275

Adv. Hort. Sci., 2022 36(4): 275­281                                                                                                    DOI: 10.36253/ahsc­12816

Combining humic acid with NPK  
fertilizer improved growth and yield of 

chili pepper in dry season 
 
 
B. Ichwan, E. Eliyanti, I. Irianto, Z. Zulkarnain (*) 
Department of Agroecotechnology, Faculty of Agriculture, University of 
Jambi, Indonesia. 
 
 
Key words:   Capsicum annuum, organic substance, soil improvement, sustainable 

agriculture. 
 
 
Abstract: This research aimed to study the effect of humic acid and NPK fertiliz­
er (15:15:15) on growth and yield of red chili, and to obtain the most suitable 
composition of humic acid and NPK fertilizer which gave the best growth and 
yield. The study used a randomized block design with five replications. The 
treatments tested were the composition of humic acid and NPK fertilizer: 100% 
humic acid; 75% humic acid + 25% NPK; 50% humic acid + 50% NPK; 25% humic 
acid + 75% NPK; and 100% NPK. Data on plant growth and yield were processed 
by Analysis of Variance, and means were compared using Fisher’s Least 
Significant Difference test. In addition, data on plant biochemical and soil 
chemical parameters were determined compositely by mixing leaves taken 
from sample plants or soil samples into one homogenous sample. Results 
showed that there was no significant difference in growth and yield of plants 
treated with 100% humic acid in comparison with those plants treated with 
100% NPK. However, in comparison with 100% humic acid, the application of 
different ratios of humic acid/NPK increased plant chlorophyll contents by 65% 
­ 82% and total sugar by 28% ­ 71%. The application of humic acid/NPK 
increased soil fertility by improving soil pH as well as N, P and K. In the combi­
nation of humic acid/NPK, the best growth and yield were obtained with the 
application of 25% humic acid + 75% NPK fertilizers. Therefore, for the sustain­
ability of chili cultivation, the use of humic acid needs to be accompanied with 
NPK fertilizers at a reduced amount, along with the increase in the dose of 
humic acid. 
 
 
1. Introduction 
 
     In Indonesia Chili (Capsicum annuum L.) is one of vegetable crops with 
high economic value due to its large domestic and export demaind and, 
from time to time, price fluctuations may cause consumer unrest. The 
national inflation rate is significantly influenced by the increase in chili 
prices in certain seasons. To control the price fluctuations the Indonesian 
government is increasing the planting area in rainy season, and control­
ling the planting area as well as production during dry season. 

(*)
 
Corresponding author:  

dr.zulkarnain@yahoo.com 
 
 
Citation: 
ICHWAN B., ELIYANTI E., IRIANTO I., ZULKARNAIN 
Z., 2022 ­ Combining humic acid with NPK fertili‐
zer improved growth and yield of chili pepper in 
dry season. ­ Adv. Hort. Sci., 36(4): 275­281. 
 
 
Copyright: 
© 2022 Ichwan B., Eliyanti E., Irianto I., 
Zulkarnain Z. This is an open access, peer 
reviewed article published by Firenze University 
Press (http://www.fupress.net/index.php/ahs/) 
and distributed under the terms of the Creative 
Commons Attribution License, which permits 
unrestricted use, distribution, and reproduction 
in any medium, provided the original author and 
source are credited. 
 
 
 
Data Availability Statement: 
All relevant data are within the paper and its 
Supporting Information files. 
 
 
Competing Interests:  
The authors declare no competing interests. 
 
