the effects of biochars and their feedstock on corn growth and k-availability in a calcareous soil.

Today, the use of biochar in the sustainable management of soil fertility, has been drawing the attention of the scientists as a multi-purpose and environmentally friendly strategic idea. There are several scientific reports implying the outstanding positive effect of biochar on soil fertility and plant growth. On the contrary, some inconsistent reports have mentioned negative or no effect of biochar. Therefore, it is necessary to investigate the effect of any biochar on the soil and plant before any widespread use of any kind. In the present study, the effect of three different biochar and their raw materials on potassium availability and corn growth was studied.

The study was carried out as a two-part-experiment, including laboratory and greenhouse parts. In both parts of the study, treatments included the control (soil without any biochar or its feedstock), Municipal Waste Compost (MWC), Biochar of Municipal Waste Compost (BMWC), Sewage Sludge (SS), Biochar of Sewage Sludge (BSS), Cow Manure (CM), and Biochar of Cow Manure (BCW). In each study, application rates of treatments to the soil, were 1% w/w. In the laboratory part, the effects of the treatments on available-K and parameters of Quantity/Intensity (Q/I) ratio of potassium were investigated. Also the effects of the treatments on plant growth, K-concentration and K-content of corn were investigated in the greenhouse part.

The CM and its biochar, highly increased the available-K by highly increasing the potassium-Q/I parameters compared to the control. While the SS and its biochar lightly increased the available-K by lightly increasing the potassium-Q/I parameters. The CMW and its biochar, intermediately increased the available-K by intermediately increasing the potassium-Q/I parameters compared to the control. Treatments could improve could improve the growth, k-concentration and k-content of corn compared to the control, excepting of MWC in the case of the plant growth, and SS and BSS in the case of k-concentration. Totally, the descending order of treatments in terms of increasing K-availability was as the follows: 1-BCM, 2- CM, 3-BMWC, 4-MWC, 5-SS and BSS, 6-control. The descending order of treatments in improving plant growth conditions and increasing dry weight of the plant was as the follows: 1-CM, 2-BSS and SS, 3- BMWC, 4- BCM, 5- Control and MWC.

Considering the superiority of BMWC to MWC, in terms of affecting on K- availability and plant dry weight, BMWC can be preferred to MWC. Considering the superiority of BCM to CM in terms of the effect on K-availability, K- concentration and content of plant compared to the control, meanwhile its decreasing effect on plant growth compared to CM, it seems that some considerations such as salinity and nutritional balance must be carefully considered and managed in the case of BCM application. Despite the similarity of BSS and SS in terms of increasing plant growth, BSS application can be preferred to SS because of the more value of PBCK, and consequently, the more continuously K-supply.