Deficiency of phyto-available sulphur, zinc, boron, iron, copper and manganese in soils of India

Nutrient deficiencies in soil–crop contexts and inappropriate managements are the important reasons for low crop productivity, reduced nutritional quality of agricultural produce and animal/human malnutrition, across the world. The present investigation was carried out to evaluate nutrient deficiencies of sulphur (S) and micronutrients [zinc (Zn), boron (B), iron (Fe), copper (Cu) and manganese (Mn)] in agricultural soils of India for devising effective management strategies to achieve sustainable crop production, improved nutritional quality in crops and better animal/human health. A total of 2,42,827 surface (0–15 cm depth) soil samples were collected from agriculture fields of 615 districts lying in 28 states of India and were analysed for available S and micronutrients concentration. The study was carried out under the aegis of All India Coordinated Research Project on Micro- and Secondary-Nutrients and Pollutant Elements in Soils and Plants. The mean concentrations were 27.0 ± 29.9 mg kg−1 for available S, 1.40 ± 1.60 mg kg−1 for available Zn and 1.40 ± 4.70 mg kg−1 for available B, 31.0 ± 52.2 mg kg−1 for available Fe, 2.30 ± 3.50 mg kg−1 for available Cu and 17.5 ± 21.4 mg kg−1 for available Mn. There were variable and widespread deficiencies of S and micronutrients in different states. The deficiencies (acute deficient + deficient + latent deficiency) of S (58.6% of soils), Zn (51.2% of soils) and B (44.7% of soils) were higher compared to the deficiencies of Fe (19.2% of soils), Cu (11.4% of soils) and Mn (17.4% of soils). Out of 615 districts, > 50% of soils in 101, 131 and 86 districts were deficient in available S, available Zn and available B, respectively. Whereas, > 25% of soils in 83, 5 and 41 districts had deficiencies of available Fe, available Cu and available Mn, respectively. There were occurrences of 2-nutrients deficiencies such S + Zn (9.30% of soils), Zn + B (8.70% of soils), S + B (7.00% of soils) and Zn + Fe (5.80% of soils) to a greater extent compared to the deficiencies of Zn + Mn (3.40% of soils), S + Fe (3.30% of soils), Zn + Cu (2.80% of soils) and Fe + B (2.70% of soils). Relatively lower % of soils were deficient in 3-nutrients (namely S + Zn + B, S + Zn + B and Zn + Fe + B), 4-nutrients (namely Zn + Fe + Cu + Mn) and 5-nutrients (namely Zn + Fe + Cu + Mn + B) simultaneously. The information regarding the distribution of deficiencies of S and micronutrients (both single and multi-nutrients) could be used by various stakeholders for production, supply and application of right kind of fertilizers in different districts, states and agro-ecological regions of India for better crop production, crop nutritional quality, nutrient use efficiency, soil health and for tackling human and animal malnutrition.

were collected from agricultural land holdings of 615 districts lying in 28 states of India, under the tutelage of All India Coordinated Research Project on Micro and Secondary Nutrients and Pollutant Elements in Soils and Plants, by following stratified random sampling procedure 24 , during April to June months of 2012-2018. Soil samples were collected using a hand-held auger made up of stainless-steel. The geographical coordinates of each sampling point were recorded using Global Positioning System. Each composite soil sample was obtained from 3 to 4 subsamples collected from a small land holding (< 1 ha), 6-7 subsamples collected from a medium land holding (1-3 ha) and 9-10 subsamples collected from a large land holding (> 3 ha), of each district. The collected samples were air dried, processed, ground to pass through a 2 mm size sieve and stored in plastic bottles for analysis.
The analysis of soil samples was carried out for available S using calcium chloride solution (0.15%) as extractant 25 and spectrophotometer (Make (model): Shimadzu (UV-1800)). Available Zn, Fe, Cu and Mn in soil samples were determined after extracting the samples with diethylene triamine penta acetic acid extractant 26 . The estimation of Zn, Fe, Cu and Mn in clear extract was carried out utilizing atomic absorption spectrophotometer (Make (model): Varian (AA240FS)). Available B was estimated after extracting the samples with hot water 27 and estimating the colour intensity developed by adding azomethine-H solution using a spectrophotometer (Make (model): Shimadzu (UV-1800)).

Statistical analysis.
The dataset related to available S, Zn, B, Fe, Cu and Mn in soil samples were subjected to statistical analysis for obtaining descriptive statistics viz., minimum, maximum, mean, standard deviation (SD), coefficient of variation (CV), skewness and kurtosis, using SAS 9.2 software package 28 . The frequency distribution of soil samples having available S and micronutrients in different concentrations and distribution of single-and multi-nutrients deficiencies were estimated using data analysis programme of Microsoft-excel. The concentrations of S and micronutrients in soil samples were categorized as acute deficient, deficient, latent deficient, marginally sufficient, adequate and high as per the generalized classification adopted for Indian soils 13 ( Table 1). The distribution maps for two and multi-nutrients deficiencies were prepared using ArcGIS software (version 10.5.1) (Environmental Systems Research Institute, Redlands, California) for power BI, in order to have better data visualization and proper understanding of distribution of nutrient deficiencies in different parts of India. The nutrient deficiencies (% of the soil samples), district boundary, state boundary and AER boundary were used as different layers of ArcGIS mapping. Two kriged distribution maps of Zn + B and S + Zn + B deficiency (considering deficient (acute deficient + deficient + latent deficient), marginal (marginally sufficient) and high (adequate + high) status) were prepared using ArcGIS software (version 10.5.1) (Environmental Systems Research Institute, Redlands, California).

