Management of arbuscular mycorrhizal inoculation for the establishment, maintenance and recovery of grasslands

Manejo de la inoculación micorrízica arbuscular para el establecimiento, mantenimiento y recuperación de pastizales

P. J. González,^I J. F. Ramírez,^II R.Rivera,^I A. Hernández,^I R. Plana,^I G. Crespo,^I P. R. Rosales,^I

^IInstituto Nacional de Ciencias Agrícolas (INCA). Gaveta Postal No.1, San José de las Lajas, Mayabeque.
^IIEstación Experimental de Pastos y Forrajes de Villa Clara. Crucero Digna, Cascajal, Santo Domingo, Villa Clara.

ABSTRACT

The inclusion of arbuscular mycorrhizal fungi (AMF) on fertilization systems for grasses and forage crops may be considered as an effective alternative to improve their productivity and nutritional value and, at the same time, to reduce the use of fertilizers. Starting from this condition, a research program was carried out for implementing an integral technology for the effective management of inoculation with AMF on these crops. This program included the selection of efficient strains of AMF, definition of mineral fertilizer dosages for establishment, maintenance and recovery of inoculated grasses, and determination of doses and frequency of inoculation for maintaining an effective mycorrhizal functioning of these crops. There was a high compatibility between the strain efficiency and type of soil on the response of grasses to inoculation with AMF. Type of soil, as well as grass species and its management, influenced on the permanence of the introduced strain, but, in all cases, inoculated grasses required lower doses of fertilizers than those with no inoculation, in order to reach adequate biomass yield and nutritional values. Inoculation with doses lower than 4x10⁵ spores ha^-1 of the efficient strain of AMF, every one or two years, depending on the duration of the effect of initial inoculation, guaranteed the permanence of an effective mycorrhizal functioning on established grasses. The introduction, at production scale, of fertilization systems, based on the inoculation of an effective strain of AMF and the application of complementary levels of mineral or organic fertilizers, contributed to save up to 50% of fertilizer doses recommended for these crops, without reducing yield or nutritional value of biomass.

Key words: mycorrhizae, mineral fertilization, organic fertilization, grasses.

RESUMEN

La inclusión de hongos micorrízicos arbusculares (HMA) en los sistemas de fertilización para los pastos y cultivos forrajeros puede constituir una vía efectiva para mejorar su productividad y valor nutritivo y, a su vez, reducir el uso de fertilizantes. A partir de esta condición, se ejecutó un programa de investigación para disponer de una tecnología integral para el manejo efectivo de la inoculación con HMA en estos cultivos. El programa abarcó la selección de cepas eficientes de HMA, la definición de dosis de fertilizantes minerales y orgánicos para el establecimiento, mantenimiento y recuperación de los pastos inoculados y la determinación de las dosis y frecuencia de inoculación para mantener un funcionamiento micorrízico efectivo en estos cultivos. Se encontró alta compatibilidad entre la eficiencia de la cepa y el tipo de suelo en la respuesta de los pastos a la inoculación con HMA. El tipo de suelo, así como la especie de pasto y su manejo, influyeron en la permanencia del efecto de la cepa introducida, pero en todos los casos los pastos inoculados requirieron dosis menores de fertilizantes que los no inoculados para alcanzar adecuados rendimientos de biomasa y valor nutritivo. La reinoculación con dosis no mayores de 4 x 10⁵ esporas ha^-1 de la cepa eficiente de HMA, cada uno o dos años, en dependencia de la duración del efecto de la inoculación inicial, garantizó la permanencia de un funcionamiento micorrízico efectivo en los pastos establecidos. La introducción, a escala de producción, de sistemas de fertilización basados en la inoculación de una cepa eficiente de HMA y la aplicación de niveles complementarios de fertilizantes minerales u orgánicos, contribuyó al ahorro de hasta 50% de las dosis de fertilizantes que se recomiendan para estos cultivos, sin reducir el rendimiento ni el valor nutritivo de la biomasa.

Palabras clave: micorrizas, fertilización mineral, fertilización orgánica, pastos.

The inclusion of AMF on fertilization systems for grasses and forage crops may be considered as an effective alternative to improve their yield and nutritional value and, at the same time, to reduce the use of fertilizers, because the benefits of these microorganisms on grassland agroecosystems are very related to the increase of the absorption surface of roots and, consequently, to the improvement of use efficiency of nutrients by plants (Verbrugen et al. 2012). 

