Perspective Chapter: Technology of Growing the Main Vegetables in Ecological Agriculture

Abstract

Ecological agriculture promotes sustainable, diversified and balanced production systems, in order to prevent crop and environmental pollution. Ecological production in plant culture, without the use of harmful traditional products, has been a special concern for several decades in economically developed countries. Interest in ecological products and production is continuously growing in our country as well. Leguminous plants play a particularly important role in ecological agriculture. The favorable effect of legumes for successor plants has been known since ancient times. This article includes the importance and biological characteristics of legumes.

1. Introduction

Ecological agriculture promotes sustainable, diversified and balanced production systems, in order to prevent crop and environmental pollution. Ecological production in plant culture, without the use of harmful traditional products, has been a special concern for several decades in economically developed countries. Interest in ecological products and production is continuously growing in our country as well. It is regrettable that the areas cultivated under ecological conditions in our country are still very small. In order to expand the organic farming system in Romania, national legislative regulations have been established regarding the production, processing and valorization of organic agri-food products, in accordance with international norms in this sense. Among these, we mention: Government Emergency Ordinance no. 34/2000, respectively Law no. 38/2001; H. G. no. 917/2001 for the approval of the methodological rules for the application of these regulations (including the annexes to the methodological rules), etc.

For the implementation of the provisions of these regulations, the National Organic Products Authority (ANPE) functions as a specialized service within the Ministry of Agriculture, Food, Forests and Environment, which ensures compliance with all specific legal provisions and ensures control over the ecological production methods of agro-food products.

Field plant technologies are developed in the spirit of these regulations, economically efficient and non-polluting, with the prevention of environmental damage and the maintenance of the fundamental resources of agriculture. It is recommended to place crops in rotation on plots converted to organic agriculture, following the best practices, some that also improve soil fertility (such as leguminous plants and green manures), the use of only fertilizers allowed in organic agriculture and the exclusion of all pesticides that pollute production and the environment.

Diseases, pests and weeds in this culture system are combated by cultivating the most resistant varieties/hybrids, by suitable crop rotations, mechanical and physical methods of combating, protecting useful entomofauna, etc. The expected technological solutions are based on the knowledge of the biological elements of plants, orienting the specialist in their application in different climate and soil conditions. The optimal vegetation conditions are highlighted, the whole complex of phytotechnical measures, in order to increase the photosynthetic yield of useful biomass production and to value the genetic potential of cultivated varieties and hybrids.

Plants provide a large part of the products necessary for human nutrition and animal feed, also representing an important source of raw materials for various industries producing consumer goods.

2. Biological importance of legumes

The plants included in this phytotechnical group have as their main product the seeds (grains) rich in protein. This includes: peas, beans, soybeans, lentils, chickpeas, beans, lupins, sorghum, peanuts and broad beans. All are part of the order Leguminosales (Fabales), family Leguminosae (fam. Fabaceae or Papilionaceae). Being from the same botanical family, these plants have certain common morphological, biological, chemical, ecological and technological properties. From the Leguminosae (Fabaceae) family, other plants with various uses (forage, vegetables, medicinal, etc.) are cultivated.

Legumes for grains were cultivated with the beginnings of agriculture, as various testimonies attest. Over 5000 years B.C.E. the inhabitants of the lakeside settlements on the current territory of Switzerland cultivated peas, chickpeas and other legumes for grains. In China, more than 3000 years B.C.E. soybeans are cultivated. The ancient Greeks and Romans appreciated the nutritional value of legumes and their favorable effect on the soil [1]. On the territory of our country, carbonized leguminous seeds were discovered in various Neolithic settlements (polished stone age, 5th–2nd millennium BC) [2]. Over the years, gradually, the number of cultivated species and biotypes increased, due to their great importance in human and animal nutrition.