Consent to participate.
The consent of all the participants of the study was obtained.
On average, about 1.10, 6.00 and 10.3% of soils were acute deficient, deficient and latent deficient in available Mn (Table 7). Whereas, 13.2, 9.10 and 60.4% of soils were marginally sufficient, adequate and high, respectively, in available Mn. Relatively, the higher % of soils in the states namely Jammu & Kashmir (3.50%), Kerala (3.40%), Punjab (7.80), and Rajasthan (5.80%) were acute deficient in available Mn. More than 20% of soils in the states namely, Bihar, Goa, Haryana, Jammu & Kashmir, Kerala, Nagaland, Punjab, Rajasthan, Tamil Nadu and Uttar Pradesh were deficient (including acute deficient, deficient and latent deficient) in available Mn.
Multi-nutrients deficiencies of available S and micronutrients. The mean deficiency of 2 or > 2-nutrients deficiency of available S and micronutrients varied from 0.10% (Zn + Fe + Cu + Mn + B) to 9.30% (S + Zn) ( Table 8). The deficiency of S + Zn was predominantly prevalent in different districts of Bihar, Gujarat, Karnataka, Madhya Pradesh, Odisha, Rajasthan, Uttar Pradesh and Maharashtra (Supplementary Figure S1). More than 20% of soils in 9 districts of Gujarat, 25 districts of Madhya Pradesh, 8 districts of Odisha and 10 districts of Rajasthan were deficient in S + Zn. The deficiency of Zn + B varied from 0.60 to 20.3% of soils in different states with mean value of 8.70%. It's prevalence in states like Bihar, Karnataka, Odisha and Tamil Nadu was higher (Fig. 1, Supplementary Figure S2). More than 20% of the sampled sites in 16 districts of Bihar, 5 districts   Figure S5). The deficiency of S + Fe, Zn + Cu and Fe + B were recorded in 3.30, 2.80 and 2.70% of the sampled sites, respectively and were scattered across the country (Supplementary Figure S6-S8). The deficiency S + Fe was higher in Gujarat, Haryana, Rajasthan and Uttar Pradesh. The deficiency of 3-nutrients namely, S + Zn + B, S + Zn + Fe and Zn + Fe + B were recorded in 2.60, 1.70 and 1.20% of soils, respectively. Relatively, the higher % of soils in Bihar, Goa, Karnataka and Odisha were deficient in S + Zn + B (Fig. 2). S + Zn + Fe deficiency was more in soils of Gujarat, Haryana, Maharashtra and Rajasthan (Supplementary Figure S9, S10). The higher % of the sampled sites in Bihar and Karnataka were deficient in Zn + Fe + B (Supplementary Figure S11). More than 20% of soils in 1 district each of Bihar, Chhattisgarh, Karnataka, Madhya Pradesh and 5 districts of Odisha were deficient in S + Zn + B. More than 20% of soils in 1 district each of Haryana, Karnataka, Maharashtra, and Uttar Pradesh and 2 districts each of Madhya Pradesh and Rajasthan were deficient in S + Zn + Fe. More than 3-nutrients deficiencies like Zn + Fe + Cu + Mn and Zn + Fe + Cu + Mn + B were very less and recorded in only 0.30 and 0.10% of soils, respectively. Less than 5% of the sampled sites in 13 districts of Bihar, 7 districts each of Punjab and Uttar Pradesh and 16 districts of Tamil Nadu were deficient in Zn + Fe + Cu + Mn. Whereas, < 5% of the sampled sites in 13 districts of Bihar, 4 districts of Punjab and 10 districts of Tamil Nadu were deficient in Zn + Fe + Cu + Mn + B.  31 , in sugarcane cultivated soils of Brazil. The factors like soil types, nature of crop plants and adoption of various soil-crop management practices influence the concentrations of available S and micronutrients in soils 12,29,32,33 . The available S concentration in soils is also influenced by occurrences of plant residues, organic matter and various salts containing S 34 . The extent of rock weathering in soil decides the concentration of available micronutrients and S in soils 12 . The lowest concentrations of available S and micronutrients prevail in the tropical soils with high levels of weathering. The availability of micronutrients in soils is primarily affected by soil parameter namely soil organic matter, soil pH, clay content, cation exchange capacity, biological activity and redox potential. The nature of crop plants, rooting pattern, root secretions and associations of plants and microbes also affect micronutrient availability in soil and plant uptake.

