micronutrient soil availability and maize plant concentration. Soil samples for micronutrient availability (n = 112) were collected from 28 farms in 7 municipalities. Plant available micro- and macro- nutrients in soil were extracted using Mehlich-3, except plant available Se was extracted using 0.1M KH₂PO₄. Result showed that on average there was no significant difference between different soil types regarding their potential in plant available nutrients. P deficiency was present both, in soil and plants in whole region. Soil extractable P was ranging from 0.003–0.13 g kg⁻¹ and total plant P was ranging from 0.79–4.95 g kg⁻¹. Zinc deficiency was observed in two locations both in soil (0.71 mg kg⁻¹; 0.79 mg kg⁻¹) and plant (11.5 mg kg⁻¹; 15.8 mg kg⁻¹). Potential Se soil deficiency was observed on some locations, while Se plant status is not high enough to meet daily requirements of farm animals. Extractable soil nutrients could be used as relatively good predictor of potential soil and plant deficiencies, but soil nutrient interactions and climate conditions are highly effecting the plant uptake potential.

KEYWORDS:

• Micronutrients
• plant uptake
• deficiency
• maize
• nutrient availability

Introduction

Micronutrients represent those trace elements, which are essential for the normal physiological development, growth and reproduction of plants, animals and humans. The trace elements: boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni) and are essential for plants, while chromium (Cr), fluorine (F), iodine (I), copper (Cu), iron (Fe), zinc (Zn) and selenium (Se) are considered essential for animals (Alloway 2008; Fageria et al. 2012). Micronutrient concentrations in feed and food derived from plants positively affect animal and human health and well-being. However, some micronutrients that are essential for growth and development of plants do not have same importance for animals and vice versa (Welch and Graham 2004; Gupta et al. 2008; Marschner 2012).

Micronutrient malnutrition results from crops produced on soil with poor phytoavailability of the elements essential for animal and human nutrition (Bouis et al. 2011; Cakmak and Kutman 2017). Globally micronutrient deficiency creates serious human health problems, largely in countries of the developing world, linked mainly to low quality and quantity of agriculture products in these countries (Bouis et al. 2011; Oliver and Gregory 2015; Paul and Dey 2015). In addition, livestock requirements for some micronutrients, e.g. Zn and Fe, are much greater than the levels sufficient for good crop yields (Gupta and Gupta 2005).

Concentrations and availability of micronutrients in soils of Western Balkan vary widely among countries. Deficient concentration of trace elements in soils, plants, and animals have been reported in several areas of Western Balkan region. Soil samples from Eastern Croatia showed low availability of Zn, Fe and Cu (Karalić et al. 2015). Concentrations of Zn in alfalfa samples from Serbia and maize samples from Croatia were below the critical deficiency level and below the dietary requirements for ruminants (Manojlović and Singh 2012). Analysis of 105 sheep and 160 cow blood samples from Bosnia and Herzegovina, Kosovo, Serbia and Croatia showed that animals have low Se nutrition, and therefore it was highlighted that animal feed needs to be supplemented by Se to ensure a better Se nutrition of animals (Ademi et al. 2015). Moreover, toxic levels of Cu, Fe and Ni were recorded in soils near heavy industry areas and mining facilities (Popovic et al. 2011; Manojlović and Singh 2012). Recent research in this region indicate that soil availability of macronutrients is mainly affected by different soil factors including: pH, soil organic matter, fertilisation application and micronutrient concentration in soil (Manojlović and Singh 2012).

Of the total area of Bosnia and Herzegovina (B&H) (51.000 km²), 50.3% is arable land and the remaining is under forests (Čustović et al. 2013). Around 15.16% of the arable land in B&H is suitable for intensive agriculture production, and it is mainly located in the northern part of the country and in the major river valleys (Alibegovic-Grbic 2009). Bosnia and Herzegovina has heterogenic soils because of a great diversity of geological base, climate, vegetation, and pedo-fauna (Manojlović and Singh 2012). This soil heterogeneity is also present in Northwest area of the B&H (Figure 1).

