RESEARCH WORK

Management alternatives of soil fertility in livestock production ecosystems

Saray Sánchez, Marta Hernández y F. Ruz

Estación Experimental de Pastos y Forrajes "Indio Hatuey". Central España Republicana, CP 44280, Matanzas, Cuba

E-mail: saray.sanchez@indio.atenas.inf.cu

Abstract

In Cuba, due to soil degradation, integrated management is required to enhance their productive capacity in benefit of man and achieve sustainable development and the necessary food security. This situation demands that the professionals, technicians and people responsible for livestock production increase their knowledge related to the management and conservation of this resource, so that with their work balance can be achieved in the soil-plant-animal system, which allows improving the environment, achieving more ecological productions, and attaining higher economic and social benefits for the country. In this paper some results are shown generated in different scientific institutions regarding the use of adequate technologies of soil fertility management in agricultural and livestock production ecosystems, as well as the experiences of their introduction in productive practice in order to contribute to sustainable development and food security in Cuba.

Key words: Ecosystem, livestock production, soil management.

Soil is a natural resource which throughout history has provided sustenance for the human population; however, the growing world population and its demand for food progressively increase the stress on this resource. In tropical zones of the world alternatives are sought to preserve soils, because it has been confirmed that hot climate is not the factor which prevents adequate land production, but rather soil inadequate management.

According to the data of the Instituto de Suelos (Soil Institute) (2006), it is important to adopt agroecological alternatives to gradually implement actions that minimize and provide short-, medium- and long-term solutions, because 69,6% of the soils have low OM content and 43,3% show strong to moderate erosion, which limits their productivity.

In this sense, many works have been conducted with the objective of improving or increasing crop yields, which include the contribution of organic fertilizer sources and the implementation of different types of biofertilizers, with diverse uses (Vilches and Núñez, 2000; Suárez et al., 2002). However, the solution of the main problems that affect agricultural soils in Cuba should be seen, as stated by Funes-Monzote et al. (2008), with a systemic and integrative approach and not as an isolated solution, because natural and anthropic factors are concatenated. For such reason, an integrated soil management- also called ecological or sustainable management- is extremely important to enhance their productive capacity to benefit man.

Among the actions to protect agricultural and livestock production ecosystems and prevent their degradation, the application of organic fertilizers is significantly important, because organic matter, and particularly humus, is the basic sustenance for life in this environment and can define its productive potential (Paneque and Calaña, 2004). In this context the following are included: animal manure, harvest residues, compost and earthworm humus, among others.

This paper presents some of the results generated in different scientific institutions regarding the use of adequate technologies of soil fertility management in livestock production ecosystems, as well as the experiences of their introduction in productive practice aiming at contributing to sustainable development and food security in Cuba.

Utilization of manures, compost and earthworm humus as organic fertilizers

A well known and widely-applied practice worldwide is the use of manure from diverse animals to return nutrients to the soil (Noriega et al., 2001). They have the advantage that in addition to returning the macro-elements, they contribute others that have been exported from the field with the harvests and enrich the soil with organic matter that is necessary to maintain its fertility.

In Cuba the manure deposited in the dairy sheds is mainly utilized. In this sense, the manure and liquid residues accumulated in livestock production facilities can become valuable resources to increase soil fertility and produce renewable energy with biogas, from anaerobic fermentation.

Biodigestors should be considered an essential component in the livestock production system and not only as a way to produce fuel from animal excreta. The treatment of agricultural and livestock production residues, in addition to its energy benefit for biogas production, has an immediate effect on environmental decontamination and also means additional biofertilizer production (Bui Van et al., 2002; Chao and Pérez, 2003).

This biofertilizer is constituted by the non-fermented fraction; due to its almost liquid presentation, it allows easy management in systems with irrigation. Its use has been tested in several countries and different crops; harvest increases and improvement of soil properties are reported, unlike chemical fertilizers, which reduce soil productivity. Manure has a large number of nutrients for plants; organic nitrogen should be turned into ammoniacal nitrogen before being absorbed by the plants. The value of nutrients in manure should be taken into consideration. A ton of typical (cow) manure, with an approximate content of 50% moisture, contains around 42 kg of nitrogen (N), 18 kg of P2O5 and 26 kg of K2O (Crespo and Fraga, 2006).

This is highly important if it is taken into account that the accumulated excreta volumes are generally large. According to Crespo et al. (2010), in typical dairy units of 120 cows more than 300 t have been quantified and in the units with 288 cows, more than 900 t in one year (table 1).

