International Journal of Agronomy

Volume 2012 (2012), Article ID 842582, 7 pages

doi:10.1155/2012/842582

Research Article

Influence of Corn (Zea mays L.) Cultivar Development on Grain Nutrient Concentration

Carla Fernanda Ferreira,¹ Antônio Carlos Vargas Motta,¹ Stephen A. Prior,² Carlos Bruno Reissman,¹ Nicolas Z. dos Santos,³ and Juarez Gabardo⁴

¹Departamento de Solos e Engenharia Agrícola, Setor de Ciências Agrárias, Universidade Federal do Paraná, 1540 Rua dos Funcionários, 80035-050 Curitiba, PR, Brazil

²ARS National Soil Dynamics Laboratory, USDA 411 South Donahue Drive, Auburn, AL 36832, USA

³Monsanto do Brasil Ltda, 12901 Nações Unidas Avenue, 7th Floor, 04578-000 São Paulo, SP, Brazil

⁴Departamento de Genética, Setor de Ciências Biológicas, Centro Politécnico, Universidade Federal do Paraná, P.O. Box 19071, 81531-990 Curitiba, PR, Brazil

Received 5 June 2012; Accepted 31 July 2012

Academic Editor: David Clay

Copyright © 2012 Carla Fernanda Ferreira et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

While corn productivity has been increased by the adoption of high-yield hybrids, there are concerns that increased grain potential may be associated with diminished grain nutrient concentration. Ten corn (Zea mays L.) cultivars representing five technological levels (landrace variety, commercial variety, and double, triple, and single cross-hybrids) were cropped on a Rhodic Ferralsol Eutric soil with high fertility in 2006 (dry year) and 2007 (normal year) in Rolândia County, Brazil. At maturity, grain was evaluated for concentrations of P, K, Ca, Mg, Fe, Mn, Zn, and Cu. In general, differences among cultivars were noted for all nutrients in both years. Concentrations of P, K, Fe, and Mn were lower in the dry year, while Ca, Mg, Cu, and Zn were higher. Soil water availability appeared to exert more influence on grain nutrient concentration than did cultivar development; nutrient removal due to grain harvest was also greatly influenced by rainfall patterns and their impact on corn productivity. Even though genetic differences were noted, which may be useful to breeding programs, long-term testing in subtropical environments will be required to clarify the interaction between genetics and climate events on grain nutrient quality and exportation.

1. Introduction

Grain nutrient concentration plays a key role in seed quality as it relates to seed reserves required to germination and nutritional feed value [1]. Grain nutrient concentration can also provide information related to nutrient exportation (i.e., removal from the field) and the necessity for soil nutrient replenishment through fertilization [2, 3]. Despite these important issues, tissue analysis has traditionally focused on leaf, rather than grain, nutrient levels to diagnose whole-plant nutritional status.

Recently, it has been suggested that genetic selection in wheat (Triticum aestivum L.) has contributed to reduced levels of some micronutrients in grain [1]. Concerns regarding diminished grain quality have spread to other crops such as corn (Zea mays L.). In a study evaluating six corn hybrids released between 1959 and 1988, lower values of micronutrients were found in the newer hybrids [4]. A study of four tropical corn cultivars released between 1970 and 1990 noted some differences among cultivars; however, it was not clear whether new cultivars designed for higher yields would result in decreased grain nutrient concentration [5]. Similar variation in grain nutrient concentrations among corn hybrids have also been reported in different field studies [3].

Other factors, such as soil type and climate, may also influence crop nutrient status. For example, soil type influenced selenium grain concentration among 14 wheat cultivars, while smaller variation was seen for Fe, Zn, and Cu [1]. Long-term Cu and Zn application increased soil availability as reflected by corn leaf concentrations; however, grain Cu was unaffected and increases in grain Zn were lower than observed in leaves [6]. Furthermore, water shortage showed little effect on grain nutrient concentrations of P, K, Mg, Ca, Zn, Mn, and Cu [5]. Nonetheless, decreased corn grain P concentration has been observed when water was not limiting [2]. These differences may help explain the variation in grain nutrients among years and the difficulty of correlating grain nutrient concentration with corn yields [3, 7].

