SAINT MARTIN’S UNIVERSITY
The Effect of Organic and Inorganic Fertilizers on the Growth and Development
of Carica papaya L.
Rosary Faleono
May 4, 2007
Senior Seminar II
Final Draft
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Table of Contents
Abstract…………………………………………………………………………..pg. 2
Introduction………………………………………………………………………pg. 2 - 6
Materials and Methods…………………………………………………………...pg. 6 - 8
Seed Management………………………………………………………...pg. 6 - 7
Application of Organic and Inorganic Fertilizer………………………….pg. 8
Measurements and Data Analysis……………………………………… pg. 9
Results….…………………………………………………………………………pg. 9 - 14
Discussion…………………………………………………………………………pg. 14 -16
Acknowledgments……………………………………….………………………..pg. 16 - 17
Literature Cited………………………………………….………………………..pg. 18
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ABSTRACT
The frequent use of fertilizers is important for the production of agriculture around the
world today. Carica papaya L. is a tropical fruit plant, a widely consumed agricultural product
for its production of papaya fruit. I hypothesized that organic fertilizer applied on a weekly basis
would generate a faster growth rate in Brazilian Sunshine papaya plants compared to inorganic
fertilizer. I used Miracle-Gro® Water Soluble All Purpose Plant Food as the inorganic fertilizer
and Alaska Fish Emulsion as the organic fertilizer. The control group was treated with tap water.
The growth rates were measured after germination for a total of four weeks. When all data had
been collected, I used Analysis of Variance tests to compare the growth rates and development of
leaf width, leaf length, and stem height among the inorganic, organic, and water treatments. My
results did not show significant differences among the growth and development of papaya plants
treated with water, organic fertilizer, or inorganic fertilizer. Also, there were no differences in
the growth and development of the papaya plants between the use of either fertilizer or water.
All the papaya plants steadily increased in size.
INTRODUCTION
Carica papaya L., commonly known as papaya in the United States is a large, woody,
fruit-bearing plant believed to have originated either from Central America or southern Mexico.
Papayas are only found in places where the weather is warm, approximately 22°C to 26°C, and
are located in every tropical and subtropical region around the world. Papayas are famous for
their fruit, also called papaya, that are pear-shaped and taste somewhat like cantaloupe. There
are many types of papaya. Homestead Selection papaya, Solo Line 8 papaya, and Brazilian
Sunshine papaya are just a few members of the papaya family (Dedolph, 1962; Aiyelaagbe et al.,
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1985). There was no particular reason why I decided to use Brazilian Sunshine papaya other
than the fact that it germinates in a matter of a few weeks under proper care.
The frequent use of fertilizers is an important part of agricultural production around the
world (Chand et al., 2006). For several years, major crop producers have preferred the use of
inorganic fertilizers due to its high yield in crop productivity. However, long-term applications
of inorganic fertilizers have caused a noticeable decrease in crop productivity and an increase in
pollution around its surrounding environment (Chand et al., 2006). Recently, many agricultural
companies have shifted from using inorganic fertilizers to organic fertilizers (Luo et al., 2006).
A study was conducted to determine the yield responses and leaf nutrient concentrations
broiler chicken manure had on lima bean production (Luo et al., 2006). Two fertilizers were
tested: organic broiler manure (BM) and inorganic ammonium nitrate (AN). During the first
year, both fertilizers were applied all at once with no further applications of fertilizers for that
year. On the second year, BM treatments were applied only once and AN treatments were split
into three separate, but equal applications. Along with the fertilizers, water was also applied to
the lima beans by the use of an overhead sprinkler. After the 2-year period, the crops were
harvested and lima bean yield was determined. Results from the study showed variance in leaf
nutrient concentrations, but fresh pod yields were an equal amount or higher with BM treatment
than AN treatment (Luo et al., 2006). These results were similar to those from previous studies
with the same fertilizers on sweet corn, cabbage, and forages, which are crops grown to feed
livestock.
