Effect of Mineral and Organic Nutrient Management on Sweet Corn Production System in Acid Lateritic Soil of India

Kanu Murmu; Dillip K Swain; Bijoy C Ghosh

doi:10.4103/2423-7752.191398

ORIGINAL ARTICLE

Year : 2016 | Volume : 2 | Issue : 2 | Page : 70-76

Effect of Mineral and Organic Nutrient Management on Sweet Corn Production System in Acid Lateritic Soil of India

Kanu Murmu¹, Dillip K Swain², Bijoy C Ghosh²
¹ Department of Agronomy, F/Ag, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, India
² Department of Agricultural and Food Engineering, Indian Institute of Technology, Kharagpur, West Bengal, India

Date of Web Publication

29-Sep-2016

Correspondence Address:
Dr. Kanu Murmu
Department of Agronomy, F/Ag, Bidhan Chandra Krishi Viswavidyalaya, P.O. Krishi Viswavidyalaya, Mohanpur - 741 252, Nadia, West Bengal
India

Source of Support: None, Conflict of Interest: None

Check

DOI: 10.4103/2423-7752.191398

Abstract

Introduction: Nutrient management plays a key role in improving crop yield with maintenance of soil fertility for sustainable production in intensive cropping. Aim: A field experiment was conducted to study the effect of organic and mineral sources of fertilizer on yield and quality of sweet corn grown in acid laterite soil of India during the years 2009 and 2010. Materials and Methods: The organic inputs were vermicompost (VC), vermiwash (VW), biofertilizer (BF), and crop residue (CR) and the inorganic input was mineral fertilizer. Results: Optimal application of N, P, and K (100% recommended dose) either through organic source or mineral source was significantly superior to their suboptimal dose in increasing the yield of sweet corn, wherein mineral fertilizer recorded maximum production. Between organic and mineral sources of fertilizer application, ascorbic acid and total phenolics content of sweet corm were higher in organic nutrient management. The ascorbic acid was higher by 133% in VC₁₀₀ and 37% in VC₅₀ + CF₅₀ compared to mineral (CF₁₀₀) treatment. But crude protein content was low by 13.5% in VC₁₀₀ and 2.9% in VC₅₀ + CF₅₀, respectively, as compared to CF₁₀₀ treatment. Organic carbon content and pH of the acid lateritic soil were improved in organic nutrient management as compared to mineral fertilizer. Conclusion: Organic fertilizer application, therefore, exhibited potential in improving sweet corn yield and quality and soil health in acid lateritic soil of the subtropical climate.

Keywords: Ascorbic acid, mineral fertilizer, organic fertilizer, phenolics, sweet corn yield

How to cite this article:
Murmu K, Swain DK, Ghosh BC. Effect of Mineral and Organic Nutrient Management on Sweet Corn Production System in Acid Lateritic Soil of India. J Earth Environ Health Sci 2016;2:70-6

How to cite this URL:
Murmu K, Swain DK, Ghosh BC. Effect of Mineral and Organic Nutrient Management on Sweet Corn Production System in Acid Lateritic Soil of India. J Earth Environ Health Sci [serial online] 2016 [cited 2023 Sep 23];2:70-6. Available from: https://www.ijeehs.org/text.asp?2016/2/2/70/191398

Introduction

Sustainable development in agriculture and yield maximization of crops can be achieved through restoration and scientific management of land productivity. For yield maximization in intensive cropping, supply of appropriate source and amount of nutrients are indispensable. In conventional practice, improved cropping system involving high value crops relies on the use of mineral fertilizer because of its immediate availability of nutrients. Though mineral fertilizers not only nourish plants but also jeopardize the environment through nitrate pollution and create adverse effects on the fragile ecosystem with elimination of beneficial soil organisms and deterioration of soil physico-chemical properties. Indiscriminate and continuous use of such mineral fertilizers leads to instability in yield and also poses a threat to soil health particularly because of micronutrients deficiency and fertilizer-related environmental pollution.^[1] Moreover, the produce so developed may raise a question about its quality and acceptability in market. A growing consciousness of such overdependence on synthetic minerals and the associated degradation in product and environmental quality led to the emergence of a farming system known as ‘‘organic farming.’’ For restoration and augmentation of soil fertility and improvement of crop yield and quality in intensive cropping system, organic farming practice can be an option.

