Characteristics of the study area

The analyzed coffee soils are found within the watershed The Switzerland located in the municipality of Montecristo de Guerrero (Figure 1), with a total area of 6 437.1 ha, of which 82% is within the REBITRI (^{Lopez et al., 2011}). According to ^{Palacios (2012)}, 55.7% of the area of the watershed is occupied with forest, 37.2% (2 391 ha) and 3.7% coffee paddocks.

Figure 1 Location of the watershed La Suiza. 

According to soil information Series II, 1: 250 000 (^{INEGI, 2006}), 95% of the area of the watershed classified as Leptosols the mollic type (product of weathered calcareous material) soils, characterized dominated by very on continuous and extremely shallow gravelly and stony rock with less than 20% (by volume) fine earth and high susceptibility to erosion (^{FAO, 2014}).

Sampling

The soil to a depth of 0-30 cm layer in which is 86% of the absorbing roots of the culture was analyzed (^{Carvajal et al., 1969)}. In each site, the physical properties were measured in five repetitions and for the case of the chemical properties of a sample of soil from the mixture of five subsamples was obtained.

Analytical methods

In 49 farms distributed throughout the watershed were determined according to the NOM-021-SEMARNAT 2000 (DOF, 2002), the following properties: texture boyoucos (% sand, silt and clay), pH in water (1:2), organic matter (%), total carbon (%), P Bray (ppm), K, Ca, Na, Mg and exchangeable acidity (KCl 1N) in cmoles +Kg^-1 and micronutrients B, Zn, Mn, Cu and Fe in ppm by DTPA.

Soil acidity

Soils are classified as moderately acid (Table 1) by presenting an average pH 5.08 (± 0.38). The pH is probably the most important soil chemical characteristic that influences almost every other aspect of it (^{Bloom, 2000}; ^{Benzing, 2001}). The saturation value as a measure of acidity percentage of cation exchange complex is occupied by aluminum and hydrogen is the best criterion for diagnosing problems acidity (^{Molina, 1998}). Although each culture has its degree of tolerance for acidity, in general terms it may indicate that almost any crop supports more than 60% saturation of acidity and the desirable value for most plants is between 10 and 25%.

In Figure 2, it is observed that the soils studied show a negative correlation between pH and Al saturation because as it increases the first, the second decreases. Based on the proportion of shared variance between two variables a 50.21% Al saturation is explained by the pH levels in the soil.

Figure 2 Influence of pH on aluminum saturation (%). 

It is common that when the pH is greater than 5.5 the toxicity problem is eliminated because it Al is precipitated as insoluble hydroxides (Agro, 2012). This remark coincides with the results of study since Al saturation decreased when pH values are greater than 5.5 and instead increased to 29.9% with lower pH values.

Because only 6 sites had levels of Al saturation > 10%, and only two of them had levels above 25% (28.8 and 29.9) noted by ^{Bertsch (1998}), as toxic for growing coffee, it follows that 96% (n= 47) of the sampled plots no problems of toxicity Al and 61% (n= 30) of them have levels zero. The limited presence of Al indicates that the main cause of low pH values is the H + exchange and in the soil solution product of the decomposition of organic matter, which is related to the high content of calcium found.

^{Valencia (1998}) notes that if the source of acidity is only the H + in the soil solution, coffee plants can normally grow at relatively low pH between 3-5-4.0. However, although the H + ions are only toxic to plants in extremely high concentrations, it must bear in mind the negative effect due to the influence of acid pH in the availability of mineral nutrients and microbial activity in the soil (^{Anzorena, 1995}).

Another factor that influences the saturation (%) in the soil is the Cation Exchange Capacity or CIC (^{Cochrane et al., 1980}), Figure 3 shows that in the soils studied Al saturation begins its increase when the CIC falls below 10 meq/100 g soil, however, only two plots have levels of Al saturation above 25% which is very likely to be Al toxicity to roots coffee plants as a result of that Al is the predominant cation exchange complex.

Figure 3 Influence of CIC (meq/100 g) in aluminum saturation (%). 

