Features of mineral nutrition and the fertilizer system for flax

Nutrition and fertilization of fiber flax

To obtain high-quality fiber flax, the correct selection of the site is critical. The crop performs best on slightly podzolic, structural, light loams. Light sandy loam and sandy soils are poorly suited for cultivation. Heavy clay soils are also unsuitable, as a dense crust forms on them after rain, preventing the emergence of delicate seedlings to the surface.

In crop rotation, fiber flax is placed after perennial and annual grasses, cereals, and row crops. The crop shows high productivity when sown on the sod and ploughed-under sod of perennial grasses. Organic fertilizers are not applied directly to flax, or well-decomposed manure is used if the predecessor was not perennial grasses. In other cases, it is more effective to apply manure under the predecessors — in a green fallow, under row crops, or winter crops.

Flax is extremely demanding regarding the nutrient regime due to its poorly developed root system, which is concentrated mainly in the plough layer. It makes poor use of sparingly soluble compounds and is sensitive to the content of mobile aluminum and an increased concentration of the soil solution. The period of maximum nutrient uptake is very short and coincides with the rapid growth phase (from the end of the "seedling" phase to flowering).

• Rapid growth period — up to 30 days
• Average application rate of mineral fertilizers — N40P60K60
• Phosphorus dose at sowing — P5–10

Each nutrient element is assimilated by flax in strictly defined developmental phases. The critical period for phosphorus demand falls on the stage from emergence to the "seedling" phase, for nitrogen — from the "seedling" phase to budding, and for potassium — in the "seedling" phase. Detailed uptake dynamics of the elements are presented in the table below:

For the correct distribution of nutrients across the flax development phases, follow the recommended sequence of operations. Remember that phosphorus-potassium fertilizers improve product quality. An excess of nitrogen, on the other hand, reduces fiber strength.

1. Apply phosphorus-potassium fertilizers in autumn under autumn ploughing.
2. Apply nitrogen fertilizers in spring under re-ploughing or cultivation.
3. At sowing, apply a starter dose of superphosphate (P5–10) into the rows.
4. If insufficient nitrogen was applied before sowing, perform top dressing in the "seedling" phase based on the results of plant diagnostics.

Nutritional features of hemp and cotton

Hemp and cotton have increased requirements for soil quality and the level of mineral nutrition. To obtain the planned yield, the agronomist must take into account the biological characteristics of element uptake by these crops. Untimely or insufficient fertilizer application sharply reduces the harvest of fiber and cotton.

Hemp provides high yields on fertile lands with a soil reaction close to neutral. The best soils for it are considered to be chernozems, river valley soils, and drained peatlands, as well as well-fertilized dark gray and light gray forest soils. In crop rotation, the crop is placed after winter cereals, grain legumes, potatoes, and root crops. Repeated sowings of hemp after hemp are undesirable. At the same time, sowing the crop on weed-infested fields and on plots infested with perennial weeds is allowed.

• Optimal soil acidity (pH) — 7.1–7.4
• Mandatory manure application rate — 20 t/ha
• Dose of mineral fertilizers — N45–60P45–60K45–60

The high demand of hemp for nutrition is associated with a short period of element assimilation. During intensive growth (from the beginning of budding to flowering), about 75% of its organic mass is formed, and up to 75% of nitrogen, phosphorus, and potassium are absorbed from their maximum content in the harvest. Nitrogen enters the plants fastest, followed by potassium — their uptake is practically completed in the flowering phase. Phosphorus is absorbed more evenly, but the need for it increases during the period of flowering and seed formation.

Fertilizer application for hemp is carried out according to the following technological scheme:

1. Apply manure (20 t/ha), nitrogen, potassium, and the majority of phosphorus fertilizers in the autumn during ploughing.
2. Apply 60–80 kg of granulated superphosphate in rows directly during sowing.