For the organic farming, organic enrichment of soil is most common through application of composted materials, microbial biofertilizer (BF) or recycling of crop wastes. Vermicompost (VC), a stable organic manure, produced as vermicast by earthworm feeding on biological wastes materials is an important source of BF material. The major constituents of VC are essential macro- and micronutrients, immobilized enzymes, vitamins, antibiotics, humic acid, and growth hormone, which is considered as a rich source of BF. The vermicomposting technology can also be utilized for generating a bioliquid termed as vermiwash (VW). VW is a liquid leachate collected by allowing excess water to saturate the actively vermicomposting substrate in such a way that the water washes the nutrients from the vermicast excreted by the earthworms feeding on the substrate as well as the earthworm’s body surface. Moreover, it is cost effective and environmental friendly being processed by recycling of animal, agriculture, and food-related industrial wastes.

There is scientific evidence that organically grown crops contain higher mineral and vitamin content^[2] higher antioxidant content^{[3],[4],[5],[6],[7]} and have better flavor^[4],[8] than that of crops produced using conventional production systems. In addition, some authors raise concern that the antioxidant content of foods grown using conventional production systems is lower than what is optimal for human health.^[3]

Sweet corn is favorable for fresh consumption because of its delicious taste, together with its soft and sugary texture compared to other corn varieties. Sweet corn has been widespread in the world. At optimum market maturity stage, sweet corn will contain 5–6% of sugar, 10–11% of starch, 3% of water soluble polysaccharides, 70% of water, as well as moderate levels of protein, vitamin A, and potassium.^[9] Sweet corn is a fairly heavy feeder, and proper soil fertility is critical for high yield.^[10] Kernel sweetness in Sweet corn is the most important quality factor in consumer satisfaction, followed by tenderness and color of kernels, and sweetness is closely related to sucrose, fructose, glucose, and total sugar concentration.^{[11],[12],[13],[14],[15],[16],[17],[18],[19]} However, the ascorbic acid concentrations of organic and sustainably grown corn varieties were 52.4% and 66.7% higher, respectively, than conventionally grown corn varieties.^[6] Among various factors responsible for yield and quality of sweet corn, fertilizer management is the important one. To date, fertilizer management for fruits and vegetables has been established primarily for productivity goal, but not many for quality improvement. Among the various factors responsible for high productivity and quality of sweet corn, fertilizer management is considered to be an important one. Nutritional status is an important factor in quality aspects at harvest and postharvest lives of crops. Fertilizer application schedule varies widely among growers, which depends upon soil type, cropping history, and soil test results. Deficiencies and excesses or imbalances of various nutrients are known to result in disorders that can limit the quality of the crops. To date, fertilization recommendations for fruits and vegetables have been established primarily for productivity goals, not as diagnostics for good flavor quality and optimal postharvest life. We conducted this experiment to analyze the effect of mineral and organic nutrient management on both yield and quality of sweet corn and on soil nutrient status in acid lateritic soil of India.

Materials and Methods

Site characteristics and cultivar

The soil of the experimental field is acid laterite (type − Haplustalf) and sandy loam in texture. It is low in organic carbon and nitrogen content, medium to low in phosphorus and low in potassium content. The initial soil pH was 5.1, organic carbon was 0.30%, and available N, P, and K content were 72.7, 11.8, and 46.9 ppm, respectively. The climate of the region is warm and humid. The annual rainfall ranges from 1300 to 1500 mm, and 85% of which is received during June–October from southwest monsoon. During the experimental period (2009–2010), the annual rainfall received was in the range 1110–1961 mm.