Hitherto, few experiments have studied grain nutrient concentration of corn cropped under tropical or subtropical conditions or the impact of genetic selection (varying from old cultivars to new hybrids) on variation in grain nutrient concentration. The objective of this study was to evaluate ten corn cultivars representing five degrees of breeding development (landrace variety, commercial variety, double, triple and single cross hybrids) to determine whether selection altered grain nutrient concentration in a Brazilian cropping system.

2. Materials and Methods

The study was conducted at the Monsanto Experiment Station at Rolandia City, Paraná State, Brazil, located at 23°16′ S latitude, 51°28′ W longitude, and 645 m altitude. The local climate is characterized as Cfa, Subtropical Humid with uniform precipitation distribution [8]. Temperature (°C) and rainfall (mm) were measured daily (Figure 1). The soil was formed from basalt and classified as a Clay Loam Rhodic Ferralsol Eutric [9]. Seeds were sown in November 2005 and October 2006. Before planting, soil samples were collected (10 cm) for chemical analyses. After drying, samples were analyzed for pH, Ca, Mg, Al, K, P, Mn, Fe, Cu, Zn, and organic matter following procedures of Embrapa [10] (Table 1).

Table 1: Study site soil chemical characteristics (0–10 cm layer) at Rolandia County, Parana State, Brazil.

pH
O.M.
P
Ca
Mg
K
H + Al
Mn
Fe
Cu
Zn

CaCl₂
g kg⁻¹
mg kg⁻¹
g/kg
cmolc kg⁻¹
mg kg⁻¹

Year 1
6.0
28.4
24.5
0.21
0.04
0.04
3.2
268
86
33
13

Year 2
5.9
29.1
40.3
0.13
0.03
0.03
3.1
308
67
24
12

(a)

(b)

Figure 1: Daily rainfall and average air temperature after planting in 2005 and harvesting in 2006 (a) and planting in 2006 and harvesting in 2007 (b). Dark arrows indicate tasseling stage dates for the ten corn cultivars.

The experiment had ten treatments, corresponding to ten cultivars represented by five pairs of corn technological levels. The experimental design was a complete randomized block with five replications. The selected cultivars ranged from highly developed hybrids to farmer selection (landrace), as represented by (a) single cross-hybrids (AG9010 and DKB950) (b), triple cross hybrids (DKB566 and AG5020); (c) double cross hybrids (AG2040 and DKB979), (d) commercial varieties (BRS4157 and BR106), and (e) landrace cultivars (Palotina and GIO45). Detailed information concerning these cultivars has been previously reported [11].

For both years, soil was moldboard plow and disk harrow twice before planting. Plots were 4 × 10 m with 6 rows of which the two central were used for data collection. Plots were hand-planted at two seeds per burrow and thinned to achieve desired plant population at the V₂ stage. Row width was 0.8 m with plant spacing within rows of 0.2 m for an established plant population of 62,500 plants ha⁻¹.

During sowing, N, P₂O₅, and K₂O were applied at 28, 70, and 70 kg ha⁻¹, respectively. The used fertilizers were MAP, ammonium sulfate, potassium chloride, and superphosphate at proportion of 34.4, 11.0, 33.4, and 21.2%, respectively. Additionally, a side dress application of 135 kg N ha⁻¹ was made using urea at the V₄ stage. Seed treatment, weed control, and other management practices were similar for both years.

