Article pubs.acs.org/JAFC
Yield, Quality, and Nutrient Concentrations of Strawberry (Fragaria ×ananassa Duch. cv. ‘Sonata’) Grown with Different Organic Fertilizer Strategies Bhaniswor Pokhrel,*,† Kristian Holst Laursen,§ and Karen Koefoed Petersen† †
Department of Food Science, Aarhus University, Kirstinebjergvej 10, DK-5792 Aarslev, Denmark Plant and Soil Science Section, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg, Denmark
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ABSTRACT: Four combinations of two solid organic fertilizers (Monterra Malt and chicken manure) applied before planting and two liquid organic fertilizers (broad bean and Pioner Hi-Fruit/K-Max) given through drip irrigation (fertigation) were compared with inorganic fertilization regarding growth, yield, nutrient concentration, and fruit quality of strawberries. Broad bean fertigation combined with Monterra Malt resulted in a similar fruit yield as inorganic fertilizer and a higher yield than Monterra Malt combined with Pioner; however, total soluble solids, firmness, and titratable acid were improved with Pioner fertigation, although these parameters were more affected by harvest time than the applied fertilizers. The concentrations of most nutrients in fruits and leaves were higher in inorganically fertigated plants. The reductions in fruit yield in three of four treatments and fruit weight in all organic treatments may be due to a combination of the following conditions in the root zone: (1) high pH and high NH4+/NO3− ratio; (2) high EC and/or high NaCl concentration; (3) cation imbalance; and (4) nutrient deficiency. KEYWORDS: fertigation, fruit quality, marketable yield, nutrient concentration, organic fertilizer, strawberry
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of soil, and fruit yield of strawberries.6 Leaf nitrogen (N) concentrations between 2.0 and 2.8% of the DM seem to be the optimal level in strawberries, and N concentrations in this range are positively correlated with fruit yield; however, the N concentration in the leaf varies according to developmental stage.13,14 Soil pH is one of several key factors that determine the availability and uptake of mineral nutrients from the root zone.15,16 The optimum range of soil pH for strawberry cultivation is 5.5−6.5, although apparently contradictory reports have been given by different researchers. Jett17 showed that the optimum soil pH for production of strawberries was between 5.8 and 6.5, whereas Milosevic et al.15 suggested a slightly acidic soil pH between 4.5 and 6. However, in the latter investigation they used soil extraction with 0.01 M KCl, which results in a pH value approximately 0.9 unit lower than water extraction.18 Nutrient uptake by strawberry plants is impaired below or above this pH range due to a reduced solubility and availability of most of the plant nutrients.15 Reduced availability of micronutrients may occur at high pH due to tight adsorption to negatively charged soil particles and soil organic matter or due to precipitation as, for example, carbonates, phosphates, or hydroxides.11,16 Wang and Lin5 and Hargreaves et al.6 suggested that composted municipal waste and manure increase soil pH and thereby reduce the concentrations of available nutrients.