Experimental details

Field experiments were conducted to study the effect of mineral and organic input management on yield and quality of sweet corn grown in acid lateritic soil. The experiment was conducted in the experimental farm of Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur (22°19′ N 87°19′ E), India during wet season (May–July) of the years 2009 and 2010. The experiment included six treatments of organic and inorganic input management and one control where nothing was added. The organic inputs were VC, VW, BF, and crop residue (CR) of previous crop. The chemical input was the Mineral fertilizer are applied in terms of Chemical fertilizer (CF) applied at recommended dose of 150:50:50 kg/ha of N:P₂O₅:K₂O for the sweet corn. The mineral fertilizer was applied through urea, single super phosphate (SSP), and muriate of potash (MOP). The organic source VC was used to supply 100%N recommendation as single source or 50%N recommendation when combined with CF or other organic sources. Other organic sources, that is, VW was applied at 650 l/ha and BF (Azotobacter sp.) at 3.5 kg/ha. For CR, the full byproduct harvest of the previous crop (tomato) was incorporated into the soil. There were seven treatment combinations, that is, control, CR, mineral fertilizer at 100% recommended dose of N, P, and K (CF₁₀₀), VC at 100%N recommendation (VC₁₀₀), VC₅₀ + CF_50, VC₅₀ + CR and VC₅₀ + VW + BF were considered and each treatment was replicated thrice in a Randomized Complete Block Design (RCBD). In total, there were 21 plots and each had dimension of 5 m × 4 m. The fertilizer was evenly applied in crop row and well mixed with soil.

The mineral fertilizer in the form of urea, single super phosphate (SSP) and muriate of potash (MOP) was broadcasted and incorporated to 15 cm depth of soil. Half dose of nitrogen and full dose of P₂O₅ and K₂O were applied as basal at sowing time and remaining half nitrogen was top dressed at 35 days after sowing. Well-composted VC and VW were collected from local farm. VW was extracted through VW-collecting device which was made up of a mud drum having capacity of 5 l and a tap at the bottom of the drum filled with broken bricks, about 10 cm thickened which was followed by sand layer of 2–3 cm thickness; lastly VC was filled with heavy population of earth worms. Into which fresh water was simultaneously added into drum and a container was kept bellow the tap of drum. Yellowish to black extract of VC i.e. VW was drained out off drum. After 1–2 days, the process of extraction has been completed. The chemical and microbiological composition of both VC and VW is given in [Table 1]. The solid VC was applied as basal before plantation of sweet corn. The total volume of VW was sprayed on the crop canopy by mixing with water at 1:5 ratio in seven equal splits starting at 35 days after sowing/planting of crop and thereafter at one week interval. The Azotobacter was applied as basal by mixing with VC of the same treatment. The control plot received no fertilizer; however the soil preparation was similar to those of fertilized treatments. Sweet corn seeds were sown with a spacing of 50 cm between rows and 15 cm between seeds on 5^th May in 2009 and on 8^th May in 2010.

Table 1: The selected chemical and microbiological composition of vermicompost (VC) and vermiwash (VW) used in the experiment

Click here to view

Crop yield record and quality analysis

The harvesting of sweet corn cob was done when the silk started turning into brown color. Harvesting was done at different plucking on net plot area basis leaving the border rows, and the cob yield was recorded after removal of husk. Thereafter, the samples were kept in deep freeze for biomineral analysis. The analysis of the quality parameters of sweet corn is explained as follows:

Ascorbic acid. The determination of total ascorbic acid was on the basis of coupling 2,4-dinitrophenylhydrazine (2,4-DNPH) with the ketonic groups of dehydroascorbic acid through the oxidation of ascorbic acid by 2,6-dichlorophenolindophenol (2,6-DCPIP) to form a yellow-orange color in acidic conditions.^[20] Twenty grams of sample was blended with 80 mL, 5% meta-phosphoric acid in a homogenizer and centrifuged. After centrifuging, 2 mL of the supernatant was poured into a 20 mL test tube containing 0.1 mL of 0.2% 2,6-DCPIP sodium salt in water, 2 mL of 2% thiourea in 5% meta-phosphoric acid and 1 mL of 4% 2,4-DNPH in 9N sulfuric acid. The mixtures were kept in a water bath at 37°C for 3 h followed by an ice bath for 10 min. 5 mL of 85% sulfuric acid was added, and the mixtures were kept at room temperature for 30 min before reading at OD 520 nm. 2,4-DNPH was added during the ice bath as a blank for a control. Commercial l-(+)-ascorbic acid was used for calibration.
Total phenolics. Total soluble phenolic levels were analyzed by using a procedure adapted from Swain and Hillis^[21] and modified by Gao et al.,^[22] using the Folin–Ciocalteu reagent. Extracts of 100 μL were diluted with 500 μL of water. A volume of 700 μL of 0.2 mol/L equivalent Folin–Ciocalteu reagent was added and the mixture was allowed to stand for 3 min at room temperature. Then 900 μL of 1 mol equivalent/L Na₂CO₃ was added and the mixture was allowed to stand for 90 min, after which, absorbance readings at 765 nm were taken in a photodiode array spectrophotometer (model 8452A; Hewlett–Packard Co., Waldbronn, Germany). Acidified methanol was used as the blank. Total phenolic contents were expressed as mg gallic acid/100 g, based on a standard curve of 0–600 μg of gallic acid/mL.
Sugar. Sugar content was analyzed by Anthrone–Sulfuric Acid Assay. The anthrone method is based on the condensation of furaldehyde derivatives, generated by carbohydrates in the presence of a strong acid, with a reagent, and in this case, anthrone (9,10-dihydro-9-ozoanthracene), was used to produce colored compounds.^[23] A cooled mixture of 2% anthrone in concentrated sulfuric acid was mixed with an aliquot of a clear sample solution containing the sugar being assayed. After incubation in a temperature-controlled environment for sufficient time to allow color development, the solution was poured into an appropriate spectrophotometric cuvette and the absorbance was measured at 625 nm.
Crude protein content. The nitrogen content of sweet corn was estimated by using modified microkjeldhal’s metho^[24] The protein content was calculated by multiplying the nitrogen content with factor 6.25 and expressed as percentage.

Soil fertility analysis

Soil samples were collected from the rhizosphere region (0–20 cm soil depth) of sweet corn crop after each season harvest and before start of the experiment. In each plot, the samples were collected from five randomly selected spots and were thoroughly mixed to prepare a homogenous sample. The soil samples were analyzed for organic carbon content^[24] (Walkley–Black method), pH^[24] (Glass electrode pH meter), and available N^[25] (Alkaline KMnO₄ method), P^[24] (NH₄F-extraction), and K^[24] (NH₄OAc-extraction) content.

Statistical analysis

All data were analyzed statistically following the standard procedures as described by Gomez and Gomez.^[26] The data were treated for analysis of variance and least significant difference (P = 0.05) for each character separately using an MSTAT-C statistical analysis package.

Results

Yield of sweet corn

Effect of different fertilizer treatments on cob yield of sweet corn is presented in [Table 2]. The maximum yield was noted in CF₁₀₀ treatment, which was at par with VC₁₀₀, VC₅₀ + CF₅₀ and VC₅₀ + VW + BF treatments during 2009 and with VC₁₀₀ and VC₅₀ + CF₅₀ during 2010. It is noted that application of nutrient through suboptimal dose of VC with other organic and BF always produced lower yield than full dose of nutrients either through sole application of organic and inorganic or their integration.

Table 2: Effect of fertilizer sources on sweet corn cob yield (kg/ha) during 2009 and 2010