Another option is compost elaboration; any organic matter can be used, if it is not contaminated. Generally, these raw materials, according to Mayea (1994), originate from:

• Harvest remains. They can be used to make compost or as mulch. Young or fresh plant remains, such as leaves, fruits and tubers, are rich in nitrogen and poor in carbon; the contrary occurs with such remains as trunks, branches, stems, sawdust, etc.
• Green manures, turfgrass residues, weeds, etc.
• Branches from pruning fruit trees and others. It is necessary to crush them before their incorporation to compost, so that the decomposition period is not too long.
• Urban remains. This refers to all those organic remains from the domestic sector, such as refuse, wastes from cooking, from slaughterhouses, from markets of agricultural products, etc.
• Animal feces. Cattle manure stands out, although chicken dung, rabbit dung, liquid manures and horse and sheep dung are of interest.
• Sea plants. Large amounts of sea phanerogams, such as Posidonia oceanica, are annually gathered on the beaches, which can be used as raw material for elaborating compost, because they are compounds rich in N, P, C, mineral nutrients and biocompounds, which utilization in agriculture as green manure can be of great interest.
• Algae. Many seaweed species, rich in antibacterial and antifungal agents, can also be used.

The chemical, physical and biological characteristics depend on the nature of the residues and the process to which they are subjected. Table 2 shows the chemical analysis of the main organic fertilizers used in agriculture. It is important to state that the values expressed in the table can serve as reference to evaluate such fertilizers, but should not be taken as definitive because they can vary according to their origin. Each farmer should have the characterization of the organic fertilizer he/she applies.

Earthworm humus known by diverse names: casting, vermicompost, among others- is considered by many researchers and farmers one of the best organic fertilizers in the world. The quantity of nutritional elements depends on the chemical characteristics of the substratum with which earthworms are fed (Martínez et al., 2003; Legall and Zoyla, 2008).

This technology of solid organic residual treatment through vermiculture has gone through several stages since its introduction in the 1980's, which have been characterized by many studies determining its progress. The most important results in this regard were pointed out by Martínez and Arias (2010); among them are:

• The determination of the humus dose applied depending on the crop and soil, which varies between 2 and 8 t/ha, but its most frequent value is 4 t/ha, together with 25-50% of mineral fertilization.
• The humus doses were determined in: tobacco, potato, sweet potato, banana (in vitro), tomato, pepper, garlic, onion, organoponic crops, rice, corn, Jamaican star grass and rhodes, papaya and guava nurseries, and in guava plantations. From these doses and with the primary chart of chemical characteristics of humus and the storage results, a handbook was prepared for the handling and use of earthworm humus, which was generalized in the provincial soil directions of the country.

The use of earthworm humus in different agricultural crops, the doses used and its potential for substituting chemical fertilizers are shown in table 3.

The research results not only contributed to increase the theoretical-practical knowledge about the characteristics of earthworm humus and its relations to soil, mineral fertilizers and plants, but they also had a positive impact on the economy of the country through beneficial modifications in the livestock production system.

This technology is one of the most generalized in the country; the benefits of earthworm humus in agricultural production and its importance in meal elaboration for animal feeding are known, which allows reorienting vermiculture integrally, with an environmental and nutritional approach to achieve sustainable endogenous development (Peña, 2009).

On the other hand, Echeverría et al. (2009) evaluated the contribution of the use of organic fertilizers in the fertilization of tropical forage crops, which were applied on lixiviated Ferralitic red soil, from Havana; grayish Brown soil, from Camagüey and ferruginous nodular Gley soil, from Villa Clara. Three treatments were evaluated: absolute control, earthworm humus at a rate of 6 or 10 t/ha depending on the soil type and fertility, and cattle manure at a rate of 25 or 40 t/ha. Earthworm humus was applied in a localized way on the row bottom at the moment of planting. The evaluated species were Glycine max, Stylosanthes guianensis and Pennisetum purpureum. Yields higher than 0,70 t/m2/year and substratum humus/conversion rates higher than 55% were achieved. The applications of 6-10 t of earthworm humus/ha on the row bottom at the planting moment increased the yields in around 50% as compared to the control, and theywere similar to the ones obtained when manure was applied in a dispersed way at a rate of 25-40 t/ha; the doses, of both organic materials, varied depending on the soil type and its fertility.

Another technology used in soil management and conservation throughout the world is that of beneficial or effective microorganisms. The concept and technology of effective microorganisms (EM) or beneficial microorganisms (BM), as they are also called, were developed by Professor Dr. Teruo Higa, at the University of Ryukyus, Okinawa, Japan (Correa, 2008).

According to this author, the main principle of this technology consists in introducing a group of beneficial microorganisms to improve soil condition, suppress putrefactive microorganisms (disease inducers) and, through them, improve the efficacy in organic matter utilization.

