(pdf)
SciELO 
SciELO 
Permalink
INTRODUCTION
The inner Bay of Puno is a small section of Lake Titicaca, located east of the city of Puno, Peru; it has an area of 16 km2 between the promontories of Uros Chulluni and Chimu, and is almost 4 km wide, but most of it is blocked by extensive reeds and leave opened a narrow 300-meter-wide channel near Chimu, which communicates with the outer bay of Puno (Municipalidad de Puno, 2008).
In recent decades, soil degradation has increased considerably and now threatens agricultural soils around the world according to Bednář & Šarapatka (2018), climate change, misuse and excess of pesticides make them susceptible to accumulation due to the processes of adsorption with organic matter and water retention (Leal et al., 2014).
The increase in the use of nutrients processed from organic matter derived from the treatment of urban wastewater, as organic fertilizers that improve the soil, has been one of the main causes contributing to the degradation of agricultural soils (Flores et al., 2007).
The Soil Health Committee of the Soil Science Society of America defines soil quality as the ability of soils to function within the parameters of a managed or natural ecosystem, which is why it is important to improve the quality of soil, water and air to make the productivity of flora and fauna sustainable by generating an ecological balance (García et al., 2012). This concept is also called edaphogenesis according to González et al. (2011), however, the ecological balance varies due to different factors, among which are mainly those of anthropogenic origin (Sánchez et al., 2017).
The evaluation of soil quality has various applications in agricultural soil management, through its influence on biogeochemical cycles and greenhouse gas emissions, this being one of the most important factors that directly impact in agricultural soils, considered the main engines of the global climate change (Askari et al., 2015; Li et al., 2018).
The quality of agricultural soils has also been measured by the presence of macrofauna, which is taken into account especially in agricultural practices. It contributes to soil aeration, formation and transformation of the structure in the litterfall according to Lavelle (1996) and it is affected mainly by tillage and misuse of chemical inputs. That is clearly reflected in the decrease in biomass of these populations, due to their susceptibility to various factors. Macrofauna is considered a parameter of soil quality according to Pareja et al. (2011) as well as the diversity of taxa and dominant groups (Huerta et al., 2008).
Macroinvertebrates provide environmental services such as nutrient sequestration, especially soil carbon, according to Nabiollahi et al., (2018). They have been considered the engineers of the ecosystem, since these activities have direct effects on the properties of soils as well as intervening in the processes of humification and mineralization of organic matter (Gutiérrez et al., 2003). These activities are carried out together with Rhizobium through the combination of pores and aggregates of different sizes (Lavelle et al., 2006), which have an impact on soil fertility. The content of organic matter, diversity of microorganisms and organisms establish the quality and condition of the soil.
Agricultural activity in Puno, Peru, is one of the main activities in the region, especially for the rural population, who is dedicated to this activity. Among the most important products grown are quinoa, cañihua, beans, oca, potatoes, barley grain, green beans and cultivated grasses, among others, which have a very good perspective at the global level because they are agro-ecological products (MINAM, 2013).
Research on the evaluation of agricultural soil quality allows constant monitoring in certain areas, identifying changes in their properties and characteristics and thus proposing appropriate management practices (Franzlubbers & Haney, 2006).
The analysis of physical, chemical and biological parameters generally allows the quantification, communication and simplification of the phenomena that determine if the use of the resource is sustainable (Bautista et al., 2004). Knowing the agricultural importance of the study zone over time and the visible anthropic contamination of the area, the objective of this work was to find out the quality of the agricultural soils in the interior Bay of Puno, Peru-2018.
METHODS
The present research work was carried out in the interior Bay of Puno, from Uros Chulluni to Chimu (Figure 1), considering 8 sampling points (Table 1).
Source: Geographic location through GPS. Modified from Google maps.FIGURE 1 Interior bay of Lake Titicaca Puno-Peru (sampling points).