INTRODUCTION The production and sale of strawberries (Fragaria × ananassa Duch.) has increased by 14.8% globally and by 13.1% in Denmark from 2010 to 20131 because of the fruit’s flavor, richness in nutrients, and availability at a reasonable price. In recent years, organic fruits and vegetables have received great public attention due to an increasing focus on human health and sustainable agricultural production.2 Organic farming is considered more environmentally friendly due to the prohibition of inorganic fertilizers and synthetic pesticides.3 The majority of studies on organic nutrient management in strawberry production have focused on soil-applied organic fertilizers (different types of compost and manure).4−6 These studies have shown that organically grown strawberries can give similar or even better yields and quality than conventionally grown strawberries.6,7 Moreover, Cayuela et al.4 reported that organically grown strawberry fruits have higher sugar and dry matter (DM) contents, whereas Hargreaves et al.6 did not find any significant difference in sugar content between organically and conventionally grown fruit. Despite the fact that higher contents of health-promoting compounds have been found in organically grown strawberries,8 controversies still exist regarding systematic differences in nutritional and quality parameters of organic versus conventionally grown produce.6,8,9 Nutrient concentrations in leaf samples are valuable indicators of the fruit yield and nutrient status of strawberry fruit.5,10,11 A high mineral content in leaf tissue often results in better plant growth as well as a higher fruit yield.11 According to Reganold et al.,8 a positive correlation was found between mineral content in leaf and fruit. In contrast, not all studies have shown positive correlations between N concentrations in fertigation and in fruit yield12 and micronutrient concentrations © XXXX American Chemical Society
Received: March 17, 2015 Revised: May 25, 2015 Accepted: May 26, 2015
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DOI: 10.1021/acs.jafc.5b01366 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry Table 1. Treatments, Growing Media, and Applied Fertilizersa treatment
peat
solid fertilizer
liquid fertilizer until 28 DAP (NPK %)
liquid fertilizer after 28 DAP (NPK %)
inorganic vegetative (130 ppm of N) broad bean (0.51−0.09−0.41)
inorganic generative (90 ppm of N) broad bean (0.51−0.09−0.41)
inorganic (IN)
Pindstrup 2
Monterra Malt + broad bean (MB) Monterra Malt + Pioner (MP) chicken manure + broad bean (CB) chicken manure + Pioner (CP)
Pindstrup 0
inorganic already included by company 33 g of Monterra Malt (4−1−5)
Pindstrup 0 Pindstrup 0
33 g of Monterra Malt (4−1−5) 66 g of chicken manure (2−1−2)
Pioner Hi-Fruit (4−1−5) broad bean (0.51−0.09−0.41)
Pioner K-max (3−1−7) broad bean (0.51−0.09−0.41)
Pindstrup 0
66 g of chicken manure (2−1−2)
Pioner Hi-Fruit (4−1−5)
Pioner K-max (3−1−7)
a
Solid fertilizers were applied to the peat before planting, and liquid fertilizers were applied via drip fertigation.
Table 2. Nutrient Concentrations, DM Content, and pH of Growing Media before and after Addition of Solid Inorganic and Organic Fertilizera growing media peat + inorganic fertilizers peat + chicken manure peat + Monterra Malt peat a
NH4 +-N (mg kg−1)
NO3−-N (mg kg−1)
total N (%)
organic C (%)
C:N ratio
total P (mg kg−1)
K (mg kg−1)
SO42− (mg kg−1)
DM (%)
pH
171.3
333.7
0.59
35.0
59
4.03
17.7
3.53
49.3
5.9
752.0 373.2 104.0
56.5 48.2 45.2
1.02 1.36 0.59
36.1 38.8 34.7
35 29 59
11.00 6.37 0.45
55.0 83.3 1.7
3.42 20.51 0.42
50.6 50.3 47.9
6.9 5.8 6.0
Values are in mg kg−1 DM or % of DM. tunnel at the Department of Food Science, Aarhus University, Aarslev, Denmark (10°27′ E, 55°18′ N). The mean temperatures outside the tunnel were 16.5, 16, and 14 °C in July, August, and September, respectively. Cold-stored strawberry tray plants (Fragaria × ananassa Duch. cv. ‘Sonata’) with 9−15 mm crown diameter were planted in plastic pots (1.4 L) on July 4, 2011. After planting, pots were placed on wooden benches (tabletops) with a distance between benches of 120 cm and a distance between plants of 20 cm, giving 4.2 plants per square meter. Biological control of aphids, spider mites, and thrips was applied every 2 weeks. In addition, 4 weeks after planting, Nemasys, a biological control agent containing the nematode Heterorhabditis spp., was applied against root cutworms. Then, from 5 weeks after planting, plants were sprayed with a 0.3% sulfur solution four times at an interval of 1 week to reduce powdery mildew (Sphaerotheca macularis) attack. Fertilizer