Figure 1. Soil map of Northern Bosnia and Herzegovina.

Maize (Zea mays L.) is the main field crop in B&H and it occupies 19% of arable land on average and it is mostly grown in the northern part of the country (Kovačević et al. 2013). Maize is extremely sensitive to micronutrient deficiency, especially Zn and Fe. In recent years, farmers recognised the need to use micronutrient fertilisers and made it a regular agronomic practice (Alloway 2009; Subedi and Ma 2009). Maize produced in B&H is predominantly used for livestock feed as grain or whole plant in the form of silage. Moreover, B&H has the highest maize consumption per person per day in Europe (181 g/person/day) (Ranum et al. 2014). High-quality maize silage includes corresponding mineral status where micronutrients play an important role. Therefore, adequate micronutrient concentrations in maize plants are very important for crop productivity and its nutritive value.

Despite the known strategies to avoid micronutrient deficiency in soils, crops and feed, there are still regions in Europe that have micronutrient deficiency symptoms in animals. As mentioned above, the reasons for this deficiency are divers form soil properties to soil-plant relationship. It is important to assess the extent of micronutrient deficiency in soils and crops in various regions and to identify regional differences so that corrective measures could be applied in that way to maximise effect under local conditions. Micronutrient availability is scarcely studied in B&H.

Therefore, the aim of this study was to asses: (1) micronutrient availability in soil (2) micronutrient status in silage maize; and (3) the relationship between micronutrient soil availability and maize plant concentration.

Materials and methods

Geographical description of the region

Northwest region of B&H is considered the border region of Pannonia basin with moderate continental climate with warm summers and cold, snowy winters. Arable land is mainly located in the Sava River valley and its tributaries Una and Vrbas and on the slopes of regional mountains Kozara, Prosara, Motajica and Manjaca, with elevation ranging from 80 to 280 m above sea level. Soils in this region are predominantly hydromorphic, with fluvisols as major soil type.

Sampling

Soil samples for micronutrient availability (n = 112) were collected from 28 locations in 7 municipalities, 4 locations per municipality, of Northwest B&H, cowering approximately 27000 ha of the arable land. Soil samples were taken from plough layer (0–25 cm), every sample consisted of 4–6 subsamples. Soil samples for pH and soil organic matter (n = 350) were collected as part of the survey performed by the Agriculture Institute of Republic of Srpska. Plant samples (n = 112) (maize ear leaf) were collected from the same locations as soil samples, where 6 maize ear leafs were collected for each sample. Both soil and plant samples were collected randomly on the maize fields so that sites together should be relatively uniformly distributed and representative for arable land and different soil types (Figure 2) in the region.

Figure 2. Soil sampling locations (farms) in Northwest Bosnia and Herzegovina.

Soil sample preparation and analysis

Soil samples were air- dried at 30°C and screened through a sieve (2 mm diameter). Soil pH was determined at a 1:2.5 soil–solution ratio in deionised water. Ten grams of air-dry soil was mixed with 25 ml of deionised H₂O and centrifuged on 4600 round/min for 10 min, pH was measured with pH meter. Soil organic carbon (SOC) was determined on a LECO elemental analyser. Plant available micro- and macro- nutrients, except Se, in soil were extracted using Mehlich-3 (M3) (Mehlich 1984) method. Analysis of M3 extracted nutrients was performed using inductively coupled plasma optical emission spectrometry (ICP-OES). Plant available Se was extracted using 0.1M KH₂PO₄, where in 5 g of soil and 20 mil of 0.1M KH₂PO₄ was mixed and shaken for 30 min at 175 round/min, solution was than filtered and 10 mil were used for further analysis. Analysis of plant available Se was performed using hydride generation atomic absorption spectrophotometry (AAS).