The harvests in 2006 and 2007 were conducted approximately 150 days after planting. Fifteen plants per plot were sampled for grain nutrient evaluation. Grain was separated and subjected to dry digestion in porcelain crucibles. Phosphorus was determined colorimetrically using an UV/VIS Spectrophotometer. Calcium, Mg, Fe, Mn, Zn, and Cu were determined by Atomic Absorption Spectrophotometry while K was determined by Flame Spectrophotometry [12]. Nutrient exportation (removed from the field) was calculated by multiplying grain dry weight by nutrient concentration. Data were analyzed by analysis of variance (ANOVA) and Duncan’s test () was performed to compare means. The yield, nutrients concentration and exportation data were submitted to correlation and regression analysis, using the Statistical Analysis System software.

3. Results and Discussion

There were differences among grain macronutrient concentrations for the tested cultivars in both years, excepting for P in the first year (Table 2) when plants experienced less rainfall (Figure 1), particularly during tasseling [11]. Observed grain P concentration fell within the range reported by others [3, 7, 13–15], but were above the 2.3 g kg⁻¹ mean reported by Altmann and Pavinato [16] for corn produced in the Cerrado Region of Brazil, where soil normally has low available P. Grain P concentration was higher in the second year (more rainfall) compared to the first year across all cultivars. In the second year, single hybrid DKB950 grain P was higher than all other cultivars. The fact that the remaining nine cultivars showed no differences suggests that grain P had undergone small variation due to crop technological level. Similarly, others have reported little variation among corn cultivars [4, 5]. However, Eghball et al. [2] reported greater grain P concentration among 12 hybrids grown under water shortage, suggesting the possibility of selecting hybrids with high soil P extraction capacity.

Table 2: Grain macronutrient concentration in ten corn cultivars representing five different technological levels in 2006 and 2007, at Rolandia County, Parana State, Brazil.

P
K
Ca
Mg
P
K
Ca
Mg

  Treatment

2006
2007

g kg⁻¹

Single
AG9010
3.0a*
3.7a
0.30b
1.37cd
4.1b
7.7b
0.12ab
0.92ab

Hybrids
DKB950
2.9a
4.0a
0.32b
1.32d
5.1a
10.3a
0.13ab
1.12a

Triple
DKB566
2.8a
3.6a
0.31b
1.59abc
3.8b
7.4b
0.10b
0.90ab

Hybrids
AG5020
3.0a
3.4b
0.38b
1.45bcd
3.5b
6.6b
0.15ab
0.94ab

Double
AG2040
3.4a
3.7a
0.49ab
1.71a
4.0b
7.7b
0.14ab
1.00ab

Hybrids
DKB979
2.9a
3.5ab
0.66a
1.39cd
4.1b
7.3b
0.13ab
0.77b

Commercial
BRS4157
3.4a
3.9a
0.46ab
1.64ab
4.0b
7.5b
0.13ab
0.91ab

Varieties
BR106
3.5a
3.9a
0.39b
1.56abcd
4.1b
8.1b
0.18a
1.09ab

Landrace
GI045
3.3a
3.8ab
0.29b
1.55abcd
3.4b
6.8b
0.10b
0.89ab

Cultivars
Palotina
3.1a
3.9ab
0.36b
1.32d
3.8b
7.7b
0.13ab
0.84ab

Coefficient of variation
14
11
46
11
18
18
33
24

* Averages followed by the same letter in a column did not differ according to Duncan’s multiple range test ().

Similarly to P, K was higher in the second, wetter year. The range in grain K concentration in the first year (Table 2) was comparable to previously reported values [4, 5, 7]; however, values in the second year were much higher than other studies [3, 13–15]. Both P and K are dependent on diffusion as an uptake mechanism and, therefore, are influenced by soil water status. It is noteworthy that our soil P and K levels were high. Once again and like P, the single hybrid DKB950 had the highest K concentration in both years (Table 2) and was significantly higher than other cultivars in the second year. Grain K concentration varied somewhat among cultivars, independently of technological level, supporting the observations made by Vyn and Tollenaar [4] and Feil et al. [5].