The importance of legumes for grains lies, first of all, in the high protein content of the seeds, giving them a high nutritional value. Some of them (soybeans and peanuts) also have a high oil content, making it possible to extract them through ordinary technical procedures, being valuable oleaginous plants. Soy is the largest producer of vegetable oil on the globe, and peanuts are in third place (after soybeans and sunflowers).

The protein content of leguminous grains is 2–4 times higher than that of cereals. In some of them (soy, lupine) the protein content exceeds the carbohydrate content. The ratio between crude protein and non-protein components is: in soy and lupine of 1/1.7; to peas 1/2.8; to beans 1/2.4 etc. So leguminous grains represent food and fodder concentrated in protein. It is also worth noting the high protein value of the grains, equivalent in some species to proteins of animal origin, containing essential amino acids. The protein from leguminous grains has a high digestibility (about 90%) and does not form uric acids (like some animal proteins) whose accumulation in the body is harmful.

To achieve, quantitatively, 1 kg of animal protein, 5–7 kg of vegetable proteins are consumed. The use of (processed) vegetable protein in higher proportions in the human diet would greatly increase the protein ration of people and including the yield of agricultural production. The protein production obtained per hectare from the main legumes for grains (peas, soybeans, etc.) exceeds that of wheat, corn, potatoes and other plants. The problem of proteins occupies a central place in the concerns regarding the present and the future of human nutrition. They are basic, essential components of food rations. As shown by I. Cerbari [3], although it seems curious, only in the middle of our century did nutritionists establish that “no human nutritional deficiency syndrome is as harmful as protein malnutrition, although since 1838 Mulder – based on finding that these complex substances containing carbon, oxygen, hydrogen, nitrogen and sulfur are found in all forms of life – he concluded that they must occupy the first place in the unfolding of vital phenomena and called them proteins” (from the Greek “proteias” which means primary, first). In 2013, Cerbari [3], in relation to the body’s needs, divided amino acids into essential (indispensable for the body) and non-essential (which can be synthesized in the body). Later it was established that (in addition to their presence) the ratio between the essential amino acids also determines the biological value of the food protein. The amount of protein in a balanced ration of an adult should represent about 11–13% of the energy value, i.e. 1–1.2 g/kg/day [3]. Man, for a rational diet, needs all 10 essential amino acids (lysine, methionine, threonine, histidine, valine, isoleucine, leucine, phenylalanine, tryptophan and arginine) found in animal protein, but also plant products (especially legumes for grains) can provide a good part of this requirement.

Ensuring the global protein requirement is increasingly dependent on the contribution of plants rich in these substances. The “Protein Consultative Group” within the F.A.O. mentions “a new green revolution – that of legumes”, and as the “main hope” for solving the protein deficit in the world, legumes for grains are considered.

In addition to proteins, leguminous seeds contain carbohydrates, fats, vitamins, mineral salts, etc., which complete their nutritional value.

In human nutrition, the dry seeds (grains) of these plants are used, as well as the pods and green grains, to prepare various dishes or preserves. The dried grains can be used in human nutrition directly or after a prior industrialization. Products similar to: milk, cheese, meat, etc. are obtained from soybeans. The coffee substitute is obtained from chickpeas and soybeans, and the flour of some legumes (soybean) can be mixed, in a certain proportion, with that of wheat, in the manufacture of bread and flour pasta.

In animal feed, the uruiala from leguminous grains is used in a mixture, in certain proportions, with cereals, which improves their nutritional value. Soy cakes are also a concentrated feed. Legumes for grains are used in the feed of animals in the green or ensiled state, alone or in a mixture. The secondary products of legumes (stems, leaves, sheaths) resulting from threshing have a high protein content (8–14%), exceeding 10 times the content of cereal straw (0.7–1.3%). For fodder purposes, pea, lentil, latir, beans and fava beans straws are used in particular. In some legumes, the stems become lignified, being consumed by animals only after possible processing (chopping, ensiling).