Click here to view

Quality of sweet corn

The quality of sweet corn is determined in terms of content of crude protein, ascorbic acid, sugar, and total phenolics. The crude protein content was significantly improved when both mineral and organic fertilizer sources were either applied in full or at suboptimal dose. Moreover, CF₁₀₀ has shown higher crude protein content than VC₁₀₀. The crude protein content was low by 13.5% in VC₁₀₀ and 2.9% in VC₅₀ + CF₅₀, respectively, as compared to CF₁₀₀ treatment. In sweet corn, sugar content expressed the consumer acceptance test, that is, the higher the sugar content the better is the acceptance. The result revealed that as compared to control or CR or VC treatment, the sugar content was significantly higher in CF₁₀₀ treatment during 2009. In the year 2010, VC-based treatments of CF₁₀₀ were at par in increasing the sugar content as compared to control [Table 3] and [Table 4]. In our experiment, mineral fertilizer and organic source applied at full dose could gain the increasing sugar content as compared to control or CR treatments. The major secondary metabolites of sweet corn were ascorbic acid and total phenolics [Table 3] and [Table 4]. The results showed that application of both mineral and organic sources of fertilizers improved the ascorbic acid content than that of control or CR treatment. The content was considerably higher in VC₁₀₀ treatment in both the years. The increase was higher by 133% in VC₁₀₀ and 37% in VC₅₀ + CF₅₀, respectively, as compared to CF₁₀₀ treatment.

Table 3: Effect of fertilizer sources on ascorbic acid, crude protein, sugar and total phenolics content of sweet corn during 2009

Click here to view

Table 4: Effect of fertilizer sources on ascorbic acid, crude protein, sugar and total phenolics content of sweet corn during 2010

Click here to view

Similarly, the total phenolic was also recorded higher when full dose of CF and VC was applied in the first year and in addition the suboptimal doses of treatments (VC₅₀ + CF₅₀ and VC₅₀ + VW + BF) in the second year as compared to CR or control treatments.

Soil properties

All VC-based treatments depicted higher pH as compared to mineral fertilizer. There was no alteration in pH level in control or CR treatment [Figure 1]. Application of mineral fertilizer and VC in the field led to build up in organic carbon content as well as nutrient status of the soil. However, the increase was much more pronounced in later than in former one, which was discernible at the end of the study period [Figure 2]. After incorporation of organic or mineral sources of fertilizer, the mineralization process released adequate quantity of nutrients in the soil. The available N was higher when mineral fertilizer source was used which was closely followed by VC treatment [Figure 3]. There was a significant gain in available N in soil due to the use of either organic or mineral sources of fertilizers. However, such an increase of N level in soil was gradual in the case of VC-related treatments which was due to slow mineralization process of organic matter with the gradual release of the nutrients. Available P and K in soil showed a similar trend of increase during the study period [[Figure 4] and [Figure 5]].

Figure 1: Effect of fertilizer sources on pH of soil during 2009 and 2010. BF = biofertilizer, CD = critical difference, CF = chemical fertilizer, CR = crop residue, VC = vermicompost, VW = vermiwash. The subscripts 100 and 50 represent their application at 100% and 50% of recommendation, respectively

Click here to view

Figure 2: Effect of fertilizer sources on organic carbon content of soil during 2009 and 2010. BF = biofertilizer, CD = critical difference, CF = chemical fertilizer, CR = crop residue, VC = vermicompost, VW = vermiwash. The subscripts 100 and 50 represent their application at 100% and 50% of recommendation, respectively

Click here to view

Figure 3: Effect of fertilizer sources on available nitrogen content of soil during 2009 and 2010. BF = biofertilizer, CD = critical difference, CF = chemical fertilizer, CR = crop residue, VC = vermicompost, VW = vermiwash. The subscripts 100 and 50 represent their application at 100% and 50% of recommendation, respectively

Click here to view

Figure 4: Effect of fertilizer sources on available phosphorus content of soil during 2009 and 2010. BF = biofertilizer, CD = critical difference, CF = chemical fertilizer, CR = crop residue, VC = vermicompost, VW = vermiwash. The subscripts 100 and 50 represent their application at 100% and 50% of recommendation, respectively

Click here to view

Figure 5: Effect of fertilizer sources on available potassium content of soil during 2009 and 2010. BF = biofertilizer, CD = critical difference, CF = chemical fertilizer, CR = crop residue, VC = vermicompost, VW = vermiwash. The subscripts 100 and 50 represent their application at 100% and 50% of recommendation, respectively

