| 17 Jul 2026
Interactive effect of biochar and potassium-solubilizing bacteria on soil depth-dependent potassium dynamics, enzymatic activities and bacterial community in acidic soil under irrigation practices
Abstract. Potassium (K), an essential macronutrient, its availability is often limited in acidic soils due to its fixation or low solubility. Meanwhile, the solubilized K fraction becomes leached under irrigation, owing to reduced K adsorption capacity of acidic soil, thus affecting soil fertility. Previous studies have demonstrated that biochar exhibits a strong potential to retain nutrients in soil. However, their effect on enhancing the K solubility and its retention capacity, especially under combined application of rice straw biochar (BC) with KSB (potassium solubilizing bacteria), remains uncleared. Therefore, an incubation study was carried out, in which a soil column containing 850-gram soil was divided into topsoil (0–15 cm) and subsoil (15–30 cm) portions. The treatment plan was as CK (without K fertilizer), K (K fertilizer), K+ BC (1 % w/w), K+ KSB inoculum (CFU 107 to 108), and K+ KSB inoculum (CFU 107 to 108) + BC (1 % w/w) with quadruplicate. K fertilizer was added only to the topsoil to assess the K retention effect. Results depicted that under integrated application of BC with KSB, soil pH and organic matter (SOM) contents in topsoil enhanced by 13.5 % and 53.9 % compared to K-treated topsoil. Meanwhile, water-soluble K and available K contents increased by 52.5 % and 49.8 % respectively. Such improvement in soil properties greatly enhanced the soil enzymatic activity and soil bacterial community (Actinomycetota and Bacteroidota) in topsoil. Thus, the overall result depicted that integrated application of BC with KSB notably increased the K bioavailability in topsoil by facilitating the KSB activity to solubilize K. Meanwhile, BC improved the K retention capacity through its enlarged surface area, porous structure, and high cation exchange capacity, thereby reduced the K leaching and enhanced the nutrient availability in acidic soil.
As far as I can judge based on the materials and methods, the experimental work has been done well and the results likely are a valuable contribution to the scientific discussion on improving nutrient use efficiencies. However, the work needs substantial rewriting: spelling, grammar and structure need to be improved. Furthermore, the knowledge gap needs to be stated more efficiently and presented concepts/information need to be explained better. I have reviewed until the beginning of the results and would only like to read further after the work has been extensively modified.
Highlights
1. Poor solubility and high leaching are contradictory. Actually, acidification of soil should improve K availability?
2. Availability rather than accessibility?
4. Remove examples of bacteria (too detailed for highlights)
Writing needs improving. Examples from the first section of the introduction:
-L58: Spelling: one of THE most, macronutrientS. Phrasing: “one of the most important” and “primary” have the same meaning, and “macronutrients” also implies it’s primary >> Potassium (K) is one of the primary nutrients for plant growth.
-L59-61: Everything after “e.g.” can be removed as it is redundant. Your work is not on the functions of K in plants.
-L63-64: Remove “the” before K fertilser. Also, due to the structure of the previous sentence, “this” seems to refer to “the growing world population”, implying that K fertilisers are applied to address the growing world population. “The growing world population is expected to reach 8.90 -10.6 billion by 2050, which poses significant challenges for global food security. To increase yields, farmers have extensively applied K fertilizerS, but a significant proportion of K is lost through leaching or fixation”
Please also note, that you move from global food security to K fertilisation, which is not logical. In cereals, the focus has mostly been on N fertilisation. More background on the need for K fertilisation is needed. Furthermore, which farmers have been applying K fertilisers? Globally? And where is “a significant proportion of K lost”? Globally?
-L65: remove “more” or add another country for comparison.
-L65-68: In L64, you mentioned losses of K through leaching or fixation. However, the combination of soil parameters you mention, seem to point towards leaching. Which of the two are you focussing on? “Acidic soil” and “low pH” mean the same. Please note that K availability is a function of several interacting soil parameters, so just low pH and low SOM is not a problem per se. I guess the low CEC (due to sandy soils?) is the main culprit, which is exacerbated by low pH and low SOM. Rephrase to:
“…. but a significant proportion of K is lost through leaching. Potassium leaching is common in soils with low cation exchange capacity (CEC) and exacerbated by low pH and low SOM, particularly under high rainfall or irrigation. This combination of soil properties occurs widely in China (REF).”