Plant sample preparation and analysis

Plant samples (maize ear leafs) were washed with deionised water and dried at 70°C for four days. Dried and ground plant samples were subjected to acid-digestion [.0.2 g sample in a mixture containing 2 mL of 30% (v/v) H2O2 and 5 mL of 65% (v/v) HNO3] in a closed-vessel microwave system. The digested material was diluted with DI water. Nutrient concentration, except Se, in the digested solution was determined by using inductively coupled plasma optical emission spectrometry (ICP-OES). Plant Se concentration analysis was performed using hydride generation atomic absorption spectrophotometry (AAS).

Statistical analysis

Descriptive statistics was used for the calculation of average values, standard deviation, and the range of values. The principal components analysis (PCA) was used to establish the relationship between the concentrations of macro- and microelements in soils and relationship between soils nutrient level and plant nutrient concentration. PCA was applied to a data matrix consisting of the concentration of macro- and microelements in plants (columns) and the observed locations (rows), data was standardised and centralised. Pearson’s correlation test was used to test correlation significance; data was log-transformed by using the generalised log transform formula [b = log(x + xmin)−log(xmin)] where it was necessary. Statistical analysis was performed by using R software, version 3.2.3.

Results and discussion

Observed soil and plant samples showed different chemical properties. The soil pH varied from acidic (4.9) to moderately alkaline (7.6), although Marković et al. (2011) reported that 60% of the soil samples in north-west of B&H had pH lower than 4.5. Considering the pH range 4.9–7.6 on observed locations, the potential phytoavailability of micronutrient is expected to be high. Soil organic carbon concentration varied among the samples, ranging from 11.2 (g kg⁻¹) to 26.8 (g kg⁻¹) (Table 1). Low soil organic matter is common in the soils of northwest B&H and it is mainly affected by the type of agriculture production in the region (Komljenovic et al. 2010; Marković et al. 2011).

Table 1. Soil pH and soil organic carbon in different soil types observed in Northwest Bosnia and Herzegovina on 28 farms.

Soil type	pH			Soil organic carbon (g kg^−1)
	Average	SD	Range	Average	SD	Range
Fluvisols	6.1	0.78	4.9–7.5	18.1	3.83	12.6–26.2
Gleysols	6.4	1.05	5.6–7.6	20.9	4.7	17.5–26.8
Podzoluvisols	5.9	0.69	5.1–6.7	18.2	5.57	11.2–21.8
Vertisols	5.5	0.79	5.1–5.9	15.2	0.63	14.7–15.8
Luvisols	5.9	0.68	5.4–6.7	15.3	3.05	14.2–16.2

Assessing the concentrations of soil extractable nutrients is good way to predict nutrient phytoavailability compared to total nutrient concentration in the soil (Brennan et al. 2008). Average soil extractable concentrations and plant concentration for analysed macronutrients K, P, S, Mg, Ca and Na are given in Table 2. Results indicate that soil extractable concentrations were sufficient for proper plant development. Although, low soil P extractable concentration is noticeable both in the region as whole (Table 2) and in different soil types (Table 3), which is a consequence of general low P status in soils of this region (Komljenovic et al. 2010; Čustović et al. 2013). Principle component analysis of soil extractable nutrients in different soil types indicated that there is a positive trend between extractable P and soil extractable S, and between soil extractable Mg and soil extractable Na. While these two groups have negative trend in between them (Figure 3). The average concentration of P, K, S, Mg, Ca and Na in samples of plants grown on different soil types did not differ significantly (Table 4). Low to deficient P plant concentrations were observed on all sampling locations. Marschner (2012) suggests that P requirements range between 3–5 mg g⁻¹ DM during the vegetative period. Although, the low P in plant samples (ear leaf) could also be related to the sampling period, which was preformed in the final stage of grain filling when much of P is mobilised from stem and leaf to grain. Other macronutrients showed no plant deficiency symptoms.

Figure 3. Principle component analysis load plot of soil extractable nutrients relation in diferent soil types. Data are collected from 28 farms in Northwest B&H.

Table 2. Summary statistics for extractable nutrient concentration in soil and total nutrient concentration in plant samples from 28 farms in Northwest B&H (values are in mg kg⁻¹ unless otherwise indicated).