 
Received for publication 16 February 2022 
Accepted for publication 3 October 2022

AHS 
Advances in Horticultural Science



Adv. Hort. Sci., 2022 36(4): 275­281

276

     Increasing production in the dry season normally 
is managed by application of inorganic fertilizers and 
use of chemicals to control pests and diseases. 
However, this practice has a negative impact on agri­
c u l t u r a l  e c o s y s t e m  a n d  t h e  e n v i r o n m e n t . 
Additionally, implementing principles of sustainable 
agriculture such as the application of humic acid, a 
soil conditioner, has the potential to improve this 
conventional agricultural practice. Humic acid has a 
complex molecular structure and capability to stimu­
late and activate biological and physiological process­
es in soil organisms. 
     The study of Abdellatif et al. (2017) showed that 
the application of 14.4 kg ha­1 humic acid to chili 
plants grown under heat stress could increase plant’s 
average height, number of flower buds, number of 
flowers, number of fruits per plant, as well as fruit 
weight. The application of 7.5­12 mL of humic acid 
into 10 kg of sterile soil increased the population of 
soil microorganisms Azotobacter beijerinckii and 
Aspergillus niger. Foliar spray of 50 mL L­1 humic acid 
significantly increased leaf area, yield and total solu­
ble solids in grapes (Popescu and Popescu, 2018). 
Onion plants sprayed with 1000 mg L­1 humic acid 
produced the highest growth rate and yield (Al­
Fraihat et al., 2018). 
     In addition to the improvement in cultivation, chili 
production can be increased by growing them during 
the dry season. Whilst a lot of land is available for 
cropping during the dry season the production is con­
s t r a i n e d  b y  t h e  l i m i t e d  a v a i l a b i l i t y  o f  w a t e r . 
Application of humic acid as a soil conditioner could 
remediate water shortage in plants due to increasing 
leaf water content, increasing photosynthesis, 
antioxidant metabolism and enzyme activity; thus 
improving plant tolerance to stress (Al­Shareef et al., 
2018). 
     Previous studies have demonstrated that humic 
acid improved plant growth and yield in a number of 
plant species. Hermanto et al. (2013) reported that 
application of 20 kg ha­1 humic acid along with 100% 
dose of NPK fertilizer resulted in maximum growth 
and yield as well as increased the availability and 
uptake of N, P, K, Zn and Fe in maize. Furthermore, 
Moraditochaee (2012) showed that the application of 
humic acid at 40 mg L­1 and 75 kg ha­1 N produced the 
highest harvest index in peanut. 
     Sustainable production of plants can be achieved 
b y  r e d u c i n g  t h e  u s e  o f  i n o r g a n i c  f e r ti l i z e r s .  
Application of humic acid could help achieve this 
important goal. Whilst humic acid has been widely 

applied to various plant species; the search of litera­
ture showed that no research has focused on the 
effect of humic acid in combination with NPK fertiliz­
er on growth and yield of chili pepper. Therefore, this 
study aimed at assessing the effect of humic acid in 
combination with NPK fertilizer on growth and yield 
of red chili, and to obtain the most suitable ratio of 
humic acid/NPK for best growth and yield in chili 
plants grown in dry season in Indonesia. 
 
 
2. Materials and Methods 
 
     The trial was conducted at the Teaching and 
Research Farm within the Faculty of Agriculture at 
the University of Jambi in Indonesia during the 2020 
dry season. The study used commercially available 
humic acid (AH­90, with 90% humic acid content) and 
inorganic NPK fertilizer (15:15:15). There were 5 
combinations tested: 100% humic acid; 75% humic 
acid + 25% NPK; 50% humic acid + 50% NPK; 25% 
humic acid + 75% NPK and 100% NPK. A randomized 
block design with 5 replications was used in this 
study. Humic acid was applied at the recommended 
dose (5 kg ha­1) and so was NPK fertilizer (700 kg  
ha­1). The humic acid and NPK were applied one week 
before planting in between rows. 
     Seeds were sown on a standard seedling medium, 
then transferred to nursery at 7 days after sowing 
and left in the nursery for 21 days. The medium used 
during the nursery growth was a mixture of soil, com­
post, and sand (2:1:1). Seedlings were sprayed every 
7 days with foliar fertilizer Bayfolan­D at 2 mL L­1 and 
i n s e c ti c i d e  ( a c ti v e  i n g r e d i e n t  A m a b e k ti n  a n d 
Mesurol) at 2 mL L­1. 
     The one­month­old seedlings were transplanted 
in the field onto the growing media supplemented 
with humic acid and NPK fertilizer at different rates 
as per treatments described above. A silvercoated 
black plastic was placed on the beds before trans­
planting the seedlings. Prior to planting, a fungicide 
(Carbofuran) was applied into planting holes at 1.5 g 
per plant. The planting space was 50 cm x 50 cm. A 
liquid NPK fertilizer (15:15:15) was applied at a con­
centration of 2 g L­1 with a volume of 100 mL per 
plant at 6, 8 and 10 weeks after transplanting.  
     Harvesting was carried out during the first flower­
ing period (10 to 13 weeks after transplanting), with 
t h e  c r i t e r i o n  t h a t  8 0 %  o f  f r u i t s  b e c o m i n g  r e d . 
Observation of vegetative growth was carried out 
during fruit enlargement period (9 weeks after trans­



