Keywords

1 Introduction

Key issues such as water scarcity, soil erosion, climate changes, population demand and environmental safety are to be addressed by improving the agriculture technology, thereby improving crop yields for ensuring food security according to demand. The soil should be supplied with sufficient nutrients and is amended with effective fertilization techniques. Balanced fertilization ensures adequate availability of nutrients in soil, so as to meet the requirement of crops at critical stages of growth. The efficiency of crops is improved by reduction of usage of chemical fertilizers, practicing conservative agriculture farming which focus on reducing the adverse impacts on the environment by promotion and utilization of biofertilizers and organic manures globally [1].

The use of biofertilizers in current agricultural practices enhances the crop growth and yield. The biofertilizers are applied along with vermicompost, organic manure and microbial inoculants [2]. The microbial biofertilizers used include seaweed liquid extracts, microbial inoculants, biostimulators and biofortification agents. All these categories of microbial biofertilizers are involved in the enhancement of plant nutrient uptake. This in turn results in crops with high vitamin and nutrient content, and high yields [3]. Agriculture should play a major role in improving nutrition, in particular by paying more attention to the nutritional quality of food. Biofortfication is a scientific method for improving the nutritional value of foods. Biofortification holds great promise for improving nutrition and should continue to be explored [4].

Biofortification has four main advantages when applied in the context of the poor in developing countries. First, it targets the poor who eat large amounts of staple foods daily. Second, biofortification targets rural areas where it is estimated that 75% of the poor live mostly as subsistent or small hold farmers, or landless labourers. These populations rely largely on cheaper and more widely available staple foods such as rice or maize for sustenance [23]. Biofortification is cost effective and has distinct advantages that can complement other traditional approaches to improve nutrition. Microbial inoculants have been the primary focus of programs to enhance staple food crops with sufficient levels of Fe, Zn, and provitamin A, carotenoids [5].

The utilization of bacterial, algal and fungal biofertilizers were recommended. In this aspect use of Spirulina application to soils along with biofertilizers or vermicompost is studied for increasing the levels of protein, macro and micronutrients in soil as well as in the yield. Spirulina platensis can be used as a microbial inoculant or a biofortification agent to the plants to enhance the nutrients and helps to improve the nutrient status of human population and in turn reducing malnutrition. Thus, the present study aims to appraise the soil fertility using Spirulina by pot studies. Field studies are carried out with different concentrations and fertilizer combination methods of application of Spirulina and study its effect on NPK status of crops and as well as soil.

2 Materials and Methods

The experiment was carried out with different methods such as soaking of seeds in Spirulina extract for different time periods, different concentrations, and different proportions of Spirulina extract mixed with biofertilizers, vermicompost, organic manure and foliar application of Spirulina extract in different concentration. Further, nutrient profile of Spirulina, soil prior to experimentation and nutrient profile of the yield has been studied.

2.1 Estimation of Nitrogen and Protein

The Nitrogen and protein content was analyzed by Kjeldahl method by kjeltech model, Pelican Kelplus—KES 12 INL [6].

2.2 Estimation of Phosphorus

The amount of phosphorous was estimated by Fiske and Subba Row Calorimetric method [7].

2.3 Estimation of Potassium and Sodium

The amount of Potassium and Sodium was estimated byElico CL 22D Flame Photometer [8].

2.4 Estimation of Nitrogen, Phosphorous and Potassium in Soil

The amount of N, P and K present in soil was estimated by Soil Testing Centre, Government Limited [9].

2.5 Protein and Nitrogen Estimation in Yield of Crops

Estimation of Protein Nitrogen in Amaranthus, Green gram and Tomato samples was carried out by Kjeldahl method Pelican Kelplus—KES 12 INL [6].

3 Results and Discussion

3.1 Estimation of Soil Nutrient Profile

The soil nutrient profile was studied and the soil was analyzed for minerals like: Nitrogen, Phosphorous and Potassium. Studies were carried out on soil properties like pH and Electric conductivity. All nutrients were high in the soil treated with Spirulina when compared with control except potassium (Table 1).

Table 1 Effect of Spirulina on selected soil nutrient profile of pot study prior and after experimentation
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The yield of the crop mainly depends on the soil health which is a crucial factor. The soil pH, conductivity and nitrogen have been reported higher when compared with control. Physical and chemical properties of soil from Olasati village were studied in detail and carried out the pot experiment analysis for response of green gram to the application of Minjingu Mazao fertilizer (31% P2O5) in Tanzania, and the results indicated that N, P, K in soil were increased [10]. Zodape et al., [11] studied the foliar application of seaweed extract. Kappaphycus alvarezii extract was applied on green gram plants (Phaseolus radiata L) to enhance the yield and nutritional quality. The yield was analyzed for total carbohydrates, total Nitrogen, total protein and various micro nutrients like Fe, Zn and Cu etc. The foliar application resulted in high yield and improved nutrients of green gram.