While larger concentrations of P and K were seen in 2007, greater concentrations of Ca and Mg were observed in 2006 which received less rainfall; however, values in both years fell within reported ranges [3–5, 7]. Differences among cultivars were observed in both years for Ca and Mg; however, patterns among cultivars greatly differed between years (Table 2). The variation in Ca and Mg concentrations cannot be explained by soil availability, since their soil levels were high in both years (Table 1). Arnon [17] indicated that a common antagonistic nutrient interaction occurs between K and Ca and/or Mg in leaves, which might help explain the inverse relationship observed between years. Nevertheless, the same author indicated that increased water supply would favor absorption of Ca and Mg over K. In our study, this behavior was observed for leaves, while stalks (data not shown) behaved similarly to grain, suggesting that this antagonistic relationship can vary among plant components [18]. Overall, soil water availability exerted a greater influence on grain macronutrient concentration than did genetics.

There were no differences in grain micronutrients in year 2 (Table 3), which experienced normal rainfall. Grain Cu and Zn tended to be higher, while Mn and Fe tended to be lower in the first year (Table 3). Concentrations of all micronutrients were close to those reported by others [3–5, 7, 13, 16]. Like Cu, the experimental area had high levels of Fe and Mn which were derived from basalt parent material (Table 1). However, unlike Cu, both Fe and Mn are normally affected by oxidation-reduction reactions which can be influenced by water soil water status. Although the Rhodic Ferralsol has good permeability, it is plausible to assume that the temporary water logging could have favored reduction reactions thereby increasing plant available Fe and Mn in the second year. Lack of Zn is a wide-spread nutritional problem under tropical conditions, thus supplemental applications are common practice. Grain Zn concentrations observed in our study suggest that soil Zn was adequate (Table 3). The double hybrid AG2040 had the highest concentration of Cu, Mn, and Zn, while the triple hybrid AG5020 and both landraces had the lowest micronutrient concentrations. Despite differences in micronutrient grain concentrations among cultivars, it remains difficult to determine the association between grain quality and cultivar development. This differs from Garvin et al. [1], who reported an inverse relationship between genetic improvement and micronutrients in wheat grain. Our results showed larger difference within the same technological level than among the five groups studied. Similar results were observed by Vyn and Tollenaar [4]. In the same way as macronutrients, soil water availability in our study appeared to exert more influence on grain micronutrient concentration than did cultivar development; however, some genetic differences exist, which may be useful in breeding programs.

Table 3: Grain micronutrient concentrations for 10 corn cultivars representing five different technological levels in 2006 and 2007, at Rolandia County, Parana State, Brazil.

Cu
Fe
Mn
Zn
Cu
Fe
Mn
Zn

Treatment
2006
2007

g kg⁻¹

Single
AG9010
7.3ab
21ab
6bc
36ab
1.1a
38a
10a
24a

Hybrids
DKB950
5.7ab
19ab
5c
30bc
0.8a
39a
11a
26a

Triple
DKB566
4.7b
18ab
7bc
32abc
0.7a
33a
12a
24a

Hybrids
AG5020
4.8ab
17b
5bc
31bc
1.0a
37a
11a
23a

Double
AG2040
9.6a
29ab
11a
39a
1.1a
37a
13a
27a

Hybrids
DKB979
5.2ab
20ab
7bc
31bc
1.1a
33a
10a
24a

Commercial
BRS4157
5.6ab
34ª
8ab
32abc
0.9a
37a
13a
31a

Varieties
BR106
2.8b
18ab
8ab
27c
0.7a
38a
11a
24a

Landraces
GI045
3.6b
18b
7abc
28c
1.3a
40a
11a
22a

Cultivars
Palotina
6.4ab
17b
6bc
29bc
0.9a
41a
12a
22a

Coefficient of variation
59
54
33
17
87
18
29
27

* Averages followed by the same letter in a column did not differ according to Duncan’s multiple range test ().