Leguminous plants play a particularly important role in ecological agriculture. In crop rotation, the favorable effect of legumes for succeeding plants has been known since ancient times. This effect derives from the symbiosis of leguminous plants with bacteria of the genus Rhizobium, which fix atmospheric nitrogen, enriching the soil with 100–300 kg of nitrogen per ha and realizing an important saving of conventional energy. The nitrogen left after legumes in the soil is in organic form, easily accessible, having a slow, prolonged action. Being spread at different depths in the soil, it favors the development of the root system of the successor plant. Legumes with high solubilizing power for phosphates (lupin, peas, etc.) make this element available to the successor plants in a more accessible form. The lupine manages to use phosphorus from very difficult to dissolve minerals, such as apatite, enriching the soil not only in nitrogen, but also in easily assimilable phosphorus.

Since all parts of leguminous plants are richer in nitrogen than other cultivated plants, they can be used as green manure for soil fertilization. result good results were obtained with lupine on sandy and acid soils. For this purpose, other legumes can be used, on various types of soil.

Leguminous grains, used in human nutrition, also present some shortcomings, among which are mentioned [4, 5]: the thick covering of the grain, with a high cellulose content, which significantly complicates digestibility; long boiling time; deficiencies in the protein composition of non-sulphured amino acids (cystine and methionine) and tryptophan (these being below the requirements indicated by the O.M.S.); the presence of some non-protein antimetabolites, which reduce the degree of digestibility, causing some states of indigestion, etc.

3. Biological peculiarities of legumes

The requirements for temperature and humidity in the process of germination—emergence differ depending on the species. The minimum germination temperature is 1–2°C for peas, 3–4°C for lupine and beans, 6–7°C for soybeans, 10°C for beans, 12°C for peanuts, etc. Below the minimum temperature, the duration of germination and emergence is prolonged, some of the seeds mold, emergence is difficult, uneven and with gaps. The amount of water absorbed by seeds to germinate, relative to their mass, is about 75% for chickpeas, 92–100% for beans, peas and lentils, 106–110% for soybeans and beans, 116–120% for species of lupine etc. This amount of water is absorbed in 24–48 h, depending on the temperature. From the determinations made for white lupine [6], it was found that legumes absorb water more intensively in the hilum area than in the rest of the seed surface, influencing the germination rate.

The emergence of legumes for grains can be epigeic, when the hypocotyl elongates a lot, raising the cotyledons to the surface of the soil (beans, soybeans, broad beans, lupins, peanuts) or hypogeic, when the hypocotyl grows a little, the cotyledons remaining in the soil (peas, beans, lentils, side) (Figure 1).

Figure 1.

Epigeic and hypogeic emergence in legumes.

In general, legumes with trifoliolate and palmate leaves have epigeic emergence (with the exception of Phaseolus multiflorus), and those with pinnate leaves have hypogeic emergence (with the exception of Arachis hypogaea).

At emergence, after the exhaustion of the reserves in the cotyledons, the plants enter a “critical period” (7–12 days after emergence), until the symbiotic bacteria penetrate the root and the symbiotic system begins to function, after which the plant grows normally. In the soils low in nitrogen, small amounts of nitrogen applied at sowing avoid these stagnations in the growth and development of legumes. Higher doses of nitrogen are not recommended, because they inhibit the symbiotic system.

The root of legumes is taproot. In the first phase of vegetation, a further increase vigorous has the main pivot, which continues its development until almost maturity. Lateral branches develop more slowly at first, then in some species they grow beyond the main pivot. According to the ratio between the main pivot and the secondary branches, Leah and Cerbari [7] distinguishes three types of roots in legumes (Figure 2, after [1]).

Figure 2.

Legume roots with nodules: 1—lupine; 2—peas; 3—beans.

Type I with thick, strong main pivot that penetrates deep into the soil. The lateral roots are few in number, short and develop later (in the second month of vegetation). Lupine species belong to this type.

