Fitociencia

 

Effects of nitrogen fertilizer input on the composition of mineral elements in corn grain

 

Efectos de la aplicación de fertilizante nitrogenado en la composición de los elementos en los granos de maíz

 

Rui Yu–kui¹*, Jiang Shi–ling², Zhang Fu–suo¹, Shen Jian–bo¹

 

¹ College of Resources and Environmental Science, China Agricultural University, Beijing 100094, P.R China.

² Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2. * Author for correspondence: (ruiyukui@163.com).

 

Received: March, 2008.
Aproved: August, 2008.

 

Abstract

Excessive and inappropriate application of industrial N fertilizer can result in severe environmental and ecological problems, but whether the input of N fertilizer could affect the composition of mineral elements in corn has not been reported. Effects of input of N fertilizer on the composition of mineral elements (Se, Mo, I, Mn, Fe, Cu, Zn, Ca, Cr, K, Na, and Mg), in corn grain were investigated by ICP–MS (inductive coupling plasma–mass spectrometry). Se, I, Mn, Fe, Zn, Cr, K and Ca were significantly lower in the treatments with N fertilizer compared to a control without N fertilizer. There was a significant negative conrrelation (R) between four mineral elements and N fertilizer input: I, –0.71; Zn, –0.65; Ca, –0.75; K, –0.89. Therefore appropriate reduction of N fertilizer input cannot only prevent environmental problems from excessive application of industrial N fertilizer, besides it might reduce the problem of malnutrition induced by mineral elements deficiency.

Key words: Corn grain, ICP–MS, plant nutrition, trace elements, urea.

 

Resumen

La aplicación excesiva e inapropiada de fertilizante comercial nitrogenado (N) puede ocasionar graves problemas ambientales y ecológicos; sin embargo, no se ha reportado si la aplicación de fertilizante N puede afectar la composición de los elementos minerales en el maíz. Los efectos de la aplicación de fertilizante N en la composición de los elementos minerales en los granos de maíz (Se, Mo, I, Mn, Fe, Cu, Zn, Ca, Cr, K, Na, y Mg) se analizaron mediante espectrometría de masas con plasma acoplado por inducción (ICP–MS, por sus siglas en inglés). Se, I, Mn, Fe, Zn, Cr, K y Ca fueron significativamente inferiores en los tratamientos con fertilizante N comparado con un control sin fertilizante N. Hubo una correlación (R) negativa significativa entre cuatro elementos minerales y fertilizantes N: I, –0.71; Zn, –0.65; Ca, –0.75; K, –0.89. Por tanto, la reducción apropiada de la adición de fertilizante N puede no sólo evitar problemas ambientales debidos a la aplicación excesiva de fertilizante comercial N, sino que además podría disminuir la desnutrición causada por la deficiencia de elementos minerales.

Palabras clave: Granos de maíz, ICP–MS, nutrición de plantas, elementos traza, urea.

 

INTRODUCTION

Mineral elements play many important roles in human health (Zeng and Zhao, 2007). Obtaining mineral elements for the human body principally depends on food; thus, content of mineral elements in farm products is a key index to appraise the quality of the latter.

Nitrogen (N) fertilizer, which is necessary to biosynthesize amino acids and carbohydrates in plants used to feed animals and humans, has played a significant role in increasing crop yield and solving malnutrition problems. Production and application of N fertilizers have increased, resulting in an excess of them in China (Sun et al., 2006; Ju et al., 2004). Excessive and inappropriate application of industrial N fertilizer can result in severe environmental and ecological problems. For example, nitrate pollution in groundwater (Ju et al., 2006; Thorburn et al., 2003), eutrophication of coastal waters (Paerl, 2006) and greenhouse gases emissions that contribute to global warming (Scheer et al., 2008). In addition, its influence on nutrient composition in farm products has received more attention (Fabio et al., 2007; Li and Guo, 2007).

Increasing the yield and improving the quality of crops have been the challenges for sustainable agriculture. A high input of N fertilizer can increase the yield and improve the composition of proteins and amino acids in farm products. However, whether the input of N fertilizer could improve the composition of mineral elements in corn has not been reported.

