Bettina Eichler-Löbermann

Unexploited potential of some biotechnological techniques for biofertilizer production and formulation

The massive application of chemical fertilizers to support crop production has resulted in soil, water, and air pollution at a global scale. In the same time, this situation escalated consumers’ concerns regarding quality and safety of food production which, due to increase of fertilizer prices, have provoked corresponding price increase of food products. It is widely accepted that the only solution is to boost exploitation of plant-beneficial microorganisms which in conditions of undisturbed soils play a key role in increasing the availability of minerals that otherwise are inaccessible to plants. This review paper is focused on the employment of microbial inoculants and their production and formulation. Special attention is given to biotechniques that are not fully exploited as tools for biofertilizer manufacturing such as microbial co-cultivation and co-immobilization. Another emerging area includes biotechnological production and combined usage of microorganisms/active natural compounds (biostimulants) such as plant extracts and exudates, compost extracts, and products like strigolactones, which improve not only plant growth and development but also plant-microbial interactions. The most important potential and novel strategies in this field are presented as well as the tendencies that will be developed in the near future.

Effect of Catch Cropping on Phosphorus Bioavailability in Comparison to Organic and Inorganic Fertilization

ABSTRACT Phosphorus (P) is a limited resource and its efficient use is a main task in sustainable agriculture. In a 3-year field experiment the effects of catch cropping [oil radish (Raphanus sativus), buckwheat (Fagopyrum esculentum), serradella (Ornithopus sativus), ryegrass (Lolium westerwoldicum), and phacelia (Phacelia tanacetifolia)] of organic fertilization (cattle manure and biowaste compost) and of inorganic fertilization (Triple-Superphosphate) on plant and soil parameters were investigated on a P-poor loamy sand in Northeast Germany. The catch crops were sown in September and remained on the plots until next spring. Then the main crops oilseed rape (Brassica napus), spring barley (Hordeum vulgare), or spring wheat (Triticum aestivum) were cultivated. The yield and P uptake of the main crops were determined. Furthermore, in the soil the organic matter content, pH, phosphorus (P) in soil solution (Psol), double-lactate and oxalate P content, P sorption capacity, and degree of P saturation were measured. All applied forms of fertilizer affected the P contents in soil and the yields and P uptakes of main crops. For green fertilization especially phacelia was found to contribute to the P supply of the main crops, since it increased the P uptake as well as the P contents in soil significantly. The cultivation of ryegrass led to a reduction of the P availability in soil. For example, in average of the three years the Psol content was 0.35 mg L− 1when phacelia was cultivated and 0.22 mg L− 1 when ryegrass was cultivated. The cultivation of phacelia had a comparable effect on soil and plant parameters as the organic and mineral fertilization. An improved P availability and P utilization by catch cropping can reduce the need for external P input which may help to save the limited P resources worldwide.

Stress-tolerant P-solubilizing microorganisms

Drought, high/low temperature, and salinity are abiotic stress factors accepted as the main reason for crop yield losses in a world with growing population and food price increases. Additional problems create nutrient limitations and particularly low P soil status. The problem of phosphate fertilizers, P plant nutrition, and existing phosphate bearing resources can also be related to the scarcity of rock phosphate. The modern agricultural systems are highly dependent on the existing fertilizer industry based exclusively of this natural, finite, non-renewable resource. Biotechnology offers a number of sustainable solutions that can mitigate these problems by using plant beneficial, including P-solubilizing, microorganisms. This short review paper summarizes the current and future trends in isolation, development, and application of P-solubilizing microorganisms in stress environmental conditions bearing also in mind the imbalanced cycling and unsustainable management of P. Special attention is devoted to the efforts on development of biotechnological strategies for formulation of P-solubilizing microorganisms in order to increase their protection against adverse abiotic factors.