Click here to view

Discussion

It is noted that application of nutrient through suboptimal dose of VC with other organic and BF always produced lower yield than full dose of nutrients either through sole application of organic and mineral or their integration. At full dose, both mineral and organic fertilizers and their combinations increased nutrient supply and enhanced absorption of nutrients by both the crops. However, the rate of mineralization differs between mineral and organic fertilizers sources. In mineral fertilizers, mineralization process was faster resulting in an immediate release of nutrients’ elements N, P, and K and with their quick availability for the crop plants and thereby maximum yield. As regard to organic source, VC contains plant growth regulators and humic acid which have additive effect on plant growth.^[27] Humic acid also attacks on soil minerals and accelerates their decomposition, thereby releasing essential nutrients as exchangeable cations. Organic, polysaccharides, and fulvic acids all can attract such cations as Fe³⁺, Cu²⁺, Zn²⁺, and Mn²⁺ from the edges of mineral structures and chelate or bind them in stable organo-mineral complexes.^[28] Thus, the yield advantage on application of VC was due to its capability to supply both essential plant nutrients as well as growth promoting substances for improvement of growth and yield of crops.

Higher crude protein content of mineral-fertilized crop was associated with higher N availability in soil from the fertilizer and thereby greater N uptake by crop [Table 3] and [Table 4]. Similar finding was also reported by Lockeretz et al.^[29] and Magkos^[30] who observed higher crude protein in conventionally grown sweet corn than by organic one.

It was reported that application of 100% Recommended Dose of Phosphorus (RDP) along with either 75% of Recommended Dose of Nitrogen (RDN) or 100% RDN of grain maize increased reducing sugar, non-reducing sugar, and total sugar.^[31] The results on consumer acceptance test revealed that kernels in treatments which received 100% RDP along with either 100% N or 75% RDN were found to have high sweetness. This could be due to increase in the content of non-reducing sugar and total sugar, which contribute to sweetness. Higher nutrient availability and higher content of secondary and micronutrients were observed in VC-related treatments which have promoted the formation of secondary metabolites like ascorbic and phenolics in plant. Moreover, in VC₅₀ + VW + BF treatment, spray of VW could supply all essential elements directly feeding to the crop which has promoted greater content of micronutrients in plant. The role of micronutrients such as Cu, Mn, and Zn play a significant role in many vital metabolic processes and cofactor of antioxidant enzymes as has been reported by Grotz and Guerinot.^[32]

Increase of pH in soil treated with organic fertilizer has been reported by Brady and Weil.^[28] Decrease in soil pH due to addition of inorganic fertilizer is explained by Belay et al.^[33] and Saha et al.^[34] On mineralization, mineral fertilizer releases ammonia gas which not only inhibits the activity of soil flora and fauna but also increases soil acidity because two moles of acidity are formed for every mole of ammonium nitrogen that undergoes nitrification to nitrates. A number of researchers have reported about increase in organic carbon content in soil with application of VC. An increase in organic carbon content in soil with the application of VC was also reported.^[35] During 2009 and 2010, there was a significant increase in organic carbon content of soil with application of VC-based treatments; the higher increase was noted in VC₁₀₀ followed by VC₅₀ + CF₅₀. At suboptimal dose, the increase in organic carbon was at lower level than that applied at full dose. VC has been demonstrated to act as valuable soil amendments that offer a balanced nutritional release pattern to plants, providing nutrients such as available N, soluble K, exchangeable Ca, Mg, and P that can be taken up readily by plants^[36] and ^[37] besides being a source of several micronutrients. The reserved nutrients were observed because of fixation and accumulation of organic nutrient elements, which are promoted by application of organic materials.^[38] In the present study, it is apparent that VC application is favorable for improving reserved nutrient status in soil due to cumulative gain during the experiment period.