Nutrient exportation or removal from the field by grain harvest was different among cultivars in both years, with the exception of Cu in the second year (Tables 4 and 5). The amount of nutrient removal was controlled by corn productivity, which was greatly influenced by rainfall patterns [11, 18]. The hybrids and commercial varieties showed a 4-fold decrease in grain production due to lower rainfall in the first year; however, the landraces were much more affected (10-fold decrease) by rainfall patterns. In general, the single, double, and triple hybrids showed higher nutrient exportation, for both macro- and micronutrients than commercial varieties and landrace cultivars. Again, this was due to greater grain biomass production for the hybrids [11]. Similar results for other corn cultivars were noted by Feil et al. [5]. Although few differences were observed among hybrids, it was interesting to note that DKB hybrids tended to have the highest grain biomass (and thus nutrient removal) in the dry year, while AG hybrids were highest in nondried year.

Table 4: Macronutrients exportation of maize cultivars in 2006 and 2007, at Rolandia County, Parana State, Brazil.

P
K
Ca
Mg
P
K
Ca
Mg

Treatment
2006
2007

kg ha⁻¹

Single
AG9010
7.0ab
8.6abc
0.74bc
3.2bc
38.0ab
70.8b
1.09abcd
8.6ab

Hybrids
DKB950
7.0ab
9.5abc
0.76bc
3.2bc
45.8a
91.8a
1.16abc
10.1a

Triple
DKB566
9.1a
11.6a
0.98b
5.1a
32.8b
63.0b
0.85bcd
7.5abc

Hybrids
AG5020
8.5ab
9.5abc
1.06b
4.1ab
35.2b
66.9b
1.55a
9.6ab

Double
AG2040
7.4ab
8.2abc
1.09b
3.7bc
37.5ab
72.1b
1.26ab
9.4ab

Hybrids
DKB979
8.7a
10.5ab
1.83a
4.2ab
38.0ab
68.0b
1.28ab
7.2bc

Commercial
BRS4157
6.9ab
7.9bc
0.92b
3.3bc
22.6cd
42.7cd
0.75bcd
5.1cd

Varieties
BR106
5.7b
6.5c
0.60bcd
2.6c
29.7bc
57.8bc
1.28ab
7.8abc

Landrace
GI045
2.3c
2.7d
0.21cd
1.1d
16.6d
32.9d
0.51d
4.3d

Cultivars
Palotina
0.7c
0.8d
0.09d
0.3d
17.8d
35.5d
0.64cd
3.9d

Coefficient of variation
18
11
10
11
11
20
22
44

* Averages followed by the same letter in a column did not differ according to Duncan’s multiple range test ().

Table 5: Micronutrients exportation of maize cultivars 2006 and 2007, at Rolandia County, Parana State, Brazil.

Cu
Fe
Mn
Zn
Cu
Fe
Mn
Zn

Treatment
2006
2007

g ha⁻¹

Single
AG9010
17.9a
51ab
16.1abc
90a
10.6a
348ab
88.5bc
222abc

Hybrids
DKB950
13.8abc
44ab
10.9bcd
73ab
7.3a
354ab
98.2abc
233ab

Triple
DKB566
14.6abc
60ab
23.0a
101a
5.7a
278bc
98.5abc
205abc

Hybrids
AG5020
13.1abc
48ab
15.4abc
87a
10.4a
381a
110.9ab
235ab

Double
AG2040
21.3a
66a
23.4a
86a
10.0a
352ab
123.0a
241a

Hybrids
DKB979
15.3ab
61ab
20.5ab
93a
9.9a
304ab
96.9abc
227abc

Commercial
BRS4157
11.1abcd
63ab
16.5abc
65ab
5.3a
211cd
70.8cde
175bc

Varieties
BR106
4.6bcd
29bc
13.4abc
44bc
4.8a
277bc
82.5bcd
169c

Landraces
GI045
2.7cd
12c
5.3cd
19cd
6.0a
189d
54.9de
109d

Cultivars
Palotina
1.2d
3c
1.4d
6d
4.2a
181d
52.6e
104d

Coefficient of variation
73
53
55
39
92
22
25
23

* Averages followed by the same letter in a column did not differ according to duncan’s multiple range test ().