Treatments. Pots were filled with peat (Pindstrup substrate 2 standard mix (1 kg m−3 16−6−20 NPK + micronutrients, 0.4 kg m−3 powdered superphosphate (Ca(H2PO4)2 + 2CaSO4), and 0.05 kg m−3 Micromax); Pindstrup Mosebrug A/S, Denmark) for the inorganic treatment and the same product without macro- and micronutrients was used for the organic treatments. Five treatments, one inorganic (IN) and four organic (Table 1), were established in four replicates in a completely randomized layout with four plants per replicate. The organic treatments were combinations of two solid organic fertilizers, composted chicken manure (2−1−2 NPK, Farmergødning, Denmark) and Monterra Malt (4−1−5 NPK, Borregaard BioPlant ApS, Denmark), and two organic liquid fertilizers, broad bean (0.51−0.09−0.41 NPK, Farmergødning, Denmark) and Pioner (Hi-Fruit 4−1−5 NPK or K-Max 3−1−7 NPK, Azelis, Denmark). The broad bean fertilizer was chosen among a very limited number of certified organic fertilizers available in Denmark. Pioner Hi-Fruit and Pioner K-Max are not from organically certified source material but are allowed for organic production. Before planting, either 66 g of chicken manure or 33 g of Monterra Malt was placed into the planting hole just underneath the root system. The nutrient content of the growing media was analyzed by a commercial laboratory (Agrolab, Germany) and is shown in Table 2. Plants were drip fertigated with one dripper per plant. Before the green fruit stage, which occurred 28 days after planting (DAP), plants were supplied with inorganic fertilizer with high N (130 ppm of N) and low K and Ca concentrations, broad bean, or Pioner Hi-Fruit. From 28 DAP plants were fertigated with inorganic fertilizer with low N (90 ppm of
Most organic fertilizers contain all essential nutrients required for plant growth and development, but at varying concentrations, and most of them have to be mineralized prior to plant uptake.5,6 Thus, the availability of nutrients for plant uptake may not be instantaneous and depends on, among other factors, temperature and humidity.19 Therefore, plants may not necessarily receive adequate amounts of nutrients during the active phases of growth, and an imbalance between nutrient release from organic fertilizers and plant uptake may lead to leaching.20 With increasing concern for the environment and food safety, fertigation (irrigation with a nutrient solution) is considered a viable option to overcome leaching by synchronizing nutrient demand and supply to the plant. However, optimal nutrient supply through fertigation with organic fertilizers is difficult due to varying rates of mineralization and the lack of organic fertilizers with only one or a few nutrients.21 Thus, the choice of suitable organic fertilizers for fertigation is imperative to prevent plant nutrient deficiency and to increase the yield and quality of organic strawberries grown in inert growing media. The effects of organic fertilizers applied via drip irrigation combined with different solid organic fertilizers on the yield, quality, and nutritional status of strawberries are poorly understood as only a very limited amount of research has been conducted within this area. In this context, we hypothesized that fertigation with organic fertilizers results in similar yields and quality of strawberries compared to fertigation with inorganic fertilizers. However, a very limited number of certified organic liquid fertilizers are available in Denmark. The study aimed at elucidating the combined effect of two different solid and two liquid organic fertilizers on the yield, quality, nutrient status, and DM content of leaf tissue and fruit. In addition, the effects on leaf chlorophyll content and pH, electrical conductivity (EC), and nutrient content of drainage water were studied.
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MATERIALS AND METHODS
Plant Material and Growth Conditions. The experiment was conducted from early July to late September 2011 in an open plastic B
DOI: 10.1021/acs.jafc.5b01366 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry Table 3. Nutrient Concentrations, pH, and EC of Applied Fertigation Solutions pH, EC (dS m−1), and nutrient content (mg L−1)
inorganic (until 28 DAP)
inorganic (after 28 DAP)
broad bean (in both periods)
Pioner Hi-Fruit (until 28 DAP)
Pioner K-Max (after 28 DAP)
pH EC NO3−-N NH4+-N P K Mg Ca S B Na Cl Mn Fe Zn Cu Mo
5.9 1.67 112 15 31 142 29 121 48 0.24 20 45 0.37 1.33 0.44 0.13 0.03
5.7 1.65 83 8.3 24 165 23 179 90 0.4 24 46 1.34 1.07 0.45 0.36 0.04
5.9 1.44 2 21.4 12 106 18 141 31 0.03 20 66 0.09 1.04 0.26 0.01