TABLE 1 Sampling points
| Nº. Point | Coordinate, UTM |
|---|---|
| 1 |
15°49’17.1599” S 69°59’28.3800” W |
| 2 |
15°49’25.3801” S 69°59’42.3800” W |
| 3 |
15°51’50.4601” S 69°59’39.5400” W |
| 4 |
15°51’48.5399” S 69°59’27.4800” W |
| 5 |
15°51’43.0801” S 69°59’06.6600” W |
| 6 |
15°51’21.2400” S 69°58’46.5600” W |
| 7 |
15°51’13.0201” S 69°58’30,1800” W |
| 8 |
15°51’09.3600” S 69°58’01,3200” W |
Forty-eight agricultural soil samples were collected at the eight sites, with six replicates from the Puno inland bay, during the months of August, September and October (the months after harvest and before the first planting). The samples were taken from 0 to 30 cm deep using the zigzag method according to the guide for soil (MINAM, 2014). Soil samples were taken in standardized plastic bags, hermetically sealed, and taken to the laboratory for detailed analysis. These samples were dried at room temperature and sieved by 0.5 mm.
Physical Parameters
For the evaluation of physical parameters, particle size analysis was performed using the Bouyoucos hydrometer method according to Sandoval et al. (2010) and, in special cases to determine the percentage of silt clay and sand, the pipette method according to Burt (2014), was used, which is considered an accurate method for particle size determination that quantifies the mineral particles in the soil in gravimetric form. Dry and wet colors were determined using the Munsel Table (Munsell Colour Company, 2000).
Chemical Parameters
In the evaluation of chemical parameters, the potentiometric method with soil-water ratio (1:2.5) according to Peech (1965), was used for pH, and the conductivity method with soil-water ratio (1:5) according to Richards (1954). was used for electrical conductivity. For the determination of organic matter, the method by wet digestion with dichromate in acid medium was used. For the determination of N, P and K, the colorimetric test methods, based on Mehlich extraction nitrate and phosphorus and the turbidity method for potassium according to Ståhlberg (1979) were used.
Biological Parameters
To evaluate biological parameters, the method of counting populations of annelids, mollusks and arthropods according to Berovides et al. (2005) was used. These organisms were counted with entomological tweezers, and once obtained they were taxonomically classified with the help of the stereoscopic and specialized literature. The method used to record the macrofauna was by direct observation using a classification and counting table (Lang et al., 2011).
Macrofauna living under the ground were sampled at two depths (0-15 cm and 0-30 cm). They were classified into groups of invertebrates according to their taxonomic characteristics.
To obtain the results, it was used the statistical package ANOVA with a 95% confidence level to determine if there were a difference between the 8 points of analysis. If a difference were found in the analysis, TUKEY analysis was applied to identify which points make the difference (Di Rienzo et al., 2008).
According to Minagri (2015) there are various world classifications of soils, in the case of Peru, FAO Classification on Geo-edaphic Regions is widely used, the area of Lake Titicaca belonging to the Kastan-Solian Region, where soils originating from lakes (planosols) and soils with poor drainage (gleysols) predominate.
This region is a traditional agricultural area, with intensive use for thousands of years, growing mainly cereals, tubers, legumes and some vegetables. The upper parts of the grasslands are used for livestock purposes and the lower parts for permanent crops such as fruit trees. The surrounding soils are of the alluvial type with slow edaphization and in some parts with a high content of organic matter, belonging to the Limnos Association and the Titicaca Association.
RESULTS AND DISCUSSION
The physicochemical properties of the soil play an important role in the development of crops, which at optimal levels allow the generation of biological properties that benefit plant growth, so it is necessary to optimize soil fertility based on the control of soil fertility and crop nutrition.
In order to know the quality of agricultural soils in the interior Bay of Puno, Peru, the soils were analyzed according to the methodology of García et al. (2012), with the objective of determining the quality of agricultural soils in the bay mentioned based on physical, chemical and biological parameters.
Physical-Chemical Parameters
The physical results of the agricultural soils were notoriously different. Points 1 and 2 were clayey, points 3, 4, 5 showed mixed characteristics between clayey and sandy, while points 6, 7, and 8 were strictly sandy with brown coloring.