Type II with thinner main pivot, having less penetration power than the previous type; instead, the secondary branches are more numerous and develop somewhat earlier, and the first-order branches approach the length of the main pivot. Among the plants that have this type of root, the grain and the chickpea have the pivot better developed than the ramifications, while in peas, lentils and peanuts the first-order ramifications approach the thickness of the main pivot.

Type III has the main root similar to type II, but branches of the 1st and 2nd order they are very numerous. Sometimes the side branches starting from near the base of the stem exceed the main axis in length. Overall, the root appears as fasciculata, being spread more laterally than in depth. Bean and soybean species have this type of root.

Nodulation and symbiotic nitrogen fixation. Some nodules (nodosities) are formed on the roots of legumes, as a result of symbiosis with bacteria of the genus Rhizobium. These bacteria fix atmospheric nitrogen, offering it to the host plant, which in turn provides the bacterium with the carbon dioxide it needs. The value of legumes as soil improvers has been known since ancient times, but only [2] highlighted the role of microorganisms in this phenomenon. Isolates bacteria from nodules, calling them Rhizobium. Klapp (1941, cited by [2]) shows that 15 races of Rhizobium are known, which cannot be replaced and that for each one cultures must be used for inoculation. Later they were considered as different species, as follows [3].

1. “lupins”—for lupine

2. “phaseoli”—for beans

3. “japonicum”—for soybeans, beans, peanuts, etc.

According to some authors, it would be Rh specific for chickpeas. chickpeas, and for peanuts Rh. peanuts [3]. Rh is also known meliloti for lucerne, sulphina and guisdia; Rh. shamrocks for shamrocks; Rh. ornithopes for the seradela, etc.

Bacteria are rod-shaped 1–7 μm long and 0.2–1 μm thick, but their shape and size vary greatly during their life cycle. In the soil, the ciliated forms of the bacteria move, and when they meet the roots of the legumes, they attach to them (specific chemotactism). The bacteria penetrate through the absorbent brushes, forming a cord that crosses the root bark (through the secretion of enzymes, it dissolves the cell walls). Until it begins to fix atmospheric nitrogen, the bacterium lives as a parasite on the host plant, which enters a “crisis” (7–12 days after emergence) of development, which it passes after the symbiotic relationships are established.

The process of biological nitrogen fixation is determined by the existence of a complex enzyme system called nitrogenesis, which mediates the central reaction of breaking the triple bond between molecular nitrogen atoms and their coupling with hydrogen atoms [4]. The entire nitrogen-fixing system is conditioned by a series of endogenous factors. Ammonium produced in nitrogenesis is used in protein synthesis, via fixation by organic acids and following the Krebs cycle, giving birth to amino acids [5].

Rhizobium species are aerobic, adapted to different pHs and are sensitive to soil dryness. They use carbohydrates (glucose, sucrose, maltose, etc.) as energy sources. In the vicinity of the cord (filament) of infection, the cells begin to divide, forming nodules. The shape, size and location of the nodules on the root is different, depending on the plant. In peas, lentils, and milkweed, the nodules are elongated, in grains and beans they are almost spherical, and in lupine they take different shapes. The nodules are arranged especially on the main pivot in lupine, and in beans and soybeans on the branches.

The number of nodules, the size and the depth of formation reach a maximum during the flowering phase of the plants (when the maximum accumulation of dry matter in the roots also occurs). In this phase, the activity of symbiotic bacteria is also at its maximum.

It was found that, when the bacteria become active, a red pigment of hemoprotein nature appears in the nodule [3]. The discovered this porphyrin with iron in the nodosis of legumes, giving it the name leghemoglobin. It is similar to the hemoglobin of the blood of invertebrates, belonging to the group of erythrocrurins [6], being found in nodules in the amount of 0.25–1.0 mg/1 g, fresh substance [1, 2, 3, 4, 5, 6, 7]; by oxidation, leghemoglobin is transformed into methemoglobin. Nitrogen fixation is closely correlated with the concentration in leghemoglobin.