Due to the low yield production of agriculture with the use of organic manures, the
application of organic fertilizers with little or no fossil fuel-based inorganic fertilizers is rapidly
gaining favor (Anwar et al., 2005). In 2005, Anwar et al. studied the effect of a combination of
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organic manures and inorganic fertilizers on the growth and quality of essential oil of European
and Reunion basil crops. There were six treatments (T) used to grow the basil crops. T1 was the
control consisting of only water; T2 was the farm yard manure (FYM); T3 was the
vermicompost, an organic fertilizer consisting of a mixture of partially decomposed organic
waste, bedding, and worm castings; T4 was the inorganic fertilizer, a standard mixture of
nitrogen, phosphorous, and potassium (NPK); T5 was a combination of FYM and NPK fertilizer;
and T6 was a combination of vermicompost and NPK fertilizer. The setup was a randomized
block design (RBD) with four replications of each plant. The treatments consisting of FYM,
vermicompost, and NPK fertilizer alone were applied to the soil before planting. The two
combination treatments were applied twice, once at the time of planting and an equal amount
was applied a month after planting. After a period of 3 months, the crops were harvested. The
essential oil from each plant was extracted, and fresh weights were recorded in each plot.
Results showed that the application of T2 thru T6 showed a significant increase in fresh
weight, dry matter, and oil yield in the basil crop over the control (T1). The application of FYM
alone showed the lowest increase over the control and the application of a combination of
vermicompost with NPK fertilizer showed the highest increase over the control followed by the
combination treatment of FYM and NPK fertilizer. Mean herb yield of the plants grown with
NPK fertilizer alone was significantly higher than the treatments consisting of either of the
organic manures applied alone. However, each of the combination treatments resulted in greater
fresh weight yield and dry matter yield than the organic or inorganic fertilizers alone. Previous
studies conducted by Patra et al. (2000) and Chand et al. (2001) also reported similar results in
menthol mint crops. At the end of the study, Anwar et al. (2005) concluded that the application
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of organic manure, combined with a minimum dose of inorganic fertilizer, was better than
inorganic fertilizer or organic manure alone for yield, nutrient uptake, and quality of basil.
A similar field experiment was conducted by Chand et al. (2006) on mint and mustard
crops in subtropical India. The setup was also similar, consisting of a RBD with 8 combination
treatments composed of different ratios of FYM and inorganic fertilizer and replicated three
times. T1 was the control, T2 was FYM alone, and T3 to T8 were inorganic fertilizers with
different NPK (nitrogen-phosphorous-potassium) ratios mixed with various amounts of FYM.
All treatments were applied continuously to the crops for 7 years.
First, the mint seeds were planted, immediately followed by irrigation. Irrigation was
then applied every 10 – 15 days (Chand et al., 2006). Half of each treatment was applied at the
time of planting, and the remaining half was applied 48 days after planting. At maturity, the crop
was harvested and weighed. Dhaincha, a weed commonly grown in India to restore nitrogen to
depleted soils, was sown and plowed down after 45 days to allow for its decomposition. Next,
mustard seeds were sown and a full supply of NPK fertilizer was applied. The crop was
harvested 4 months later and weighed. Results from the experiment showed that the highest
increase in dry matter was in T4, which was NPK 133:40:40 fertilizer mixed with an equal
amount of FYM as in T3, with an increase of 92.8% over the control (T1). Chand et al. (2006)
concluded that a combination of organic manure and inorganic fertilizer increased the yield and
dry matter of mint and mustard crops.
The purpose of my research study was to measure the effects of organic and inorganic
fertilizers on the growth and development of Carica papaya L. The plants were grown in a
controlled environment under warm, moderate temperatures with three different treatments of
fish manure, inorganic fertilizer, and water to promote plant growth. This experiment examined
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the rates at which the fertilizers increased the growth of papaya plants. I hypothesized that the
use of 100 ml of organic fertilizer on Brazilian Sunshine papaya plants on a weekly basis would
generate faster growth compared to the application of 100 ml of inorganic fertilizer or water,
because previous studies had concluded that organic manures mixed with little inorganic
fertilizer increases the growth of agricultural products.
MATERIALS AND METHODS
Seed Acquirement and Management
Papaya plants are fast growing, woody, tropical plants that produce flowers and fruits.
Papaya plants are easy to grow from seeds, producing mature fruit within 9 - 12 months after
sowing (Gonsalves, 1998). However, papaya fruit are sensitive to changes in climate. Fruit
production can be affected by climatic factors such as drought and extremely cold or warm
temperatures (Aiyelaagbe et al., 1986). The plant itself is susceptible to changes in climate and
can also be affected by drought or extreme temperature changes.