According to the granulometric analysis, it was determined that the agricultural soils of the Uros-Chulluni and Chimu population centers have texture classes sandy loam and loamy loam, according to the United States Department of Agriculture's triangular texture scheme USDA-NRCS (2005). Sandy soils lack metal fixing capacity and the water table may be contaminated. In addition, they present soft characteristics with 1% of organic content and hydromorphic soils with calcium horizons, molic gleysols in the flat lands, solonets and solonshack in the depressions.
As observed in the month of August after harvest, points 2 and 3 presented the highest percentage of nitrates; points 3, 1 and 4 presented the highest amount of potassium; points 3, 8 and 1 the highest amount of phosphorus; points 5, 2 and 4 the highest percentage of organic matter; points 1 and 2 with the highest pH and finally points 7, 8 and 2 presented the highest electrical conductivity (EC). In Table 2, the results related to the physical characteristics of each sampling point are shown. These results are related to the presence in the area of waste drains and agricultural soils rich in fertilizers, which contain high levels of nitrogen (N) and phosphorus (P), so it can be considered that the fertility of the arable layer is moderate, as it presents high levels of organic matter and phosphorus, and medium levels of potassium, with a suitability for pasture.
The pH of the soils sampled are moderately alkaline (Table 2 and Table 4), mostly found within the range of Canadian soil quality standards (pH: 6-8), except for points 1 with pH = 8.71 and 2 with pH = 8.61, possibly in the presence of calcium carbonate, which indicates that precipitation occurs as hydroxides. However, in very alkaline environments these hydroxides can pass back into solution as hydroxycomplexes. Clayey soil usually contains 40 to 50 percent clay, little organic matter and a high proportion of calcium carbonate.
It is important to remember that according to Villar & Villar, (2016), the distribution of nutrients in the soil occurs mainly through concentration gradients, where elements such as phosphorus and potassium move from the concentration gradients, i.e. at high speed, which have to be redistributed in the soil to be absorbed by the plants' root system, so this may be the reason why a higher percentage is found in the ploughable area of the sampling points.
TABLE 2 Physical-chemical parameters of the agricultural soils in the interior Bay of Puno, Peru
| Sampling points | Physical and chemical parameters | |||||
|---|---|---|---|---|---|---|
| Nitrate (%) | Potassium (mg/kg) | Phosphorus (mg/kg) | Organic Matter (%) | pH | CE (µs/cm) | |
| 1 | 0.147 | 66.24 | 36.8 | 3.5 | 8.71 | 247 |
| 2 | 0.589 | 27.6 | 27.6 | 3.66 | 8.61 | 359 |
| 3 | 0.552 | 80.96 | 55.2 | 2.86 | 8.37 | 205 |
| 4 | 0.368 | 66.24 | 36.8 | 3.66 | 8.21 | 329 |
| 5 | 0.368 | 44.16 | 27.6 | 3.9 | 8.24 | 149.4 |
| 6 | 0.221 | 36.8 | 27.6 | 3.32 | 8.3 | 302.6 |
| 7 | 0.368 | 44.16 | 27.6 | 3.02 | 8.22 | 983 |
| 8 | 0.221 | 44.16 | 55.2 | 2.94 | 8.48 | 519 |
In the month of August after the harvest, it was observed that 87.5% of the agricultural soils presented a condition of nitrate above the optimum, 100% presented a condition of very low potassium, 50% of phosphorus presented a medium condition and 50% in optimum condition. Regarding electrical conductivity, 62.5% presented a condition above the optimum followed by 25% that presented an optimum condition and 12.5% that presented a medium condition (Table 3). These conditions have been compared with those established by Villar & Villar, (2016), adapted from FAO for the analysis of soil fertility.
These results demonstrate the excessive use of nitrogen fertilizers in the study area, which can cause losses of nitrogen to the subsoil in the form of nitrates (NNO3), with risks of contaminating the aquifers and consequently the pumping water used to irrigate the crops and making the plants toxic. Therefore, it can be said that there is an over-fertilization with nitrogen in the area, which affects the levels of potassium and phosphorus and adversely affects the productivity and quality of cultivated food.