The field experiment was carried out to study the effect of chemical fertilizers, Biofertilizers, Organic matter, vermicompost combination with Spirulina and soaking in Spirulina hydrolysate to enhance the level of minerals like P, K, Zinc and Iron, the components like Nitrogen and Protein in Amaranthus, Green gram and Tomato plants. Due to the leaching of Nitrogen, phosphorous and potassium from the soil the amounts of these elements have to be replenished in soil with fertilizers. Chemical fertilizers like Urea, super phosphates and potassium fertilizers are widely used.

The Table 2 shows the effect of various experimental methods resulting in increased status of NPK levels in Amaranthus plants. Time period soaking is a traditional approach that allows the transport of mineral ions between Spirulina extract and Amaranthus seeds. Different concentrations method also works on same principle but the equilibrium of ions is established at a certain concentration. Spirulina in combination with biofertilizer, vermicompost, organic manure and chemical fertilizer work at different proportions and is evident from the table. Foliar application is a novel method that directly interacts with the plant leaf cells allowing the entry of mineral ions improving their concentrations [12]. The combination of cyanobacteria and flyash has known to improve the total soil nitrogen status and as well as other mineral status in rice crops and soil in which they were grown [13].

Table 2 Effect of Spirulina supplementation on Amaranthus plants
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Seed priming is one of the promising technologies that influence the plant—soil interactions, mineral status and microbial community colonization in root zones of plants. Seed biopriming with Spirulina (soaking) has turned out to be novel method that improves soil as well as crop mineral characteristics. Therefore, seed priming enables to improve the soil mineral levels and thereby also help to increase crop growth and yield [19].

The Table 3 describes the effect of various experimental methods in improving the yield of green gram plants by utilization of Spirulina. High amounts of nitrogen (%N) were observed in experimental set up Spirulina + biofertilizer combination in 25:75 proportions. Increased amounts of phosphorus were observed in soaking method using 15 g of Spirulina. Potassium levels were found to be increased in the experimental method of Spirulina + chemical fertilizer in 25:75 proportions. The treatment of soil and chick pea crops with a combination of cyanobacteria and bacterial biofilms have enhanced various physical, biochemical and morphological parameters of the crops and also the mineral status of soil due to increased nitrogen availability in soil [14].

Table 3 Effect of Spirulina supplementation on green gram plants
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Soil microbial interactions play a major role in soil amendments that in turn increase the overall availability of soil minerals to crops due to which the crop growth and yield are increased. In this experimental method, the synergistic interactions between Spirulina and biofertilizers were thought to have an important role in increasing soil nitrogen, phosphorus and potassium status [18].

Table 4 depicts the effect of Spirulina on tomato plants using different experimental methods. In tomato plants the % of Nitrogen was found to be higher in Spirulina + organic manure method in 50:50 proportions. Phosphorus levels were higher in Spirulina + biofertilizer and Spirulina + vermicompost methods in 75:25 proportions. High potassium levels were found in 5 h soaking method. Increased qualitative and quantitative traits have been observed in cherry tomato plants. The plant seeds were treated with combination of brown algae Ascophyllum nodosum and vermicompost extracts. The experiment resulted in overall increase of all parameters of crops and the experiment was carried out in hydroponic conditions [15].

Table 4 Effect of Spirulina supplementation on tomato plants
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Integrated nutrient management of soil and crops is essential to improve the crop yield of tomato. Conventional agricultural methods are followed by application of biofertilizer and organic manures increased the plant morphological characters, yield and physiological status was improved by increased nutritional status. Utilization of effective soil amendment methods had resulted in increase in the yield of tomato in the current experiment [20]. The Table 5 shows increase in % Nitrogen in post harvest soil of three experimental plants. High amounts of Nitrogen were found in green gram plants in 5 g soaking method followed by Amaranthus plants in Spirulina + chemical fertilizer method in 75:25 proportions. The high amount of nitrogen in tomato plants was 0.80 ± 0.00 and was reported in 5 h soaking method.

Table 5 Effect of Spirulina supplementation on % nitrogen in post-harvest soil of experimental plants
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Soil mineral status is known to improve by crop—soil interactions along with soil amendments. The utilization of biofertilizers, organic manure and vermicopost increased soil fertility by increasing soil nitrogen status. Soil nitrogen is improved by reducing the soil acidity and also preserving the root zone microorganisms attracting more microbes with root exudates. Application of biofertilizers along with Spirulina helped increasing the protein content of crops and nitrogen levels of soil since, Spirulina is protein rich cyanobacterial member that obviously contributes more nitrogen to post harvest soil [21]. The N, P and K in soil were found to increase significantly due to inoculation of cyanobacteria. High NPK levels were observed when the seed soaking + soil drench +75% of N was applied to plants [24].

The Table 6 shows the post-harvest phosphorus levels in soils after growing the experimental plants Amaranthus, Green gram and Tomato. High amounts of phosphorus were reported in green gram plants in soaking in 25 g concentration method. The high amounts of phosphorus levels were followed in soils after harvesting Amaranthus plants. The high amounts were observed in experimental methods of soaking in 30 g concentration, Spirulina + biofertilizers in 25:75 proportions and Spirulina + organic manure in 50:50 proportions. Foliar application of Spirulina was proved to be equally effective as NPK fertilizers in enhancing soil NPK status. This can be evident by study of yield of eggplants using a foliar Spirulina fertilizer called Spirufert. Soil mineral status is also improved with supplementation of biofertilizers and organic manures that stabilize soil acidity and prevent phosphorus leaching increasing phosphorus status of the soils [22].

