MATERIALS AND METHODS

The study was carried in 2015 (first semester), in different localities in the departments of Antioquia, Cundinamarca and Santander. In Antioquia, two experimental plots were established in two localities: CI La Selva (altitude of 2120 m, annual average temperature of 17 °C, average annual rainfall of 1850 mm, at 06°08'06''N, 75°25'03W), with climbing beans ICA-Viboral and Corpoica LAS-106 (both at a planting distance of 0.23 m among plants and 1.2 m among rows). The other locality was CI El Nus (altitude of 848 m, annual average temperature of 24 °C, average annual rainfall of 2500 mm, at 06°26'17.2''N, 74°49'32.1''W), with the bush bean varieties Quimbaya and Citará (both at a planting distance of 0.15 m among plants and 0.5 m among rows), in which it was evaluated the effect of several treatments with biological fertilizers. The treatments used were: Organic matter (poultry manure) (2 t ha^-1); Rhizoglomus sp. (15 g per plant), with a concentration of 250 spores g^-1, with 50 infective mycorrhiza propagules g^-1; commercial strains of Rhizobium (100 bacteria g^-1) (0.01 L per kg of seed) and/or with phosphate rock (PR) (600 kg ha^-1), in simple and combined form. All treatments received 20 g of KCl per linear meter, except for the chemical farmer treatment (control) (350 kg ha^-1 of 10-30-10). Each experimental unit consisted of six rows, 10 m long and 0.6 m wide each. A randomized complete block experimental design with four replications, was used.

In Cundinamarca, a plot was established in the municipality of Pasca (at an altitude of 2180 m, annual average temperature of 17 °C, an average annual rainfall of 1100 mm, at 4°18'27"N 74°18'03"W), with climbing bean "Cargamanto Rojo" (at a planting distance of 0.23 m among plants and 1.2 m among rows). The treatments used were: Organic matter (poultry manure) (2 t ha^-1); with Rhizoglomus sp. (15 g per plant), with a concentration of 250 spores g^-1, with 50 infective mycorrhiza propagules g^-1; commercial strains of Rhizobium (100 bacteria g^-1) (0.01 L per kg of seed) and/or with phosphate rock (PR) (600 kg ha^-1), in simple and combined form. All treatments received 20 g of KCl per linear meter, except for the chemical farmer treatment (control) (350 kg ha^-1 of 10-30-10). Each experimental unit consisted of six rows, 10 m long and 0.6 m wide each. A randomized complete block experimental design with four replications, was used.

In Santander, two experimental plots were established in two localities: CI El Arsenal (altitude of 1450 m, annual average temperature of 22 °C, average annual rainfall of 1292 mm, at 6°40'05"N 72°42'00"W), with the bush bean variety ICA-Rovirense. The other locality was Curití (at an altitude of 1409 m, annual average temperature of 20 °C, an average annual rainfall of 1500 mm, at 6°36'16"N 73°04'05"W), with the bush bean variety ICA- Radical-J1J1. In both localities were used a planting distance of 0.15 m among plants and 0.5 m among rows, in which the effect of three strains of Rhizobium (P4, P8, and P14), and two inoculum of mycorrhiza MVA (Rhizoglomus occultum and Acaulospora spp.) were evaluated on the yield of bush bean varieties, ICA-Rovirense and Radical-JIJI. Each experimental unit consisted of six rows, 10 m long and 0.6 m wide. A randomized complete block experimental design with four replications was used. The study consisted in the evaluation of seven treatments; in Curiti was included a control, that involved the application of the combination of Trichoderma lignorum, and a mixture of mycorrhizal fungi (Rhizoglomus occultum and Acaulospora spp.), plus the inoculation of the seeds with Rhizobium sp.

RESULTS AND DISCUSSION

At C.I. La Selva, when performing a combined analysis during two consecutive cycles, in Corpoica 106 and ICA-Viboral, significant differences were present among treatments. As it can be seen in Table 1, the yield obtained with chemical fertilization in the variety Corpoica 106 was equal to that obtained with organic and biological fertilization, either with double inoculation, mycorrhizae plus Rhizobium, and/or with the application of PR. This agrees with several authors who report a positive effect of the different strains, both in their simple as in its combined forms, presenting the greatest effects when double inoculations were used (^{Saravesi et al., 2014}; ^{Galindo and Clavijo, 2009}; ^{Caldera et al., 2013}; ^{Clua et al., 2013}; ^{Granda et al., 2016}; ^{Romero et al., 2016}).

Table 1 Yield of climbing beans Corpoica-LAS 106 and ICA-Viboral, during two consecutive cycles. CI La Selva. 

It should be noted that the treatment with less yield was the one in which no poultry manure was applied, for both bean materials. This aspect is important due to the fact that, when the poultry manure is combined with inoculations of Rhizobium and mycorrhizae, the first one can act as a stimulator. In the variety Corpoica LAS-106, chemical fertilization can be replaced with the use of biofertilizers; contrary, the ICA-Viboral variety, responded better to the application of chemical fertilizer (350 kg ha^-1 of 10-30-10) than to the application of biofertilizers. According to ^{Osorio (2016)}, arbuscular mycorrhizal fungi can improve the ability of the root system to absorb nutrients and improve the effect of phosphate amendments. Likewise, the rhizobium-legume association is considered a highly efficient process in biological fixation of atmospheric nitrogen (BNF); it is estimated that nitrogen fixation varies from 24 to 584 kg ha^-1; it has the capacity to supply up to 90% of the needs of the plant (^{Ángeles-Núñez and Cruz-Acosta, 2015}). However, ^{Osorio (2018)} reports that there are differences in mycorrhizal dependence among cultivars of the same species.

