Supachai Lorlowhakarn Paper on Organic Asparagus in Thai J of Ag Sci (2008)

www.thaiagj.org Thai Journal of Agricultural Science 2008, 41(1-2): 63-74

Organic Asparagus Production as a Case Study for Implementation of the National Strategies for Organic Agriculture in Thailand

S. Lorlowhakarn1, 2, S. Piyatiratitivorakul3 and W. Cherdshewasart1, 2,*

1Agricultural Technology Program, Faculty of Science, Chulalongkorn University

and the National Innovation Agency, Bangkok 10330, Thailand 2Department of Biology, Faculty of Science, Chulalongkorn University

Bangkok 10330, Thailand 3Department of Marine Science, Faculty of Science, Chulalongkorn University

Bangkok 10330, Thailand

*Corresponding author. Email: [email protected]

Abstract

Organic asparagus production at a field trial scale in Sa Kaeo Province was monitored to test whether the national strategies proposal on organic farming could be implemented in practice. The asparagus field trial was set up to examine all aspects of organic asparagus production, from effect of input levels of different fertilizers and difference irrigation systems, to soil properties analysis and nutrient analysis of fresh asparagus between organic and conventional farming. The trial was evaluated for the benefits obtained and any impediments that may happened during such implementation. The quantitative and qualitative analysis of the harvested asparagus indicated that the organic asparagus farm can be sustainable commercialized managed. It could be concluded on the basis of this case study that the national strategies for organic agriculture is possible to be effectively implemented in practice and would provide a very effective platform for dynamic development of the Thai organic agriculture sector. Keywords: national strategy, Asparagus officinalis L., organic agriculture, irrigation system, organic fertilizer

Introduction Organic markets in developed countries are

growing at 20-30% a year. In 2005, the global organic markets worth US$40 bn. (Willer and Yusefi, 2006). Analysts expect these markets to show sustained and buoyant growth over the coming 5-10 years. With the evidence of comparative advantages of Southeast Asian countries for organic production, there is considerable potential for Asian producers and exporters to supply for these key markets (Thode-Jacobsen, 2006).

On the supply side, there is ample underutilized agricultural land within the region, especially in upland areas, where pesticide use is minimal, and

which may be ideal for establishing certified organic production zones without the need to pass through a long transition period before certification is granted. As an environmental friendly production system, organic systems are well suited to fragile upland agro-ecosystem, where pesticide use poses possible health hazards for inexperience workers, as well as environmental risks.

Yet, despite triple-digit growth in the rate of farm conversion in Asia, supplies are failing to keep pace with the rapidly increasing global and regional demand (Organic Monitor, 2006). Constraints to conversion include lack of land tenure, inadequate access to technical training, information and support mechanisms, farmers’ perception of

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risk, and high compliance costs. In economic terms, this gap means that opportunities for increasing organic exports are not being captured, and in environmental terms, there are continuing risks to natural resources arising from current agricultural practices.

From 2005-2006, the Geneva-based UN International Trade Centre (ITC) provided financial assistance for Thailand’s National Innovation Agency (NIA) to implement a project in Thailand entitled, “Strengthening Thailand’s Organic Agriculture Export Capacity” (Lorlowhakarn et al., 2006). The project was co-funded by NIA and the EU under the Asia Trust Fund program. The project identified a range of challenges to development of both domestic and export markets, and generated a series of national-level recommendations. Its three objectives were to a) develop an innovative national organic model (strategy) for organic agriculture; b) facilitate the coordination of relevant government agencies in the implementation of organic projects in a synergistic manner; and c) strengthen Thailand’s government control system and requisites to prepare for application for inclusion in the EU’s ‘Third countries list’ (Article 11 of EC Regulation 2092/91), the direct channel for EU member countries to accept imports of organic products from Thailand. The project’s final report including full recommendations are available in full at http://www.nia.or.th/organic.

Materials and Methods Plant Material and Field Trials

Asparagus (Asparagus officinalis L.) production under contract farming of Swift Co., Ltd., was selected in order to reduce sources of variance among treatments in the study such as asparagus variety, farm regulations and fresh produce standards. Organic asparagus was cultivated at Sa Kaeo Province, Eastern Thailand (latitude 13°18′N, longitude 102°19′E, altitude 161 meters). The soil fertility, asparagus production yield, and gross income from organic farming were compared among the productions using different organic agricultural practices. The field trial was carried out on the asparagus farm that has been established for the first year after transplanted.