The papaya seeds used for this study were Carica papaya Brazilian Sunshine, ordered
from Trade Winds Fruit (www.tradeswindsfruit.com/order.htm). Three greenhouses were
constructed to house the papaya seeds, and 2 trays were placed in each greenhouse to hold the
runoff water. Each greenhouse contained two 40 watt fluorescent bulbs as a source of light and
heat for the plants. The lights were placed 12 inches above the plants so as not to cause
excessive heat that might burn the seeds or plants. There were 60 replicates using thirty 32ounce transparent plastic cups per experimental group. Transparent cups were used to allow
observation of root growth of the papaya plants. Using small scissors, the bottom of each cup
was punctured with five small holes about 0.7 mm in diameter for water drainage from the soil.
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Each cup was ¾ filled with a soil made with a mixture of 1 part vermiculite and 1 part
Greensmix® potting soil (Waupaca Northwoods LLC, Waupaca, WI). Vermiculite was used in
order to help the papaya plants increase their absorption of moisture and nutrients when applying
the fertilizers or water. The seeds were divided into three sampling units, with 60 seeds per
group: 1) inorganic fertilizer, 2) organic fertilizer, and 3) control group of water. The soil was
warmed overnight to raise the temperature of the soil to between 18°C-38°C, because this was
the optimal range for successful papaya growth (Alarcon et al., 2002). The next day, the
temperatures were checked with a digital thermometer. Noting that the soil in each cup had
reached the desired temperature range, two seeds were planted in each cup, approximately one
inch into the soil, allowing room for root growth. I placed 10 transparent cups per experimental
group, 5 cups per tray, in each greenhouse as shown in Figure 1.
Inorganic
Organic
Water (Control)
Figure 1. The positioning of the experimental groups in each greenhouse. This was the order in which all
the plants were set up in each greenhouse.
The greenhouses were covered with large transparent garbage bags to trap the heat from
the light fixtures inside the greenhouses. I also turned the thermostat up in the lab to warm the
room to the minimum/maximum temperatures of 23.7/26.4°C, the optimal temperature range for
papaya growth. Light from the light fixtures were left for 24 hours per day. I recorded the
temperature of each greenhouse before applying the fertilizers and water to make sure the
greenhouse temperatures were within the optimum range for papaya growth.
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Application of Organic and Inorganic Fertilizer
The inorganic fertilizer solution was made with ¼ teaspoon of Miracle-Gro® Water
Soluble All Purpose Plant Food (Scotts Miracle-Gro, Marysville, OH) containing 15 parts
nitrogen to 30 parts phosphorous to 15 parts potassium, or an NPK of 15-30-15, in 1L of water.
The organic fertilizer solution was made with 1 teaspoon of Alaska Fish Emulsion (Lilly Miller
Brands, Walnut Creek, CA) with an NPK of 5-1-1 in 1L of water. The solutions were made in
compliance with the manufacturer’s instructions. At the time of planting, 100 ml inorganic
fertilizer solution was applied to each pot in the inorganic fertilizer experimental group, 100 ml
organic solution was applied to each pot in the organic fertilizer experimental group, and 100 ml
tap water was applied to each pot in the control group. For the inorganic and control groups,
treatments were applied weekly, unlike the organic group with treatment occurring every two
weeks according to the manufacturer’s instructions. Water was applied to the organic group
every other week when organic fertilizer was not applied. The amount of water applied to the
control group was based on a study that measured the required average values of water needed
for growth of the papaya plant (Aiyelaagbe et al., 1985).
Measurements and Data
At the end of each week, for a total of 4 weeks, measurements were taken from each
plant with a centimeter ruler. Measurements for leaf length started from where the bottom of the
leaf and the stem touched to the tip of the leaf, leaf width was measured from the widest part of
the leaf, and stem height was measured from the bottom of the stem just above the dirt to the
closest branch of sprouting leaves from the bottom. Twelve Analysis of Variance (ANOVA)
tests were run to compare the mean growth of leaf length, leaf width, and stem height among the
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inorganic fertilizer, organic fertilizer, and control per week. The ANOVA tests determined
whether there were statistical significant differences in growth among the 3 treatments per week.
If there were any significant differences in growth of leaf length, leaf width, or stem height for
the experimental groups, then I used Tukeys multiple comparisons tests for further analysis of
the data using MiniTab (Version 15.0, January 2007, Minitab Inc., State College, PA).