Maintaining the biological balance and soil fertility is of great importance in the intensity of nitrogen fixation by bacteria. The irrational use of phytopharmaceutical products, herbicides and other physical-chemical treatments disrupts the activity of nitrogen-fixing microflora. When the conditions of their application are respected, the danger is minimal.

Inoculation (infection) with specific bacteria can also be done artificially. For this, the preparation “Nitragin” (produced in our country), which contains bacterial cultures, is used. It is distributed in colored vials, to protect the bacteria from light, on the label mentioning the species for which the treatment technique can be used. For inoculation, the culture of bacteria from 3 to 4 vials is mixed with 0.5–2 l of water, forming a suspension of bacteria with which the seed used for one ha is sprinkled. The treatment is done in the shade and around the sowing area. Artificial inoculation is necessary especially for leguminous plants newly introduced to culture in certain areas, where specific bacteria are not found in the soil, as is the case of soybeans, on some soils. Good results were obtained, however, with other leguminous plants treated with Nitragin.

Symbiosis, both with bacteria from the soil or artificially inoculated, gives results in favorable conditions of fertilization with N.P.K., Ca and microelements (boron, molybdenum, etc.). In soils with a large amount of assimilable nitrogen, the penetration of bacteria into the roots, the formation of nodules and the nitrogen fixation process are inhibited.

At I.C.C.P.T. A special device was made at the bottom, equipped with nozzles attached to the sowing coulters (S.P.C., S.U., S.U.P.) with which the bacterial suspension can be applied by spraying (pressure 0.5 atmospheres) directly in the furrow (Ştefanic, 1979). Thus, the labor consumption used to treat the seeds is reduced, the treatment does not have to be repeated in case of sowing interruption, the seeds can be treated with fungicides (which are toxic to the bacteria with which the seeds are inoculated). For 1 ha, 18–20 l of liquid are used, when sowing with S.P.C, and 60–80 l when sowing in dense rows with S.U. or S.U.P.

It sometimes happens that the bacterial strains with which the inoculation was done cannot penetrate the roots, due to the invasion of ineffective, more vigorous strains existing in the soil (antagonism between the strains). The existence of bacteriophage viruses, which destroy bacteria of the genus Rhizobium, is also reported, which partly explains the failure of some legumes on certain soils.

The stem differs depending on the genus (species), being: erect in broad beans, soybeans, chickpeas, lupins, broad beans; fickle take climbing or recumbent beans to peas and broad beans. As for the branching, it is more pronounced in soybeans, beans, chickpeas, lupins, latir, groundnuts and less branched in peas and beans. In the cross-section, the stem can be round (lupin and peas), prismatic (lard and beans), or transitional (beans, soybeans and lentils).

The possibility of mechanizing the harvest is conditioned by the erect position of the stem and the place of insertion of the ramifications on the stem.

Legume leaves are compound, having a pair of more or less developed stipules. The leaves are different in type (conformation) and size, shape, color, hairiness of leaflets and stipules. They have even-pinnate leaves: the pea, the bean, the pea, the groundnut, the lentil, and the odd-pinnate leaves: the chickpea. Trifoliate leaves are in beans, soybeans and broad beans, and in lupine they are palmate (Figure 3, after [1]).

Figure 3.

Legume leaves: 1—peas; 2—chickpeas; 3, 4—lupine; 5—peanuts; 6—beans; 7—soy; 8—grain; 9—lateral.

Stipes in some species are larger than the leaflets (peas), smaller (chickpeas, beans, lentils) or absent (beans). Some legumes (lupin, beans, soybeans and chickpeas) show heliotropic movements; the leaflets in strong light are arranged obliquely, to avoid it, and in weak light they are oriented perpendicularly, to retain it.