Advisory grower groups were established for each system. All treatments were completely randomized designed (CRD) with 4 replicates. Field trials were conducted to study factors that affect the yield of asparagus, including irrigation system and fertilization application level on the asparagus production. The marketable yield of asparagus produced from the experimental subplot replication (30 m2) was weighed and recorded after sorted into 10 grades according to the regulation of the contract company on a daily basis. The standard of marketable size of asparagus is summarized in Table 1.

Table 1 Green asparagus grading system used by Swift Co., Ltd.

Grade Qualification Diameter (cm) Price (baht kg-1) A Straight spear with compact tip, green in color for 25 cm length

without defect from pest and disease > 1 44

B Straight spear with little feathered spear has green in color for 25 cm length without defect from pest and disease

> 1 33

C Straight spear with compact tip, green in color for at least 20 cm length without defect from pest and disease, has whitish end

> 1 40

D Straight spear with little feathered spear has green in color for at least 20 cm length without defect from pest and disease, has whitish end

> 1 30

E Straight spear with compact tip, green in color for at least 20 cm length without defect from pest and disease, has whitish end

0.8-0.9 26

F Straight spear with little feathered spear has green in color for at least 20 cm length without defect from pest and disease, has whitish end

0.8-0.9 21

G Straight spear with compact tip, green in color for at least 20 cm length without defect from pest and disease, has whitish end

0.6-0.7 15

H Feathered spear with total length less than 20 cm, pale green color, spear is not round or distorted spear, little defect from pest and disease

> 1 13

I Feathered spear with total length less than 20 cm, pale green color, spear is not round or distorted spear, little defect from pest and disease

0.6-0.9 7

J Small spear with both compact and feathered tip 0.3-0.4 4

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Harvesting usually begins after a full year after establishment of asparagus field. The length of harvest is depend on the vigor of the plants which in turn is controlled by the growing conditions, particularly climate and plant fertility. Plants were grown during winter with shorter growing seasons are typically harvested for 2 to 4 weeks while in summer the harvest period may last up to 6 weeks. The annual duration of harvesting may be gradually increased up to 30 weeks in subsequent years. Manual harvesting and grading was daily operated, started early morning and finished just before noon.

In this study, two organic fertilizers i.e. bovine manure compost, commercial certified organic fertilizer and commercial seaweed extract biofertilizer (Ekólogik, Berlin Biotechnologia S.L., Tudela, Spain) which the composition were organic nitrogen (N, 2%), phosphoric anhydride (P2O5, 0.2%), potassium oxide (K2O, 1.0%), Magnesium oxide (MgO, 0.04%), Calcium oxide (CaO, 120 ppm) and Boron (B, 9 ppm), were treated. The bovine manure compost was manufactured by the members of the grower group, using the government facilities nearby the cultivation area. The cow manures were obtained from a certified GAP farm in Sa Kaeo Province. The other commercial brand of certified organic fertilizer (Sakura, Chiang Mai, Thailand) was used as positive control. Nutrient composition of the organic fertilizers used in the study is summarized in Table 2.

The Effects of the Level of Organic Fertilizer and Biofertilizer Applied on Asparagus Farm

Asparagus yield among various levels of organic fertilizer treated every 15 days (200, 500 and 800 kg rai-1 of bovine manure compost and 500

kg rai-1 of commercial brand organic fertilizer), were recorded. The data was collected for 1 year of asparagus production which composed of 5 crops per year, started in early January and ended in late November, 2007. The annual production of this field trial is summarized in Figure 1. The test for commercial brand biofertilizer (Ekólogik, Berlin Biotechnologia S.L., Tudela, Spain) efficiency in combination with the application of organic fertilizer, was performed in the pre-assigned plot of the 200BM (200 kg rai-1 of bovine manure compost applied every 15 days), started in June, 2007. The seaweeds extract (Ascophyllum nodosum) fertilizer was certified for organic agriculture in accordance with 2092/91/UE standard. The 2-capful (20 mL) of fertilizer were added into a 20-liter backpack sprayer, and applied to the base of asparagus fern once a month.

The Effect of Organic Fertilizer and Combination of Chemical Fertilizer (N:P:K: 15:15:15) on Asparagus Yield

The conventional experimental plot was located in Wattananakorn District, Sa Kaeo Province (70 km away from organic plantation). The field trials were divided into 16 randomized plots for 4 levels of fertilizers applied with 4 replications. The different levels of fertilizer in the study were 800 (800BM), 500 (500BM), 200 (200BM) kg rai-1 of organic bovine manure compost and the last treatment were the 200 kg rai-1 bovine manure compost with the 30 kg rai-1 chemical fertilizer (200BM+CF) applied every 15 days. The grower who handled the plot was trained to follow the sorting standard. Data on yield of marketable size asparagus were recorded.

