Effect of organic manures, theirs biochar and mycorrhizae fungi application on the chemical forms of potassium in a calcareous soil

Introduction: nowadays, application of organic and biological fertilizers in organic agriculture has become widespread due to their considerable benefits. Recently, the conversion of organic manures into biochar, as an alternative and stable organic fertilizer, has been paid attention by many researchers. Potassium is an essential nutrient for crop production. Application of various organic materials to the soil may effect on the content of potassium chemical fractions. The purpose of the present study was to investigate the effect of mycorrhizae fungi, animal fertilizers (sheep and chicken), and their biochar on the concentration of potassium chemical forms and the relationship between these forms with potassium content of maize plant in a calcareous soil.
Material and methods: A factorial experiment as completely randomized design with three replication was done under greenhouse conditions. Treatments included five levels of organic fertilizer (without addition, sheep manure, poultry manure, sheep manure biochar, poultry manure biochar, each at 2 % w/w) and fungal inoculation in three levels (without inoculation, inoculation with Funneliformis mosseae and Glomus versiforme). Biochars were prepared under limited oxygen conditions at 500 0C for 4 hours. Appropriate amount of surface layer of a calcareous soil was collected and after passing through 2 mm sieve, were treated by organic fertilizers and arbuscular mycorrhizae fungous according to the experimental design. Then, 5 corn seeds (Zea mays L. 704) were planted at 2 cm depth in plastic pots. During plant growth, the soil moisture was maintained about 80 % field capacity level by distilled water. After 10 weeks, shoots were harvested and roots were separated from soils. After air drying and passing soil samples through 2 mm sieve, the concentration of potassium chemical forms (soluble, exchangeable and non-exchangeable) were measured. Also, the potassium uptake by shoots was also calculated by multiplying the potassium shoot concentration in dry matter yields.
Results: Results indicated that organic manures and their biochars increased the contents of soluble, exchangeable and non-exchangeable K (8-65, 43-128 and 29-72 mg kg-1, respectively as compared to control). Generally, sheep manure and its biochar increased all K forms more than poultry manure and its biochar. Conversion of manures to biochar decreased soluble K and increased exchangeable and non-exchangeable K. Application of Funneliformis mosseae decreased soluble K and increased non-exchangeable K; while application of glomus versiforme decreased soluble K and increased exchangeable K. The amount of K extracted by HNO3 (sum of K forms) in treated soils with organic manures was lower than treated soil with biochars. Application of poultry manure biochar led to an increase in the effect of mycorrhiza species on the K content in soil while, application of sheep manure biochar caused a decrease in the effect of these fungous on three chemical forms of K. Organic materials and biofertilizers application significantly increased K uptake (16-217 and 14-36 mg pot-1, respectively as compared to control). Potassium concentration in shoot of maize plant had significant and positive relationships with all forms of K in soil.
Conclusion: applied organic manures (sheep and poultry) in increasing the soluble form of K were more effective than their biochars while, biochars increased the content of exchangeable and non-exchangeable forms of K more than raw materials. Also, application of each mycorrhizae species caused a decrease in soluble form of K. Generally, it can be concluded that organic materials and mycorrhizae fungi application may affect the K uptake or its leaching potential due to their effects on different forms of soil K.