In recent years, as the degradation of soil quality in China has gradually worsened, soil conditioning has attracted growing attention and soil conditioners have become popular accordingly. Let us first look at the relevant concepts:
Soil conditioning: mainly refers to action to improve the soil by physical, chemical or microbiological means.
Soil conditioner: a material added to soil to improve its physical and/or chemical properties and/or its biological activity — for example quicklime and purple sand soil, which we use to adjust soil acidity.
Commercial soil conditioner: mostly a compound formulation; a single conditioner may possess several characteristics and functions at once, with the primary function of ameliorating the soil constraint factor while also addressing soil fertility, plant nutrition and even microbial status, with a small amount of fertiliser or microbial preparation added.
Types of soil conditioner
Soil conditioners are usually classified by their main raw material or by their functional characteristics. The table below classifies them by main raw material:
Classification of soil conditioners. Source: “Progress in the Research and Application of Soil Conditioners”, Sun Jifeng
By functional characteristics they can be broadly divided into three types: mineral-source conditioners, soil acid/alkali regulators, and loosening agents or no-till deep-loosening agents.
Mineral-source conditioners. The mineral sources currently used as soil improvement regulators are mainly limestone, dolomite, bentonite, peat, peat blue iron ore, vermiculite, diatomite, soapstone and sepiolite. These minerals often have special physical properties and are used to improve soil.
Acid and alkali regulators. The powdery acid soil conditioner produced mainly from alkali residue (soda waste) is one of the more effective acid soil conditioners. Alkali residue is the waste of alkali plants; its main components are calcium salts such as calcium carbonate and calcium sulphate and magnesium hydroxide, it is alkaline (pH 9–12) and is rich in calcium, magnesium, selenium and other elements beneficial to crop growth.
Loosening agents or no-till deep-loosening agents. These are activated by water and act vertically on the soil, releasing hydrogen ions adsorbed by the soil, increasing the soil's cation exchange capacity, creating more pores, improving soil aggregate structure and enhancing soil aeration and water and fertiliser infiltration, thereby loosening the soil.
Main functions of soil conditioners: (1) regulate the sand–clay ratio, improve soil structure, promote the formation of aggregates; raise the soil's water-holding capacity and increase the supply of available water. (2) Regulate soil pH, reduce or diminish aluminium toxicity; improve saline-alkali soil, regulate base saturation and cation exchange capacity. (3) Rebalance a disturbed soil nutrient system and promote the supply of available nutrients; remediate contaminated soil through passivation of heavy-metal ions. (4) Regulate the soil microflora and maintain a sound soil microbial environment.
Points to note when using soil conditioners
(1) Use according to the actual soil conditions. The purpose of using a soil conditioner is to improve problems such as poor workability, salinity and alkalinity, acidification, contamination by toxic substances and nutrient imbalance. So one must start from the actual condition of the soil, choose a product suited to one's own soil and use it in a targeted way if good results are to be obtained. Nor can soil conditioners be used at will on every kind of land or in every environment.
(2) Use together with conventional fertilisers. It should be made clear here that the main role of a soil conditioner is to improve the soil environment and solve soil constraint problems. Compound commercial products contain a little nutrient, but they cannot be used directly as, let alone in place of, fertiliser.
A soil conditioner must be used together with locally conventional fertiliser, and the optimal combined application scheme needs to be determined through field trials according to local soil texture, salinity, water and fertiliser conditions and economic returns.
(3) Avoid over-use. The main role of a soil conditioner is to improve soil that is too acidic, too alkaline, salinised or compacted, so it cannot be used over the long term, otherwise over-correction occurs and this is even less favourable to vegetable growth. The quantity and frequency of use should therefore vary with the degree of degradation.
(4) Attend to the method of use. With soil conditioners, method of use must be carefully observed. Taking soil-loosening and no-till deep-loosening conditioners as an example, the correct dosage must be mastered according to the type of soil.
For soil that is cloddy and compacted, highly clayey, with uneven water and fertiliser distribution and a shallow plough layer, use it twice a year, then reduce the dosage year by year until it is no longer applied.
The dosage must be correctly controlled: too low and the improvement is hard to achieve; too high or applied too often and it is wasted.
Water is the carrier of the biological activity of a no-till agent: if the soil does not hold sufficient moisture, the biological activity of the agent cannot be activated. So after applying a soil-loosening and no-till deep-loosening conditioner, the soil must be kept at a certain moisture level.
As cultivated area grows and with continuous cropping, excessive chemical fertiliser use and so on, soil problems will continue to worsen, and the use of soil conditioners will become ever more widespread.
At present the soil conditioner market is a mix of good and bad, lacking standards, with uneven quality and all manner of claimed functions. The actual performance of some conditioners is very different from what is claimed, and some even have side effects — for example those made from smelter slag waste carry a risk of heavy-metal accumulation in the soil.
Here we remind our farmer friends: when using soil conditioners, be sure to verify the manufacturer and trademark, and choose quality products!