Figure 1 The field trial data of average total yield in the each harvesting day during 2006. Typical pattern of 5 harvesting per year collected from common rate of organic fertilizer application at 200 kg rai-1.

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Table 2 Nutrient composition of fertilizers used in the study.

Bovine manure compost (BM)1/

Commercial organic fertilizer (OF)2/

pH 7.2 6.4 EC (dS m-1) 5.68 2.51 Total N (%) 1.50 0.84 Total P2O5 (%) 0.92 0.53 Total K2O (%) 1.64 1.20 Total Ca (%) 0.89 0.16 Total Mg (%) 0.20 0.12 Total Zn (mg kg-1) 73.40 67.40 Total Mn (mg kg-1) 899 958 Total Fe (mg kg-1) 10264 7820 Total Cu (mg kg-1) 23.20 20.40 Total Na (mg kg-1) 1404.30 451.80 1/ Organic bovine manure compost (BM), Taptim Siam

02 – Occupation Training Center, Sa Kaeo province. 1/ Organic fertilizer (OF), Sakura brand, Chiang Mai

province.

The Effect of Irrigation System in Combination with Organic Fertilizer Levels

The randomized complete block design (RCBD) was applied to an asparagus field with 2-rai area which had 27 ridges of asparagus. The first and last 5 rows were assigned to dripping irrigation, row number 6 – 8 and 20 – 22 were set up with mini sprinkler system. The last irrigation system was 1.2 m height sprinkler. The sprinklers were set up on the alternate row of asparagus. The yield of asparagus from the first and second crop on the different types of irrigation system was analyzed. In the third and forth crop, the effect of irrigation system in combination with organic fertilizer levels was studied. The organic fertilizer was applied to the experimental plot in the progressive levels of 200, 500 and 800 kg rai-1 broadcasted every 15 days.

Soil Analysis

Soil samples were collected from a 0-15 cm layer on each experiment plot. One composite

sample consisted of 4 portions was collected from the center of asparagus rows of each subplot at approximately 1 meter from the ends of the rows. The soil samples were air-dried by exposing in a dry, ventilated room at approximately 25oC for 3-4 days. All dried soil samples were stored in plastic-sealed bags and transported to the laboratory. Soil samples were ground in a stainless steel soil grinder, except samples for soil texture determination which were ground with a pestle and mortar, and passed through a 2-mm sieve. The procedure used for particle size analysis was the hydrometer method (Bouyoucos, 1962; Day, 1965). The sieved soils were collected and the sub-samples (approxi- mately 500 g) were stored in plastic bags for further analyses.

The pH of soil samples was determined based on the 1:1 (soil:water) suspension (McKeague, 1978; McLean, 1982). Rapid salinity in soil was measured by electrical conductivity (EC) from soil sample extracts (1:5 soil:water) (Richards, 1954). Cation exchange capacity (CEC) was determined with normal ammonium acetate extraction procedure (Hasse, 1972; Jackson, 1958).

The determination procedure of soil organic matter (OM) involved with reduction of potassium dichromate by organic carbon compounds and subsequent titration with ferrous ammonium sulfate (Walkley and Black, 1934). Total soil nitrogen (N), mainly organic N, was measured after wet digestion using semi-micro Kjeldahl method. The sodium bicarbonate method for available phosphorus (P) determination was used with some modification in color development procedure in the soil extracts (Bray and Kurtz, 1945). Extractable-K along with the soluble calcium (Ca) and magnesium (Mg) content were obtained by extracting with neutral salt solution followed by the measurement of their concentrations in the extract by atomic absorption spectrophotometer (Chapman, 1965).

Nutrient Analysis of Harvested Asparagus

Three asparagus samples were harvested from the certified organic farm, Sa Kaeo Province (latitude 13° 18′ N, longitude 102° 19′ E, altitude 161 meters), whereas another 3 samples were conventional asparagus, cultivated under EurepGAP regulation at Nakornpathom Province (latitude 13° 58′ N, longitude 99° 58′ E, altitude 10 meters).

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Spears were manual harvested by twisting the spears under the ground, washed and cut for 25 cm long. Approximate 1 kg of spears diameter greater than 1 cm with compact tip (grade A, Table 1) were sampled and placed into perforated plastic bags, keep refrigerated before sending to the accredited laboratory (IQA Laboratory Co., Ltd., Bangkok, Thailand) for the nutritional analysis in the next morning after harvesting.

The nutrition values of interest for this study were based on the labelling regulation of vegetable based processed products of Thailand and USA (NLH, 1995). The whole length of the harvested asparagus was 25 cm according to the grading system. When it arrived at the factory process line, the spear was cut to the length of 17 cm for packing. Therefore, all of the nutritional analysis in this study was based on the 17 cm length spear and calculated for 100 g of fresh asparagus. Nutritional values of asparagus were determined using official methods (AOAC, 2000a, f; AOAC, 2005). All analyses were done in duplicate.