In order to study effects of input of N fertilizer on the composition of mineral elements in corn grain, different N fertilizer inputs in soil were used. Besides, concentration of Se, Mo, I, Mn, Fe, Cu, Zn, Ca, Cr, K, Na, and Mg were determined in seed after harvesting. T

 

MATERIALS AND METHODS

Materials

Corn seeds

The corn seeds, Denghai 3719, were produced and donated by Shandong Denghai Seeds Co., Ltd.

Fertilizers

The N fertilizer used was urea, total N no less than 46.4%, produced by PetroChina Ningxia Petrochemical Company Beijing xilu No. 1338 (Yinchuan city, Ningxia province, P.R. China). The P fertilizer was superphosphate, no less than 16% P₂O₅, produced by Yunnan Honglin Chemicals Co., Ltd (Kaiyuan city, Yunnan Province, P. R. China). The K fertilizer was KCl, no less than 60% K2O, produced by Ural Potassium fertilizer joint–stock company (Berezniki city, Perm State, Russia). The Zn fertilizer was ZnSO₄, no less than 95% ZnSO₄, produced by Shandong Zouping Zhenzhong Chemicals Co., Ltd (Zouping city, Shandong province P. R. China).

Field management

Experiments were carried out in a field at Shangzhuang experimental station, China Agricultural University, Beijing. The corn variety was Denghai 3719, sown on April 25, 2007, and harvested on September 20, 2007. Density was 100 000 plants per km². Four treatments were applied to the same P, K and Zn fertilizer and each treatment was repeated four times. Properties of soil are found in Hu's et al paper (2006).

Fertilization scheme

For the four treatments, P fertilizer, K fertilizer and micronutrient were the same: 90 kg P₂O₅ ha^–1 (superphosphate), 80 kg K2O ha^–1 (KCl), 15 kg Zn ha^–1 (ZnSO₄). The difference was the N fertilizer input (Table 1).

Treatment 1 (control, TR 1): no N fertilizer during the growth period of corn.

Treatment 2 (optimized treatment, TR 2): fertilizing according to the needs of the plants to obtain the best ratio of yield to input and for detecting results of N fertilizaer in soil.

Treatment 3 (TR 3): N fertilization time was the same as TR2, but the fertilizer input was 30% more.

Treatment 4 (TR 4): N fertilization time was the same as TR2, but the fertilizer input was 30% less.

Field observation

The seedlings emerged on May 6, additional seedlings were planted on May 10, irrigations (45 mm) were carried out June 15–16 and July 16, maize worm was controlled with Furadan on June 21–22, manual weeding was carried out on June 22–35. There were two rains: June 30–31 and July 13.

Detecting methods

Samples were treated as described by Rui et al. (2007) and Rui et al. (2006). Briefly, 0.5 g of corn grain powder, fixation from six ears was weighed and placed into quartz crucibles for digestion with 1.5 mL HNO₃ and 0.5 mL H₂O₂. The digestion procedure was as follows: 150 °C for 15 min at 500 W; 200 °C for 20 min at 800 W; 100 °C for 10min at 400 W power. The solution was diluted to 10 mL after digestion. The diluted solutions were analyzed for Se, Mo, I, Mn, Fe, Cu, Zn, Ca, Cr, K, Na and Mg using ICP–MS (ELAN DRCII, PE company, USA).

Parameters for inductively coupled plasma (ICP)

Parameters for ICP were those of Huang method (Huang et al., 2003; Liu et al., 2002): 1200 W; flow rate of cooling gas (Ar), 15.0 L min^–1; flow rate of supplemental gas (Ar), 1.80 L min^–1; flow rate of carrier gas (Ar), 0.95 L min^–1. Parameters of mass spectrometry: vacuum of analysis chamber, 5.89X10"⁶ Tor r; impulse voltage, 1200 V. Parameters for detection: resolution (10% peak height); 0.8 amu (Nor), 0.6 amu (H); retention period, 100 ms; times of replication, 5; times of circulation, 10; mode of analysis, scanning of mass, period of analysis, 72 s; rate of sample, 1mL min^–1.

Statistical analysis

Data was analyzed by one–way analysis of variance using SPSS 11.5 for Windows and Excel. The data presented is the mean of three replications.