The results from yield [11] and nutrient concentration correlation indicated that there was an inverse relationship between yield and N concentration for 2006/2007 growing season (Table 6). This fact could be indication of dilution as result of yield increment and suggest a decrease on nutritional values of grain.

Table 6: Correlation between nutrients (macro and micro) concentration and yield for ten corn cultivars representing five different technological levels, harvesting in 2006 and 2007, at Rolandia County, Paraná State, Brazil.

2005/06
Yield
C
N
P
K
Ca
Mg
Cu
Fe
Mn

C
−0.18

N
−0.28
0.10

P
−0.14
0.07
0.18

K
−0.26
0.05
0.02
0.76**

Ca
0.12
0.11
0.28
0.13
−0.03

Mg
0.08
0.04
0.11
0.85**
0.55**
0.21

Cu
0.12
0.23
0.13
−0.05
−0.18
0.27
0.01

Fe
0.11
0.14
0.12
0.21
0.06
0.53**
0.32
0.38

Mn
0.15
0.10
0.28
0.27
0.02
0.37
0.43*
0.54**
0.55**

Zn
0.37
0.04
0.02
0.25
0.09
0.27
0.32
0.66**
0.44*
0.68**

2007
Yield
C
N
P
K
Ca
Mg
Cu
Fe
Mn

C
0.04

N
−0.69**
0.29

P
0.19
0.32
0.08

K
0.09
0.30
0.10
0.87**

Ca
0.05
−0.05
0.19
0.13
0.17

Mg
0.06
0.04
−0.01
0.58**
0.51**
0.28

Cu
0.04
−0.08
−0.09
−0.03
−0.07
−0.11
0.33

Fe
−0.12
0.11
−0.01
0.30
0.21
0.52**
0.35
0.29

Mn
−0.15
0.21
0.15
0.16
0.08
−0.30
0.30
0.09
0.58**

Zn
0.03
0.02
0.24
0.21
0.26
0.51**
0.14
−0.01
−0.39
−0.15

; .

There was a consistent relationship between concentrations of P × K and P × Mg for both year’s crops (Table 6). Our results confirm earlier observation that there is a synergic interaction between P, and Mg on plant absorption [17].

The amount of nutrients exported by grain was well associated with yield, especially for C [11], N [11], P and K (Table 7). The results indicated an exportation and necessity of soil reposition of 13.4, 4.3, and 7.9 in 2005/2006 and 16.3, 3.1, and 2.6 in 2006/2007 for N, P, and K in each 1000 kg grain (Figure 2), respectively.

Table 7: Correlation between yield and amount of nutrients for the grain in ten corn cultivars representing five different technological levels in harvesting in 2006 and 2007, at Rolandia County, Paraná State, Brazil.

C
N
P
K
Ca
Mg
Cu
Fe
Mn
Zn

2006
0.87**
0.88**
0.86**
0.85**
0.62**
0.84**
0.61**
0.69**
0.72**
0.85**

2007
0.99**
0.98**
0.79**
0.75**
0.43*
0.68**
0.34*
0.63**
0.68**
0.70**

; .

(a)

(b)

(c)

(d)

(e)

(f)

Figure 2: Regression between yield (kg ha⁻¹) and exportation of N, P, and K (kg ha⁻¹) in the grain in ten corn cultivars representing five different technological levels harvesting in 2006 and 2007, at Rolandia County, Paraná State, Brazil. ***.

4. Conclusions

Evaluation of various corn cultivars commonly used in Brazilian cropping systems did not indicate an obvious association between grain quality and cultivar development. In this study, soil water availability appeared to exert more influence on grain nutrient concentration than did cultivar development. Similarly, nutrient removal due to grain harvest was also greatly influenced by the impact of rainfall patterns on corn productivity. Genetic differences were noted which might be useful for breeding programs. However, long-term studies covering multiple years and, accordingly, varying rainfall patterns would be helpful for elucidating the influence of genetics (and their interaction with weather) on grain nutrient quality and exportation.