Statistical Analysis

Daily field trials observations data from each replication were sum for the cumulative yield of each harvesting. Asparagus yield were average from 4 replications by treatment of fertilizer application and subjected to analysis of variance (ANOVA) test. Multiple range test of means was done on significant ANOVA tests with Turkey HSD (p<0.05) using statistical software (SPSS 15.0, SPSS Inc., Chicago, IL). Pair comparison was applied to test the significant different in nutritional composition of organic versus conventional asparagus produces.

Results The Effects of Organic Fertilizer Levels and Biofertilizer on Asparagus Yield

Quality of fertilizer is one of the most important factors resulting in their success/acceptance or failure/rejection by the end use farmers (Bulluck et al., 2002). However, there was no significant difference in asparagus yield between the application of bovine manure compost and another commercial brand organic fertilizer. The levels of bovine manure fertilizer applied to the plot (200, 500 and 800 kg rai-1) did not significantly increase the yield

of the asparagus of the first 3 crop harvested during January until July (Figure 2a). It suggests that there were no overall improvement in soil quality, at least beyond the 7 months of experimental duration.

After the third crop of harvesting, the field trial included the test for biofertilizer efficiency (Ekólogik), in combination with the application of organic fertilizer. The pre-assigned plot of 200BM (200 kg rai-1 of bovine manure compost applied every 15 days) was selected, and biofertilizer was sprayed on to the soil at the base of asparagus fern once a month staring from August. As shown in Table 3, the application of biofertilizer resulted in approximately 3 kg higher in yield of asparagus in the final crop (P < 0.05) compared with other levels of fertilizer application (Figure 2b). Though, the significantly increasing in the yield could not be obtained from the harvesting after immediate application of the biofertilizer in the fourth harvesting. It was found that the 200 kg rai-1 of organic fertilizer (200BM) treatment gave the lowest yield. The highest yield was achieved from the treatment of the 200 kg rai-1 organic fertilizer in combination with biofertilizer application (200BM+BF).

The Effect of Organic and Combination of Chemical Fertilizer on Asparagus Yield

The yield resulted from conventional agriculture (CA) was selected and compared with the yield obtained from organic farming. The organic agriculture (OA) plot selected for comparison was also from the third years of organic farming using same irrigation system, i.e. sprinkler, and having similar harvesting time, in raining season. The results show that there was no significant difference in the total weight (Figure 3) and income generated from the asparagus harvested from the organic agriculture practice on the organic farm management (OA-June 11 to July 10, 30 days) and the conventional agriculture practice which applied only the organic fertilizer or the combination of organic fertilizer and synthetic fertilizer (CA – July 25 to August 19, 26 days). In this case, it should be noted that the factors affecting the results include the differences in location, agricultural management and experience in grading of the asparagus produce. The conventional farm was 70 km away from the organic farm, and the growers were not under the contract farming arrangement with the company so they were less

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Table 3 Asparagus total yield from 3rd crop during August 13 to September 28 (47 days) and 4th crop during November 5 to December 15 (41 days) crop on the effects of organic fertilizer application and combined biofertilizer.

Organic fertilizer level (kg rai-1)

800BM 500BM 200BM 200BM + BF1/ 500OF Yield (g)