Ichwan et al. ‐ Humic acid and NPK fertilizers improved growth and yield of chili pepper

277

planting) on the following parameters: plant height, 
number of productive branches, leaf area, and plant 
total dry weight. The leaf area was measured using 
gravimetric method with the following formulae 
(Sitompul and Guritno, 1995): 
 

Leaf area (cm2) = (x/y)·z 
 
where x = total leaf dry weight, y = sub sample leaf 
dry weight, and z = sub sample leaf area. 
     Observation of plant biochemical measurements 
were made on chlorophyll content, total sugar, and 
relative leaf water content (RLWC). Composite leaf 
samples were made by physically mixing individual 
leaves taken from 3 sample plants of 3 replicates into 
one homogenous sample. Compositing reduced the 
n u m b e r  o f  a n a l y s e s  t o  b e  p e r f o r m e d  a n d  w a s 
designed to provide a representative sample of the 
treatment. Ten youngest mature leaves on main 
stem were collected at 9 weeks after transplanting 
(WAT). Clean and dry leaf samples were placed in a 
sample bag prior to laboratory analyses. Chlorophyll 
analysis was carried out using Acetone method 
(Arnon, 1949), and total sugar was analyzed using 
Anthrone method (Yoshida et al., 1976). Relative Leaf 
Water Content (RLWC) was determined according to 
González and González­Vilar (2001) method. 
     Data on yields in terms of number of the fruits 
and fruit weight per plant were collected at harvest 
time. In addition, soil chemical analyses were per­
formed before transplanting and after the last har­
vest. Soil analyses included pH, moisture content, 
organic C based on Walkley­Black method (Walkley 
and Black, 1934), total N using Kjeldahl method 
(Kjeldahl, 1883), available P applying Bray­I method 
(Bray and Kurtz, 1945) and exchangeable K (NH4OAc 
1N extraction at pH 7) using method as described in  
(Warncke and Brown, 1998).  
     The data were scrutinized employing an analysis 
of variance (ANOVA) from Microsoft Excel application 
(Version 16.63.1, 2022, Microsoft Corporation, USA). 
Fisher’s Least Significant Difference (FLSD) at 5% level 
of probability was used to compare means of treat­
ments. 
 
 
3. Results 
 
     Analysis of variance showed that the application 
of humic acid (HA) and NPK fertilizer did not signifi­
cantly affect plant height, number of branches, total 

leaf area, and dry weight. However, application of 
25% HA in conjunction with 75% NPK fertilizer result­
ed in enhanced growth compared to other treat­
ments (Fig. 1). In addition, the application of 25% HA 
+ 75% NPK improved growth compared with 100% 
HA application whereby plant height, number of 
branches, leaf area and plant dry matter increased by 
29.46%, 21.96%, 23.59% and 28.42% respectively. 

 
     The measurement of biochemical parameters 
showed that the application of 100% HA resulted in 
the lowest chlorophyll content (2.40 mg L­1) and total 
sugar (0.07%). Furthermore, the lowest relative leaf 
water content (RLWC) was found on 100% NPK appli­
cation (Table 1). 

Fig. 1 ­ Growth of chili on various ratios of humic acid (HA)/NPK 
at 9 weeks after transplantation (A = plant height, B = 
number of branches, C = leaf area, D = total dry weight). 
Error bars indicate the Standard Error (n=5).