Organic matter and carbon

The average organic matter content is 8.51% (±, 4.40) with a range between 2.61 and 21.81% (Table 1) showing a wide variability between farms (CV= 51.7%). A third of the plots (n= 16) have low and very low content with values less than or equal values of 6% organic matter; 48% (n= 24) present media content between 6.1 and 10.9% and only 18.36% (n= 9) have high content and high with values greater than 11%. It is very likely that in the plots with medium and high organic matter content acidity conditions are holding back the development of bacteria and folding down the mineralization process (^{Noriega et al., 2014}).

According to ^{Valencia (1998}) a response to nitrogen application is expected as 81% (n= 40) of the coffee plots are located in the minimum range with a lower content of 11.4% organic matter. The average carbon content (Table 1) is 4.94% (± 2.55) with a range between 1.5 and 12.7% carbon.

They possess organic matter soils comes from the litter produced by coffee plants and shade trees. ^{Farfan and Urrego (2007)}, in a study conducted at the experimental station Paraguaicito, Colombia, estimated a contribution of 1 kg plant^-1 of coffee and 1.5 kg tree^-1 shade. Avila and Zamora (2010), found in coffee plantations deciduous forest of Veracruz, Mexico that total litter production was 2 626.5 kg ha^-1 yr^-1, higher than at 49 and 45% to that in the coffee plantations jungle sub perennifolia medium and low high evergreen forest.

The cation exchange capacity (CIC)

The CIC is the total number of exchangeable cations that can be retained by a soil depending on the magnitude of its negative charges (^{Chavez, 2012}). It is one of the most important parameters of soil fertility because of its role as a store of K, Mg and Ca readily available, but protected from the leaching process (^{Benzing, 2001}; ^{Arcila and Farfan, 2010}). The higher the CIC, potentially more cations and exchange may retain soil.

On average soils have a CEC of 16.4 (± 7.96) meq/100 g with a minimum value of 3.5 and a maximum of 47 with a wide variability evidenced by C.V. 48.5% (Table 1). The 47% of the analyzed plots (n= 49) have low levels of CIC with Cmoles' below 15 kg^-1 values, another 47% have average levels between 15-25 and only three plots are above 25 Cmoles' kg^-1 corresponding to newly built properties to productive activity.

In the Figure 4 shows the influence of soil pH on the CIC of the soils studied. Observed that 32% of the behavior of the CIC is explained by the level of acidity of the soil, the lowest values of CIC occur when the pH is below 5.5 and the highest when the pH has values between 6 and 7.

Figure 4 Effect of pH on the CIC. 

This dependence on the CIC with the acidity is because with increasing soil pH new negative charges are generated in the exchange complex and is reported by ^{Anzorena (1995)} and ^{Benzing (2001)}, as a variable CIC, which is more common in the CIC from organic matter, which clays. ^{Foth and Ellis (1996)} indicate that in mineral soils with low organic matter content, the influence of pH on the CIC is minimal. This variability can be deduced that a large part of the CIC in soils of the watershed comes from humus organic matter.

The 14.5% of the behavior of the CIC is explained by the level of organic matter in the soil, in Figure 5, it is observed that in some soils lower CIC values occur when this presents values below 10%; however, there are also plots with low CIC with very high values, which could be influenced by the high level of acidity which limits the rate of humification and mineralization of organic matter.

Figure 5 Influence of organic matter in the CIC. 

For its part the clay has little influence (r2= 0.0457) on the behavior of the CIC, which may be due to the sandy loam soil texture represented by 43% (± 11.48) sand, 28.8% (± 7.93) clay and 28.2 (± 6.14) of silt.

Based on the above it follows that the dynamics of the CIC in coffee soils of the watershed La Suiza, is influenced by the pH and organic matter content.

Phosphorus

This nutrient has a great variability between plots with C. V. 110% (Table 1). On average the content is 25 ppm (± 27.5) with a minimum value of zero and a maximum of 140.6. There are five plots where the content is zero and two with a very high content with 141.89 and 83 ppm. Almost half (49%) of the plots have lower content of 15 ppm, which could be a response to the application of phosphate fertilizer (^{International Plant Nutrition Institute, 2014}). A moderate positive influence of the CIC (r2= 0.3921) and Ca (r2= 0.433) on the content of P in soil was observed. P is likely to react with the calcium this form calcium phosphate salt is a completely insoluble and very stable which does not allow P to be assimilated by plants (^{Sephu, 2013}).