Crop 4 Crop 5 Crop 4 Crop 5 Crop 4 Crop 5 Crop 4 Crop 5 Crop 4 Crop 5

Grade A 12,023 ± 1,534

10,438 ± 699ab

11,684 ± 2,586

10,098 ± 1,046a

10,649 ± 2,398

9,658 ± 1,095a

11,071 ± 1,941

12,685 ± 1,253b

11,859 ± 1,180

10,507 ± 1,043ab

Grade B 1,683 ± 61 90 ± 29 1,693 ± 137 115 ± 60 1,670 ± 151 118 ± 15 1,638 ± 38 145 ± 30 1,685 ± 57 97 ± 29 Grade C 90 ± 21 - 85 ± 34 - 53 ± 31 - 60 ± 38 - 81 ± 27 - Grade D 23 ± 3 - 25 ± 6 - 15 ± 13 - 33 ± 33 - 21 ± 15 - Grade E 1,236 ± 83 1,208 ± 13a 1,158 ± 142 1,215 ± 31a 1,101 ± 141 1,205 ± 34a 1,120 ± 27 1,325 ± 61b 1,169 ± 46 1,215 ± 31aGrade F 540 ± 21 485 ± 21 510 ± 20 505 ± 37 483 ± 46 480 ± 18 498 ± 51 190 ± 23 520 ± 24 473 ± 30 Grade G 448 ± 36 395 ± 6 399 ± 23 410 ± 29 384 ± 79 393 ± 17 436 ± 54 418 ± 30 444 ± 26 375 ± 33 Grade H 303 ± 31 220 ± 37 255 ± 18 243 ± 33 228 ± 66 205 ± 21 235 ± 67 245 ± 39 254 ± 29 215 ± 47 Grade I 368 ± 25 265 ± 10 320 ± 21 303 ± 40 306 ± 55 253 ± 29 328 ± 62 305 ± 19 343 ± 29 263 ± 22 Grade J 264 ± 40 190 ± 14a 223 ± 6 220 ± 47ab 185 ± 60 168 ± 10a 219 ± 93 255 ± 34b 228 ± 30 182 ± 17aTotal weight (kg) 16.9 ± 1.7 13.3 ± 0.7 a 16.4 ± 2.8 13.1 ± 0.8 a 15.1 ± 2.9 12.5 ± 1.1 a 15.6± 2.4 15.9 ± 1.2 b 16.6 ± 1.3 13.3 ± 0.9 a

Price(Baht) 647 ± 70 515 ± 30 a 627 ± 121 503 ± 43 a 577 ± 118 481 ± 48 a 597 ± 93 620 ± 55 b 636 ± 54 518 ± 43 a 1/ The pre-assigned plot of the 200BM were selected to test for the biofertilizer efficiency, 2-capful (20 mL) of biofertilizer were added

into a 20-liter backpack, and sprayed at the base of asparagus plant, once a month frequency staring from August; The different letters indicated significantly differences (P < 0.05) compared within the same crop for different level of fertilizer application.

familiar with the grading categories. Some differences were found in several grades, which were rather considered as the difference in decision making of the grower’s when they graded the asparagus produce.

The yield from each treatment of fertilizer application either from organic or combination with chemical fertilizer was not significantly different in both crops. It could be suggested that the addition of chemical fertilizer did not give any advantage to the asparagus production. The quality indices of soil before and after the experiment are presented in Table 4. Soil in the subplot the applied with synthetic fertilizer became more acidic as the pH of soil decreased from 6.5 down to 5.7 after completed the experiment in December. It should be noted that the plot in which combined organic and chemical fertilizer was used had a very high level of phosphorus, 437 ppm, compared to the plots which applied only with the bovine manure compost, 254 ppm, at the same amount of organic fertilizer applied (200 kg rai-1).

Figure 2 (a) Effects of fertilizer levels application on cumulative total yield of organic asparagus during 5 harvesting seasons in 2007, (b) The expanded scale from the 3rd to 5th harvesting indicated improving in total marketable yield from 200 kg rai-1 bovine manure compost with biofertilizer application (200 BM+BF).

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Table 4 Soil index of the experiment plot on the testing the effects of organic fertilizer application and combined chemical fertilizer.

Soil index Fertilizer treatment applied every 15 days

800BM 500BM 200BM 200BM + CF Before experiment

Soil texture Loam Loam Loam Loam pH 6.7 6.3 6.5 6.4 EC (dS m-1) 0.91 0.67 0.91 0.9 CEC (cmol kg-1) 17.4 15.4 15 13.4 OM (%) 2.6 1.7 2.3 2.4 N (%) 0.09 0.07 0.08 0.09 P (ppm) 165 78 369 119 K (ppm) 180 190 260 220 Ca (ppm) 1800 1520 1520 1600 Mg (ppm) 360 380 350 360

After experiment Soil texture Clay loam Clay loam Clay loam Clay loam pH 5.9 5.7 5.7 5.7 EC (dS m-1) 0.59 0.71 0.65 0.62 CEC (cmol kg-1) 20.2 18.8 16.8 18.8 OM (%) 2.2 2.2 2.6 2.8 N (%) 0.19 0.01 0.12 0.13 P (ppm) 225 239 254 437 K (ppm) 190 230 210 280 Ca (ppm) 1920 1600 1680 1640 Mg (ppm) 370 350 320 370

The Effects of Irrigation Systems on Asparagus Yield

The field trial was conducted to evaluate suitable irrigation systems, namely, dripping water, mini sprinkler, and sprinkler, on the yield of asparagus. There was no effect of irrigation system on asparagus yield from the first harvesting after setting up the irrigation system. The first crop was harvested during February; but the second crop harvested during April, the sprinkler system outperformed significantly giving higher yield (p < 0.05) than other systems (data did not shown). The mean of the total weight of marketable yield from the sprinkler system was 4.7 kg, while the dripping and mini sprinkle gave only 1.5 – 2 kg 30 m-3 of experimental plot, which is equivalent to 1,567 kg ha-1 from sprinkler system compare to 500-667 kg ha-1 from dripping and mini

sprinkler, respectively. This second crop was harvested for 21 days during April 1- 21.

