Introduction

In Bolivia there are about 872000 agricultural production units (APU), 92 % are family farmers, 7 % are medium-sized farmers, 1 % are large farmers¹, most of which are located in the highlands, characterized by low incomes, greater vulnerability and low productivity levels².

Agriculture in the Altiplano is at high risk, with adverse climatic events such as drought, frost, irregular rainfall, hail, strong winds, low availability of water for irrigation, loss of soil fertility and threats to agricultural productivity³, influenced by the climatic variability of the area, farmers' perception of climate change (CC), indicate that the loss of their production is due to drought (83.6 %), frost (7.4 %), wind (6 %) and hail (1.5 %)⁴.

A traditional system (TS) of agricultural production is characterized by the absence of capital, excessively fragmented land, scarce technology, which makes it impossible to expand the cultivable area and technology, therefore, the Altiplano has the lowest productivity indexes compared to other sectors of the country's economy⁵, in contrast, as an alternative to improve the agro-ecological method, biointensive agriculture (BIA), based on the use and incorporation of organic matter (OM), as well as optimization of the use of water and soil⁶.

BIA is defined as the intensification of agricultural productivity through biological means on a minimum area of land, improving the soil at the same time, combining principles of biodynamic agriculture⁷, based on agro ecological principles, indigenous technology, knowledge, experience, needs and an analysis of the negative impact on conventional agriculture⁸. BIA decreases dependence on seasonal rainfall, takes advantage of small available land, improves soil quality by applying high level fertilization, the use of drip irrigation and the rational use of irrigation water⁹, diversified production, with high yields¹⁰.

The importance of introducing new production systems such as BIA for vegetables lies in increasing yields 6 times more in small extensions³. The vegetable yield in the Altiplano is below national production, characterized by inadequate soil management and little agricultural technology, which results in low yields.

In this research, we evaluated the effect of the two biointensive agricultural production systems compared to the TS on agronomic parameters of vegetables, soil fertility, amount of fungi and water consumption.

Materials and methods

The study was conducted at the Condoriri Agricultural Experimental Center (central highlands) of the Technical University of Oruro¹¹, together with PRORURAL, an institution whose objective is to contribute to the economic, social and environmentally sustainable development of vulnerable rural men, women and youth³ in the highlands of Bolivia. The study was conducted during the 2017 to 2018 agricultural seasons, the soil has a loamy texture, moderate OM, with low nitrogen content, phosphorus, potassium in moderate concentrations, average annual relative humidity 49 %, it is characterized by an annual maximum temperature of 27.2º C, a minimum of -15º C, an average of 9.5º C, frost frequency of 162 days and an annual precipitation of 461. 2 mm¹² Two experimental plots of 425 m² were established, distributed in 12 treatments, 2 production systems (biointensive, traditional) and six vegetables (turnip, radish, beet, lettuce, carrot, onion), the six species were sown per production system and randomly distributed in each repetition, The plots were arranged from north to south with a spacing of 2 m between them to control factors that could influence the treatments, distributed in a factorial arrangement arranged in completely randomized blocks (CRB)¹³. In both systems, 5 kg m^-2 of manure (cattle manure) was incorporated before pre-soil preparation. In addition, in the biointensive system (BIS), also known as biointensive agriculture, 35 cm high beds were prepared and a drip irrigation system was established. The BIS, a 60 cm double-digging technique¹⁴.

The agronomic parameters evaluated were plant weight (PW) (g), root length (RL) (cm), plant height (PH) (cm), upper and lower bulb diameter (ULBD) (cm), plant height (AH) (cm) and yield (kg m^-2)¹⁵, for leafy vegetables (PW) (g), number of leaves (NL) (units), RL (g), AH (cm) and yield (kg m^-2)¹⁶.

Likewise, the volume of irrigation water was estimated in 2 systems by drip (BIS) and flooding⁹ (TS), the influence of agricultural production on soil fertility⁵ was determined in both systems, the quantity of fungi by the method of soil dilution analysis in plates which is the weight of 10 g of soil and then introduced into 500 mL Erlenmeyer flasks, to this was added 90 mL of sterile distilled water and shaken for 10 min (standard solution 1:10), from this solution 1 mL was taken with the pipette and mixed with 9 mL of sterile distilled water in a test tube suspended to solution 1:100, this step was repeated until the desired dilution was obtained¹⁷, OM (calcination method), chemical properties Ca, Mg, Na, K, P, (Atomic Absorption method), total N (Kjeldahl method)¹⁸, soil samples were taken by treatment and homogenized, the microbiological analysis was carried out in the laboratories of the Department of Agriculture of FCAN¹⁹ and the chemical analysis in the IBTEN laboratory.