The bean yield with this treatment was statistically superior to the different combinations of Rhizobium, phosphate rock and mycorrhizae (Table 1). As in the variety Corpoica LAS-106, in the ICA-Viboral, there was a significant response when poultry manure was applied, being this an activator of the biological-mineral fertilization. Organic fertilizers are a crucial element for the regulation of many processes related to agricultural productivity and can be a complement or replacement of synthetic fertilizers (^{Ramos and Terry, 2014}). It may be argued that in the poultry manure, the microorganisms producers of organic acids can make more available the phosphate ions released from the phosphate rock, and thus improve yield (^{Osorio and Habte, 2013}; ^{Ramírez et al., 2013}; ^{Tamayo and Osorio, 2017}). In both materials, yield per hectare during the two growing cycles was acceptable and, in some cases, exceeded the yields of the region (1.2 t ha^-1).

In medium climate conditions (CI El Nus) (Table 2), the Quimbaya and Citara bean materials showed a better yield response, when the control treatment (chemical)was applied, due to the soils of this area are low in fertility, very low in organic matter and exchangeable bases, and with acid pH. Although, it has been reported that in soils with very low organic matter there is a better response to organic applications than when applying chemical sources (^{Ramírez et al., 2008}; ^{Ramos and Terry, 2014}; ^{Hartmann et al., 2014}; ^{Guénon and Gros, 2015}), In this study, the application of the biofertilizers was not enough to obtain the yields that were achieved with the chemical treatment, possibly because the applied doses were low. The treatments without poultry manure produced the lowest yields (936 and 352 kg ha^-1) for the bush varieties Citara and Quimbaya, respectively. A similar situation occurred in the locality of C.I. La Selva with climbing materials. The Quimbaya variety did not respond as significantly to the biological-mineral sources as did the climbing beans of moderate cold climate; however, there are reports of other mid-climate locations where their response has been positive. In all the varieties, the effect of the poultry manure on the yields is substantial (Table 2).

Table 2 Effect of biological-mineral fertilization on yield of bush bean in soils of medium climate. CI El Nus. 

In Pasca, the yield in the bean "Cargamanto Rojo" fluctuated between 568 and 2000 kg ha^-1. Table 3 shows significant differences among the treatments; the chemical farmer treatment (control), does not differ statistically from the treatments of poultry manure plus Rhizobium, phosphate rock and mycorrhizae and Rhizobium. These yields, despite being from medium to low, the trend they present is the same of that obtained in C.I. La Selva with the ICA-Viboral bean, probably because poultry manure could improve the physical and biological conditions and help the activity of mycorrhiza and Rhizobium in the soil.

Table 3 Effect of organic and biological fertilization on the yield of climbing bean. Municipality of Pasca. 

In Table 4, it is observed that in the locality C.I. "El Arsenal", there were statistical differences (P≤ 0.05) among treatments, with a mean of 2354.5 kg ha^-1 and a coefficient of variation of 14.67%.

Table 4 Average yield (kg ha-1) in Santander with regional bean varieties. 

The combination of AMF mycorrhizae (Rhizoglomus spp. + Acaulospora) and Rhizobium P14 strain, presented the highest yield (2839.5 kg ha^-1), while the lowest yield was shown in the treatment that included the Acaulospora combination and the Rhizobium P8 strain, with 1992.7 kg ha^-1. The combined use of both types of microorganisms (Rhizobium and mycorrhizal fungi) produces better effects than the individual use of them, the use of microorganisms in the form of biofertilizers improves soil nutrition and plant growth (^{Grageda et al., 2012}; Elein et al., 2013; ^{Lozano et al., 2015}; ^{Gardezi et al., 2016}). In the locality of Curití, no significant differences among treatments were observed, in relation to the average yield of bean in kg ha^-1.

The highest effectiveness with respect to the yield was detected in the locality CI "El Arsenal", probably due to the quality of the organic medium, to the presence of existing beneficial microorganisms, which give the root greater capacity to explore the soil in search of water and nutrients, that results in higher yields; these results are similar to those obtained by ^{Flores et al. (2014}) in Stylosanthes guianensis. This allows to consider, that the combination of compost and biological agents in the management of the nutrition of the cultivated plants is beneficial, which represents for the farmers of bean, to produce more quantity and quality of food at a lower cost, preserving the environment.

CONCLUSIONS

The use of biofertilizers (mycorrhizae fungi and Rhizobium) improved yields in the bean crop, with the materials used (climbing and bush beans) and in the localities studied.

There is an additive effect in the applications of the biofertilizers evaluated, since a higher yield was observed in the bean crop when these were applied combined than individually.

Disclaimer of Liability

The source of research funding was obtained by the Corporacion Colombiana de investigación Agropecuaria. The authors state that the research was carried out in the absence of commercial or financial relationships that could be interpreted as a possible conflict of interests.