After the second crop the organic fertilizer was applied to the experimental plot in the progressive levels at 200, 500 and 800 kg rai-1 for every 15 days. It was found that the third crop, during June 11 to July 10, the asparagus yield did not respond to the fertilizer level. The results were more pronounced in the later crop, during August and September (4th crop). Figure 4 summarize the results on the effects of irrigation system and the applied levels of organic fertilizer. The amount of fertilizer applied gave significantly different results when compared in the same irrigation system (P < 0.05). Organic fertilizer at the level of 800 gave higher yield than the level of 500, in contrast with the level of 200 kg rai-1 organic fertilizer gave the lowest yield.

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Nutritional Compositions of Conventional and Organic Asparagus

Nutritional analysis was conducted according to regulation of Thai RDI, U.S. Recommended Daily Allowance (USRDA) and Canada labeling standard. It was found that the asparagus contained approxi- mately 93% of water on wet basis and had very low calories, only 27 kcal for 100 g of fresh asparagus was found. It also had very low in fat and sodium but loaded with vitamins and minerals.

Table 5 shows the nutrition content of 100 g fresh asparagus produced under difference agriculture system. Organic asparagus samples were harvested from Sa Kaeo Province while conventional asparagus were collected from Nakornpathom Province. Carbohydrate and sugar content of the organic asparagus were significantly higher than conventional asparagus (P < 0.001). Asparagus carbohydrate composes of two main portions of dietary fiber and sugar. From Table 5, organic asparagus had higher total sugar than conventional asparagus but not in dietary fiber. However the result was unable to conclude since the samples were collected from two different locations. This part of the study required further field trial to confirm the results.

Discussion

Soil Quality Soil organic matter has a major influence on soil

aggregation, nutrient reserve and its availability moisture retention and biological activity (Fließbach et al., 2007; Ryan et al., 2001). After the application of organic fertilizers, slight improvement of soil organic matter (OM) resulting in soil texture improvement from loam to clay loam, causing the increase of the value of cation exchange capacity (CEC). CEC is also influenced by soil pH (Richard, 1954). Therefore, the decrease in soil pH after the experiment should resulted in increasing value of CEC. Thus, nutrients can be held in the soil and not lost through leaching and can subsequently be released for crop uptake.

After the experiment, the value of electrical conductivity (EC) decreased reflecting lower soil salinity (Richard, 1954). This may indicate that the soil is more suitable for growing crops. It should be noted that, in this study, high level of phosphorus found in combined organic and chemical fertilizer might harm the balance of soil in long run.

Table 5 Nutritional composition of organic asparagus from farm in Sa Kaeo province with difference in cultivation year.

Nutrition per 100g OA CA Calories (kcal) 28.4 ± 0.4 a** 25.6 ± 0.6 b** Calories from fat (kcal) 2.73 ± 0.36 1.85 ± 0.19 Fat (g) 0.30 ± 0.04 0.21 ± 0.02 Protein (g) 2.24 ± 0.03 2.41 ± 0.10 Carbohydrate (g) 4.19 ± 0.06 a*** 3.53 ± 0.01 b*** Dietary fiber (g) 1.64 ± 0.06 1.68 ± 0.01 Total sugars (g) 2.12 ± 0.08 a* 1.60 ± 0.10 b* Vitamin A (µg) 22.7 ± 5.2 21.2 ± 0.8 Vitamin B1 (mg) 0.08 ± 0.01 0.08 ± 0.01 Vitamin B2 (mg) 0.05 ± 0.01 0.04 ± 0.00 Vitamin C (mg) 18.8 ± 1.5 16.7 ± 1.1 Water (g) 92.5 ± 0.1 b** 93.1 ± 0.1 a** Ash (g) 0.74 ± 0.04 0.76 ± 0.01 Calcium (mg) 14.6 ± 1.3 15.0 ± 1.0 Iron (mg) 0.72 ± 0.09 0.60 ± 0.02 Sodium (mg) 2.3 ± 0.1 2.1 ± 0.1

1/ The different letters indicated significantly difference in pair comparison; * indicated significantly difference at 95 percent of confident (p<0.05); ** indicated significantly difference at 99 percent of confident (p<0.01), *** indicated significantly difference at 99.9 percent of confident (p<0.001).