-L68: “In addition” is in correct. Also “Leaching” is a “soil degradation process”, so “enhances” is incorrect.
-L68-70: add references
-L71: What do you mean with sustainable? This is a container word without meaning if you don’t provide context. I would recommend to remove the word. And what is soil health? Another buzzword that is somewhat meaningless.
-L75: Facilitating release and enhancing retention are contradictory. Please explain.
-L76: “Enlarged” is incorrect without a comparison. “High” would be correct.
-L80: “direct plant uptake” seems to contract with nutrient retention properties of biochar. The phrase “protection net” seems incorrect, as it is more of a sponge rather than a net.
-L83-88: I cannot follow, it currently says (1) biochar enhances conversion of K to more soluble forms, (2) these forms are more prone to leaching and (3) biochar reduces leaching. Please structure the writing everywhere, it currently seems full of contradictions.
-L86: “Plant uptake” is much more common than plant assimilation.
-L89: replace ‘it’ which ‘biochar’
-L89-90: “increases the soil pH, which prevents the K from fixation”. Do you mean leaching rather than fixation? Otherwise I don’t understand. First of all, all of the previous text is about leaching, secondly, a higher pH actually fixes K (lots of H+ in acidic soils, which outcompete K at the surfaces of clay and SOM, so low pH = lots of K in solution).
-L95: You mention clay minerals, but I presume most of the K leaching problems occur in sandy soils. You need to include something on texture in the introduction, as well as numbers or percentages how common K leaching soils are in China. Furthermore, I don’t understand (yet) why you look into K solubilising bacteria, as you mostly seem to have an issue with leaching. Again: you need to structure the writing, so every section logically follows on the previous one. Now the bacteria really come out of nowhere.
-L118: in THE current study
-L121-123: “Enumerate” is incorrect. “artificially induced rainfall-driven leaching conditions”? >> “(1) investigate the SEPARATE and COMBINED effectS of biochar AND KSB on soil chemical properties, enzymatic activities and K leaching under artificial rainfall conditions;”
-L123-124: The difference compared to what? Retention of K fractions? >> “(2) explore the different soil K fractions and K retention at different soil depths in response to applied amendmentS;”
-L127: “enhance K bioavailability and retain it in topsoil” As said before, this seems highly contradictory. It doesn’t have to be, but you need to explain the underlying mechanisms, presumably the biochar acts as a kind of buffer that quickly adsorbs a surplus of K, while at the same time it slowly releases K into the soil solution? I assume this has been studied before? If so, what is new about your work? Please include more relevant references on the functioning of biochar in relation to K leaching and availability, particularly throughout a growing season.
-L129: “artificially induced rainfall conditions” This phrasing is strange and it is also redundant (it’s M&M).
-L148: Why this particular soil? I am particularly surprised to see it’s clayey (150). Although kaolinite tends to have a lower CEC then other clay minerals, it’s still much higher than sand! Also, why hasn’t CEC been measured and reported in Table S1?
-L153: sieved at what size?
-L157: BC is not introduced before
-L165: better compared to what?
-L168: with four replicates
-L171-172: units?
-L174: 60% WHC cannot be saturated. When were bacteria inoculated?
-L176: unclear sentence. When did you inoculate second and third time? Directly after each inoculation they were in the dark 10 days?
-L179: remove artificial. How much water did you add?
-L190: Why enzyme analysis? This does not correctly relate to any of your research objectives.
-L192: “daily” is incorrect
-L196-199: references needed
-L233: What did you do if the assumptions of ANOVA were violated?
-Section 3.1: It is very difficult to read this section, it is a summation of a lot of results, try to write more concise and leave out redundant results. Is it relevant to discuss result on N and P if the focus is on K? I would recommend to remove 1% everywhere, is redundant (specified in M&M). Consider using “biochar” instead of BC in the text, as there already are many abbreviations.
-L256: improved compared to what? Also, I would use ‘increased’, as ‘improved’ indicates a better state
-L259: remarkably is subjective
-L258-259: Sentence is incomplete