Single nutrient deficiencies of available S and micronutrients.
On an average, the concentration of available S in about 11.4, 29.4 and 17.8% of soils were acute deficient, deficient, and latently deficient range, respectively ( Table 2). There were differences in deficiency levels of available S in the districts of the states. Several districts in the states like Madhya Pradesh, Gujarat, Odisha, Rajasthan and Manipur had deficiency in available S in > 50% of soils. This is mainly ascribed to variations in cultivation of S-loving crops and less or no addition of S containing fertilizers. The deficiency of available S could be efficiently alleviated by adopting site-specific S manipulation strategies in various soil-crop contexts. In parallel to our findings, several scholars recorded S deficiency in different soil-crop contexts and responses of various crops to different S doses in various states of India 13,35-37 . On average, the extent of deficiency (acute deficient + deficient + latent deficient) Multi-nutrients deficiencies of available S and micronutrients. There were 2 and > 2-nutrients deficiencies of available S and micronutrients in soils different states of India. The extent of these deficiencies followed the order: S + Zn (9.30%) > Zn + B (8.70%) > S + B (7.00%) > Zn + Fe (5.80%) > Zn + Mn (3.40%) > S + Fe (3.30%) > Zn + Cu (2.80%) > Fe + B (2.70%) > S + Zn + B (2.60%) > S + Zn + Fe (1.70%) > Zn + Fe + B (1.20%) > Zn + Fe + Cu + Mn (0.30%) > Zn + Fe + Cu + Mn + B (0.10%) ( Table 8). The different states and AERs of the country had various levels of 2 and > 2-nutrients deficiencies of available S and micronutrients. S + Zn defi- www.nature.com/scientificreports/ ciency was prevalent in > 15% of soils of Odisha, Rajasthan, Madhya Pradesh and Goa. This was also prevailed in higher extent in soils of AER 5,8,9,10 and 13. The deficiency of Zn + B was prevalent at greater extent in soils of Odisha, Tamil Nadu, Karnataka and Bihar falling in the AER 5, 8, 12 and 13. The soil of the states namely Jharkhand, Odisha, Kerala, West Bengal and Uttarakhand had higher levels of S + B deficiency. The levels of Zn + Fe deficiency were more in Rajasthan, Gujarat, Karnataka and Maharashtra and AER 2, 5, 6 and 8. As discussed earlier, this spatial variations in prevalence of multi-nutrients deficiencies are ascribed to different soils, crops, climates and soil-crop manipulation practices. These multi-nutrients deficiencies could be alleviated by production, distribution and application of S and micronutrients containing customized fertilizers prepared based on prevailing nutrient deficiencies in various AER, states and districts of the country. This will help to a greater extent in maintaining soil health, having sustainable crop production and better quality of crops 40,41 . The information from the study could suitably be used by the different stake holders (policy makers, planners and fertilizer industries) associated with production and distribution of S and micronutrients containing straight and customized fertilizers to various targeted areas of the country. There are responses of different crops to the addition of available customized fertilizers in different parts of India [42][43][44] . However, there is an urgent necessity for development, distribution and application of S and micronutrients containing straight and customized fertilizers for different areas of the country, based on the current knowledge on S and micronutrients deficiency. It will be useful to a greater extent for alleviating S and micronutrients deficiencies in soils, maintaining soil health, sustainable crop production, increased crop quality and better health of animals and human being.

Conclusions
The present study highlighted the existence of wide variability in available S and micronutrients status in cultivated soils of various states of India. On average, the extent of deficiencies (considering acute deficient, deficient and latent deficient together) of the studied nutrients in soils of the country followed the order: available S > available Zn > available B > available Fe > available Mn > available Cu. The higher % of soils in Kerala, Odisha and West Bengal were acute deficient in available S and available B. Whereas, the higher % of soils in Rajasthan, Madhya www.nature.com/scientificreports/ Pradesh, Goa, Odisha and Karnataka were acute deficient in available Zn. The existence of 2 or > 2 nutrients deficiencies of available S and micronutrients is restricted to limited areas of different districts of various states. On average, the levels of deficiencies of S + Zn, Zn + B, S + B and Zn + Fe were higher than the deficiencies of other multi-nutrients. This knowledge could be used for area-specific S and micronutrients management for better crop production and crop quality. Further, district-and state-specific S and micronutrients based customized fertilizers could be developed and distributed based on the information generated from the study. However, there is a need for periodic assessment of available S and micronutrients status in cultivated soils of various states, at 3-5 years interval, as the status of these nutrients change with soil-crop management practices. Further, development of kriged distribution maps of available S and micronutrients (using geostatistical tools) for different districts, states and at country level is needed for preparing site-specific nutrient management strategies. This type of study needs to be carried out in cultivated soils pf other parts of world for effective S and micronutrients needed for substantiable crop production, crop quality and good health of soils, crops, animals and human being.

Data availability
The data are available from the corresponding author upon reasonable request.