Nutrient	Soil			Plant
	Average	SD	Range	Average	SD	Range
K (g kg^−1)	0.20	0.12	0.08–0.59	14.5	3.08	7.51–19.8
P (g kg^−1)	0.04	0.03	0.003–0.13	2.47	0.85	0.79–4.95
S (g kg^−1)	0.27	0.44	0.10–2.49	1.77	0.33	1.24–2.54
Mg (g kg^−1)	0.26	0.14	0.11–0.63	3.53	1.70	1.46–6.60
Ca (g kg^−1)	30.1	23.9	6.65–93.3	9.93	1.77	6.19–13.7
Na	30.6	10.2	18.6–60.1	56.7	24.9	27.8–125
Fe	291	93.5	91.8–485	125	48	62.9–307
Cu	3.73	2.38	0.96–8.50	12.0	4.85	7.77–29.5
Mn	144	59.1	37.5–275	174	116	29.7–357
Zn	2.17	1.15	0.71–5.27	51.8	21.8	11.8–90.6
B	0.58	0.88	0.01–4.17	9.71	2.77	5.40–15
Ni	3.59	3.09	0.74–12.1	0.36	0.39	0.00–1.92
Se (μg kg^−1)	4.71	3.74	1.52–17.6	116	128	46.4–522

Table 3. Summary statistics for soil extractable nutrient concentration in different soil types from 28 farms in Northwest B&H (values are in mg kg⁻¹ unless otherwise indicated).

Nutrient	Soil type
	Fluvisols			Glaysols			Vertisols			Luvisols			Podzoluvisols
	Average	SD	Range	Average	SD	Range	Average	SD	Range	Average	SD	Range	Average	SD	Range
K	237	146	91.8–594	164	59.5	110–249	128	5.47	121–134	109	28.2	82.5–148	211	84.3	97.7–304
P	44.3	28.5	6.97–101	38.9	49.3	3.40–112	45.1	4.18	40.2–49.1	56.3	52.6	5.61–125	36.4	36.6	13.9–100
S	190	62.4	100–277	203	68.0	158–303	245	39.8	203–292	142	42.2	103–201	209	33.8	175–259
Mg	371	475	109–1917	360	205	180–636	136	11.2	128–144	326	186	161–586	273	145	153–489
Ca (g kg^−1)	38.1	29.4	11.7–93.3	36	19.1	15–55	6.69	0.05	6.65–6.72	22.1	15.1	8.1–42.7	24.9	14.5	9.25–40.1
Na	31.6	9.92	18.5–53.90	38.1	15.6	23.1–60.1	22.9	3.66	20.2–25.3	26	1.20	24.4–27.3	29.1	9.71	22.5–45.5
Fe	283	106	91.8–484	251	96.9	132–334	308	87.1	244–367	357	77.0	249–421	302	80.5	209–395
Cu	4.86	2.62	1.39–8.50	4.50	1.60	3.59–6.89	1.16	0.05	1.12–1.19	1.77	0.87	0.96–2.96	2.8	1.43	1.05–4.32
Mn	165	66.67	57.3–274	131	38.2	93.5–169	197	4.93	179–223	82.0	38.2	37.5–129	135	42.2	92.8–182
Zn	2.53	1.07	1.19–4.61	2.68	1.76	1.44–5.27	1.01	0.26	0.79–1.38	1.19	0.39	0.71–1.67	2.12	0.78	1.05–3.17
B	0.91	1.19	0.08–4.17	0.54	0.25	0.32–0.86	0.04	0.02	0.01–0.06	0.17	0.17	0.04–0.40	0.32	0.27	0.09–0.76
Ni	4.54	3.58	0.86–12.09	4.12	0.56	3.51–4.72	1.30	0.31	0.90–1.62	3.20	4.30	0.74–9.63	2.02	1.56	0.84–4.35
Se (μg kg^−1)	6.2	4.9	2.12–17.6	5.52	5	1.52–12.9	3.67	0.87	3.04–4.30	2.26	0.38	1.84–2.76	4.06	2.26	1.96–7.48

Table 4. Summary statistics of the nutrient concentration in plants in different soil types from 28 farms in Northwest B&H (values are in mg kg⁻¹ unless otherwise indicated).