Humic acid/NPK
Chlorophyll 

content  
(mg·L­1)

Total  
sugar  
(%)

RLWC  
(%)

100% HA 2.40 0.07 92.6
75% HA/25% NPK 3.97 0.12 93.3
50% HA/50% NPK 4.15 0.12 93.7
25% HA/75% NPK 4.37 0.09 93.0
100% NPK 4.30 0.11 91.3

Table 1 ­ Effect of different ratios of humic acid) HA / NPK on 
chlorophyll content (*), total sugar, and relative leaf 
water content (RLWC) at 9 weeks after transplantation

(*) Chlorophyll content and total sugar were determined compo­
sitely by physically mixing individual leaves taken from each 3 
sample plants of 3 replicates into one homogenous sample. 



Adv. Hort. Sci., 2022 36(4): 275­281

278

     Analysis of variance showed that the application 
of different ratios of HA/NPK had no significant effect 
o n  t h e  n u m b e r  a n d  w e i g h t  o f  f r u i t s  p e r  p l a n t . 
However, among the combinations tested the 25% 
HA + 75% NPK resulted in the highest number of 
fruits, and the 50% HA + 50% NPK produced the 
largest fruit weight (Fig. 2). 
     The results of soil chemical analyses (Table 2) 
showed that the application of various ratios of 
HA/NPK had altered soil chemical properties such as 
pH, organic C, total N, P, K, and soil water content. 
Generally, the application of HA along with NPK fer­
tilizer improved N, P and K content. Whereas soil pH 

and organic carbon are highest when 100% HA is 
applied (Table 2). 
 
 
4. Discussion and Conclusions 
 
     The application of different humic acid/NPK ratios 
had no significant effect on growth and yield of chili 
as measured by plant height, total leaf area, number 
of branches and total dry weight, as well as number 
of fruits and average fruit weight. This means that 
humic acid can substitute NPK fertilizer. However, 
when compared to the use of only humic acid or NPK 
fertilizer, the application of different ratios of humic 
acid/NPK improved plant height, total leaf area, num­
ber of branches, total dry weight, fruit numbers and 
fruit weight. 
     NPK is widely used to improve plant growth and 
yield of many horticultural crops (Nafiu et al., 2011; 
Agbede et al., 2017; Achiri et al., 2018; Adekiya et al., 
2019; Nwokwu et al., 2020). However, the use of 
inorganic fertilizers such as NPK to help increase 
plant growth and yield need to be carefully consid­
ered, due to their detrimental impact on soil struc­
ture and soil biota. According to Adekiya et al. (2019) 
NPK fertilizer did not increase soil organic matter, nor 
reduced soil bulk density. Krestini et al. (2020) 
claimed that NPK fertilizer did not provide carbon 
compounds that contributed to the improvement of 
soil physical and biological properties. In addition, 
Agbede et al. (2017) reported that continued applica­
tion of inorganic fertilizers can increase soil acidity 
and soil degradation because inorganic fertilizers 
release nutrients more quickly. Therefore, balanced 
fertilization is recommended to increase the efficien­
cy of fertilizer use and help improve physical, chemi­
cal, and biological properties of soil. 
     The results obtained here show that application of 
100% humic acid provided less growth and yield in 

Fig. 2 ­ Effect of different ratios of humic acid (HA)/NPK on num­
ber of fruits (A) and fruit weight (B). Error bars indicate 
the Standard Error (n=5).

Humic acid/NPK pH
C­organic 

(%)
N­total 

(%)
P 

(ppm)
K  

(cmol+/kg)

Water  
content 

(%)
100% HA 6.09 1.55 0.22 104.50 0.06 7.70
75% HA/25% NPK 6.02 1.45 0.29 124.80 0.19 7.56
50% HA/50% NPK 5.47 1.28 0.28 152.30 0.47 7.61
25% HA/75% NPK 5.52 1.20 0.24 144.70 0.62 7.67
100% NPK 5.32 1.22 0.23 227.30 1.07 7.50