In Cuba, there has been a progressive advance in researches on the use and management of AMF on a wide range of crops. The results of these researches have led to obtaining high yields through the use of inoculation of efficient strains, substituting between 30 and 50 % of the organic and mineral fertilizers, depending on crop, soil and availability of nutrients (Rivera and Fernández 2007). However, there is scarce information related to grasses.

Taking into consideration these premises, as well as the need of improving food production for cattle and reducing the use of inputs, a research program was carried out in order to implement an integral technology for the effective management of arbuscular mycorrhizal fungi for the establishment, maintenance and recovery of grasslands. This paper presents the main results from the implementation of this research program.

MATERIALS AND METHODS

The program was implemented on cattle agroecosystems from Artemisa, La Habana and Villa Clara. The types of soil were lixiviated red ferrallitic, vertisol pelic gley and ferruginous nodular gley (Anon 1999). This study included the implementation of the following experiments:

Selection of AMF strains, efficient per type of soil and grass species. The inoculation effect of  Glomus cubense, Funneliformis mosseae and Rhizoglomus intraradices AMF strains was evaluated in each soil, as well as a control without inoculation, in Brachiaria decumbens cv. Basilisk, Brachiaria brizantha cv. Marandú, B. hibrido cv. Mulato II (CIAT 36061) and Panicum maximum cv. Likoni grasses. A random block design, with factorial arrangement and four replications, was used in every case. The experiments lasted two years.

Determination of optimal doses of mineral and organic fertilizers for grasses inoculated with efficient strains of AMF. Two experiment groups were implemented. The first was carried out on a lixiviated red ferrallitic and vertisol pelic gley soil, evaluating doses of N (0, 100, 200 and 300 kg ha^-1 year^-1), P₂O₅ (0, 30, 60 and 90 kg ha^-1) and K₂O (0, 50, 100 and 150 kg ha^-1), alone and combined with the inoculation of the most efficient HMA strain, according to the results of the experiments from the previous group, for the establishment and maintenance of Brachiaria species, cultivated under an intensive cut regime. The second experiment was performed on a lixiviated red ferrallitic and ferruginous nodular gley soils, and doses of cattle manure (0, 15 and 30 t ha^-1) were evaluated, alone or together with applications of N, and combined to the inoculation of the most efficient AMF strain, for the establishment and maintenance of B. hibrido, under a less intensive cut regime, and for the rehabilitation of P. maximum. A random block design, with factorial arrangement, was used in every case, and the experiments lasted from three to six years.

Determination of doses and frequency of application of mychorrizal inoculation for maintaining an effective mychorrizal functioning on grasses. Doses of the mychorrizal inoculant were evaluated, which provided from 0 to 10 x10⁵ spores ha^-1 of AMF strain, efficient for each type of soil, on B. decumbens cultivated in a lixiviated red ferrallitic soil and on P. maximum, cultivated on ferruginous nodular gley soil. A random block design, with four replications, was used in both cases, and the experiments lasted from two to three years.

General procedure. In the case the grasses were sown, the sowing was performed in furrows separated at 70 cm and at steady flow, with doses of 6-8 kg of total seed ha^-1(1 kg ha^-1 of germinable pure seed). The inoculation of AMF strains was performed in the sowing moment by the method of seed covering, with an amount of inoculant equivalent to 10 % of its weight. For established grasses, a suspension of mycorrhizal inoculant and water was prepared, at a proportion of 1:10. It was applied over the grass surface after a cut and at the beginning of rainy season. The EcoMic® mycorrhizal inoculant, produced in INCA, was used in every case, with a concentration of 30-35 spores g^-1 of inoculant. Cut frequency depended on availability of inputs from each unit.

RESULTS AND DISCUSSION

There was a positive response of grasses to inoculation in every case because AMF strains increased yield, regarding the non inoculated control (table 1). Nevertheless, per each type of soil, there was a strain that produced the highest effects. The strain with the best performance for cultivated grasses in pelic vertisol soil was R. intraradices, while G. cubense and F. mosseae were the best for those cultivated in lixiviated red ferrallitic and ferruginous nodular gley soils, respectively. It was demonstrated the high mycorrhizal dependence of these species and the existence of high degree of compatibility between soil type and strain efficiency in the response of grasses to AMF inoculation. 