Acknowledgments

The authors acknowledge Barry G. Dorman and Jerry W. Carrington (USDA-ARS National Soil Dynamics Laboratory) and Julierme Zimmer Barbosa (UFPR—Soil Science Graduate student) for their assistance.

References

D. F. Garvin, R. M. Welch, and J. W. Finley, “Historical shifts in the seed mineral micronutrient concentration of US hard red winter wheat germplasm,” Journal of the Science of Food and Agriculture, vol. 86, no. 13, pp. 2213–2220, 2006.

B. Eghball, J. F. Shanahan, G. E. Varvel, and J. E. Gilley, “Reduction of high soil test phosphorus by corn and soybean varieties,” Agronomy Journal, vol. 95, no. 5, pp. 1233–1239, 2003.

J. R. Heckman, J. T. Sims, D. B. Beegle et al., “Nutrient removal by corn grain harvest,” Agronomy Journal, vol. 95, no. 3, pp. 587–591, 2003.

T. J. Vyn and M. Tollenaar, “Changes in chemical and physical quality parameters of maize grain during three decades of yield improvement,” Field Crops Research, vol. 59, no. 2, pp. 135–140, 1998.

B. Feil, S. B. Moser, S. Jampatong, and P. Stamp, “Mineral composition of the grains of tropical maize varieties as affected by pre-anthesis drought and rate of nitrogen fertilization,” Crop Science, vol. 45, no. 2, pp. 516–523, 2005.

G. G. Payne, D. C. Martens, C. Winarko, and N. F. Perera, “Form and availability of copper and zinc following long-term copper sulfate and zinc sulfate applications,” Journal of Environmental Quality, vol. 17, no. 4, pp. 707–711, 1988.

M. F. Hossain, “Nutrients removed in harvested portion of crop by continuous corn receiving organic and inorganic fertilizers,” Journal of Plant Sciences, vol. 1, pp. 264–272, 2006.

W. Köppen, Climatologia com um estudio de los climas de la tierra, Fondo de Cultura Economica, 1948.

FAO, “Food and Agriculture Organization of the United Nations,” 2007, http//www.fao.org

Embrapa, Centro Nacional de Pesquisa de Solosz: Manual de métodos de análise de solos, Embrapa, Rio de Janeiro, Brazil, 2nd edition, 1997.

N. Z. Santos, S. A. Prior, J. Gabardo, J. C. Valaski, A. C. V. Motta, and A. F. Neto, “Influence of corn (Zea mays L.) cultivar development on residue production,” Journal of Plant Nutrition, vol. 35, pp. 750–769, 2012.

A. P. L. Martins and C. B. Reissmann, “Material vegetal e as rotinas laboratoriais nos procedimentos químico-analíticos,” Scientia Agraria, vol. 8, pp. 1–17, 2007.

V. Pauletti, Nutrientes: teores e interpretações, Fundação ABC para Assistência e Divulgação Técnica e Agropecuária, 2nd edition, 2004.

B. V. Raij, H. Cantarella, J. A. Quaggio, and A. M. C. Furlani, Recomendações de adubação e calagem para o estado de São Paulo, Instituto Agronômico e Fundação IAC, 2nd edition, 1997.

Comissão De Química E Fertilidade Do Solo-Rs/Sc, Manual de adubação e calagem para os Estados do Rio Grande do Sul e Santa Catarina, Porto Alegre, 10th edition, 2004.

N. Altmann and A. Pavinato, “Experiencias da SLC agricola no manejo da fertilidade do solo no cerrado,” Informações Agronômicas, vol. 94, pp. 1–4, 2001.

L. Arnon, Mineral Nutrition of Maize, International Potash Institute, 1975.

C. F. Ferreira, Diagnose nutricional de cultivares de milho (Zea mays L.) de diferentes níveis tecnológicos [M.S. thesis], Universidade Federal do Paraná, Curitiba, Brazil, 2009.