Table 2 ­ The effect of different ratios of humic acid (HA)/NPK on soil chemical properties



Ichwan et al. ‐ Humic acid and NPK fertilizers improved growth and yield of chili pepper

279

c h i l i  p l a n t s  c o m p a r e d  w i t h  m i x t u r e  o f  h u m i c 
acid/NPK during the one growth season of this 
research. However in a longitudinal experiment on 
peanut Li et al. (2019) demonstrated that significant 
increase in N, P and K content of soil was found after 
three years continuous application of humic acid. 
     The reason for this increase is due to humic com­
pounds high stability rate, and therefore the mineral­
ization process can occur very slowly. As a conse­
quence, humic acid cannot be used as a source of 
plant nutrition (Canellas et al., 2015). In research 
reported here the chemical analyses indicated soil 
that was treated with 100% humic acid was lower in 
N, P and K content, but higher in organic carbon and 
soil moisture content in comparison with those treat­
ed with different humic acid/NPK ratios (Table 2). 
This was in accordance with (Li et al., 2019; 2020) 
findings that the application of humic acid­based fer­
tilizer could increase soil nutrient contents, including 
the total soil nitrogen, phosphorus, and potassium.  
     Increase in soil water content was aligned with 
increase in relative leaf water content (RLWC) in chili 
plants (Table 1). Al­Shareef et al. (2018) reported 
that the application of humic acid as a soil enhancer 
could overcome water shortage in plants by increas­
ing RLWC, thereby increasing plant tolerance to 
stress. Further, Xu et al. (2015) stated that the appli­
cation of soil enhancers such as humic acid could 
increase plant growth by retaining available water 
and nutrients, therefore reducing the impact of 
drought stress and nutrient loss. 
     The application of 100% humic acid also increased 
soil pH from 4.43 to 6.09, resulting in better plant 
growth and development due to improved availabili­
ty of various nutrients in the soil at pH of 6.09. 
Wahyudi (2007) reported that the application of 
humic acid might reduce the amount of exchange­
able aluminum and increase chelating aluminum in 
soil, thereby increasing soil pH. Hasanudin (2003) 
suggested that the reduction in exchangeable alu­
minum was due to the formation of complex organo­
metal compound (Al­chelate). Increase in soil pH will 
increase the availability of soil nutrients needed by 
plants (Gardner et al., 1985). In peanut, Li et al. 
(2019) found that compared with control, humic acid 
significantly increased the yield and quality of peanut 
in continuous cropping. Their results showed that 
application of humid acid significantly increased the 
soil total nitrogen, total phosphorus, total potassium, 
available N, available P, available K, and organic mat­
ter from second year, with maximum effect displayed 

in third year. 
     Chili plants treated with different humic acid/NPK 
ratios showed better growth and yields in compari­
son to those plants treated with humic acid or NPK 
alone. The composition of 25% humic acid + 75% NPK 
fertilizer produced the highest growth (plant height, 
leaf area, number of branches and plant dry matter), 
as well as the highest yield (number of fruits) com­
pared to other compositions. Furthermore, applica­
tion of 50% humic acid + 50% NPK fertilizer resulted 
in the highest fruit weight. This result is in line with 
the increase in plant chlorophyll content, where the 
composition of 25% humic acid + 75% NPK fertilizer 
caused higher plant chlorophyll content. An increase 
in chlorophyll content intensifies the ability of plants 
to carry out photosynthesis, thereby increasing plant 
growth (Ferrara and Brunetti, 2010). 
     Increase in soil K content due to humic acid / NPK 
application caused better K uptake, increasing plant 
g r o w t h  a n d  y i e l d  i n  p o t a t o  ( X u  e t  a l . ,  2 0 1 5 ) . 
Potassium is crucial in plant photosynthetic activity 
(Marschner, 2012) and assimilate translocation effi­
ciency (Sawan, 2018). This is in line with our results 
where application of humic acid and NPK (75% HA 
and 25% NPK or 50% HA and 50% NPK) increased 
sugar content in plant tissue (Table 1). 
     The composition of 50% humic acid + 50% NPK 
and 25% humic acid + 75% NPK in this study provided 
better growth and yield of chili plants than 100% 
humic acid or 100% NPK applications. This indicates a 
positive effect of the use of humic acid in partially 
replacing the role of NPK fertilizer. The ability of 
humic acid to replace NPK fertilizer is probably due to 
the ability of humic acid to modify the plant root sys­
tem architecture as well as improving the capacity of 
soil to bind water, thus enabling plants to acquire 
water and nutrients more easily (Suwahyono, 2011; 
Canellas and Olivares, 2014), reducing plant stress in 
dry land cultivation during periods of drought (Xu et 
al., 2015).  
     The analysis of soil water content for different 
ratios of humic acid/NPK showed medium treated 
with humic acid has a better water content than 
those treated with 100% NPK (7.56­7.7 versus 7.5). In 
addition, the relative leaf water content (RLWC) at 
various ratios of humic acid / NPK was higher than 
that of 100% NPK application (Table 1). 
     Our findings are consistent with a number of pre­
vious studies indicating that the application of humic 
acid needs to be accompanied by NPK fertilizer to 
help improve plant productivity (For example in 