These results revealed a higher effectiveness of the introduced strains, regarding the resident AMF, to increase grass yield. They indicated that the management of arbuscular mycorrhizal symbiosis, through inoculation, could be assumed as an effective agronomic practice to improve the productivity of forage species, which coincides with the findings of Oliveira et al. (2014).

After selecting the most efficient AMF strain for each edaphic condition, the most suitable doses of mineral or organic fertilizers for the establishment, maintenance and recovery of inoculated grasses are defined, as well as the doses and frequency of application of mycorrhizal inoculant, needed to maintain an effective mycorrhizal functioning of these crops. Table 2 shows the obtained results.

Inoculation at the moment of sowing, together with the application of doses of mineral or organic fertilizers, adjusted to the need of the inoculated grass, produced, during the first one or two years, similar yields to those reached with fertilizer doses needed to achieve the highest yields in the absence of inoculation. The permanence of the initial inoculation effect depended on the type of soil, grass species and its management.

In B. decumbens, cultivated in lixiviated red ferrallitic soil, under conditions of high inputs (high doses of mineral fertilizers and with irrigation availability), the effect was maintained only during the first year. In P. maximum, cultivated in the ferruginous nodular gley soils and under low input conditions (low availability of mineral fertilizers and without irrigation), the effect was maintained during the first two years.

The experiments evaluating doses and frequency of application of the inoculant (not shown data) showed that the application of 4x10⁵ spores ha^-1 of the most efficient strain for each edaphic condition, was enough to achieve an effective mycorrhizal functioning cash in grasses grown in lixiviated red ferrallitic soil and ferruginous nodular gley soil. In addition, they demonstrated that the duration of inoculation effectiveness was similar to that observed when they were inoculated using the method of seed covering.

The positive effect of arbuscular mycorrhizal inoculation on the reduction of fertilizer doses was related to its contribution to the improvement of use efficiency of nutrients. The fact that with the use of AMF strains, which were more effective in each edaphic condition plus the application of lower doses of fertilizers, similar yield levels to those with higher fertilizer doses were achieved in absence of inoculation, indicates that plants had a better access to soil resources. This contributed to the increase of yield (Castillo et al. 2014).

Experimental results were validated at production scale, in 300 ha cultivated with B. hibrido cv. Mulato at the EPG “Niña Bonita” and 20 ha of guinea grass (P. maximum cv. Likoni), with a high degree of degradation, at the EA “Santo Domingo”, which were inoculated with the AMF strain recommended for each edaphic condition and fertilized with doses of mineral and organic fertilizers, respectively, which were more adequate to inoculated grasses. The EPG “Niña Bonita” saved 300 kg ha^-1 year^-1 of balanced fertilizer (9-13-17 formula) and 132 kg ha^-1 year^-1 of urea. This meant a saving of 230 Cuban pesos ha^-1 year^-1. The EA “Santo Domingo” saved 15 t ha^-1 year^-1 of cattle manure and, consequently, 120 Cuban pesos t ha^-1 year^-1, due to the reduction of manure doses, traditionally used for grassland rehabilitation.

REFERENCES

Anon, A. 1999. Nueva versión de clasificación genética de los suelos de Cuba. La Habana, Cuba: AGROINFOR, 64 p.

Castillo, C., Fredericksen, C., Koch, R. & Sieverding, E. 2014. “Effect of seed treatment with natural products on early arbuscular mycorrhizal colonization of wheat by Claroideoglomus claroideum”. Journal of Applied Botany and Food Quality, 87: 117.

Oliveira, T. B., de Mello, A. H. & Ferreira, L. A. 2014. “Influência da inoculação de fungos micorrízicos em amendoim forrageiro (Arachis pintoi) em pastagens no projeto de assentamento Belo Horizonte I em São Domingos do Araguaia-Pa”. Enciclopédia Biosfera, 10 (18): 1988.

Rivera, R., Fernández, F., Fernández, K., Ruiz, L., Sánchez, C. & Riera, M. 2007. “Advances in the management of effective arbuscular mycorrhizal symbiosis in tropical ecosystesm”. In: Hamel C. & Plenchette C. (eds.), Mycorrhizae in Crop Production, Binghamton, N. Y.: Haworth Press, pp. 151–196, ISBN: 978-1-56022-306-1.

Received: November 24, 2015
Accepted: January 11, 2016

P. J. González, Instituto Nacional de Ciencias Agrícolas (INCA). Gaveta Postal No.1, San José de las Lajas, Mayabeque. Email: pgonzalez@inca.edu.cu