Agrochemical characteristics of soils of Russia

Sod-podzolic soils

Sod-podzolic soils have:

• an acidic reaction — pH 4–5;
• exchangeable acidity 1–2 mg·eq/100 g, of which 80–90% is due to aluminum;
• hydrolytic acidity 3–6 mg·eq/100 g;
• CEC 5–15 mg·eq/100 g;
• base saturation 30–70%.

In most cases, sod-podzolic soils need liming.

Agrochemical indicators depend on particle-size distribution and degree of cultivation. Sandy and sandy loam soils are characterized by low humus content up to 0.5–1.0%, nitrogen up to 0.003–0.08%, phosphorus 0.03–0.6%, potassium 0.5–1.0%, calcium, magnesium, and other macro- and micronutrients. Loamy and clayey soils contain 2–4% humus, 0.1–0.2% nitrogen, 0.07–0.12% phosphorus, and more than 1.5% potassium.

Most sod-podzolic soils are poor in mobile forms of nitrogen and phosphorus, and light soils in potassium. With a high degree of cultivation, acidity decreases to pH 5.1–6.0, and the humus content increases to 2.5–4.0%, mobile phosphorus to 150–200 mg/kg, potassium to 200–300 mg/kg, CEC, base saturation, and availability of other nutrients increase.

Since these soils are mainly concentrated in the zone of sufficient moisture, fertilizer application and liming show high efficiency. Nitrogen most often appears as the first limiting factor, and on poorly cultivated soils phosphorus as well. On light soils, along with nitrogen-phosphorus fertilizers, the application of potassium and magnesium fertilizers is effective.

Gray forest soils

The thickness of the humus horizon, humus content, and degree of podzolization in gray forest soils can vary greatly.

In light gray soil:

• pH 4.8–5.4;
• humus content 1.6–3.4%;
• H_hyd and S are respectively 2.3–3.8 mg·eq/100 g and 10–18 mg·eq/100 g;
• V 72–82%;
• content of mobile forms of phosphorus and potassium within class 3.

For gray forest soils, the indicators are better and reach a maximum for dark gray forest soils:

• pH 5.5–6.0;
• humus 3.5–7.0%;
• H_hyd and S are respectively 2.3–5.4 mg·eq/100 g and 20–36 mg·eq/100 g;
• V 80–86%;
• availability of mobile phosphorus and potassium corresponds to class 4.

Nitrogen is the first limiting factor on light gray and gray forest soils, phosphorus is the second; on dark gray soils the reverse order is possible. The need for potassium fertilizers appears when cultivating potassium-loving crops.

Depending on the level of agricultural intensification, such agrochemical indicators as pH and the availability of mobile forms of elements may change for better or worse.

Chernozem soils

Chernozem soils contain in the arable horizon:

• 4–12% humus;
• total nitrogen 0.2–0.5%;
• total phosphorus 0.1–0.3%;
• total potassium 2.5–3.0%;
• reaction from neutral for typical chernozems to slightly acidic for leached and podzolized subtypes;
• hydrolytic acidity increases from typical to leached subtypes from 0.5–3.0 to 5–7 mg·eq/100 g.

When moving south from the ordinary to the southern subtype:

• it becomes alkaline to pH 7–8;
• hydrolytic acidity disappears;
• maximum CEC 50–60 mg·eq/100 g;
• humus content 8–12%;
• total nitrogen 0.4–0.5%;
• total phosphorus 0.25–0.35% in typical chernozem decreases when moving to northern and southern subtypes.

The availability of mobile forms of phosphorus and nitrogen in long-cultivated, poorly fertilized, or unfertilized soils decreases and often does not exceed class 2–4. On such soils, phosphorus fertilizers are effective, and under favorable moisture conditions, nitrogen fertilizers are effective. On long-cultivated and poorly fertilized soils under potassium-loving crops, along with phosphorus-nitrogen fertilizers, potassium fertilizers are effective. In moist regions of the west of the Chernozem zone, fertilizer efficiency is higher; to the east, depending on climate aridity, efficiency decreases.

Chestnut soils

When moving from north to south, chestnut soils are divided into subtypes: from dark to light chestnut. Their fertility decreases. Humus content decreases from 4–5 to 2–3%, total nitrogen from 0.2–0.3% to 0.10–0.15%, phosphorus from 0.1–0.2% to 0.08–0.15%, CEC from 30–35 mg·eq/100 g to 12–15 mg·eq/100 g, slightly alkaline reaction (pH_salt) from 7.0–7.2 to 7.4–8.0, and among absorbed cations the proportion of sodium increases.

Chestnut soils contain fairly large reserves of potassium but have low availability of plant-available forms of nitrogen and phosphorus. With insufficient moisture, the efficiency of phosphorus and nitrogen fertilizers decreases. Under rainfed conditions on chestnut soils, minimal doses (10–15 kg/ha) of phosphorus fertilizers are recommended, which are applied at sowing. Under irrigation, the efficiency of nitrogen and phosphorus fertilizers increases sharply; potassium fertilizers are often ineffective.

Among chestnut and especially light chestnut soils, with an increase in the proportion of sodium in the soil exchange complex and alkalinity of the reaction, variants with varying degrees of solonetzicity occur. To increase the fertility of solonetzic soils, actual and exchangeable alkalinity is neutralized by gypsum application or acidification.

References

Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Edited by B. A. Yagodin. Moscow: Kolos.