**3. Results and discussion**

#### **3.1 Overview of dairy and beef cattle farms in Antioquia**

Cattle farms are located in mountain landscapes and are mostly small producers (**Figure 1**). Approximately 70% of farms visited have an area of less than 30 hectares, indicating that most belong to small producers. They are distributed throughout the department. Many of the producers use some amendments and fertilisers in the pasture fertilisation programmes (**Table 1**).

The size of the farms visited was between 2 and 20 ha for most of the dairy farms and between 2 and 100 ha for the beef cattle farms (**Figure 2**). In Antioquia, the predominant area of rural farms is less than 100 ha [13]. In Colombia, 83% of the Agricultural Production Units dedicated to beef cattle have an area of less than 20 ha, which indicates that the predominant area of beef cattle farms in Antioquia is larger than the average for the country [14].

According to the United Nations, the dairy sector can contribute to a selection of sustainable development goals, such as "No poverty in rural areas," as most dairy farms are small and located in developing countries [15]. Added to this, other authors [16] indicate that milk is mainly produced in mixed crop-livestock systems by small farmers in low-income countries. The authors also consider that dairy farms increase pressure on natural resources as most production systems tend to increase the size of their livestock to meet the growing demand for dairy food.

Most of the cattle farms in the study area were owned by farmers (**Figure 3**). This is encouraging as it contributes to the permanence of farming families in the Colombian countryside. Official data reported eight years ago indicated that 72% of dairy farms were owned by producers in the Department of Antioquia [14]. Studies in

**Figure 1.**

*Typical dairy and beef farms in Antioquia. (a) Author: Manuela Ortega Monsalve. (b) Author: María Mercedes Murgueitio.*

other countries, such as Turkey, highlight the importance of the role of small families in dairy production; with farms averaging just 7.2 hectares and the contributions of all family members in activities related to animal production [17]. Women are involved in production, harvesting, processing, transport, and other important activities in agricultural production systems [18]. The participation of women in dairy farming systems assists towards their economic independence, which should be a blueprint for all women worldwide. It is worth noting that according to the SDGs 5 "Gender Equality," there have been achievements, but many challenges remain [19].

Rotational grazing is the predominant system with 93% of the cattle farms visited (**Figure 4**). In this grazing system, animals start from an initial paddock and then

*Sustainability of Soil Chemical Properties and Nutrient Relationships in Dairy and Beef Cattle… DOI: http://dx.doi.org/10.5772/intechopen.104647*


#### **Table 1.**

*General information of the farms visited.*

**Figure 2.** *Size of dairy and beef cattle farms in the subregions evaluated.*

**Figure 3.**

*Type of ownership of dairy and beef farms.*

**Figure 4.** *Grazing systems used in the dairy and beef farms visited.*

*Sustainability of Soil Chemical Properties and Nutrient Relationships in Dairy and Beef Cattle… DOI: http://dx.doi.org/10.5772/intechopen.104647*

**Figure 5.** *Types of fertilisers used on dairy and beef cattle farms.*

go through other paddocks until they return to the first when it is ready to be grazed again [20, 21]. In a study of beef cattle systems in Antioquia, using Criollo cattle breeds, it was found that 96% of producers use rotational grazing systems, and 4% use silvopastoral systems [22]. Silvopastoral systems include trees, shrubs, pastures, animals, and other crops, provide a good forage supply for animals, contribute to biodiversity conservation, contribute to nutrient recycling and soil fertility conservation, and provide shade, amongst other benefits [23, 24]. This indicates that amendments and fertilisers are required in most cattle production systems. However, there has been an increase in the establishment of silvopastoral systems in the country in recent years; these systems could positively contribute to the reduction of agrochemical application, and thus to environmental sustainability.

The type, amount, and form of application of fertilisers can affect the sustainability of pasture production. Of the 488 dairy farms in this study, 58% of farms do not have fertilised pastures, whilst the other 41.6% have fertilised pasture present. Approximately 33.4% of the farms use chemical fertilisers, 5.7% use organic fertilisers, 2.5% use a mixture of chemical and organic fertilisers and 0.4% of the dairy cattle farmers did not answer the survey question. In contrast, of the 428 beef cattle farms, it was found that 94.2% do not fertilise their pastures, while the remaining 4.7% do fertilise their pastures. 2.1% of the producers use organic fertilisers, 2.1% of the farms use chemical fertilisers, and 0.5% use a mixture of chemical and organic fertilisers. In addition, 1.2% of beef cattle producers did not answer the survey question (**Figure 5**). The above described demonstrates the low technological level of fertilisation management in beef cattle production systems compared to dairy cattle production systems.

According to the SDGs, implementing agricultural sustainability can help reduce poverty [25]. Although it was found that most farmers do not apply fertilisers, it is important to conserve the soil as the basis of agricultural production. For this reason, nutrient levels in soils must be determined in order to help implement rational management programmes according to the needs of the pastures. In this way, it contributes to the sustainability of livestock production in the conditions of the Colombian tropics.

#### **3.2 Variability of the chemical parameters of the soils**

There is a high variability of the chemical parameters of the soils in the Department of Antioquia. We show partial information on the descriptive statistics for some chemical parameters found for each subregion (**Table 2**). The maximum and minimum values found for most of the parameters presented very extreme values, which may indicate that in some farms the producers use high applications of fertilisers and amendments or it could also be that the taking of some soil samples for chemical analysis performed on recently fertilised paddocks. The general fertility parameters of the soils analysed are in accordance with that described by other authors [10]. Moreover, the levels found for soil nutrients are compared with the levels established for Colombia according to the ICA (Colombian Agricultural Institute) [26].