RESULTS
The rate of growth and development for the inorganic group, organic group, and control
group were determined by averaging the measurements of leaf width, leaf length, and stem
height of all the plants on a weekly basis.
Table 1 shows the mean growth for plants grown under inorganic fertilizer, organic
fertilizer, and water treatments. Measurements of leaf width, leaf length, and stem height were
taken after seed germination and each week prior before fertilizing or watering the plants. At the
first week, 14 inorganic plants, 7 organic plants, and 13 control plants were measured. At week
two, 14 inorganic plants, 7 organic plants, and 10 control plants were measured. At week three,
15 inorganic plants, 9 organic plants, and 14 control plants were measured. At week four, 17
inorganic plants, 10 organic plants, and 17 control plants were measured. Twelve one-way
ANOVA tests were run to compare the growth of leaf width, leaf length, and stem height among
the inorganic, organic, and water treatments per week. Tukeys multiple comparison tests were
used to further analysis my data.
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Table 1. Means of leaf width, leaf length, and stem height of Carica papaya ‘Brazilian Sunshine’ treated
with inorganic and organic fertilizers, and water. Values were determined based on growth per week and
not over time. Data in this table is the same for the following figures.
Inorganic
Organic
Control
Week 1
1.4
1.3
1.5
Inorganic
Organic
Control
Week 1
1.9
1.7
2.0
Inorganic
Organic
Control
Week 1
3.5
3.5
3.9
Leaf Width
Week 2
2.1
1.9
2.3
Leaf Length
Week 2
2.9
2.6
3.1
Stem Height
Week 2
4.0
4.0
4.4
Week 3
2.9
2.8
3.1
Week 4
3.3
3.3
3.2
Week 3
3.8
3.7
3.7
Week 4
4.0
4.1
3.7
Week 3
4.2
3.9
4.0
Week 4
4.3
4.0
4.0
Figure 2 shows the mean size and standard deviation at the first week of measurements.
Each bar represents the growth of each experimental group for the three parameters that were
measured. Growth obtained from the inorganic fertilizer group, organic fertilizer group, and
control group using a Tukeys multiple comparisons test showed no significant differences for
leaf width (F = 0.57; d.f. = 2; P = 0.570), leaf length (F = 0.99; d.f. = 2; P = 0.374), and stem
height (F = 2.12; d.f. = 2; P = 0.138).
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Week 1
4.5
f
4
Plant growth (cm)
3.5
Inorganic
3
Organic
2.5
Control
2
1.5
1
0.5
0
Leaf Width
Leaf Length
Stem Height
Figure 2. The measurements of papaya leaf width, leaf length, and stem height obtained from inorganic,
organic, and water treatments. Each bar represents the average growth of leaf width, leaf length, and stem
height for the first week of measurements. There were 14 plants measured in the inorganic group,
7 plants in the organic group, and 13 plants in the control group. Each error bar represents one standard
deviation from the mean.
Figure 3 shows the mean size and standard deviation during the second week of
measurements. The graph shows that leaf width, leaf length, and stem height increased from the
first week. Growth obtained from the inorganic fertilizer group, organic fertilizer group, and
control group using a Tukeys multiple comparisons test showed no significant differences for
leaf width (F = 1.79; d.f. = 2; P = 0.170), leaf length (F = 1.24; d.f. = 2; P = 0.292), and stem
height (F = 1.10; d.f. = 2; P = 0.346).
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Week 2
5
Plant growth (cm)
d
4.5
4
3.5
3
Inorganic
2.5
Organic
2
Control
1.5
1
0.5
0
Leaf Width
Leaf Length
Stem Height
Figure 3. The measurements of papaya leaf width, leaf length, and stem height obtained from inorganic,
organic, and water treatments. Each bar represents the average growth of leaf width, leaf length, and stem
height for the second week of measurements. There were 14 plants measured in the inorganic group,
7 plants in the organic group, and 10 plants in the control group. Each error bar represents one standard
deviation from the mean.