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Quantitative Analysis of Harvested Asparagus Usually in the winter, asparagus fern remains

green and the harvesting can be prolonged, while the harvesting in the summer (April-May) had shorter harvesting period but higher yield. Figure 3 shows the typical cumulative plot of asparagus yields obtain in 1 year of cultivation.

The more organic fertilizer applied, the higher asparagus yield obtained. The level of organic fertilizer application affected the yield of asparagus in the 3-year old plot but did not affect the 1-year old plot. The first year of asparagus production was not responded well to the amount of organic fertilizer supplied to the soil. There was no significant difference in the yield obtained from the 200, 500 and 800 kg rai-1 organic fertilizer applications. Sea weed extract biofertilizer in combination with 200 kg rai-1 of bovine manure compost significantly increased the yield of asparagus.

Then, the selective comparison was made from 2 sets of the data, the 26-day harvesting during June and July from the organic farming system with the 30-day harvesting of the closest harvesting crop in conventional farming system, during July and August. Asparagus yields in the organic farming system were not significantly different from conventionally managed farm or identically managed first-year transitional plots. Since the organic fertilizer treatment at the rate of 200, 500 and 800 kg rai-1 applied to the plots that has been prevented from synthetic chemical application could also consider as the transitional period.

There was the study reported that poorly adapted cultivar was partially responsible for lower yields in organic farming system when compared with conventional farming system (Murphy, 2007). The soil properties of organic and conventional managed asparagus field in Sa Kaeo Province were not significantly different, except that conventionally managed soil had higher phosphorus deposit.

Within the irrigation systems chosen, namely, dripping water, mini sprinkler and sprinkler system, the sprinkler system was the most suitable irrigation system for the asparagus cultivation. Asparagus yield obtained from the field irrigated with the sprinkler system was twice higher than the mini sprinkler system and 4 times higher than the dripping irrigation. Nevertheless, there was a serious disadvantage of the sprinkler system as it helps to

Figure 3 Asparagus yield between organic and conventional farming systems during crop of June-August, 2006. The legends of total yield comprised of 10 marketable grades classification.

Figure 4 Effects of organic fertilizer levels and irrigation system on asparagus yield during crop of August 8 – September 11, 2006. spread out the weeds, and in organic agriculture removing the weed generally takes up a lot of time. Although the higher the fertilizer applied the greater yield of asparagus was obtained; there was a more distinct trend in the latest crop for the increasing as obtained from Figure 4. However, the major factor contribution to the different in asparagus yield was the irrigation system while the effect of organic fertilizer was less pronounced.

Improper or inadequate control of weeds was one of the primary factors which reduced the plant growth and development, and consequently yield, of asparagus. Weeds have been a major concern in asparagus production since deep plowing was not possible and because asparagus did not produce a dense canopy to shade out weeds. Field trial that set up for irrigation experiment was the 3-year old organic asparagus field, so the problem of weed control was critical. The weed problem was also enhanced by the sprinkler water system, since the

72 S. Lorlowhakarn et al. Thai Journal of Agricultural Science

water was sprayed all over and between the ridges of the asparagus, enhanced spreading out of weeds. Generally, the asparagus cultivation area of 2-rai (0.32 ha), would require at 2 manpower to provide efficient care, because the weeds in organic agriculture have to get rid of manually.

Qualitative Analysis of Harvested Asparagus

Asparagus is one of the most nutritionally well-balanced vegetables in existence. It leads nearly all produce items in the wide array of nutrients it supplies in significant amounts for a healthy diet. Organic asparagus derived from Sa Kaeo Province had significantly higher sugar content than the conventional asparagus derived from Nakornpathom Province, which indicates that the organic asparagus would be sweeter in taste and probably gain more preferences among the consumers. Even though there was no difference in the dietary fiber content, consumers may prefer sweeter taste of organic asparagus than the conventional asparagus. There were the confirmation from the study of Worthington (2001) for the relationship between the production of carbohydrate and protein in plants. Nitrogen from any kind of fertilizer affects the amounts of vitamin C as well as the quantity of protein produced by plants. When plant harbors a lot of nitrogen, protein production is increased and carbohydrate production is reduced. However, the increased protein that is respond to high nitrogen levels contains lower amounts of certain essential amino acids such as lysine and consequently has a lower quality in terms of nutrition. If there is more nitrogen than the plant can metabolize into increased protein production, the excess nitrogen is accumulated as nitrates and stored predominantly in the green leafy part of the plant. Because organically managed soils generally provide plants with lower amounts of nitrogen than chemical fertilizing soils, it would be expected that organic crops would have more vitamin C, less nitrate and less protein but of a higher quality than comparable conventional crops. Protein content of conventional asparagus were significantly higher than that of organic asparagus (P < 0.001), but the difference was not found in vitamin C content. The average protein content in conventional asparagus was 2.5 g 100 g-1 while organic asparagus had 2.0 g 100 g-1 of fresh asparagus sample, respectively.

