In the Andes, little is known about the relationships among current land uses and their effect on soil fertility. Corn ( Zea mays L.) was used to evaluate soil quality for plant growth on soils of four land uses, along an expected gradient of fertility: native forests (Nf) > pastures (Pa) > Eucalyptus globulus Labill. plantations (Eg) > Pinus patula Schlecht. plantations (Pp). Corn was grown in soils taken from four different areas, for the four land uses in each. In a common garden, a randomized block design was used with four treatments: controls (C), ammonium nitrate (N), triple superphosphate (P), and combined N and P fertilizers (N + P). On soils from Nf, Pa and Eg, fertilization response was N + P > P > N > C; corn biomass (g/pot -1) averaged 4.5 in N + P, 3.3 in P, 1.8 in N, 1.7 in C; P content (mg/pot -1) averaged 12 in N + P, 11.9 in P, 2.3 in N, 2 in C. N + P enhanced growth the most. Mortality was high on Pp soils, growth weak, and fertilization response was P > N + P > C ≥ N; corn biomass (g/pot -1) was 0.9 in P, 0.5 in N + P, 0.8 in C, 0.4 in N; P content (mg/pot -1) was 4.4 in P, 2.3 in N + P, 1.8 in C, 1 in N. All soils had P, K, Ca and Mg deficiencies. Al toxicity possibly occurred only in Pp soils. All control soils had low fertility. Responses to N and P were high except for Pp. Pastures and plantations were once natural forests converted to agriculture, then to pastures as soil fertility declined. Plantations were likely established on poorest pastures; only pine grew on poorest soils. This land use endpoint has the lowest agricultural potential; other land uses have limitations in P, N, and potentially K.
Throughout the last five decades, the agricultural sector in the high Andes of Ecuador has experienced political and social changes that have promoted a rapid expansion of agricultural and forestry land use. On one hand, these changes have caused a reorientation of cultivation practices towards large-scale agri-businesses motivated by increased food exportation [
The loss of soil fertility, increased rates of rainfall runoff and accelerated water erosion in the high Andes are current and serious concerns [
The exotic trees Eucalyptus globulus Labill. [
Identifying which soil nutrients are most affected by the various types of land use and the extent to which soils have lost their agricultural potential (plant biomass production capacity) has important implications for future land use planning. Of particular concern is whether subsequent rotations of P. patula can be established, or if a return to pasture or annual crops is possible.
Therefore, the objective of this study was to measure the growth of a common Andean agricultural crop, corn (Zea mays L.), in soils from several common Andean land use types, varying from native forest stands, pastures, and to exotic tree plantations (E. globulus and P. patula). Furthermore, we measured the effect of phosphorus and nitrogen fertilization on corn grown in these soils to see if growth was improved. Specifically, the following hypotheses were formulated: 1) generally, P will be more depleted than N in these volcanic ash Andean soils; 2) P depletion will increase with: a) increasing intensity of soil use or history of use (shown by a stronger effect of fertilization on corn growth), or b) the presence of non-native vegetation (exotic plantations > pastures > native forests); and 3) soils from pine plantations will produce slower growth of corn and less reaction to N and P fertilization than soils from eucalyptus plantations because of their lower soil pH and cation concentrations.
Soils from four different land use types were sampled in four geographically different regions where the same four land use types were present, within and out of the Paute watershed in the southern Ecuadorian Andes (
All sites that were sampled had similar slopes and quality of soil drainage. For the native forests and E. globulus plantations, no age assessment was possible. The native forests were currently being used for selective fuel wood extraction, and the E. globulus plantations were growing in their second or third resprouting stages. The P. patula plantations ranged in age from 15 to 17 years. All were first rotations, and no fertilization had occurred. All pastures from which soil samples were taken were actively used by grazing cattle. The choice of the forested stands was made according to: 1) closed canopy and the presence of shrubs and trees taller than four meters with trunk diameters at breast height (DBH) ≥ 5 cm for the native forests, and 2) stands with trees of homogenous DBH (≥20 cm) for the plantations.
In each of the land use types, for each of the four regions, a 20 m × 20 m plot was established. Approximately 0.05 m3 of soil was collected from the first 20 cm of surface soil in five sub-sampling points within each of the plots (four corners and the centre of the 20 m × 20 m grid). Soils from each of the sub-sampling points were pooled into one sample for each plot and transported to a common garden in the Río Mazán preserve (Region 2,
A randomized block design was established so that each of the four regions corresponded to each of four blocks (
At the end of three months, each of the two plants of Zea mays L. per pot was carefully separated from the soil and washed. Each plant consisted of leaves, stem and roots as flowers or fruits were absent at this immature plant state. Each plant was taken to the laboratory in individual sealed plastic bags.