Figure 4 shows the mean size and standard deviation during the third week of
measurements. The graph shows that while leaf width and leaf length have continued to increase
in growth, there is a slight decrease in growth for stem height. Growth obtained from the
inorganic fertilizer group, organic fertilizer group, and control group using a Tukeys multiple
comparisons test showed no significant differences for leaf width (F = 0.42; d.f. = 2; P = 0.656),
leaf length (F = 0.11; d.f. = 2; P = 0.897), and stem height (F = 0.34; d.f. = 2; P = 0.712).
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Week 3
5
f
4
Plant growth (cm)
4.5
3.5
3
Inorganic
2.5
Organic
2
Control
1.5
1
0.5
0
Leaf Width
Leaf Length
Stem Height
Figure 4. The measurements of papaya leaf width, leaf length, and stem height obtained from inorganic,
organic, and water treatments. Each bar represents the average growth of leaf width, leaf length, and stem
height for the third week of measurements. There were 15 plants measured in the inorganic group,
9 plants in the organic group, and 14 plants in the control group. Each error bar represents one standard
deviation from the mean.
Figure 5 shows the mean size and standard deviation during the fourth week of
measurements. The graph shows that leaf length and stem height are in the same measurements
with each other showing the same mean growth during this last week. However, growth
obtained from the inorganic fertilizer group, organic fertilizer group, and control group using a
Tukeys multiple comparisons test showed no significant differences for leaf width (F = 0.14; d.f.
= 2; P = 0.868), leaf length (F = 0.62; d.f. = 2; P = 0.540), and stem height (F = 0.61; d.f. = 2; P
= 0.546).
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Plant growth (cm)
i
Week 4
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Inorganic
Organic
Control
Leaf Width
Leaf Length
Stem Height
Figure 5. The measurements of papaya leaf width, leaf length, and stem height obtained from inorganic,
organic, and water treatments. Each bar represents the average growth of leaf width, leaf length, and stem
height for the fourth week of measurements. There were 17 plants measured in the inorganic group,
10 plants in the organic group, and 17 plants in the control group. Each error bar represents one standard
deviation from the mean.
DISCUSSION
My hypothesis was that the use of organic fertilizer will contribute to faster growth and
development of papaya plants than the use of inorganic fertilizer or water, because it does not
contain harmful chemicals and is healthy for the plants. However, the results of my research did
not show any significant differences among the growth and development of plants treated with
water, organic fertilizer, or inorganic fertilizer. Also, there were no differences in the growth of
the papaya plants between the use of either fertilizer and the use of water. Since p-values for
each week was greater than 0.05, I rejected my null hypothesis.
There was a noticeable trend in my data that all papaya plants steadily increased in
growth. An important factor to consider was the successful germination of papaya seeds,
because of the frequent failures of papaya seed germination in greenhouse and laboratory
experiments (Lange, 1961). Sawant (1958) studied low temperatures, approximately 4.4°C and
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below, are lethal to papaya species. The weather conditions here in Lacey, Washington during
the time of the experiment were not favorable for papaya growth. Although the plants were
grown indoors, the temperature of the lab was maintained at the optimal temperature range
between 18-38°C for the survival of the plants.
The most obvious reason why my hypothesis was rejected is that there is no difference
between the use of organic and inorganic fertilizers or that organic fertilizer is not better than
inorganic fertilizer for faster growth of papaya plants. So, for future experiments, I recommend
testing different types of organic and inorganic fertilizers. Organic manures like broiler manure,
farmyard manure, wood ash, and bone-meal could be used for organic fertilizer to test which one
is best for papaya growth. Inorganic fertilizers with different NPK ratios could also be used to
test growth of papaya plants to see which one works best for faster growth. I also recommend
testing different varieties of papaya to test which one grows faster. I also recommend expanding
the time of the experiment between 6 to 9 months, instead of a short period of 8 weeks. The data
might show different results in papaya growth. Also, the productivity of fruit could play a major
role in determining which treatments yield the highest dry weight of papaya fruit. Instead of
starting measurements when the first leaves had developed, germination of the seeds should be
measured first to keep track of the first plants that sprouted. I recommend measuring the leaf
width and leaf length on each plant as I did in the later part of my experiment rather than in
earlier measurements when I measured the leaf length of all the leaves first, then went back to
measure leaf width.