In general terms, the only nutrient with high levels in the soils studied is iron, the one with low levels in all soils is sodium. The electrical conductivity values (0.17–1.12 dS/m) and sodium levels (0.15–0.45 cmol(+)/kg) of the soils analysed indicate that they do not present salinity problems. In Colombia, soil sodium levels (Na < 1 cmol(+)/kg) are considered ideal values. Macronutrients, such as phosphorus, potassium, and sulphur, had high levels in some dairy areas (North and Valle de Aburrá subregions). These values were higher than 30 mg/kg, 0.4 cmol(+)/kg and 10 mg/kg for P, K, and S, respectively. In the other subregions, these nutrients had medium to low levels.

The Ca and Mg available bases are low for all subregions, except for the Urabá and "Occidente" subregions. However, the Ca:Mg ratio in these two subregions is low. This indicates that amendments containing calcium and magnesium need to be applied in all subregions, either to raise the levels of available bases or to improve the Ca:Mg ratio, which is recommended to be maintained at 3:1. The application of amendments would help to neutralise the exchangeable aluminium and as a consequence increase the pH, which tends to be acidic in most of the subregions of Antioquia.

Micronutrient levels are adequate for most of the soils analysed under the sampling conditions of this study. Cation exchange capacity (CEC < 10 cmol(+)/kg) is low in all subregions, except in the Urabá subregion (CEC = 15.83 cmol(+)/kg).

Although most areas have low to medium levels of organic matter (OM < 10%), the total soil nitrogen level is medium to high (TSN from 0.16 to 1%), which possibly indicates high mineralisation rates due to tropical conditions and in other cases could be due to excessive nitrogen application, mainly in dairy pastures. In the soils analysed, the loam textural class predominates, indicated by sand levels in the range of 36–52%, clay levels from 8 to 34%, and silt levels from 20 to 43%. The subregions of Urabá and Occidente present a clay loam textural class.

Previous reports on some dairy farms in the Oriente subregion were also characterised by acidic soils (low pH and exchangeable aluminium values of 1.2 cmol (+)/ kg), similar Na values (0.02 cmol(+)/kg), and also low P levels (3 mg/kg). In contrast to this, there were low levels of available bases found for Ca, Mg, and K (0.09, 0.16 and 0.1 cmol(+)/kg respectively), while organic matter (OM > 22%) and boron (0.7 mg/kg) levels were high [27]. Another author [28] reported similar levels of P (9.4 mg/kg), K (0.29 cmol(+)/kg) and organic matter (OM = 5%) in pasture soils of the Occidente subregion. They also presented clay loam texture (34.7% sand, 34.5% clay, and 30.8% silt) similar to that found in this study. The other chemical parameters presented higher levels than those found on farms in the Occidente subregion, mainly pH 6.94 and available bases of 24.7 and 10.2 cmol(+)/ kg for Ca and Mg, respectively [28]. In another study in the Norte subregion, similar levels of pH, Al, EC, and K and different values for organic matter and phosphorus were found [29].

*Sustainability of Soil Chemical Properties and Nutrient Relationships in Dairy and Beef Cattle… DOI: http://dx.doi.org/10.5772/intechopen.104647*



*\*\* Values in parentheses correspond to the median value. \*\*\* NA = not available.*

**Table 2.**

 *Some physicochemical parameters of the soils in the subregions of Antioquia.* *Sustainability of Soil Chemical Properties and Nutrient Relationships in Dairy and Beef Cattle… DOI: http://dx.doi.org/10.5772/intechopen.104647*

Some models were selected based on the verification of the significance of each effect and the lowest Bayesian Information Criterion (BIC). For the variables, soil organic matter and total soil nitrogen a value of R2 > 0.85 was found, while the other variables showed a lower adjustment (**Table 3**).

The distribution of some chemical parameters in the department is related to the geographical location. It was found that parameters, such as pH and calcium level, showed homogeneous variations according to latitude and longitude, while some parameters, such as organic matter and phosphorus level, were highly variable and did not show any distribution according to geographical location (**Figure 6**).

#### **3.3 Relationships amongst some of the chemical parameters of the soil**

The soil parameters organic matter, total nitrogen, and calcium were positively correlated. Calcium levels showed a negative correlation with exchangeable aluminium, which is common for acidic soils in the tropics (**Figure 7**). Similarly, organic matter and calcium parameters also showed positive relationships for dairy cattle soils in the Norte subregion of Antioquia [29].

The altitude of the farms influences the pH values of the soil. Soils with acidic pH have low levels of calcium readily available (**Figure 8**). The low amount of available calcium is normal in tropical soils with naturally acidic conditions due to high rates of mineralisation and leaching of soil bases. In addition, it was found that medium to low levels of calcium and potassium are positively related to phosphorus levels (**Figure 8**). However, this relationship does not occur when phosphorus levels are high, due to the high applications of phosphorus fertilisers in some cattle farming areas, which also occurs in several crops in other areas of the country [30].


#### **Table 3.**

*Parameters of the selected models for the analysis of some variables.*

**Figure 6.** *The general behaviour of some chemical parameters of dairy and beef cattle soils in Antioquia, Colombia.*