Nutrient	Soil type
	Fluvisols			Glaysols			Vertisols			Luvisols			Podzoluvisols
	Average	SD	Range	Average	SD	Range	Average	SD	Range	Average	SD	Range	Average	SD	Range
K (g kg^−1)	14.9	3.98	7.51–19.8	12.7	1.74	10.4–14.7	14.7	0.74	14.2–15.3	15.8	2.16	13.2–18.1	14.1	2.28	11–16.7
P (g kg^−1)	2.31	0.71	0.79–3.96	2.30	1.35	1.39–4.28	2.13	0.29	1.93–2.34	2.45	0.24	2.14–2.72	3.16	1.07	2.26–4.95
S (g kg^−1)	1.76	0.32	1.24–2.51	1.68	0.15	1.55–1.88	1.60	0.10	1.52–1.67	1.75	0.51	1.46–2.51	1.98	0.36	1.64–2.54
Mg (g kg^−1)	3.46	1.78	1.47–6.60	4.16	1.67	2.38–6.05	2.25	0.14	2.15–2.35	3.79	1.91	1.46–5.61	3.51	1.98	1.51–5.62
Ca (g kg^−1)	9.68	1.19	7.57–11.4	11.8	1.94	9.18–13.7	7.51	1.87	6.19–8.84	9.84	1.48	7.84–11.4	10.1	2.16	7.53–12.4
Na	55.5	27.2	27.8–114	61.7	21.0	33.2–83	96.7	40.1	68.3–125	49.5	7.44	42.6–56.2	45.8	13.4	34–61.8
Fe	132	61.6	78.9–307	131	56.2	62.9–200	113	36.2	86.9–138	113	29.8	73.6–141	117	5.60	111–126
Cu	12.8	6.25	7.77–29.5	11.6	3.08	8.13–15.2	9.96	2.56	8.15–11.8	10.3	3.16	8.51–15	12.3	4.26	8.10–19.1
Mn	161	120	29.7–352	127	83.4	44.9–200	148	133	53.4–242	217	138	46.0–352	221	125	80.2–357
Zn	47.7	21.6	11.8–90.6	48.1	19.4	27.3–66.9	38.7	11.4	30.6–46.7	54.9	27	15.6–76	67.9	21.6	44.0–89.0
B	9.90	2.75	5.98–14.8	11.0	3.16	7.54–15	6.68	1.61	5.54–7.82	9.30	3.97	5.40–14.8	9.68	1.52	8.43–12.3
Ni	0.41	0.50	0.00–1.92	0.30	0.34	0.02–0.79	0.26	0.34	0.02–0.51	0.47	0.37	0.13–0.95	0.25	0.19	0.09–0.54
Se (μg kg^−1)	160	171	46.4–522	125	108	50–281	70	23.6	53–86	59.8	10.1	52–75.9	60	13.1	48.1–81.4

In relation to dairy cattle nutrient requirements of 32–44 g kg⁻¹ DM (NRC 2001), P concentration in this study is not meeting the dairy cattle needs. Requirement for K is10 g kg⁻¹ DM (NRC 2001), which is fully met on all plant-sampling locations. Considering the physiological importance of S, its dairy cattle requirements are as high as 20 g kg⁻¹ DM (NRC 2001), while observed plant concentration ranged from 1.24 to 2.54 g kg⁻¹ on different locations (Table 4). Requirement for Mg of 1,9 g kg⁻¹ DM (NRC 2001) were mostly met on all sampling locations. Calcium dairy cattle requirements range from 53 to 67 g kg⁻¹ DM (NRC 2001) which are much higher than the plant Ca content (Table 4). Although, with regards to Ca forage concentration, it is important to mention the Ca:P ratio. The range of Ca:P from 1:1 to 7:1 is considered satisfactory, otherwise growth and feed efficiency decreases (Suttle 2010). The Ca:P ratio of 3:1 in observed maize samples seems to be quite favourable. Sodium requirements for dairy cattle range between 0,6 and 0,8 g kg⁻¹ DM (NRC 2001), while Na concentration in plant sample ranged from 27.8 to 125 mg kg⁻¹ (Table 4), showing that they are below the animal requirement.