There are several ways to maintain the productivity of agriculture. The use of fertilizers,
inorganic and organic alike, play a major role in the production of agriculture worldwide (Chand
et al., 2006). However, the use of inorganic fertilizer on crops over a period of several years
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may cause long-term damage to the agriculture and the surrounding economy (Chand et al.,
2006). Organic fertilizer is rapidly growing in favor, because it provides and recycles
supplemental nutrients to crops and its non-chemical components greatly reduces waste products
(Luo et al., 2006).
The incorrect fertilizer on papaya plants could lead to failure of germination or growth in
laboratory and greenhouse experiments, or might not increase growth in the plants. This is the
case for all plants, but the ability of Carica papaya L. plants to grow up to 12 feet tall in one year
compliments its uniqueness. These exotic, tropical plants are fast growing producing fruit within
9-12 months after the seeds are planted (Gonsalves, 1998). Not many plants are known to
produce fruit or produce fruit in a matter of months. Therefore, researching or testing the best
fertilizer for faster growth of papaya plants may get you papaya fruits sooner than later.
ACKNOWLEDGEMENTS
I would like to give special thanks to the following individuals for there continued
support and guidance during my senior research project. I would like to thank Dr. Mary Jo
Hartman for helping me with my literature reviews, editing my papers, analyzing my results, and
also helping to put together my results for my final presentation. I would also like to thank Dr.
Margaret Olney for helping me with questions concerning the maintenance of my plants, editing
my papers, giving much needed constructive criticism, and always keeping a good attitude
throughout the year. Much appreciation goes out to lab technician Cheryl Guglielmo for her
helpful tips on soil and fertilizers to use for my project and also for helping to order the lab
equipment and papaya seeds for my experiment. I also thank my friends, Si’i Vulangi and Agnes
Uti for escorting me to lab during the late night hours and for lending a helping hand towards
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treating my plants. Last, but definitely not least, I would like to thank these special individuals,
Pelenita Tu’upo, Krystle Antolin, Sothear Sam, and Sonya Ramos for their much needed
constructive criticism and guidance throughout the entire research process. I am grateful for
these individuals and appreciate all their help with much gratitude.
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LITERATURE CITED
Aiyelaagbe, I.O.O., Fawusi, M.O.A., Babaloa, O. 1985. Growth, development and yield of
pawpaw (Carica papaya L.) ‘Homestead selection’ in response to soil moisture stress. Plant
and Soil. 93: 427-435.
Alarcon, A., Davies, F.T.D. Jr., Egilla, J.N., Fox, T.C., Estrada-Luna, A.A., Ferrera-Cerrato, R.
2002. Short term effects of Glomus claroideum and Azospirillum brasilense on growth and
root acid phosphatase activity of Carica papaya L. under phosphorous stress. Revista
Latinoamericana de Microbiologia. 44: 31-37.
Anwar, M., Patra, D.D., Chand, S., Alpesh, K., Naqvi, A.A., Khanuja, S.P.S. 2005. Effect of
organic manures and inorganic fertilizer on growth, herb and oil yield, nutrient accumulation,
and oil quality of French basil. Communications in Soil Science and Plant Analysis. 36:
1737-1746.
Chand, S., Anwar, M., Patra, D.D. 2006. Influence of long-term application of organic and
inorganic fertilizer to build up soil fertility and nutrient uptake in mint-mustard cropping
sequence. Communications in Soil Science and Plant Analysis. 37: 63-76.
Dedolph, R.R. 1962. Effect of benzothiazole-2-oxyacetate on flowering and fruiting of papaya.
Botanical Gazette. 124: 775-78.
Gonsalves, D. 1998. Control of papaya ringspot virus in papaya: a case study. Annu. Rev.
Phytopathol. 36: 415-437.
Lange, A.H. 1961. Effect of the sarcotesta on germination of Carica papaya. Botanical Gazette.
122: 305-311.
Luo, Y.G., Muchovej, R.M., Hanlon, E.A. 2006. Response of lima bean to inorganic nitrogen
and broiler manure sources and rates. Communications of Soil Science and Plant Analysis.
37: 587-603
Minitab ® Release 14.20.2005. Minitab Inc.
O’hara, B.P., Hemmings, A.M., Buttle, D.J., Pearl, L.H. 1995. Crystal structure of glycyl
endopeptidase from Carica papaya: a cysteine endopeptidase of unusual substrate
specificity. Biochemistry. 34: 13190-13195.
Sawant, A.C. 1958. Crossing relationships in the Genus carica. Evolution. 12: 263-266.
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