Basic cations (K, Ca, Mg, Na)

The base saturation has little variability between plots with C.V. 7.5% (Table 1). On average has a value of 97% (± 7.3) and 88% of the plots are located in the range of 90-100%. This high saturation of the CIC bases, highlights the absence of H and Al ions in colloids (FAO, 2014) and more presence of metal cations. In the Figure 6 shows the contents of K, Ca, Mg and Na in soil and shows that regardless of the total of exchangeable cations always predominates Ca between the four cations (Figure 6), which is related to the geology of soils in the watershed.

Figure 6 Contents of K, Ca, Mg and Na in the soils studied (n= 49). 

Table 2 shows the criteria for adequate saturation of the CIC by K, Ca and Mg proposed by Valenca (1998), highlights the imbalance up having the Ca in 63.2% of the plots with a higher percentage of saturation to 75 %. It also stands out that 35% of the plots have an imbalance down the saturation percentage K.

Table 2 Classification of soil saturation percentage as Ca, Mg and K. 

The 92% of the plots have adequate levels of K with values above 0.3 meq/100 g, including one could say that some plots have excess conditions. ^{OIRSA (2001)} points out that excess of this element causes increased fruit drop (which ferment on the ground hurting quality) and can also induce Mg deficiency and to a lesser degree of Ca, although in this case observed by correlations a positive relationship between K and Mg (r= 0.4382) and between K and Ca (r= 0.2355).

With respect to calcium, 67% of the plots with high content with values above 10 meq/100 g soil, 18% is located with an average content and only 14% in classes low and very low. The excess of this element is antagonistic with the K, Mg and Na (^{Valencia, 1998}). According to the ^{International Plant Nutrition Institute (2014)}, generally 100% of the plots do not show Ca deficiency because its content is greater than 0.5 meq/100 g of Ca, considered critical level, in fact the minimum value found is 1.7 is 3.4 times greater than this critical value. In particular for the cultivation of coffee, according to the criteria proposed by ^{Valencia (1998)}, 90% of the plots have no problems introducing Ca deficiency values well above the critical level of 1.6 meq/100 g.

According to the ^{International Plant Nutrition Institute (2014)}, 100% of the plots have no Mg deficiency because its content is greater than 0.2 meq/100 g of Mg considered critical level fact Pussycat found value of 0.7 is 3.5 times greater than this critical value. By this means ^{Bertsch (1998)}, 98% (n= 48) of the parcels are within the range of 1-10 meq/100 g considered ideal. According to NOM-021- SEMARNAT-2000 (^{DOF, 2000}) and ^{Valencia (1998)}, 90% of the plots have no Mg deficiency problems. Comparing the different classifications proposed for Mg, it follows that there is an adequate and excess in soils.

The cationic relationships are other criteria support the interpretation of soil analysis, particularly between bases (^{Chavez, 2012}). Referencing the general critical values suggested by ^{Bertsch (1998)}, it was found that more than one third of the plots (39%) show a positive imbalance in the Ca/Mg and Ca/K ratio, indicating an excess content Ca which could induce deficiencies of Mg and K. 26% of the plots have a negative imbalance in the Mg/K ratio indicating an excess of K that could induce Mg deficiency. As for the ratio Ca + Mg/K a 22.4% of the plots have negative imbalance where the K content is higher and the lower Ca. According to these criteria follows that the high values of Ca could be inducing deficiencies of Mg and K in coffee plants, in cases where the Ca/Mg and Ca/K ratio present a positive imbalance.

Micronutrients (B, Cu, Fe, Mn and Zn)

Of all the micronutrients analyzed boron is the most deficient in 84% of the plots of the watershed The Swiss, followed to a lesser extent by zinc in 16% of the plots element. ^{Valencia (1998)}, indicates that boron (as Ca) is related to the absorption of macro- and micronutrients (P, Mg and Ca), root growth (associated with calcium), growth, number of side branches , number and differentiation of flower buds, pollen germination and tube growth of pollinators and fruit growth. Excess manganese in soils with an average content of 43.7 ppm (± 34.11) well above the critical level of 1 ppm, may be related to low physiological ability of plants to absorb and store (^{Rodriguez and Morales, 2005}).