Agrochemical foundations for designing a crop nutrition system

An effective fertilizer system in crop rotation is not just about general standards, but an individual nutritional plan for every field. To ensure it boosts the harvest, an agronomist must link the crop's biology with the characteristics of the soil, the climate, and the properties of the fertilizers themselves. This approach allows for precise calculation of doses, selection of the correct forms of active ingredients, and determination of optimal application timing.

Biological features of crops: what the plant consumes and when

Each crop has its own nutritional profile. For example, sunflower and sugar beet remove significantly more potassium from the soil than cereal crops, while legumes require an increased amount of molybdenum. It is also important to consider the dynamics of nutrient consumption during the growing season.

Nutrient consumption is uneven. Cereal crops absorb the bulk of their nutrients in the first half of the growing season — from tillering to heading. At the same time, grain legumes consume nutrients much more evenly throughout their entire life cycle.

The placement depth of fertilizers is directly influenced by the development pattern of the root system. Cereal crops have fibrous roots that do not grow deep, so fertilizers must be in their accessible zone. Grain legumes and other crops with a taproot system penetrate deep into the soil, which requires deeper application of nutrients.

• Peak consumption of cereals — from tillering to heading
• Increased demand of sunflower and beet — potassium
• Increased demand of grain legumes — molybdenum

Soil and climate: how external conditions change fertilizer performance

The effectiveness of mineral fertilizers depends directly on the soil texture. In heavy clay soils, nutrients are firmly held and move slowly with water, so higher doses are justified here. In light sandy soils, water quickly washes away nutrients, which requires split application and timing adjustments.

Before drawing up a nutrition plan, it is essential to assess potential soil fertility using agrochemical cartograms. These are used to determine the content of humus, mobile nitrogen, phosphorus, and exchangeable potassium. If necessary, chemical amelioration is planned: for acidic soils — liming (assessing pH, hydrolytic acidity, and the sum of exchangeable bases); for alkaline soils — gypsuming (assessing cation exchange capacity and sodium content).

Weather and water regime determine whether a fertilizer will work at all. During severe drought, fertilizer application is useless and can even harm plants by causing burns. Conversely, with a moderate moisture deficit, proper nutrition helps plants use water more economically and efficiently.

Temperature regime also makes its own adjustments. It determines not only the length of the growing season and crop selection, but also the timing of tillage. Temperature directly affects the microbiological activity of the soil and the rate of accumulation of available nutrient forms, especially nitrogen.

An important condition is the residual effect of fertilizers, which determines the application rates for subsequent crops in the crop rotation. Organic and phosphorus fertilizers have a particularly long residual effect.

Combined use of organic and mineral fertilizers is one of the main principles of a fertilizer system. D.N. Pryanishnikov wrote about this: "Maximum yields are achieved by a combination of manure and mineral fertilizers, which allows for abundantly supplying plants with assimilable food at the first stages of development while simultaneously providing a reserve of nutrients from the manure that come into action gradually" (Selected Works, vol. 1, 1952, p. 563).

The combination of manure with mineral fertilizers in most cases exceeds the effectiveness of these fertilizers when applied separately in equivalent amounts of nutrients, which is due to the stimulation of microbiological activity in the soil. It also reduces the fixation of phosphorus from mineral fertilizers in the soil.

Combined use of manure and mineral fertilizers is most desirable when cultivating crops that are sensitive to high concentrations of the soil solution (cucumber, onions, garlic, and others).

Adherence to agrotechnical practices significantly increases the effectiveness of fertilizers. The timing and depth of tillage influence the accumulation of nutrients in a form accessible to plants. Early tillage allows for the accumulation of significantly more mineral nitrogen. Consequently, the demand for nitrogen fertilizers decreases.

Special attention during fertilizer application should be paid to the weed infestation of crops and the control of weeds in the agrophytocenosis. If proper measures are not taken, fertilizer application can increase weed infestation and not only reduce the yield increase from fertilizer application but even decrease the overall yield.

As a rule, weed infestation increases with:

• shallow fertilizer incorporation;
• sparse sowing.

In some cases, on heavily weed-infested fields, it is advisable to temporarily refrain from applying fertilizers, especially nitrogen ones.

The effectiveness of fertilizers varies depending on the cultivar of the crop being grown. The most responsive cultivars utilize nutrients from both the soil and applied fertilizers more productively. Such cultivars have a larger proportion of the productive part of the harvest, making them more profitable to fertilize.

Failure to observe optimal sowing dates and inappropriate plant density leads to a decrease in the effectiveness of fertilizer application. Generally, when applying fertilizers, especially at higher application rates, the plant stand density should be lower. In fertilized crops, plants tiller (or branch) more vigorously, leaves become larger, and their surface area increases, which can lead to shading in the lower canopy. The optimal leaf area is:

Different agricultural plants have significant differences in their nutrient consumption. By alternating crops in a crop rotation, soil nutrients and fertilizers are used more productively. For example, when sowing winter wheat after different predecessors, the need for fertilizers will vary.

Specific effects of predecessors:

• After the harvesting of grain legumes (e.g., peas), the soil is easily worked and becomes loose. A long period passes before the sowing of winter crops, so the demand for nitrogen fertilizer will be lower.
• After late-harvested grain corn, little mineral nitrogen accumulates in the soil, and the demand for nitrogen fertilizer increases sharply.
• Legume crops require fewer nitrogen fertilizers, and perennial legumes enrich the soil with nitrogen. Therefore, fewer nitrogen fertilizers are applied to crops following legumes.
• Large amounts of nitrogen should not be applied to a cover crop (under which perennial grasses are undersown).

With crop rotation and lower fertilizer application rates, higher yields are obtained compared to monoculture without rotation.

With long-term fertilizer use in crop rotation, the demand for nitrogen fertilizers increases, while the demand for phosphorus and potassium fertilizers decreases.

When planning a fertilization system, it is necessary to calculate the capacity required for fertilizer storage and the availability of machinery for the application of basal fertilizer, starter fertilizer at sowing, and top dressing. For the application of organic fertilizers, appropriate machinery for preparation, transportation, and application is required.

Based on economic conditions, projected yield increases from fertilizers are determined, and the most cost-effective application rates and methods are selected. For example, localized fertilizer application is 2–3 times more effective than broadcast application. Accurate determination of fertilizer needs also makes it possible to save funds. The economic efficiency of the developed fertilization system is then calculated.