Results

Agronomic parameters. In Table 1, turnip cultivation in BIS obtained the highest PW with 758.7 g, higher than TS with 118.9 g, as well as in RL and AH. The yield in the BIS was 18 kg m^-2 higher than the traditional with 4.5 kg m^-2. In radish the PW was 65.4 g BIS, a higher yield with 3 kg m^-2 superior to the traditional with only 2.1 kg m^-2. In beet, the BIS presented a higher weight with 118.9 g, higher than the traditional one with 106.0 g, similarly, the yield was higher with 4 g m^-2 and 2.7 g m^-2. In lettuce, greater weight and NL were observed in the BIS compared to the traditional with 633.3 and 333.9 g, 15 and 13 leaves, respectively. In the carrot crop, the PP was 69 g in the intensive system, higher than in the traditional system with only 29 g. In the onion crop, the PW was higher with 157 g compared to the traditional with 63 g, in the same way, the bulb diameter and yield reported superiority in the biointensive production.

Water use. The volume of water applied in the entire vegetative cycle of the crop in the BIS was 63.9 m³ with drip irrigation, lower than the flood irrigation system of 282.2 m³, regarding the application efficiency the drip irrigation system reports 90 % efficiency, flood irrigation reports an efficiency of 47 %, re-porting a net volume of water applied of 57.5 m³ by drip and 132.65 m³ by flood.

Microorganisms. The amount of fungi in the two systems (Figure 1), there is a higher amount of fungi in the biointensive system compared to the ST. The BIS reported an average of 6.5x10⁴ CFU g/soil, higher than the traditional system, which reported an average of 1.5x10⁴ CFU g/soil.

Organic matter. The biointensive plot presents 1 % of OM, above the traditional one (Figure 2).

Chemical properties. Calcium in both systems is found in high concentrations. Magnesium in the biointensive plot is high and moderate in the traditional plot, sodium in both cases is very low, potassium reports high contents, total nitrogen high and - assimilable phosphorus very high in both systems.

Figure 1 Number of fungi in biointensive and traditional biointensive and traditional production systems 

Figure 2 Organic matter in biointensive and traditional biointensive and traditional management systems 

Discussion

This analysis shows that even under adverse conditions, with the implementation of agroecological²⁰ and biointensive technologies, the yield was higher in relation to a vegetable production TS, this could be due to the higher fertilization in the plots with 5 kg m^-2/²¹ that not only provides nutrients, but also reactivates the microbial activity of the soil²², it has been established that soils with high OM content tend to contain more microorganisms with complex mandates²³. A synergy, symbiosis is generated between microorganisms and crops²⁴, this is indicated by the microbiological analysis obtained in the BIS with an average of 6.5x10⁴ CFU of fungi; it is important to mention that bacteria and actinomycetes also act in the soil as OM decomposers²³, in contrast to the TS 1.5x10⁴ CFU²⁵, however, in both soils the same amount of fertilizer has been incorporated²⁶. The difference between the results could be due to the fact that there is a greater volume of soil or arable layer due to the use of the high 60 cm plantain bed technique, in comparison with the TS, which has 30 cm²⁷, the crops develop a greater number of roots and interact better with the microorganisms²⁸. On the other hand, drip irrigation generates little compaction, as opposed to flood irrigation²⁹.

After evaluating the two production systems on agronomic parameters, soil fertility and water consumption, it can be observed that there is a statistical difference, reporting high yields in most of the orchards with the BIS. It has been determined that yields increase by an average of 30 % in a conventional production in the first year³⁰. Yields compared with the average for vegetables in Bolivia³¹, the results show to be high (Table 4), which constitutes an alternative to increase them, especially in family agriculture.

In relation to the other chemical parameters³², the differences are minimal, this could be due to the characteristics and nature of the soils of the Bolivian Altiplano, the incorporation of fertilizer would generate better conditions for the development of crops and microorganisms³³, under the logic that the soil has recovered and becomes a "Living Soil".

According to the results obtained from the evaluation of two production systems, on agronomic parameters, soil fertility and water consumption, it can be observed that there is a statistical difference in yield and agronomic variables in most of the vegetables, showing a superiority with the BIS.

The BSI, in comparison with the traditional one, influenced the quantity of soil microorganisms by more than 50 %. For the other chemical components analyzed, a slight superiority is observed in the bio-intensive system in the first year of implementation.

The volume of water consumed shows that there is greater efficiency in the use of the drip irrigation system with 90 % efficiency, the flooding system has an efficiency of 47 %. The APU is adapted to the gradual reduction of the water supply for irrigation that currently exists in the Altiplano, making it a mechanism for adapting to climate change.

Biointensive APU´s are an alternative for family farming in the highlands of Bolivia, they are adapted to the low level of land tenure of small farmers, improve food productivity to ensure food security for farmers and take advantage of livestock manure, water, soil, but with agroecological methods that contribute to the sustainability of agro-ecosystems and local livelihood systems.