properties and growth and yield of carrot. ­ J. Hortic. 
Res., 25(1): 81­88. 

AL­FRAIHAT A.H., AL­TABBAL J.A., ABU­DARWISH M.S., 
ALHROUT H.H., HASAN H.S., 2018 ­ Response of onion 
(Allium cepa) to foliar application of humic acid under 
rain‐fed conditions. ­ Int. J. Agric. Biol., 20(5): 1235­
1241. 

AL­SHAREEF A.R., EL­NAKHLAWY F.S., ISMAIL S.M., 2018 ­ 
Enhanced mungbean and water productivity under full 
irrigation and stress using humic acid in arid regions. ­ 
Legume Res., 41(3): 428­431. 

ARNON D.I., 1949 ­ Copper enzymes in isolated chloroplas‐
t s .  P o l y p h e n o l o x i d a s e s  i n  B e t a  v u l g a r i s .  ­  P l a n t 
Physiology, 24(1): 1­15. 

BRAY R.H., KURTZ L.T., 1945 ­ Determination of total, 
organic, and available forms of phosphorus in soils. ­ 
Soil Sci., 59(1): 39­46. 

C A N E L L A S  L . P . ,  O L I V A R E S  F . L . ,  2 0 1 4  ­  P h y s i o l o g i c a l 
responses to humic substances as plant growth pro‐
moter. ­ Chem. Biol. Technol. Agric., 1(3): 1­11. 

CANELLAS L.P., OLIVARES F.L., AGUIAR N.O., JONES D.L., 
NEBBIOSO A., MAZZEI P., PICCOLO A., 2015 ­ Humic 
and fulvic acids as biostimulants in horticulture. ­ Sci. 
Hortic., 196: 15­27. 

FERRARA G., BRUNETTI G., 2010 ­ Effects of the times of 
application of a soil humic acid on berry quality of table 
grape (Vitis vinifera L.) cv Italia. ­ Span. J. Agric. Res., 
8(3): 817­822. 

GARDNER F.P., PEARCE B., MITCHELL R., 1985 ­ Physiology 
of crop plants (1st Edition). ­ Iowa State University 
Press, Ames, IA, USA, pp. 327. 

GONZÁLEZ L., GONZÁLEZ­VILAR M., 2001 ­ Determination 
of relative water content, pp. 207­212. ­ In: ROGER 
M.J.R. (ed.) Handbook of plant ecophysiology tech‐
niques. ­ Kluwer Academic Publishers, The Netherlands, 
pp. 468. 

HASANUDIN, 2003 ­ The increasing of nutrient availability 
and uptake of N and P and yield of corn through innoc‐
ulation of mycorrhiza, azotobacter, and organic matter 
on Ultisol. ­ J. Ilmu Pert. Indon., 5(2): 83­89. 