The average soil extractable concentrations of the observed micronutrients: Fe, Cu, Mn, Zn, B and Ni showed that the region has no wide spread soil micronutrient deficiencies (Table 2). Although, there is a significant difference between different soil types where higher extractable values of micronutrients were observed in fluvisol and glaysols compared to other three soil types (Table 3). Locally, only low Zn extractable concentrations were observed with values less than 1 mg kg⁻¹, which indicates potential deficiency of this micronutrient (Behera et al. 2011). PCA showed that micronutrient extractable concentrations were positively correlated with pH and Ca in soils except for Fe (Figure 3) which could be related to fact that Mehlich 3 extractable Fe decreases with pH over 6.5 (Wang et al. 2004). Plant micronutrient concentrations (Table 4) of Mn, Fe, Cu, B and Ni, indicate some variations between plants grown on different soil types, but no plant deficiency symptoms were observed. In the case of Zn, two locations showed plant concentrations of 11.5 mg kg⁻¹ and 15.8 mg kg⁻¹, which were below the critical level of 20 mg kg⁻¹ DM (Welch and Shuman 1995; Marschner 2012), and it was related to low Zn soil availability on those specific locations.

Considering the requirements of dairy cattle (NRC 2001) for Fe (12.3–18 mg kg⁻¹), Cu (9–11 mg kg⁻¹), and Mn (12–14 mg kg⁻¹) DM, observed plant levels were sufficient to meet this requirements, while Zn only partly met the dietary requirement of 43–60 mg kg⁻¹ DM.

Selenium is not of significant importance for plants as it is for animals (Gupta et al. 2008). Considering that maize is the most important feed source and Se is recognised as deficient in certain regions of B&H and Balkan (Ademi et al. 2015), Se was included in this field study. Concentrations of soil extractable Se ranged from 1.52 to 17.6 μg kg⁻¹ (Table 2) with Luvisol having the lowest extraction rate (Table 3) which could be related to low pH and high extractable Fe soil concentration (Zhao et al. 2005). Zhao et al. (2005) also indicate that KH₂PO₄ extractable Se is positively correlated with soil extractable Ca and soil pH. This trend was also observed on load plots of analysed soil samples (Figure 3), with significant correlation (r = 0.84; p < 0.001). Plant Se concentrations were ranging from 46 to 522 μg kg⁻¹, while the majority of the locations showed less than 100 μg kg⁻¹ which is recommended level to avoid feed Se deficiency (Fisher 2008; Suttle 2010). When compared to dairy cattle requirements of 300 μg kg⁻¹ DM it is obvious that potential Se deficiency could occur if additional Se supplements are not added to daily ration.

Considering the sensitivity of maize growth and development on Zn and Fe soil status, and importance of these two micronutrients together with Se for animal nutrition, PCA was applied in order to observe possible correlations between soil extractable macro and micronutrients with plant concentration at different locations (Figures 4 –6). When compered, Zn plant status showed negative relation with soil extractable Mn, P and S, while some positive interaction with soil extractable Fe was observed (Figure 4). Pearson’s correlation test showed that significant negative correlation (Zn_p ∼ Mn_soil; r(26) = −0.52; p < 0.05) existed only with soil extractable Mn. This negative correlation could be related to the fact that during soil development Zn tends to concentrate in Mn oxides (He et al. 2005; Xue et al. 2014), when this oxides dissolve in soil solution both micronutrients appear in Zn²⁺, Mn ²⁺, as antagonistic nutrients (Kabata-Pendias 2004). In addition, Mn soil abundance, under reducing soil conditions and low pH, contribute to Mn to become more plant available then other micronutrients (Sparks 2003; Marschner 2012). Although it was not significant, the positive trend between plant Zn and soil extractable Fe could be related to the fact that under low Zn conditions, phytosiderophores released by Zn-deficient plant can efficiently mobilise both micronutrients (von Wiren et al. 1996).