TABLE 3 Evaluation of the chemical parameters (in percentage) of the agricultural soils in the interior Bay of Puno, Peru after the harvest
| Condition | Chemical Parameters | |||||||
|---|---|---|---|---|---|---|---|---|
| Nitrate | Potassium | Phosphorus | CE (µs/cm) | |||||
| Frec. | % | Frec. | % | Frec. | % | Frec. | % | |
| Very poor | 0 | 0 | 8 | 100.0 | 0 | 0 | 0 | 0 |
| Poor | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Medium | 1 | 12.5 | 0 | 0 | 4 | 50.0 | 1 | 12.5 |
| Optimal | 0 | 0 | 0 | 0 | 4 | 50.0 | 2 | 25.0 |
| Above optimal | 7 | 87.5 | 0 | 0 | 0 | 0 | 5 | 62.5 |
| Total | 8 | 100.0 | 8 | 100.0 | 8 | 100.0 | 8 | 100.0 |
Source: Own elaboration.
For the month of October before sowing, point 1 showed a higher percentage of nitrate, points 2 and 3 a higher quantity of potassium, points 1, 2, 3, 4, 5, 6 and 8 a higher quantity of phosphorus, points 8 and 4 a higher percentage of organic matter; points 8, 4 and 5 showed the highest pH and finally points 7, 2 and 6 showed the highest electrical conductivity (Table 4).
The excess of nitrates detected indicates that the doses of nitrogen applied to the soil are high or that the current fertilization recommendations for the area's crops are not the most appropriate for the region. In the case of pH, the plants grown generally show their best development in values close to neutral, since in these conditions the nutrients are more readily available and in a more appropriate balance, which, in this case, causes an increase in the presence of potassium and phosphorus, although generally the soils in agricultural areas normally have pH values between 4,5 and 9,5.
TABLE 4 Chemical parameters of agricultural soils in the interior Bay of Puno, Peru before the harvest season
| Sampling Points | Chemical Parameters | |||||
|---|---|---|---|---|---|---|
| Nitrate (%) | Potassium (mg/kg) | Phosphorus (mg/kg) | Organic Matter (%) | pH | CE (µs/cm) | |
| 0.552 | 58.88 | 36.8 | 3,47 | 7.9 | 240 | |
| 0.147 | 110.40 | 36.8 | 3,50 | 7.51 | 270.5 | |
| 0.037 | 117.76 | 36.8 | 3,40 | 8.45 | 198.5 | |
| 0.037 | 58.88 | 36.8 | 3,80 | 8.9 | 198.4 | |
| 0.221 | 58.88 | 36.8 | 3,50 | 8.9 | 112.9 | |
| 0.147 | 51.52 | 36.8 | 3,10 | 8.6 | 268.4 | |
| 0.221 | 58.88 | 27.6 | 3,16 | 8.28 | 349 | |
| 0.074 | 58.88 | 36.8 | 3,94 | 8.91 | 189.1 | |
Source: Own elaboration.
The 37.5% of the agricultural soils presented a condition of nitrate above the optimum, it was observed that 25% presented a medium condition, with the same percentage was observed a very low condition and 12.5% with a low condition. In addition, 100% presented a very low potassium condition, 87.5% presented an optimum phosphorus condition and 12.5% a medium condition, 37.5% presented an electrical conductivity condition above the optimum and the same percentage, an optimum condition followed by 12.5% that presented a medium condition and the same percentage a low condition (12.5%) (Table 5).
According to Gian (2015) the population center of Uros-Chulluni, presents a moderate capacity of use of the soils, observing that at least a third of the lands of the Titicaca-Desaguadero-Poopó-Salar de Coipasa (TDPS) system are being overexploited above their capacity of use, above all in the marginal lands and not suitable for annual, permanent crops, with a loss of agricultural soils determined basically by erosion and salinization.
