Technical (non-row) crops is a group of crops in a crop rotation that includes flax, hemp, cotton, rape, and others.They are characterized by high removal of nutrients from the soil while being highly demanding to fertility. For example, high yields of hemp are possible on highly fertile soils, the so-called “hemp land” with the application of high doses of manure or other organic fertilizers.
Predecessors of technical crops
Cottonwood
Cotton plants are less susceptible to the negative effects of repeated sowing, but are responsive to predecessors.
The best preceding crop for cotton is alfalfa, good ones are leguminous, corn and sorghum. The important role in repeated sowing of cotton is played by stubble crops of fodder and green manure crops.
In the countries of Central Asia and Transcaucasia, where cotton sowing is well developed, alfalfa produces 60-80 tons of green mass or 15-20 tons of high-quality hay from 1 hectare if it is cultivated and irrigated. It enriches the soil with organic matter at the expense of root and crop residues. In irrigated agriculture it contributes to soil desalinization and reduction of wilt.
Cotton is cultivated in alfalfa-cotton crop rotations after perennial grasses and after sorghum, corn and leguminous crops. The best raw cotton yields are obtained after perennial grasses or one year after them.
Flax
Flax is a demanding crop for fertility and clean fields from weeds. It does not tolerate repeated sowing. Flax is not subjected to manure as it worsens the quality of fiber.
According to the All-Russian Flax Research Institute, one of the best predecessors of flax is clover of the first and second year of use and a mixture of clover with timothy (or other cereal grasses) of the second year of use. Perennial grasses enrich the soil with organic matter and nitrogen, significantly improving fertility and phytosanitary state of the soil, resulting in a reduction of infestation by fusarium and other diseases. The condition for sowing flax after perennial grasses or one year after them is to carry out extermination measures against pests, diseases and weeds.
Flax can also be preceded by seeded fallows, potatoes, and grain legumes following perennial grasses.
According to the Pskov Regional Agricultural Experimental Station, the infestation of flax crops after perennial grasses is twice lower than after winter rye. Flax can return to its former place in 5-6 years.If there is insufficient area of perennial grasses, flax can be placed after row crops on well fertilized soils such as potatoes and corn, as well as after winter crops and barley following perennial grasses.
Hemp
Hemp is demanding to soil fertility, but allows repeated sowing.
Winter wheat and rye, sugar beets, corn, potatoes, spring wheat, legumes, vegetables, perennial grasses, and forage lupine can be the predecessors.
Tobacco
Scientifically grounded inclusion of tobacco in crop rotation allows to increase tobacco yield by 1,5-2 times in comparison with the permanent and repeated crops.
According to the All-Russian Research Institute of Tobacco, tobacco is recommended to be placed on light sandy loamy, podzolized foothill soils with low humus content after perennial grasses; on rich fertile soils – one year after perennial grasses, in some cases the third year after perennial grasses.
Good predecessors include winter and spring cereals, corn and annual cereal grasses.
Tobacco is not placed after potatoes, tomatoes, eggplant and other nightshades.
Rapeseed
The best preceding crops for rape are legumes, potatoes, corn for silage or green fodder, and winter cereals following good predecessors. Repeated sowing and predecessors from the cruciferous family lead to a sharp decrease in rapeseed yields because of specific diseases and pests. The period of returning to the former place of cultivation is from 3 to 5 years.
Technical crops as predecessors
After flax, potatoes, spring cereals, buckwheat can be cultivated in crop rotations; in areas with later sowing dates of winter cereals – winter wheat and winter rye.
Well-fertilized fields under flax, rape, and hemp retain effects for several years, so they are suitable for cultivation of winter and spring cereals, with yields comparable to those after the seeded fallow or leguminous crops.
Rape has a positive effect on soil fertility and structure, and is therefore sometimes used as a green manure on farms.
Repeat sowings
Technical crops have different attitudes to repeated crops, primarily because of biological reasons for crop rotation. High doses of manure and mineral fertilizers make it possible to re-cultivate hemp without reducing yields. However, long-term permanent hemp crops reduce yields because of the spread of specific pests and diseases: hemp flea, stem moth, fusarium. Therefore, in crop rotations specializing in hemp production, repeated crops are interrupted for 1-2 years by corn, potatoes, perennial grasses or leguminous crops.
Fiber flax does not tolerate repeated crops or short return periods to the same field. It is associated primarily with a strong lesion of fusarium, flax fatigue of the soil and the inhibitory effect of some groups of soil microorganisms. In the crop rotations of Novgorod, Smolensk and other regions, the period of return to the same field is 6-8 years.
Sources
Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. – Moscow: Publishing House “Kolos”, 2000. – 551 с.
Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.