Conclusion

There is an increasing worldwide requirement for agricultural and horticultural produce not only to meet high standards of quality but also to be produced using environmentally sound practices. To this end, principles of sustainability and resilience have an increasingly important part to play in the drafting of economically viable production protocols. The increasing interest in organic production systems is in response to notions that they are inherently more sustainable. The effectiveness of mineral source of nutrient was better pronounced in increasing sweet corn yield and of organic nutrient source in improving the sweet corn quality. Combined application of organic and inorganic sources of nutrient could be able to maintain the cob yield with better quality, while improving the nutrient status of acid lateritic soil.

Acknowledgements

This study was conducted as part of the doctoral research program. The authors acknowledge all individuals who assisted with the collection and analysis of the experimental data.

Financial support and sponsorship

Nil.

Conflict of interest

There are no conflicts of interest.

References

1.	Prasad R, Power JF. Nitrification inhibitors for agriculture, health and the environment. Adv Agron 1995;54:233-81.
2.	Worthington V. Iron Content and Bioavailability of Organically Versus Conventionally Grown Crops. Baltimore, MD: Johns Hopkins University; 1998.
3.	Woese K, Lange D, Boess C, Bögl KW. A comparison of organically and conventionally grown foods − Results of a review of the relevant literature. J Sci Food Agric 1997;74:281-93.
4.	Weibel FP, Bickel R, Leuthold S, Alföldi T. Are organically grown apples tastier and healthier? A comparative field study using conventional and alternative methods to measure fruit quality. Acta Hortic 2000;517:417-26.
5.	Heaton SA. Organic Farming, Food Quality and Human Health: A Review of the Evidence. Bristol, UK: Soil Association; 2001. p. 88.
6.	Asami DK, Hong YJ, Barrett DM, Mitchell AE. Comparison of the total phenolic and ascorbic acid content of freeze-dired and air-dired marionberry, strawberry and corn grown using conventional, organic and sustainable agricultural practices. J Agric Food Chem 2003;51:1237-41. [PUBMED]
7.	Chassy AW, Bui L, Renaud EN, Van Horn M, Mitchell AE. Three-year comparison of the content of antioxidant microconstituents and several quality characteristics in organic and conventionally managed tomatoes and bell peppers. J Agric Food Chem 2006;54:8244-52. [PUBMED]
8.	Reganold JP, Glover JD, Andrews PK, Hinman HR. Sustainability of three apple production systems. Nature 2001;410:926-30. [PUBMED]
9.	Oktem AG, Oktem A. Effect of nitrogen and intra row spaces on sweet corn (Zea mays saccharata Sturt) ear characteristics. Asian J Plant Sci 2005;4:361-4.
10.	Fernandez Santos FX, Zekri S, Herruzo Casimiro A. Environmental economic impact of the use of nitrogen in the Guadalquivir basin irrigation. Agric Res Econ 1992;7:325-38.
11.	Brecht JK. Sweet corn. In: Gross KC, Wang CY, Saltveit M, editors. The Commercial Storage of Food, Vegetables, and Florist and Nursery Crops. Agriculture Handbook 66. Beltsville, MD: U.S. Department of Agriculture, Agricultural Research Service; 2004.
12.	Flora LF, Wiley RC. Sweet corn aroma, chemical components and relative importance in the overall flavor response. J Food Sci 1974;39:770-3.
13.	Hale TA, Hassell RL, Phillips T, Halpin E. Penetrometre and taste panel perception of pericap tenderness in su, se and sh2 sweet corn at three maturities. HortTechnology 2004;14:521-4.
14.	Kemble JM. Commercial Sweet Corn Handling. Alabama A and M and Auburn Universities, Alabama Cooperative Extension System Publication ANR-584; 2001.