Plant tissues were oven dried at 50˚C for 72 hours. Each individual plant was weighed separately to measure biomass. For chemical analyses, the two plants of each pot were combined into one sample. Tissues were
ground to a fine powder in a cutting mill. Sub-samples of 0.2 g (for some smaller samples weight was recorded and the entire sample was used) were placed in digestion tubes with a solution composed of Li2SO4, selenium powder, H2O2 30% and H2SO4 18 M [
Soil samples were air dried in a dark room at 14˚C. After air drying, they were passed through a 2 mm sieve for all extractions except for
All plant tissue and soil variables were analyzed by a nested analysis of variance and a method for the determination of residual error [
For all of the soil chemical properties, the analysis of variance revealed a strong and significant effect of land use (p < 0.0001;
For the corn biomass and biomass nutrient content after conclusion of the bioassay experiment, the analysis of variance revealed a very strong treatment effect (p < 0.0001;
From the four land use types, across the four regions, statistically significant differences were found for the soil variables that are linked to the pH. Soil pH, Ca and Mg concentrations were statistically lowest in pine soils, whereas
Corn mortality occurred only in pine soils. Percent mortality of corn grown in soil from pine plantations and subjected to fertilizer treatment was: N = 75% > C = 50% > NP = 38% > P = 25%. One corn seedling survived in each pine soil pots given N-treatment in two blocks, and none survived in the other two blocks. In the P-treated pine soil pots, one seedling died in only one block out of four. This high mortality rate did not allow
Treatment | Land use | Region | Residual | |||||
---|---|---|---|---|---|---|---|---|
Variable | F | p-value | F | p-value | F | p-value | ||
Soil chemical properties | pH | --- | --- | 28.5 | 0.000 | 0.1 | 0.977 | 0.0 |
SOM | --- | --- | 3.2 | 0.016 | 4.0 | 0.033 | 129.0 | |
--- | --- | 14.6 | 0.000 | 0.5 | 0.673 | 1.2 | ||
--- | --- | 8.3 | 0.000 | 0.9 | 0.488 | 77.8 | ||
--- | --- | 20.9 | 0.000 | 0.4 | 0.740 | 3.3 | ||
ECEC | --- | --- | 18.6 | 0.000 | 1.3 | 0.320 | 7.3 | |
K | --- | --- | 87.7 | 0.000 | 0.8 | 0.539 | 0.0 | |
Ca | --- | --- | 53.7 | 0.000 | 0.8 | 0.511 | 2.4 | |
Mg | --- | --- | 18.9 | 0.000 | 0.6 | 0.615 | 0.1 | |
Al | --- | --- | 96.2 | 0.000 | 0.5 | 0.692 | 0.3 | |
Fe | --- | --- | 10529.0 | 0.000 | 0.4 | 0.731 | 0.0 | |
Mn | --- | --- | 34.7 | 0.000 | 0.2 | 0.883 | 0.0 | |
Corn bioassay | Total biomass | 24.8 | 0.000 | 3.4 | 0.001 | 0.5 | 0.716 | 0.1 |
Total N | 108.2 | 0.000 | 1.3 | 0.234 | 1.6 | 0.222 | 14.4 | |
Total P | 294.5 | 0.000 | 1.2 | 0.271 | 1.9 | 0.179 | 0.3 | |
Total K | 87.3 | <0.000 | 4.1 | 0.000 | 2.1 | 0.145 | 57.1 | |
Total Ca | 69.1 | 0.000 | 2.8 | 0.005 | 0.7 | 0.555 | 3.7 | |
Total Mg | 91.7 | 0.000 | 2.0 | 0.040 | 2.7 | 0.088 | 0.6 |
SOM = soil organic matter. ECEC = effective cation exchange capacity. Degrees of freedom for Treatment was 48; for Land use, 12; for Region, 3. Values in bold are statistically significant.
