Soil Problems: Improving the Soil Is the Key to Solving the Root Cause (Part 1)

Soil is the most critical physical foundation for producing high-quality, high-yield agricultural products. Once soil structure and the arable topsoil are damaged and the soil degrades, cultivating crops becomes like trying to grow a tree without roots or draw water from a dry well—yielding not only poor harvests but also shortening the service life of greenhouses. Therefore, dear farmers, if the soil is compromised, no amount of additional chemical fertilizer will boost yields; the key lies in finding ways to address soil problems.

What aspects are included in soil degradation?

1. Deterioration of soil physical properties

A soil’s physical structure is known as “soil aggregate structure,” meaning the soil is composed of small clumps—much like earthworm castings. A well‑developed aggregate structure promotes aeration, retains water and nutrients, and even enhances drought resistance. However, this structure is highly unstable and easily disrupted by external factors, including human activities. For example, watering too frequently or excessively, applying uncomposted organic fertilizers, or spraying certain chemical fungicides—especially herbicides—can all damage the soil’s aggregate structure. Once the aggregate structure is compromised, the tiny clumps that make it up disintegrate, leaving the soil in a flat, compacted state that readily leads to soil compaction. Many farmers mistakenly believe that soil compaction simply means the soil has become harder; in reality, it results from the destruction of the soil’s physical structure.

2. Deterioration of Soil Chemical Properties

(1) Soil acidification

The typical neutral soil pH is around 7, though it varies from region to region. Taking Hebei’s soils as an example, they are generally slightly alkaline, with a pH of approximately 7 to 7.5. Meanwhile, most of the fertilizers currently in use are acidic; in particular, those produced by smaller manufacturers often fail to meet quality standards and exhibit even greater acidity. Since fertilizers themselves are essentially salts of strong acids and weak bases, their long-term, heavy application can lead to soil acidification and a decline in soil pH. In some areas, soil pH has dropped as low as about 4, indicating severe acidification.

The wider the colored and gray bars, the higher the nutrient uptake efficiency; the narrower the bars, the lower the uptake efficiency. The numbers indicate the soil’s pH level. 。

The adverse effects of soil acidification include: ① impaired uptake of nitrogen, phosphorus, potassium, and micronutrients, as the bioavailability of micronutrients varies significantly across different soil pH levels; ② soil acidification can lead to crop maladaptation and a sharp decline in stress tolerance.

(2) Soil salinization

Fertilizers themselves are inorganic salts composed of salt ions; for example, potassium sulfate dissociates into K⁺. + And SO 4 2- , K + , K + It can be absorbed by crops, but SO 4 2- It remains in the soil, and the same principle applies to potassium chloride. When excessive ions persist in the soil, they lead to an excessively high soil salinity.

The harmful effects of soil salinization are manifested as follows:

① The root system cannot absorb water properly, hindering the growth of vegetable plants; in severe cases, the vegetables may appear as if planted in saltwater, with symptoms such as root suffocation and plant death.

② Salt ions can exert antagonistic effects, thereby affecting the absorption and utilization of various nutrients by vegetables.

Soil salinization varies in severity:

         ① In the early stages, after about a year of vegetable cultivation, a lush green layer of moss—known as “qing shuang”—will appear on the soil. The bluish-green color is the earliest sign of soil salinization.

② Moderate soil salinization is characterized by the appearance of reddish, gelatinous patches when soil moisture is high. As the soil dries, these give way to flaky, brick‑red crusts—known as “red efflorescence.” At this stage, adverse effects such as leaf wilting occur, ultimately reducing crop yields.

         ③ A more severe manifestation of soil salinization is the appearance of a thin layer of “white frost” on the soil surface during dry conditions. At this stage, salinization has become particularly pronounced: vegetable root systems inside greenhouses are markedly reduced, and in later growth stages, plants exhibit widespread wilting, stunted development, and severe premature senescence. Water may flow backward through the roots, causing the root cortex to turn reddish, while the stems show wilting and rot.

3. Deterioration of soil biological properties

Soil is teeming with microorganisms, which interact and influence one another. In newly constructed greenhouses, the soil’s biological properties are relatively favorable, with harmful and beneficial microbial communities in a state of balance. However, as cultivation continues and chemical fertilizers are repeatedly applied, the soil microbial community gradually becomes imbalanced: the population of pathogenic microbes grows while that of beneficial microbes declines. Over time, root diseases become increasingly severe, crop yield and quality deteriorate, and eventually, no matter how much fertilizer is applied, yields fail to improve. Vegetable growers often focus solely on chemical fertilization, neglecting the vital role of activating soil biological health; the deterioration of soil biota is one of the primary factors driving reduced crop productivity.

4. Soil compaction

         Many vegetable growers mistakenly believe that soil “compaction” simply means the soil has hardened, preventing roots from penetrating. In reality, even the hardest soils can still support root penetration—often quite deep. Vegetable roots need to breathe and require oxygen; compaction reduces soil aeration. If heavy irrigation is added on top of this, water can displace the oxygen in the soil, suffocating the roots and leading to root rot and eventual root necrosis. By the mid‑growth stage, the rate of root decay can outpace root growth, causing premature root senescence—roots become progressively shallower, especially in older greenhouses. For tomatoes and cucumbers, roots typically extend only about 10 centimeters downward, with most growth shifting to lateral roots that spread laterally along the plastic mulch. Even when you dig up the roots, they may appear long, but in fact, lateral roots dominate.

         Shallow root systems can impair a crop’s ability to absorb water and nutrients. When applying fertilizer through irrigation—whether by furrow irrigation or flood irrigation—if 15 cm of water is applied to the soil surface, in a typical loamy soil, the moisture can typically penetrate to about 50 cm. In other words, with a single watering‑fertilization event, both water and nutrients are present within the top 50 cm of the soil. However, the crop can only effectively take up nutrients from the upper 10 cm or so; once that shallow layer has been depleted, the plant will again exhibit symptoms of water and nutrient deficiency.

         Soil physical, chemical, and biological properties, as well as soil compaction, mutually influence one another. When soil becomes compacted and fertilizers are applied under such conditions, soil salinization and acidification are exacerbated, and the soil’s biological characteristics deteriorate accordingly. Therefore, when planning soil improvement, a comprehensive approach should be adopted.