The studies and field works in all continents have proven that the inoculation of EM cultures to the soil/plant ecosystem improves soil quality, crop growth, yield and quality (Daly and Stewart, 1999). When using EMs in animal production systems and environmental management benefits have also been found in health and immunological response and increases in animal management results (Uribe et al., 2001).

• The effects of microorganisms in the soil are framed in the improvement of physiological and biological characteristics and disease suppression. Among them, according to Correa (2008), the following can be mentioned:
• Effects on the soil physical conditions: they improve soil structure and particle aggregation, reduce its compaction, increase porous spaces and improve water infiltration. Thus, the irrigation frequency is decreased; soils are capable of absorbing 24 times more water from rain and erosion due to particle washout is prevented.
• Effects on soil microbiology: they suppress or control the populations of pathogenic microorganisms which are developed in the soil; they increase microbial biodiversity, which generates the necessary conditions for native beneficial microorganisms to prosper.

The use of effective microorganisms does not substitute the other soil conservation and improvement alternatives, but constitutes a step further in their optimization. Table 4 shows the benefits that are reported with the utilization of efficient microorganisms in compost elaboration, with regards to time, quality and improvement of the biological activity (APROLAB, 2007).

Use of biofertilizers and biostimulators in soil protection and improvement

According to Dibut (2009), the term biofertilizer can be defined as preparations that contain living or latent cells of efficient nitrogen-fixing, phosphorus-solubilizing or nutrient-enhancing microbial strains; they are applied to seeds or the soil in order to increase the number of these microorganisms in the medium and accelerate microbial processes, so that the nutrient quantities which can be assimilated by plants are increased or the physiological processes that influence crop growth and yield are accelerated.

A biostimulator is defined as the product that contains living or latent cells of microbial strains, previously selected, which produce physiologically active substances (auxins, gibberellins, cytokinins, aminoacids, peptides and vitamins) which when interacting with the plant system trigger different metabolic events to stimulate the growth, development and yield of cash crops.

Unlike biofertilizers, biostimulators are not directly associated to the substitution of doses of chemical fertilizers (N and P) in the crops, but they are used independently from the application or not of these inputs.

Conversely, their producing activity of physiologically active substances and their effect on the plant reach their maximum expression when the plant is adequately nourished. Thus, although no fertilizers are applied, a remarkable stimulating effect on yield is obtained; but in this case fertilization should be made with organic amendments to prevent soil impoverishment along several harvest cycles.

In general, in conventional as well as in sustainable agriculture, including urban agriculture, biostimulators and biofertilizers have found a unique space, because through their application beneficial effects have been achieved on crops over large surfaces, including seed production (Medina, 2009). Table 5 shows the main characteristics of these products, which have been applied in recent years in Cuba.

Mycorrhizal fungi, based on the biopreparation Ecomic®, constitute nowadays the biofertilizer of higher action spectrum among agrobiological fertilizers. There are many results which show the advances in the effective management of inoculation in tropical agroecosystems in different economically important crops, such as: soybean, beans, peas, corn, sorghum, sunflower, wheat, cotton, banana, roots and tubers, vegetables, coffee seedlings and fruit trees; they were obtained in a wide range of conditions, on very low to high fertility soils (Rivera et al., 2009).

The results of the extension campaign during 2007-2008 and 2009-2010 made by a group of researchers, according to Rivera et al. (2010) proved the benefits in yield and from the economic point of view, and thus the feasibility of the inoculation of cassava with this biofertilizer at productive scale. These authors found in the 31 localities, belonging to the Guantánamo, Cienfuegos, Villa Clara, Matanzas and Havana provinces, a positive effect of inoculation on yield, with an average increase of 4,7 t.ha-1 which corresponds to 33% increase over the control treatment.

The inoculation of arbuscular mycorrhizal fungi (AMF) can be an economically and ecologically effective way to improve pasture nutrition. In this sense, a research program was developed in order to establish some scientific-technological bases for the effective management of mycorrhizal associations in these crops. The program comprised the performance of a group of trials and extension tests in pasture agroecosystems, located in the Havana, Villa Clara and Camagüey provinces, on calcic soft Brown soils (calcic Cambisol), lixiviated Ferralitic red soils (rodic Nitisol), nodular ferruginous Gley soils (plintic Gleysol) and ochric grayish Brown soils (haplic Cambisol).

The trials proved the possibility of achieving an effective management of the mycorrhizal associations in pastures through the inoculation of efficient AMF strains, and although to guarantee an adequate functioning of the symbiosis and high biomass yields, a nutrient supply from mineral or organic sources was necessary, the applied amounts were lower than those necessary to obtain similar yields in non-inoculated pastures (González et al., 2007a; González et al., 2007b; González et al., 2007 c; Calderón and González, 2007; González et al., 2008; Baños et al., 2008).