averages to be made of two plants to assess biomass and nutrient contents per plant as it did in all other experimental groups. Instead, individual values for corn biomass were summed when two plants survived per pot. When only one plant survived, this single biomass value was used. Therefore, data for biomasses and nutrient contents in
Total corn biomass was statistically different among land use types only with the NP-treatment. Biomasses of corn were always significantly lower when grown in pine soils than if the corn were grown in native forest soils, with NP-treatment in both (p ≤ 0.05;
Corn total N, total Ca and Mg were consistently and significantly higher in native forest soils than in pine soils with NP-treatment (p ≤ 0.05;
Native forest | Pasture | Eucalyptus globulus | Pinus patula | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | 5.2 | (9) | ab | 5.6 | (3) | a | 5.5 | (6) | a | 4.9 | (3) | b |
% SOM | 39.9 | (68) | a | 30.1 | (47) | a | 29.7 | (66) | a | 36.6 | (18) | a |
3.9 | (86) | a | 5.0 | (59) | a | 3.0 | (50) | a | 6.6 | (47) | a | |
mg/kg−1 | ||||||||||||
42.3 | (74) | ab | 19.8 | (33) | b | 25.6 | (42) | ab | 46.1 | (16) | a | |
mg∙kg−1 | ||||||||||||
8.9 | (58) | a | 6.7 | (128) | a | 3.3 | (2) | a | 6.3 | (51) | a | |
mg/kg−1 | ||||||||||||
ECEC | 19.1 | (78) | a | 8.6 | (29) | a | 7.9 | (17) | a | 7.1 | (16) | a |
cmol/kg−1 | ||||||||||||
K | 0.8 | (118) | a | 0.3 | (17) | a | 0.5 | (65) | a | 0.2 | (20) | a |
cmol/kg−1 | ||||||||||||
Ca | 12.1 | (124) | a | 6.0 | (43) | ab | 4.2 | (47) | ab | 0.9 | (55) | b |
cmol/kg−1 | ||||||||||||
Mg | 1.6 | (86) | a | 0.9 | (31) | ab | 1.0 | (41) | a | 0.2 | (26) | b |
cmol/kg−1 | ||||||||||||
Al | 4.0 | (151) | ab | 1.0 | (53) | b | 1.9 | (61) | ab | 5.3 | (24) | a |
cmol/kg−1 | ||||||||||||
Fe | 0.063 | (180) | a | 0.002 | (89) | b | 0.004 | (122) | b | 0.054 | (73) | a |
cmol/kg−1 | ||||||||||||
Mn | 0.1 | (73) | a | 0.1 | (42) | a | 0.1 | (122) | a | 0.1 | (140) | a |
cmol/kg−1 |
SOM = Soil Organic Matter. ECEC = Effective Cation Exchange Capacity. Numbers in parentheses are coefficients of variation (in %). Different letters represent significant differences at p ≤ 0.05 between land use types.
lower in pine soils with N-treatment (p ≤ 0.05;
Within land use types, significant treatment effects were absent for corn N, P and K in pine soils and corn K in all land use type soils. In soils from native forest, pasture and eucalyptus land use types, corn N significantly increased only with the NP-treatment, whereas the N-treatment produced a corn N content very similar to that of the P- or control treatments (p ≤ 0.01;
Corn P, K, Ca and Mg contents increased according to the incremental increase in corn biomass (
Comparisons of nutrient concentrations in corn leaves analyzed in this experiment with critical nutrient concentration standards revealed nutrient deficiencies (
Native forest | Pasture | Eucalyptus globulus | Pinus patula | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Total | C | 1.61 | (57) | a | b | 1.57 | (17) | a | b | 1.87 | (24) | a | b | n = 2 | 0.82 | (8) | a | a |
Biomass | N | 1.77 | (73) | a | b | 1.88 | (25) | a | b | 1.69 | (30) | a | b | n = 2 | 0.41 | (56) | a | a |