TABLE 5 Assessment of chemical parameters (in percentage) of agricultural soils in the interior Bay of Puno, Peru (month of October before planting)
| Condition | Nitrate | Potassium | Phosphorus | CE (µs/cm) | ||||
|---|---|---|---|---|---|---|---|---|
| Frec. | %. | Frec. | % | Frec. | % | Frec. | % | |
| Very poor | 2 | 25.0 | 8 | 100.0 | 0 | 0 | 0 | 0 |
| Poor | 1 | 12.5 | 0 | 0 | 0 | 0 | 1 | 12.5 |
| Medium | 2 | 25.0 | 0 | 0 | 1 | 12.5 | 1 | 12.5 |
| Optimal | 0 | 0 | 0 | 0 | 7 | 87.5 | 3 | 37.5 |
| Above optimal | 3 | 37.5 | 0 | 0 | 0 | 0 | 3 | 37.5 |
| Total | 8 | 100.0 | 8 | 100.0 | 8 | 100.0 | 8 | 100.0 |
Source: Own elaboration.
In previous studies, it has been shown that, agricultural, urban, forest and grassland land use types, have a positive relationship with nutrients, sediments and pesticide compounds used in a watershed (Sun et al., 2013).
Biological Parameter
During the evaluation of the biological parameter it was observed that the number of organisms belonging to the macrofauna increased as the planting months approached, with more organisms being found at sampling point 7 followed by 8, where a sandy substrate with high concentrations of nitrate, organic matter and higher electrical conductivity was observed (Figure 2). That indicates that agricultural soils improve their quality and fertility thanks to the presence of these organisms in the soil. These results are similar to those obtained by Lang et al. (2011), who worked evaluating the behavior of soil macrofauna in mango and sugarcane plantations in the state of Veracruz Mexico, which concluded that worms in mango constitute the main reference of soil quality, explained mainly by its organic matter content (3.98%).
The benthic macrofauna of Lake Titicaca has also reacted to the strong local eutrophication of the interior Bay of Puno and to the mining effluents of the main lake. In the first case, several evidences show that the eutrophication of the interior Bay of Puno is already quite advanced and reaches a strong level of environmental stress which reflects that the soils of the study areas present high concentrations of nutrients that benefit the presence of this type of fauna.
According to FAO (2009), because the soil would run out of enough water to feed all the mesofauna and plants that depend on the soil to survive.
FIGURE 2 Evaluation of the biological parameters of agricultural soils in the interior Bay of Puno, Peru Source Own elaboration.
Due to the growing state of environmental degradation on a global scale, Velasquez & Lavelle (2019), refer that the use of tools such as quality indicators is required to evaluate each situation, forecast trends and implement activities that lead to prevention, correction, mitigation or recovery. The use of macroinvertebrates, due to their low cost, facilitates their use by technicians and farmers with the help of basic manuals and minimal training in the field. In the same way, macroinvertebrate communities present in the soil can be evaluated and a general appreciation of the quality of the soil can be achieved.
According to Siebert et al. (2019), earthworms are among the organisms of particular importance, which can modulate the effects of climate change on soil organisms by modifying the biotic and abiotic conditions of the soil. However, their abundance decreases with intensification of management, justifying their use as a key biotic indicator to demonstrate the poverty of the soil due to the intensification of agriculture.
In the region of Puno, there is an urgent need that has required continuous studies of the quality of agricultural soil for years due to the presence of organic and bacteriological pollutants of anthropogenic origin, particularly from organic and mining waste. According to UNEP (1996), the most contaminated area affected by sewage discharges is the interior Bay of Puno, which suffers a moderate eutrophic process resulting of discharges from the city of Juliaca and Lake Uru Uru, due to discharges from the city of Oruro.
CONCLUSIONS
The agricultural soils of the interior Bay of Puno after harvest and before sowing, during the months of August-October in terms of chemical parameters, maintain an optimal condition for the agricultural development of the area.
Despite the high levels of nitrate and solid waste observed in the study areas, the agricultural soils of the interior Bay of Puno, still maintain the basic conditions for planting and harvesting native products.
The increase in organisms belonging to the macrofauna during the months of assessment showed that the soils are now being prepared for future planting and allow the organisms to take advantage of the relationship between soil quality and fertility to fulfill their biological cycles.
This type of research contributes to decision making in efforts to recover degraded or degrading soils and, therefore, to environmental protection.