Phosphorus Fertilizing Effects of Biomass Ashes

The reutilization of biomass ashes in agriculture is important to create nutrient cycles. In field and pot experiments we investigated the fertilizing effects of different biomass ashes (rape meal ash, straw ash, and cereal ash) for eight different crops on a loamy sand and a sandy loam. Special emphasis was given to phosphorus (P). The ashes showed large differences in their elemental composition. The highest P contents (10.5%) were measured in the cereal ash, and lowest in straw ash (1% P). The solubility of P in water was low; however, about 80% of P was soluble in citric acid. Generally, the P fertilizing effect of ashes was comparable to that of highly soluble P fertilizers such as triple superphosphate. The ash supply resulted in an increase of P uptake of cultivated crops as well as in increased soil P pools (total P, water-soluble P, double-lactate-soluble P, oxalate-soluble P) and P saturation. The ash effects depended also on the cultivated crop. Good results were found in combination with phacelia, buckwheat, and maize. Provided that biomass ashes are low in heavy metals and other toxic substances, the ashes can be applied in agriculture as a valuable fertilizer.

Phosphorus distribution and availability in untreated and mechanically separated biogas digestates

Biogas digestates contain valuable nutrients but also have high water contents. Di-gestates were sampled from two different biogas facilities before and after solid-liquid separation and were analyzed with regard to their composition and phosphorus (P) fractions. Additionally, to investigate the P fertilizer effects of these digestates in comparison with undigested slurry or TripleSuper-P (TSP), they were applied in a pot experiment (6 kg soil per pot) in an amount corresponding to 200 mg P per pot in combination with various crops (amaranth, maize, maize + beans mixed cropping, sorghum). A separation of digestates resulted in higher P concentrations of the solid fraction in comparison with the liquid fraction. The proportion of the readily soluble P fractions (H2O-P, NaHCO3-P) to the total P was higher than 70 % in all digestates. The digestates increased P uptake of the tested crops and concentrations of bioavailable P in the soil to the same extent as highly soluble TSP. Activities of soil enzymes were lower after application of the digestates in comparison to unfermented slurry. The fertilizer management of digestates can be improved by a solid-liquid separation since the solid fraction showed a relatively high concentration of P resulting in a reduction in application doses required to meet the P demands of crops.

Improvement of Soil Phosphorus Availability by Green Fertilization with Catch Crops

The efficient use of phosphorus (P) is a main task in sustainable agriculture. In pot and field experiments, the effects of green fertilization with catch crops and P supply with organic and inorganic fertilizers on plant and soil parameters were investigated on a P‐poor loamy sand. For the field experiment, the catch crops were sown in September and remained on the plots until next spring. As the main crops, oilseed rape (Brassica napus), spring barley (Hordeum vulgare), and spring wheat (Triticum aestivum) were cultivated. The yield and P uptake of the main crops were determined. In the soil, the organic matter content, pH, P in soil solution (Psol), double‐lactate and oxalate P content, P sorption capacity, and degree of P saturation were measured. Soil from plots of selected fertilizer treatments of the field experiment [without P, cattle manure, compost, triple‐super P, green fertilization with Phacelila (Phacelia tanacetifolia)] was used for the pot experiment. Maize (Zea mays), ryegrass (Lolium westerwoldicum), and buckwheat (Fagopyrum esculentum) were cultivated for 3 months in pots with 6 kg soil. All applied forms of fertilizer affected the P contents in soil and the yields and P uptakes of main crops in both experiments. For green fertilization especially, phacelia was found to contribute to the P supply of the main crops, because it increased the P uptake as well as the readily available P contents in soil significantly. The cultivation of ryegrass led to a reduction of the P availability in soil. The DPS was also affected due to the catch crops. In average of the three years of the field experiment the DPS was 47.0% when phacelia was cultivated and 44.5% when ryegrass was cultivated. A better P availability and P utilization by catch cropping can help to reduce the need for external P input.

Biogas digestates affect crop P uptake and soil microbial community composition.