g/pot−1 | P | 3.37 | (73) | a | a | 3.43 | (46) | a | a | 3.17 | (43) | a | ab | n = 3 | 0.90 | (53) | a | a |
NP | 5.88 | (65) | a | a | 3.54 | (31) | ab | a | 4.06 | (45) | ab | a | n = 3 | 0.51 | (62) | b | a | |
C | 28.65 | (60) | a | b | 27.82 | (24) | a | b | 29.73 | (36) | a | b | n = 2 | 21.44 | (17) | a | a | |
Total N | N | 52.70 | (51) | ab | ab | 60.43 | (18) | a | b | 57.51 | (14) | a | b | n = 2 | 15.66 | (53) | b | a |
mg/pot−1 | P | 45.55 | (67) | a | b | 43.61 | (59) | a | b | 47.48 | (49) | a | b | n = 3 | 21.93 | (57) | a | a |
NP | 165.79 | (62) | a | a | 111.67 | (24) | ab | a | 129.75 | (53) | ab | a | n = 3 | 21.29 | (63) | b | a | |
C | 1.91 | (35) | a | b | 2.21 | (34) | a | b | 2.07 | (16) | a | b | n = 2 | 1.78 | (16) | a | a | |
Total P | N | 2.39 | (47) | a | ab | 2.58 | (44) | a | b | 1.96 | (25) | a | b | n = 2 | 1.04 | (27) | a | a |
mg/pot−1 | P | 15.23 | (64) | a | a | 9.46 | (52) | a | a | 11.24 | (79) | a | a | n = 3 | 4.43 | (47) | a | a |
NP | 17.01 | (70) | a | a | 8.44 | (38) | a | a | 10.57 | (71) | a | a | n = 3 | 2.27 | (54) | a | a | |
C | 55.68 | (85) | a | a | 60.85 | (39) | a | a | 47.03 | (32) | a | a | n = 2 | 8.35 | (8) | a | a | |
Total K | N | 59.94 | (95) | a | a | 47.45 | (41) | a | a | 46.51 | (59) | a | a | n = 2 | 3.47 | (69) | a | a |
mg/pot−1 | P | 126.10 | (105) | a | a | 94.20 | (64) | a | a | 101.79 | (80) | a | a | n = 3 | 7.66 | (60) | a | a |
NP | 139.05 | (88) | a | a | 96.88 | (60) | a | a | 125.13 | (95) | a | a | n = 3 | 4.36 | (58) | a | a | |
C | 10.51 | (74) | a | b | 9.95 | (30) | a | b | 9.22 | (56) | a | b | n = 2 | 1.33 | (18) | a | ab | |
Total Ca | N | 10.20 | (75) | a | b | 10.85 | (14) | a | b | 9.04 | (41) | a | b | n = 2 | 0.48 | (86) | a | b |
mg/pot−1 | P | 27.51 | (71) | a | a | 23.10 | (39) | a | a | 20.85 | (38) | a | a | n = 3 | 4.50 | (75) | a | a |
NP | 38.09 | (66) | a | a | 27.73 | (37) | ab | a | 22.25 | (57) | ab | a | n = 3 | 1.23 | (68) | b | ab | |
C | 5.41 | (80) | a | a | 4.46 | (37) | a | b | 5.47 | (43) | a | a | n = 2 | 1.20 | (17) | a | ab | |
Total Mg | N | 5.73 | (87) | a | a | 5.47 | (21) | a | b | 5.46 | (29) | a | a | n = 2 | 0.47 | (33) | a | b |
mg/pot−1 | P | 10.66 | (84) | a | a | 9.50 | (45) | a | ab | 13.96 | (72) | a | a | n = 3 | 2.40 | (35) | a | a |
NP | 17.29 | (65) | a | a | 13.33 | (31) | ab | a | 13.12 | (61) | ab | a | n = 3 | 0.85 | (42) | b | ab |
Total = Stem + Leaf + Root. Biomass data are the sum of two plants per pot, or one plant when mortality occurred. C = Control. N = Ammonium-nitrate fertilizer. P = Triple super phosphate fertilizer. NP = Combined N-P fertilizers. Numbers in parentheses are coefficients of variation (in %). Different bold letters represent significant differences between land use types (horizontally) at p ≤ 0.05. Different italic letters represent significant differences between treatments (vertically) at p < 0.01.
in the control and N-treatments. Critical K and Ca concentrations were found in corn grown in pine soils only, irrespective of treatment (except for Ca in P-treatment). Corn foliar Mn concentration was above maximum normal level in pine soils for control and P-treatments.