Generally, the effects of nitrifying symbiotic bacteria, mycorrhizae and phosphobacteria have been separately evaluated; but the combination of these organism groups has not been sufficiently studied. The results of these studies worldwide, with the use of combined inoculations of rhizobia and mycorrhizal fungi in legume crops, have provided increases in plant growth and yield, and the importance of this joint practice stands out (Hernández and Hernández, 1996; Corbera and Hernández, 1997; Corbera, 1998; Hernández and Cuevas, 2003; Corbera and Núñez, 2004; Hernández, 2008; Corbera and Nápoles, 2010).

A good response has been also obtained with the co-inoculation of rhizospheric bacteria, mainly Rhizobium, Azospirillum and Azotobacter. This has allowed the development of mixed biofertilizers, which represent a highly safe alternative, in balance with the environment, for the integrated management of plant nutrition; in this sense, the AMF association with these rhizobacteria represents a good example of this potential (Dibut, 2009).

The joint application of AMF with earthworm humus, under greenhouse conditions, showed that it is feasible to obtain acceptable tomato yields without using chemical fertilizers, which contributes to the non-contamination of the environment (Cun et al., 2008).

Another alternative that has received increasing interest in ecological soil management is the progressive introduction of green manures. In this regard, there are many definitions. García et al. (2001) define it as the practice of incorporating non-decomposed phytomass, from in situ or imported cultivated plants, to the soil, aiming at the preservation or restoration of the productivity of agricultural lands. Da Costa (cited by Álvarez et al., 1995) provided a wider concept; he states that they are plants used in rotation, succession or association with the crops, which incorporated to the soil or left on the surface, are capable of maintaining or improving the soil physical, chemical and biological characteristics.

According to León and Ravelo (2005) this also constitutes a cheap source of N supply to the plants, if it is taken into consideration that most of the species used belong to the legume family and that they fix N symbiotically from air, which volume contains 78% of this element.

The inclusion of green manures in agricultural systems allows obtaining an economic effectiveness which oscillates between $ 623 and $ 1 503 Cuban pesos/ha depending on the crops and the species; the earnings are due, mostly, to the high increases of crop yield with this alternative and, to a lesser extent, to the possibility of substituting chemical fertilizers (García, 1998).

The introduction of green manures at a larger scale depends on many factors, among them: the need to produce seed in the same units where they will be used, their inclusion in rotation plans and in the association of cash crops in the farms, as well as the need of higher awareness of this practice among farmers.

Livestock production systems are an important element for the integration of soil conservation measures. Under monocrop conditions or in little diversified agricultural systems it is difficult to fulfill the proposed objectives, for which the diversification and integration of the agricultural activity with livestock production is an efficient strategy to achieve adequate nutrient management and soil fertility, as well as to utilize efficiently the available natural resources (Funes-Monzote and Monzote, 2001; Funes-Monzote and del Río, 2002).

Some authors state that agroecological systems, with high agrobiodiversity and integration, allow adequate soil use, optimize nutrient and energy flows, and fulfill multiple functions which comprise ecological, economic and social objectives (Altieri, 2002; Funes-Monzote et al., 2008). Nevertheless, it is still necessary to continue documenting this type of interactions, because they guarantee sustainability at system level.

It is highly important to consider that the introduction of trees is a favorable alternative in the restoration, maintenance and sustainability of natural resources in livestock production areas of Latin America (Murgueitio, 2003). They offer socioeconomic and ecological benefits, proved by diverse scientific studies and successful experiences of livestock production farmers (Ibrahim and Mora, 2006). In general, trees can be the element of efficacious management to increase biodiversity in the pasturelands, extract nutrients and water from the deepest soil layers, produce biomass in different strata, propitiate a favorable environment for the development of associated pastures and livestock, create a microclimate for the edaphic fauna activity and achieve litter productions that participate in the biogeochemical cycle of nutrients in the soil (Lok et al., 2006; Wencomo, 2006; Sánchez et al., 2008).

Until now, in most cases the measures that help to protect the soil and maintain its fertility have been described. Nevertheless, many authors coincide in stating that no adequate and ecological soil management will by achieved by using only one or two of these technologies, but an integral system should be arrived at employing a combination of several of these measures according to the site conditions (Altieri, 2002; Brechelt, 2004; Leyva et al., 2010).

CONCLUSIONS

In Cuba, due to the degradation of soils, an integrated management is required to enhance their productive capacity to benefit man, and achieve sustainable development and the necessary food security. This situation demands that professionals, technicians and the persons responsible for livestock production increase their knowledge related to the management and conservation of this resource, so that with their work balance can be achieved in the soil-plant-animal system, allowing the improvement of the environment, the attainment of more ecological productions and higher economic and social benefits for the country.