Fermentation residues from biogas production are known as valuable organic fertilisers. This study deals with the effect of cattle slurry, co-digested cattle slurry, co-digested energy crops and mineral fertilisers on the activity and composition of soil microbiota. Furthermore, the effect of solid-liquid separation as a common pre-treatment of digestate was tested. The fertilising effects were analysed in an 8-week pot experiment on loamy sand using two crops, Amaranthus cruentus and Sorghum bicolor. Amaranth, as a crop with significantly higher P uptake, triggered stress for occurring soil microbes and thereby caused a reduction of microbial biomass C in the soil. Irrespective of the crop, microbial basal respiration and metabolic quotient were higher with the digestates than with the untreated slurry or the mineral treatments. Community level physiological profiles with MicroResp showed considerable differences among the treatments, with particularly strong effects of solid-liquid separation. Similar results were also found on a structural level (PCR-DGGE). Alkaline phosphatase gene analyses revealed high sensitivity to different fertilisation regimes.

Animal bones char solubilization by gel-entrapped Yarrowia lipolytica on glycerol-based media.

Citric acid was produced with free and k-carrageenan-entrapped cells of the yeast Yarrowia lipolytica in single and repeated batch-shake-flask fermentations on glycerol-based media. Simultaneous solubilization of hydroxyapatite of animal bone origin (HABO) was tested in all experiments. The highest citric acid production by free yeast cells of 20.4 g/L and 18.7 g/L was reached after 96 h of fermentation in the absence and presence of 3 g/L HABO, respectively. The maximum values for the same parameter achieved by gel-entrapped cells in conditions of single batch and repeated-batch fermentation processes were 18.7 g/L and 28.1 g/L registered after 96 h and the 3d batch cycle, respectively. The highest citric acid productivity of 0.58 g L−1 h−1 was obtained with immobilized cells in repeated batch mode of fermentation when the added hydroxyapatite of 3 g/L was solubilized to 399 mg/L whereas the maximum efficiency of 89.0% was obtained with 1 g/L of HABO.

Recycled Products from Municipal Wastewater: Composition and Effects on Phosphorus Mobility in a Sandy Soil

Recycled products from wastewater may contain high concentrations of phosphorus (P) and are thus promising alternative fertilizers. However, to better predict their P fertilizer efficiency and potential for P leaching, investigations on P forms and P mobility in soil are essential. In this study, different recycled products-an untreated sewage sludge ash (SSA), an HSO-digested SSA, four thermochemically treated SSAs (two Mg-SSAs and two Ca-SSAs), and struvite-were investigated using a combination of wet chemical methods and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy concerning their composition and their effects on P sorption in a sandy soil in comparison to triple superphosphate. Most of the P in the SSAs was associated with Ca in stable P fractions. The lowest P values in labile fractions (HO-P, NaHCO-P) were found for the untreated SSA and struvite. However, the addition of struvite resulted in an immediate increase in the bioavailable P fractions and the degree of P saturation in soil after only 1 d of incubation. This suggests a high P fertilizer potential for struvite but also a risk of P losses. Among the SSAs, the two Mg-SSAs increased the bioavailable P fractions in soil the most, whereas the lowest values were measured after application of the untreated SSA. Our results demonstrate that chemical analyses of recycled P products may involve the risk of misjudging the fertilizer quality when performed alone, without considering the behavior of these products in soil.

Handling the phosphorus paradox in agriculture and natural ecosystems: Scarcity, necessity, and burden of P

This special issue of Ambio compiles a series of contributions made at the 8th International Phosphorus Workshop (IPW8), held in September 2016 in Rostock, Germany. The introducing overview article summarizes major published scientific findings in the time period from IPW7 (2015) until recently, including presentations from IPW8. The P issue was subdivided into four themes along the logical sequence of P utilization in production, environmental, and societal systems: (1) Sufficiency and efficiency of P utilization, especially in animal husbandry and crop production; (2) P recycling: technologies and product applications; (3) P fluxes and cycling in the environment; and (4) P governance. The latter two themes had separate sessions for the first time in the International Phosphorus Workshops series; thus, this overview presents a scene-setting rather than an overview of the latest research for these themes. In summary, this paper details new findings in agricultural and environmental P research, which indicate reduced P inputs, improved management options, and provide translations into governance options for a more sustainable P use.