Table 6 demonstrates the nutrition information of raw asparagus provided by the USDA National nutrient database for standard reference. Even though, the asparagus cultivated in Thailand and in the United States differs in varieties. The varieties of asparagus planted in Thailand were generally Brooke’s or Brooke’s improved variety. It is surprised to note that the average vitamin C content of Thai asparagus (17 mg) was 3 times higher than that of the USDA standard (5.6 mg).

The yields as well as the nutrient analysis in this study demonstrated that organic asparagus production is viable and sustainable, provided that a suitable approach is taken by the farmers. The project may lead to a number of conclusions with important implications for the national strategies for organic agriculture in Thailand.

First, there is a prospect for broadening the production base for organic agriculture in selected crops. Contract farming, as demonstrated in this study, would be necessary to broaden the production base of organic products. The farmers should not only be supplied with high quality seedlings, but also the consultancy throughout the cultivation process. Only through this measure, the companies would be able to collect enough products to supply to the market. At the same time, the farmers would also benefit from the reasonable price for their harvested crops. Our research incorporated the concept of contract farming in the organic agriculture model consistent with the national strategies developed. The results of this study suggest that this unique model of organic asparagus production is possible to apply to other crops which possess similar characteristics to asparagus, such as baby corns and spices. The basic knowledge in this research is also helpful for further in-depth research, such as finalization of the optimum application of organic fertilizer or formulation of biofertilizer for asparagus and other selected crops.

Second, Thai organic products have high potential to compete in the world’s markets. The results of this study demonstrated that organic asparagus had significantly higher sugar content than the conventional asparagus. Moreover, the research showed that organic asparagus contained very high content of vitamin C. In comparison with asparagus produced in the United States, the vitamin C levels in Thai organic asparagus are

Vol. 41, No.1-2, 2008 Organic asparagus production for organic agriculture strategies in Thailand 73

Table 6 Nutrition values of raw asparagus spears from Thailand and United States.

Nutrition per 100g Thailand1/ US2/ Calories (kcal) 27 ± 1 20 Calories from fat (kcal) 0.26 ± 0.06 0.12 ± 0.01 Fat (g) 2.20 ± 0.27 2.20 ± 0.02 Protein (g) 4.01 ± 0.27 3.88 Carbohydrate (g) 1.6 ± 0.1 2.1 Dietary fiber (g) 1.97 ± 0.25 1.88 Total sugars (g) 21 ± 5 38 Vitamin A (µg) 0.074 ± 0.008 0.143 ± 0.016 Vitamin B1 (mg) 0.043 ± 0.005 0.141 ± 0.007 Vitamin B2 (mg) 17.0 ± 2.1 5.6 ± 0.21 Vitamin C (mg) 92.81 ± 0.28 93.22 Water (g) 0.71 ± 0.06 0.58 ± 0.01 Ash (g) 13 ± 2 24 ± 1 Calcium (mg) 0.57 ± 0.11 2.14 ± 1.35 Iron (mg) 2.18 ± 0.11 2.00 ± 0.26 Sodium (mg) 27 ± 1 20 1/ Mean value and standard deviation of asparagus from Thailand obtained from 12 samples. 2/ Mean value and standard deviation of asparagus from US obtained from USDA database

(http://www.nal.usda.gov/fnic/foodcomp/search/) of approximately 4-6 samples.

approximately 3 times higher than those of US asparagus. This nutrient analysis has positive implications for consumer tastes, enabling Thai organic produce compete successfully in the world’s markets.

The extension of this study to other selected crops will significantly broaden the organic agriculture production base in Thailand. This will provide a basis for Thailand to become a center of excellence in organic agriculture in this region. In light of the foregoing, it is very clear that the organic agriculture can be implemented successfully in Thailand. The research and development into the proper techniques used for each selected crop would be vital to the success of the production of organic products.

Acknowledgments

We are very grateful to Mr. Paichayon Uathaveekul,

chairman of Swift Co., Ltd., for assistantship and facilitating in the field trials from the company’s contract farmers. Part of this work is most grateful to financial contribution from the International Trade Center of European Union (ITC-EU) Asia

Trust Fund and Thailand’s National Innovation Agency (NIA). The authors are also grateful to Dr. Athapol Noomhorm and Ms. Weena Srisawas of Asian Institute of Technology and the staff of NIA who provided outstanding support to this study.

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Manuscript received 10 April 2008, accepted 6 May 2008

Now online at http://www.thaiagj.org