Figure 4. Principle component analysis load plot of soil extractable nutrients in relation to zinc plant concentration. Data are collected from 28 farms in Northwest B&H.

Figure 5. Principle component analysis load plot of soil extractable nutrients in relation to iron plant concentration. Data are collected from 28 farms in Northwest B&H.

Figure 6. Principle component analysis of soil extractable nutrients in relation to selenimu plant concentration. Data are collected from 28 farms in Northwest B&H.

Iron is highly abundant micronutrient in soils of B&H (Manojlović and Singh 2012), although extractable Fe was week predictor for plant Fe concentration (Figure 5). Positive trend was observed between Fe plant concentration and extractable S, P and SOC (Figure 5). Pearson’s correlation test showed that significant positive correlation existed with soil extractable S (log Fe_p ∼ log S_soil; r(26) = 0.48; p < 0.05), while 90% significant positive correlation was with soil extractable P (log Fe_p ∼ log P_soil; r(26) = 0.33; p = 0.09). Sulphur is an essential macronutrient required for plant growth (Zhao et al. 1997). In particular, it indicates that leaf Fe concentration was lower in maize (Zea mays L.) plants grown in S deficienct conditions than in corresponding plants grown in the sufficient presence of the macronutrient (Bouranis et al. 2003; Astolfi et al. 2004). Graminaceous species respond to Fe deficiency by the release of phytosiderophores (PS) and a highly specific uptake system for ferrated PS. Biosynthesis of PS requires methionine and methionine biosynthesis requires sulfur (Römheld and Marschner 1986). Positive correlation between Fe and P can be related to existing P deficiency in soils. Root exudates of plants grown under deficient P conditions contain organic acids which can solubilise unavailable soil Fe phosphates, and by that increase the plant availability of this micronutrient (Dakora and Phillips 2002).

PCA Load plot showed that there is a positive trend between Se plant concentration and soil extractable Se, and Ca (Figure 6), while significant correlation was observed only with soil extractable Se (log Se_p ∼ log Se_soil; r(26) = 0.70; p < 0.001). Plant uptake Se in selenate and selenite forms (Marschner 2012). It is known, that selenate is a chemical analogue of sulphate; they compete for the same transporters during uptake (Chilimba et al. 2012). Although, interaction between plant Se concentration and soil extractable S was not observed, which is due to low soil Se concentrations. Exposure of plants to higher soil level of Se leads to increased expression of sulphate transporters and consequentially enhanced Se accumulation and assimilation in plants (Na and Salt 2011). The existing positive trend between Se plant concentration and soil extractable Ca can be related to the positive effect of increased soil Ca levels on Se soil extractability (Zhao et al. 2005).

In conclusion, the results of this study indicate that soils in northwest B&H have on average moderate plant availability of both macro- and micro- nutrients, except P which showed regional deficiency although P fertilisation is common practice. Average plant concentrations also showed that region could produce good quality silage maize, which could met the requirements of dairy cattle to certain extent. Extractable soil nutrients could be used as relatively good predictor of potential soil and plant deficiencies, but soil nutrient interactions and climate conditions are highly effect the plant uptake potential.

On farm level there is an indication of existing and potential soil and plant Zn deficiency, this could become even more emphasized in the future with increase of agriculture production if not properly addressed. Selenium soil availably is fairly good in the observed region without deficiencies. Although, plant Se concentration is not high enough to meet daily requirements of grazing animals and additional supplementation can be recommended.

Acknowledgements

We acknowledge the contribution of the Agricluture Insitut of Republic of Srpska and the dr. Tihomir Predic, leader of Department of Agrochemistry and Agroecology.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Djordje Grujcic, MsC, is PhD candidate on Norwegian University of Life Sciences. He received his MsC degree at the University of Novi Sad, in Novi Sad, Serbia. He worked as research assassinate at the Agricultural Institute of Republika Srpska, Banja Luka, Bosnia and Herzegovina. His current PhD project is: Bioavailability of essential trace elements in fodder crops and feed.