The high mortality rate and low response to fertilization in Pinus patula plantation soils indicate a low potential for agriculture on these soils. In contrast, there was a 100% survival rate of corn in all other soils and treatment groups. Generally, corn growth responded to P and NP-fertilizers in soils, excluding those from the pine plantations (
N | P | K | Ca | Mg | Mn | ||
---|---|---|---|---|---|---|---|
% | % | % | % | % | mg/kg−1 | ||
Land use types | Treatments | ||||||
Nf | C | 2.2 | 0.22 | 2.9 | 0.72 | 0.5 | 83 |
Pa | C | 2.2 | 0.17 | 3.8 | 0.85 | 0.4 | 74 |
Eg | C | 1.8 | 0.13 | 2.6 | 0.80 | 0.5 | 60 |
Pp | C | 2.9 | 0.31 | 1.0 | 0.34 | 0.4 | 201 |
Nf | N | 3.8 | 0.32 | 2.6 | 0.61 | 0.5 | 83 |
Pa | N | 3.4 | 0.14 | 2.5 | 0.78 | 0.4 | 79 |
Eg | N | 3.7 | 0.14 | 2.7 | 0.82 | 0.6 | 86 |
Pp | N | 3.9 | 0.36 | 0.8 | 0.19 | 0.3 | 36 |
Nf | P | 2.0 | 0.76 | 2.8 | 0.97 | 0.4 | 118 |
Pa | P | 1.6 | 0.29 | 2.9 | 0.92 | 0.4 | 78 |
Eg | P | 1.8 | 0.33 | 2.9 | 0.88 | 0.5 | 77 |
Pp | P | 3.0 | 0.82 | 1.1 | 0.84 | 0.6 | 173 |
Nf | NP | 3.7 | 0.49 | 1.8 | 0.69 | 0.4 | 95 |
Pa | NP | 3.4 | 0.24 | 2.4 | 0.88 | 0.5 | 81 |
Eg | NP | 3.4 | 0.27 | 2.4 | 0.71 | 0.4 | 61 |
Pp | NP | 4.5 | 0.72 | 0.8 | 0.39 | 0.4 | 138 |
Critical concentrationa | 2.5 | 0.15 | 1.2 | 0.47b | 0.1 | 15 | |
Max. normal concentrationa | 3.5 | 0.50 | 2.5 | 1.50 | 0.6 | 150 |
aCritical concentration and maximum normal concentration for corn taken from OMAF [
sustain crop production. For example, experiments with potatoes grown in Ecuadorian Andisols required P applications every cycle to obtain adequate yields [
The results presented here do not show that N and
The contents of P, Ca and Mg, but not K, statistically increased with P additions as opposed to N additions. One hypothesis is that
With regard to soil properties of the land use types reported here, the differences in corn biomass production and nutrient content are better compared between native forest, pasture and eucalyptus soils, exclusive of pine soils, which always produced lower biomass and nutrient contents, and can thus be considered to have lower productivity and fertility than all the other soils. Soils from native forests, pastures and eucalyptus plantations produced similar corn biomass and had similar nutrient contents, although some cation deficiencies are likely in pasture and eucalyptus soils. Corn accumulated statistically more N and P in the N-treatment grown in pasture soils than in pine soils, although its biomass was comparable. These results suggest additional deficiencies in the availability of other nutrients, such as K, Ca and Mg, because of a N and
The results presented in this paper show that nutrient deficits impeded corn growth. Whether or not specific P and N deficiencies are present among the different land use types studied, soil deficiencies are indeed present at the land use level for K, Ca, and Mg. In the case of the soils associated with pine plantations, reduced K, Ca and Mg seems to be aggravated by a lower pH. We can conclude that fertilizer applications in the studied soils should include K, Ca and Mg in order to increase pH and to enhance SOM mineralization. Long term studies of soil phosphorus application [
The bioassay response to N and P fertilization indicated a low potential for agricultural production without nutrient amendments on all land use types. This potential was lowest for pine plantations and was not restored with N and P application. It is difficult to tease apart the role of inherent low soil nutrient availability from that of land uses. Nevertheless, it is likely that all land use types have been subjected to past impacts that have lowered soil fertility. Pine plantations represent an end point that may combine originally poor site and soil conditions with non-sustainable former land uses. Because agriculture, grazing pasture, afforestation of degraded lands and exotic forestry production continue to rise in the Andes of Ecuador, these results have far-reaching implications for sustainable land use management by large-scale agri-businesses, medium and small-sized farms, as well as government agencies interested in crop productivity. If better land use management is not practiced, soils will continue to decline in fertility, causing a continued decrease in agricultural productivity.
We gratefully acknowledge the Universidad del Azuay and ETAPA for laboratory facilities, equipment and logistics. We also wish to acknowledge the Biodôme de Montréal and Macdonald College (McGill University) for providing facilities for soil and plant tissue analyses. Thanks to Dr. Kathleen Farley, Dr. Wayne Hanson and an anonymous reviewer whose comments have helped to improve this paper. Thanks also to Jheimy Pacheco for drafting the map of the study area.
GustavoChacón,DanielGagnon,DavidParé, (2015) Soil Agricultural Potential in Four Common Andean Land Use Types in the Highlands of Southern Ecuador as Revealed by a Corn Bioassay. Agricultural Sciences,06,1129-1140. doi: 10.4236/as.2015.610108