Table 6 Effect of Spirulina supplementation on % phosphorous in post-harvest soil of experimental plants
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Table 7 shows post-harvest soil levels of potassium. Post harvestings of experimental plants with various methods using Spirulina have reported with increased levels of potassium. High amounts of potassium were found in soils of tomato plants with experimental method Spirulina + biofertilizer in 25: 75 proportions. The high values were followed by green gram plants in Spirulina + vermicompost (25:75) method and 3 h time period soaking. Soil health reflects the soil mineral status.

Table 7 Effect of Spirulina supplementation on % potassium in post-harvest soil of experimental plants
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Increased phosphorous and Potassium levels were observed in both seasons when mung bean plants are supplemented with phosphorus and potassium fertilization [25].

Sustainable agricultural practices increase the soil health and fertility. The sustainable agricultural practices include bio inoculation of soils with marine microalgae, cyanobacteria and combination methods including bio fertilizers, green manures and vermin compost. These methods improve overall soil health and crop yields. These methods also ensure the environmental safety and food security [16].

3.2 Figures

The Fig. 1 helps to detect the increase in % nitrogen in Amaranthus, Green gram and Tomato plants as a comparison. High % of nitrogen is observed for Amaranthus among 3 plants and was found in experimental method Spirulina + vermicompost.

Fig. 1
figure 1

Percent increase in nitrogen of Amaranthus, green gram and tomato by supplementation of Spirulina when compared with control *Set-1 Time period soaking, Set-2 Soaking in different concentrations of Spirulina, S:B—Spirulina: Biofertilizer, S:V—Spirulina: Vermicompost, S:O—Spirulina: Organic manure, S:C—Spirulina: Chemical Fertilizer, S/W—Spirulina/Water

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The Fig. 2 describes the % increase of phosphorus compared among three experimental plants. High amounts of phosphorus among 3 plants were observed in Amaranthus in Spirulina + organic manure method. Figure 3 is about effect of Spirulina on 3 experimental plants in increasing the potassium levels by different experiment methods. High % of potassium was found in tomato plants in 5 h soaking method.

Fig. 2
figure 2

Percent increase in phosphorus of Amaranthus, green gram and tomato by supplementation of Spirulinawhen compared with control *Set-1 Time period soaking, Set-2 Soaking in different concentrations of Spirulina, S:B—Spirulina: Biofertilizer, S:V—Spirulina: Vermicompost, S:O—Spirulina: Organic manure, S:C—Spirulina: Chemical Fertilizer, S/W—Spirulina/Water

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Fig. 3
figure 3

Effect of Spirulina supplementation on potassium of Amaranthus, green gram and tomato yield when compared with control *Set-1 Time period soaking, Set-2 Soaking in different concentrations of Spirulina, S:B—Spirulina: Biofertilizer, S:V—Spirulina: Vermicompost, S:O—Spirulina: Organic manure, S:C—Spirulina: Chemical Fertilizer, S/W—Spirulina/Water

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The growth periods of three types of plants used in the experiment were different. Here, only the influence on nutrient status in pre and post experimental treatments in crops and soil were discussed due to difference in growth, morphology, fruit and time of harvest and yields. This can be evident by evaluation of NPK in 3 plants as given in Figs. 1, 2 and 3. The experimental crops were compared with controls.

4 Conclusion

The overall outcome of the experiment evaluated was the nutrient profile of crops and postharvest soil with the use of Spirulina and other fertilizer combinations and their role in increasing the mineral status. The NPK had shown increase in overall growth of morphological parameters of plants and also maintained the soil fertility. The total increase in growth of plants also results in increase of nutrient content in the plants. In the field study the supplementation of Spirulina through different methods and also in combination with other biofertilizers, vermicompost, organics manure and chemical fertilizers had been used. The synergistic effect of these combinations had shown significant impact on the growth of plants. The soil supplementation of Spirulina platensis to plants had improved the soil mineral content. The increased soil phosphorus and potassium had greatly influenced the availability of iron and zinc to the plants. The soil nitrogen influenced the protein content in the plants and also the concentration of pigments like chlorophyll has been increased.

The NPK levels in the soils were increased due to the supplementation of Spirulina to the soil and in turn resulted in the overall growth and enhanced the minerals levels in the crops. The potassium is much required for water movement and stomatal movement in the leaves. Thus increased potassium levels helped the crops to uptake sufficient waters and also zinc by foliar application results in good overall growth of plants. This was evident by previous studies in which Spirulina application has increased the zinc levels in plants [17].

With the observed results, it can be concluded that Spirulina platensis is not only a simple protein supplement, but it can be a good biofortification agent to crops to enhance their mineral nutrient status. Further, this can be proved by complete bioavailability studies and molecular studies. Finally, the present study proves the efficiency of Spirulina platensis as a biofortification agent as it has enhanced the mineral nutrient level in the yield of all the three crops and also improves the soil fertility.