Results Composition of mineral elements in corn grains

Elements analyzed were Se, Mo, I, Mn, Fe, Cu, Zn, Ca, Cr, K, Na and Mg (Table 2). Elements detected at the ng g^–1 level were: Se, Mo, I and Cr; elements at the µg g ^–1 level were: Mn, Fe, Cu, Zn, Ca, K, Na and Mg. Concentration ranges for Se, Mo, I, Mn, Fe, Cu, Zn, Ca, Cr, K, Na and Mg, were: 24.04 to 32.58 ng g^–1, 588.48 to 942.46 ng g^–1, 5.56 to 31.52 ng g^–1, 2.06 to 6.91 µg g^–1, 13.04 to 43.49 µg g^–1 2.32 to 3.75 µg g^–1, 11.93 to 23.95 µg^–1, 12.21 to 20.36 µg g^–1, 243.87 to 411.62 µg g^–1, 3069.60 to 3907.36 µg^–1, 2.81 to 21.48 µg g^–1and 879.65 to 1265.22 µg g^–1.

 

Differences in mineral elements composition from N fertilizer input

The contents of the 12 elements detected in corn grain were different among treatments. Thus, these 12 elements could be classified into five groups: a) Se and I, with the highest contents in corn grain for zero N fertilizer (TR1), and the contents in optimized treatment (TR2) were higher than in TR3 and TR4; b) Mn, Fe, Zn, Cr, and Mg, with the highest contents for zero N fertilizer (TR1); c) Mo, which was lowest for zero N fertilizer (TR1), and highest for TR2 and TR3; d) Cu and K, which was not different between treatments; e) Na, with the highest content for TR4. From the above data, the contents of Se, I, Mn, Fe, Zn, Ca and Cr in corn grains from TR1 were significantly higher than for the other treatments (Table 2)

 

DISCUSSION

Mineral elements play a key role in metabolism and maintenance of tissue function; therefore, an adequate intake is necessary to sustain metabolism and tissue function (Shenkin, 2006). Today, many countries and areas are still severely short of mineral elements required for human health (Barclay et al., 2003). So far, the prevailing solutions are fortification (Reilly, 1996) and transgenic biotechnology (Goto et al., 1999), but both of them are faced with the food safety problem. On this regard, Jiang et al. (2007) reported that most of the other mineral element contents in rice are significantly correlated, but there are few reports about the relationship between mineral contents with N fertilizer input in corn.

In our study, we analyzed the effects of N fertilizer input on the content of twelve mineral elements. It was found a significant negative correlation (R) between four mineral elements and N fertilizer input: I, –0.71; Zn, –0.65; Ca, –0.75; K, –0.89. These elements are deficient in food in many parts of the world. These elements were 38% to 210% higher in TR1 than in the other treatments with N fertilizer (Figure 1), which agrees with reports by Ray et al. (2007), Müller et al. (2007) and Zimmermamm and Hurrell (2007).

The negative correlation between contents of elements and N fertilizer input migh be due to: 1) N fertilizer urea is hydrolyzed into NH₄⁺, which might compete at the absorption point with other cations, including K, Na, Mg, Ca, Zn, Cu, Fe and Mn, so the accumulation of these elements in the kernels diminishes as the fertilization increases (Shi et al., 1999); 2) urea can acidify the soil, which would accelerate the leaching of K, Na, Mg and Ca, reducing their accumulation in the kernels as the fertilization increases (Shi et al., 1999); 3) as soil is acidified by urea, the amount of I and Se as I ^–, IO ^–₃, SeO₃^2–, SeO₄^2– that can be absorbed by the plant, will decrease in soil and the accumulation of these elements in the kernels is reduced (Xie et al., 2007).

 

CONCLUSIONS

Altogether, an appropriate reduction of N fertilizer input can prevent many environmental problems caused from excessive and inappropriate application of industrial N fertilizer. Besides, the problem of malnutrition might be reduced by increasing the composition of mineral elements, which is more effective than fortification and biotechnology of mineral elements.

 

ACKNOWLEDGEMENTS

The authors appreciate the financial support from China National Nature Science Foundation (NO 30571296 and NO 30500352), National Project of Scientific and Technical Supporting Programs in the Eleventh Five–year Plan Period Funded by Ministry of Science & Technology of China (NO 2006BAD25B02) and Program for Changjiang Scholars and Innovative Research Team in University (NO IRT0511). Thanks are also expressed to Ms. Wang Xiaoyan from Peking University Health Science Center for technical assistance.

 

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