The flowers are grouped in axillary inflorescences (racemes), except for lupine species that have a terminal raceme. The calyx consists of 5 concretized sepals (gamosepal); corolla of 5 free petals (banner, wings and inner part), differently colored; the androecium is composed of 10 stamens, diadelph (9 united + 1 free) or monadelph (all united); gynoecium with superior ovary, monocarpellar, with different number of ovules according to gender, and stigma crushed. The flowers are hermaphrodite, having autogamous pollination (peas, soybeans, lentils, white lupine and blue lupine), with varying degrees of allogamy (peas, soybeans, beans, etc.) or strongly allogamy (yellow and perennial lupine, beans, beans), pollination making it through insects. A common characteristic of legumes is staggered flowering (from the base to the top of the inflorescence) and a low percentage of binding (sometimes it reaches 15–20%). Through a sprinkling irrigation during flowering, fertilization is favored. One of the causes of low fruiting of legumes is the low relative humidity of the air during binding.

The fruit is a pod of different shapes, sizes and colors, dehiscent on the welding line of the valves (sheaths) of the pericarp (beans, peas, broad beans) or indehiscent (chickpeas, lentils, beans) (Figures 4 and 5, after [1]).

Figure 4.

Legumes: 1—beans; 2—white lupine; 3—peas; 4—soy; 5—peanuts; 6—lateral; 7—chickpeas; 8—lentils.

Figure 5.

Transverse section through the pericarp of the pea fruit: A—microscope view; ep—epidermis; sc—sclerenchyma; f—free-woody bundles; sp—parchment layer; p—parenchyma; B—overview; cs—sclerenchymatic cord; tp—parchment tissue; f—free-woody bundles.

The seeds (grains) are caught in the fruit on the ventral side, having different shapes, colors and sizes, depending on the species. The hilum—the place of fixation of the ovary ovule, respectively of the pericarp seed—is a characteristic of the species, variety or even variety, being different in placement, shape, size, color. In the hilum area, the two cotyledons are joined by the crucible. Legume seeds do not have endosperm, this being consumed by the embryo during growth; a “rest” of endosperm is found only in chickpeas.

Characteristic for legumes are the so-called “hard seeds”, which germinate with difficulty, because they have a palisadic, dense cellular layer in the shell, hardly permeable to water and air (Figure 6, after [1]).

Figure 6.

Transverse section through the integument of the leguminous seed: A—lupine; t—test composed of palisade layer and mossor cell layer; tgm—tegmen; B—beans; t—test composed of palisade layer and mossor cell layer; tgm—tegmen; p—tissue formed by cells with thin walls; C—chickpea; t and s—testa consisting of palisade layer and mossor cell layer; tgm—tegmen.

In the cotyledons, there are large starch granules and very fine aleurone granules. The formation of the fruit and the seed begins after fertilization, and after a while it enters the three ripening phases:

• green ripening (milk), when the plant, the pods and the seeds are green, continuing to grow, and the content of the seeds is soft, milky;

• yellow ripening (or ripening), when the whole grain becomes yellow, the pods are yellowed, the seeds become consistent like wax, their color being characteristic of the species, the variety and variety to which they belong;

• full ripening, when the vine is completely dry, the fruits and seeds are hard, in dehiscent ones the fruits burst, shaking the seeds and causing losses.

Organogenesis—the differences at the level of the growth cone are barely visible and happen very quickly. At the appearance of the first leaves, the growth tip takes a hemispherical shape, and later secondary cones appear at its base, which gradually give rise to the fruiting organs, the primordia of the flower buds, and then to the flower organs. Details on organogenesis will be presented for each individual plant.

4. Conclusions

Grain-producing leguminous crops: soybeans, beans, peas, chickpeas, lentils, broad beans, broad beans and peanuts are sources of cheap, valuable and absolutely necessary vegetable protein for the national economy.

Romania’s sustainable agriculture system can be directed through the implementation, use and modeling of scientific achievements in plant engineering, plant breeding, animal husbandry, economy, biomechanization, environmental protection, fair remuneration of specialists, agricultural producers, etc., with the achievement of quantitative production efficiency and quality of agricultural production.