HERMANTO D., DHARMAYANI N.K.T., KURNIANINGSIH R., 
KAMALI S.R., 2013 ­ The Influence of humic acid as fer‐
tilizer supplement to nutrient availability and uptake on 
maize plant in unirrigated land of Kec. Bayan‐NTB. ­ 
Ilmu Pertanian, 16(2): 28­41. 

KJELDAHL J., 1883 ­ Neue methode zur bestimmung des 
stickstoffs in organischen körpern. ­ Zeitschrift für 
Analytische Chemie, 22(1): 366­383. 

KRESTINI E.H., SUSILAWATI A., HERMANTO C., 2020 ­ Effect 
of NPK fertilizer and microbial consortium to growth 
and production of garlic (Allium sativum L.), pp. 03010. 
­ In: MURSYIDIN D.H., and E. BADRUZSAUFARI (eds.)  
First International Conference on Tropical Wetland 
Biodiversity and Conservation (ICWEB 2019). EDP 
Sciences, Web of Conferences, Les Ulis Cedex, France, 
1­2 November, 2019. 

280

Adv. Hort. Sci., 2022 36(4): 275­281

peanut (Moraditochaee, 2012), tomato (Sarno et al., 
2015) and cocoa (Santi, 2016)). The slow rate of 
humic acid mineralization needs to be followed by 
the application of NPK fertilizers. This is aimed to 
increase the availability of nutrients for plants, espe­
cially in relation to the relatively short lifespan of the 
chili plant which is only 3 ­ 4 months. In addition, it is 
also necessary to consider the amount of humic acid 
and the time of application, so that the use of NPK 
fertilizer as a source of plant nutrition can be further 
reduced. 
     Data presented here indicate that the application 
of different ratios of humic acid / NPK could greatly 
increase the growth and yield of chili pepper grown 
in dry land cultivating, where the composition of 25% 
humic acid + 75% NPK fertilizer resulted in improved 
plant growth and yield. It was found that the applica­
tion of humic acid could reduce the use of NPK fertil­
izers by up to 50%. Thus, for sustainable chili produc­
tion in dry land cultivation, application of humic acid 
in conjunction with NPK fertilizer is recommended at 
a reduced amount. 
 
 
Acknowledgements 
 
     This research was supported by University of 
Jambi through Internal Competitive Research Grant 
(Contract No. 410/UN.21.18/PG/SPK/2020 dated 20 
April 2020). The authors would like to thank the 
Rector of University of Jambi for financial support 
provided to conduct this research. 
 
 
References 
 
ABDELLATIF I.M.Y., ABDEL­ATI Y.Y., ABDEL­MAGEED Y.T., 

HASSAN M.A.­M.M., 2017 ­ Effect of humic acid on 
growth and productivity of tomato plants under heat 
stress. ­ J. Hortic. Res., 25(2): 59­66. 

ACHIRI T.D., MICHELE T.Z.S., KONJE C.N., NJUALEM D.K., 
2018 ­ Effect of NPK fertilizer and animal manure on 
some biometric parameters of irish potato (Solanum 
tuberosum L.) in Bougham, West Region Cameroon. ­ 
Asian J. Crop Sci., 2(1): 1­10. 

ADEKIYA A.O., AGBEDE T.M., ABOYEJI C.M., DUNSIN O., 
UGBEA J.O., 2019 ­ Green manure and NPK fertilizer on 
soil properties, growth, yield, mineral and vitamin C 
composition of okra (Abelmoschus esculentus (L.) 
Moench). ­ J. Saudi Soc. Agric. Sci., 18(2): 218­223. 

AGBEDE T.M., OLASEKAN A.A., EIFEDIYI K., 2017 ­ Impact 
of poultry manure and NPK fertilizer on soil physical 



Ichwan et al. ‐ Humic acid and NPK fertilizers improved growth and yield of chili pepper

281

LI Y., 2020 ­ Research progress of humic acid fertilizer on 
the soil. ­ Journal of Physics: Conference Series, 1549: 
022004. 

LI Y., FANG F., WEI J., WU X., CUI R., LI G., ZHENG F., TAN 
D., 2019 ­ Humic acid fertilizer improved soil properties 
and soil microbial diversity of continuous cropping 
peanut: A three‐year experiment. ­ Sci. Rep., 9: 12014. 