Milanka Drinic, PhD, is full-time professor at the Faculty of Agriculture, University of Banja Luka, Banja Luka, Bosnia and Herzegovina. She received her PhD at the University of Novi Sad, Novi Sad, Serbia. Her research is focused on ruminant nutrition and feed quality and safety.

Iva Zivanovic, MsC, is PhD candidate in Norwegian University of Life Sciences. She received her MsC degree at the University of Belgrade, Belgrade, Serbia. Her current PhD project is: Critical P-dilution Curve in Herbaceous Crops/Dilution curve of critical phosphorus concentration in the canopy – a tool for identifying suboptimal P nutrition and for avoiding excess P application in cereals and forage crops.

Ismail Cakmak, PhD, is professor at the Sabanci University, Biological Sciences and Bioengineering, in Istanbul. He received his Ph.D. at the University Hohenheim in Stuttgart, Germany. He is editorial board member of the journal ‘Plant and Soil’ (Springer) and Review Editor of ‘Frontiers in Plant Nutrition’ (Frontiers Journals). He was also ‘Honorary Theme Editor’ of the ‘Encyclopedia of Life Support Systems’ and edited the section entitled ‘Impacts of Agriculture on Human Health and Nutrition’ published by UNESCO. He was also member of the CIMMYT-Board of Trustees between 2005 and 2007. He is elected member of ‘The Academy of Europe’, and received IFA (International Fertilizer Association -Paris) ‘International Crop Nutrition Award’ in 2005 and ‘Georg Forster Research Award’ from the Alexander von Humboldt Foundation-Germany in 2014. He has published over 160 peer-reviewed journal articles, and these articles received more than 7950 citations (H-Index: 50). Over the past 7 years, he has been coordinating HarvestZinc project (www.harvestzinc.org) in 12 countries under HarvestPlus program. His main research is focused on i) enrichment of cereals with zinc, iron and iodine for better human nutrition and ii) better understanding of the role of mineral nutrients in improving tolerance of crop plants to environmental stress conditions. One of the important tasks in the global HarvestZinc project is to study the role of seed micronutrient density in seed germination, seedling development and seed yield.

Bal Ram Singh, PhD, is a professor emeritus at the Norwegian University of Life Sciences. He earned his Ph.D. degree from G.B. Pant University of Agriculture & Technology, India. His program focuses on bioavailability and mobility of heavy metals in the soil and plant system, fertility management and agricultural sustainability in soils of the tropics and on carbon sequestration in soils. He has served as Chairman of the program board ‘Soils and Plants’ of the Research Council of Norway and as Deputy Head of the Department, in addition to many national and international committees. He chaired the Cost Action FA0905 (EU) on ‘Mineral Improved Cop Production for Healthy Food and Feed’, in which more than 200 scientists from 31 countries participated. He has supervised 76 graduate students and 16 visiting fellows/scientists from 20 countries and published 430 articles, of which 240 in peer-reviewed journals and books. Prof. Singh is a fellow of ASA (2004) and SSSA (2005) and recipient of International Award in Soil Science (SSSA) in 2011. He is currently Chair of Division 3 of the International Union of Soil Science, President of the Norwegian Society of Soil Science and member of the Geomedicine committee – Food, Environment and Health of the Norwegian Academy of Science and Letters.

Additional information

Funding

This study is a part of the projects: 1) ‘Mineral Improved Food and Feed Crops for Human and Animal Health (project number 09/1548) (grant number 332160UA)’, which was supported by a grant from the Norwegian Royal Ministry of Foreign Affairs under the Program for Higher Education, Research and Development (HERD) in Western Balkan. 2) COST Action FA 0905 ‘Mineral Improved Crop Production for Healthy Food and Feed’ project, supported by the European Commission.