For cotton cultivation, soils ranging from sandy loam to clay are suitable, but light loamy varieties are best suited for both irrigated and rain-fed conditions. Heavy clay soils are less favorable due to high tillage costs. Sandy loam soils are also less suitable due to low water-holding capacity and rapid drying. The suitability of the soil and climatic conditions of the North Caucasus for cotton was proven by the first field experiments in the Kuban region in the early 20th century.

Cotton is cultivated in specific crop rotation systems, where alfalfa is recognized as the best predecessor. It improves the physical properties of the soil, accumulates nitrogen, and suppresses cotton wilt pathogens. At the same time, the nutrient removal directly depends on the yield level: with high harvests (45–50 c/ha or more), the ratio between vegetative and reproductive organs improves, so the consumption of nutrients per 1 ton of seed cotton decreases.

Plants consume nutrients differently for the formation of a unit of yield. To plan the fertilizer system, it is important to know the exact volumes of nutrient depletion from the field. Comparative data on the removal of nitrogen, phosphorus, and potassium for flax, hemp, and cotton are presented in the table:

Cotton nutrition regime: from alfalfa sod to top dressing

Cotton consumes nutrients unevenly and over a long period. From the beginning of budding to mass flowering, plants absorb 25–30% of nitrogen and 15–20% of phosphorus and potassium. The main peak of consumption occurs in the period from flowering to mass boll ripening — during this time, cotton takes 65–70% of nitrogen, as well as 75–80% of phosphorus and potassium, from the soil. To obtain a high yield of seed cotton, it is critically important to ensure a sufficient level of plant nutrition specifically in the second half of the growing season.

• Humus in cotton soils — 1–4%
• Manure application rate — 20–40 t/ha
• Maximum nitrogen dose — 300 kg active ingredient/ha
• Phosphorus during sowing — P20–40

The crop is mainly grown on sierozem-meadow and meadow-boggy soils with low humus content, which are often poor in phosphorus and potassium, and are also prone to salinization. To maintain soil fertility, cotton-alfalfa crop rotations are used, where 2–3 fields are allocated to alfalfa and 5–9 fields to cotton. Alfalfa saturates the soil with nitrogen, which allows for savings on mineral fertilizers in the first years after its ploughing. As for alfalfa itself, as a legume crop, it primarily requires phosphorus fertilizers.

Organic fertilizers are applied in the 4th–5th year of cotton cultivation after alfalfa under autumn ploughing. As an alternative or supplement, it is effective to use green manure (siderates) from intermediate crops.

When growing cotton after a sod and sod turnover of alfalfa, nitrogen application rates are reduced. The further cotton moves in the crop rotation from alfalfa, the higher the nitrogen fertilizer rates, the greater the need for potassium, and the less for phosphorus. The maximum nitrogen dose is 300 kg/ha of active ingredient, and specific rates are determined by the mineral nitrogen content in the soil. If the planned rate does not exceed N100, the entire dose is distributed only in top dressing. At higher rates, ammonium and amide forms are used according to the following scheme:

1. Before sowing: application of N30–70.
2. During sowing: application of N10–20.
3. At the 2–4 leaf stage: top dressing of N30–50.
4. At the beginning of budding: top dressing of N30–75.
5. At the beginning of flowering: top dressing of N30–75.

Phosphorus fertilizer rates are calculated based on the content of mobile phosphorus in the soil. With a base nitrogen dose of N200, refer to the following figures:

During sowing, P20–40 is additionally applied into the rows.

Doses of potassium fertilizers also depend on soil analysis. If the mobile potassium content is very low, K100 is applied; at higher levels, K50 is applied. If the calculated potassium rate is K50 or less, the entire dose is applied as a top dressing at the budding stage.

When applying fertilizer to forage crops, remember that it is important not only to increase overall yield but also to obtain quality feed. Rational selection of application rates and timing of fertilizer application allows for a significant increase in protein content, carotene, vitamins, and minerals.