MARSCHNER P., 2012 ­ Marschner’s mineral nutrition of 
higher plants. ­ Elsevier, London, UK, pp. 651. 

MORADITOCHAEE M., 2012 ­ Effects of humic acid foliar 
spraying and nitrogen fertilizer management on yield 
of peanut (Arachis hypogaea L.) in Iran. ­ ARPN J. Agric. 
Biol. Sci., 7(4): 289­293. 

NAFIU A.K., TOGUN A.O., OLABIYI A.M., CHUDE V.O., 2011 
­ Effect of NPK fertilizer on growth, drymatter produc‐
tion and yield of eggplant in southwestern Nigeria. ­ 
Agric. Biol. J. N. Am., 2: 1117­1125. 

NWOKWU G.N., OGBONNA L.C., EGWU P.N., 2020 ­ Effect 
of NPK fertilizer rates on growth and yield components 
of eggplant (Solanum melongena) cultivars. ­ Niger. 
Agric. J., 51: 530­537. 

POPESCU G.C., POPESCU M., 2018 ­ Yield, berry quality and 
physiological response of grapevine to foliar humic acid 
application. ­ Bragantia, 77(2): 273­282. 

SANTI L.P., 2016 ­ Effect of humic acid on the growth of 
cocoa (Theobroma cacao) seedlings and microbial pop‐
ulation in the humic Dystrudept. ­ J. Tanah dan Iklim, 
40(2): 87­94. 

SARNO S., SAPUTRA A., RUGAYAH R., PULUNG M.A., 2015 ­ 
Pengaruh pemberian asam humat (berasal dari batu 
bara muda) melalui daun dan pupuk P terhadap per‐
tumbuhan dan produksi tanaman tomat (Lycopersicum 

esculentum Mill). ­ J. Agrotek. Trop., 3(2): 192­198. 
SAWAN Z.M., 2018 ­ Mineral fertilizers and plant growth 

retardants: Its effects on cotton seed yield; its quality 
and contens. ­ Cogent Biol., 4: 1459010. 

SITOMPUL S.M., GURITNO B., 1995 ­ Analisis Pertumbuhan 
Tanaman. ­ Gadjah Mada University Press, Yogyakarta, 
pp. 412. 

SUWAHYONO U., 2011 ­ Prospek teknologi remediasi lahan 
kritis dengan asam humat (humic acid). ­ J. Teknol. 
Lingk., 12(1): 55­65. 

WAHYUDI I., 2007 ­ Peran asam humat dan fulvat dari 
kompos dalam detoksifikasi aluminium pada tanah 
masam. ­ Buana Sains, 7(2): 123­130. 

WALKLEY A., BLACK I.A., 1934 ­ An examination of the 
Degtjareff method for determining soil organic matter 
and proposed modification of the chromic acid titration 
method. ­ Soil Science, 37(1): 29­38. 

WARNCKE D., BROWN J.R., 1998 ­ Potassium and other 
b a s i c  c a ti o n s ,  p p .  3 1 ­ 3 3 .  ­  I n :  B R O W N  J . R .  ( e d . ) 
Recommended chemical soil test procedures for the 
N o r t h  C e n t r a l  r e g i o n .  ­  M i s s o u r i  A g r i c u l t u r a l 
Experiment Station SB 1001, University of Missouri, 
Columbia, USA. 

XU S., ZHANG L., MCLAUGHLIN N., MI J., CHEN Q., LIU J., 
2015 ­ Effect of synthetic and natural water‐absorbing 
soil amendments on photosynthesis characteristics and 
tuber nutritional quality of potato in a semi‐arid region. 
­ J. Sci. Food Agric., 96: 1010­1017. 

YOSHIDA S., FORNO D.A., COCK J.H., GOMEZ K.A., 1976 ­ 
Laboratory Manual for Physiological Studies of Rice (3rd 
edition). ­ The International Rice Research Institute, Los 
Baños, Laguna,The Philippines, pp. 83.