15.	Reyes FG, Varseveld GW, Kuhn MC. Sugar composition and flavor quality of high sugar (shrunken) and normal sweet corn. J Food Sci 1982;47:753-5.
16.	Showalter RK, Miller LW. Consumer preference for high-sugar sweet corn varieties. Proc Fla State Hortic Soc 1962;75:278-80.
17.	Suslow TV, Cantwell M. Tomato. Technology Research and Information Centre. Davis, CA: Department of Plant Sciences, University of California; 2006. Available from: http:/postharvest.ucdavis.edu/prduce/producefacts/veg/tomato.shtml. [Last accessed on 2007 Oct 21].
18.	Wiley RC. Sweet corn aroma: Studies of its chemical components and influence on flavor. In: Pattee HE, editor. Evaluation of Quality of Fruits and Vegetables. Westport, CT; AVI Publishing Company; 1985. p. 349-66.
19.	Wong AD, Juvik JA, Breeden DC, Swiader JM. Shrunken2 sweet corn yield and the chemical components of quality. J Am Soc Hortic Sci 1994;119:747-55.
20.	Pelletier O. Vitamin C (l-Ascorbic and Dehydro-l-Ascorbic Acids); 1985. p. 303-47.
21.	Swain TR, Hillis WE. The phenolic constituents of Purmus domestica. I. The quantitative analysis of phenolic constituents. J Sci Food Agric 1959; 10:63–8.
22.	Gao L, Wang S, Oomah BD, Mazza G. Wheat quality: Antioxidant activity of wheat millstreams. In: Ng P, Wrigley CW, editors. Wheat Quality Elucidation. St. Paul, MN: AACC International; 2002. p. 219-33.
23.	Dische Z. Color reactions of hexoses. In: Whistler RL, Wolfrom ML, editors. Methods in Carbohydrate Chemistry, vol 1. New York: Academic Press Inc.; 1962. p. 488-94.
24.	Jackson ML. Soil Chemical Analysis. New Delhi: Prentice Hall of India Pvt. Ltd.; 1973.
25.	Subbiah BV, Asija GL. A rapid procedure for estimation of available nitrogen in soil. Curr Sci 1956;25:259-60.
26.	Gomez KA, Gomez AA. Statistical Procedures for Agricultural Research. New York: Wiley-Interscience Pub., John Wiley and Sons; 1984.
27.	Tomati U, Grappelli A, Galli E. The hormone-like effect of earthworm casts on plant growth. Biol Fertil Soils 1988;5:288-94.
28.	Brady NC, Weil RR. The Nature and Properties of Soil. 13th ed. Prentice Hall: Pearson Education Inc.; 2002.
29.	Lockeretz W, Shearer G, Kohl DH. Organic farming in the corn belt. Science 1981;211:540-7. [PUBMED]
30.	Magkos F, Arvaniti F, Zampelas A. Organic food: Nutritious food or food for thought? A review of the evidence. Int J Food Sci Nutr 2003;54:357-71. [PUBMED]
31.	Arun Kumar MA, Gali SK, Hebsur NS. Effect of different levels of NPK on growth and yield parameters of sweet corn. Karnataka J Agric Sci 2007;20:41-3.
32.	Grotz N, Guerinot ML. Molecular aspects of Cu, Fe and Zn homeostasis in plants. Biochim Biophys Acta 2006;7:595-608.
33.	Belay A, Claassens AS, Wehner FC. Effect of direct nitrogen and potassium and residual phosphorus fertilizers on soil chemical properties, microbiological components and maize yield under long-term crop rotation. Biol Fertil Soils 2002;35:420-7.
34.	Saha S, Prakash V, Kundu S, Kumar N, Mina BL. Soil enzymatic activity as affected by long term application of farm yard manure and mineral fertilizer under a rainfed soybean-wheat system in N-W Himalaya. Eur J Soil Biol 2008;44:309-15.
35.	Masciandaro G, Ceccanti B, Garcia C. Soil agro-ecological management: Fertirrigation and vermicompost treatments. Bioresour Technol 1997;59:199-206.
36.	Edwards CA. Breakdown of animal, vegetable and industrial organic wastes by earthworms. In: Edwards CA, editor. Earthworm Ecology. Boca Raton, Florida; CRC Press/Lewis; 1998. p. 237-354.
37.	Edwards CA, Fletcher KE. Interactions between earthworms and microorganisms in organic-matter breakdown. Agric Ecosyst Environ 1988;20:235-49.
38.	Savant NK, De Dutta SK. Nitrogen transformations in wetland rice soils. Adv Agron 1982;35:241-302.