Expl Agric.

: page 1 of 15 
C Cambridge University Press 2017

doi:10.1017/S0014479717000254

R E L AT I V E P E R F O R M A N C E O F B O RO N, S U L P H U R A N D
Z I N C C OAT I N G S O N TO P R I L L E D U R E A F O R I N C R E A S I N G
P RO D U C T I V I T Y A N D N I T RO G E N U S E
EFFICIENCY IN MAIZE

By VIJAY POONIYA, YASHBIR SINGH SHIVAY§, MADAN PAL

and RADHIKA BANSAL
Division of Agronomy, ICAR-Indian Agricultural Research Institute, New Delhi 110012, India

(Accepted 6 May 2017)

SUMMARY
Deficiencies of micro (Zn, B) and secondary (S) nutrients are well-documented in soil as well as in cereal
crops, leading to decreased crop yields and low nutritional quality of food. We evaluated the effects of
coated urea on maize yield, N and Zn uptake, and input cost relationships. Field experiments were
conducted on maize to test boron-coated (BCU), sulphur-coated (SCU) and zinc-coated urea (ZnCU)
during 2013 and 2014. On the basis of 2 years’ average data, the highest grain yield was achieved with
0.5% BCU, 5% SCU and 2.5% ZnCU as zinc sulphate hepta hydrate. These treatments increased yields
by 5.4, 12.8 and 9.9% over prilled urea (PU), respectively. Application of 0.5% BCU (supplying 1.4 kg B
ha–1 ), 5% SCU (supplying 14.1 kg S ha–1 ) and 2.5% ZnCU (supplying 7.05 kg Zn ha–1 ) registered the
highest N concentrations and uptake in grain and stover. Total N uptake (grain + stover) was increased
by 7.6, 16.7 and 17.1% with BCU, SCU and ZnCU treatments over PU. As compared to PU, Zn
concentration in maize grain was significantly higher and total Zn uptake (grain + stover) increased by
32.4% with 2.5% ZnCU. Coated urea materials also enhanced the partial factor productivity (PFPN ),
agronomic efficiency (AEN ), recovery efficiency (REN ) and harvest index (HIN ) over those of PU. From
the economic viewpoint this study suggests that coating of urea with 0.3% boron, 5% sulphur or 2% zinc
gives maximum net returns and benefit-cost ratio. Our data indicate that coating of B, Zn and S onto
urea increases maize yield, profitability and nitrogen use efficiency in the western Indo-Gangetic plains of
India.

I N T RO D U C T I O N

Maize is one of the most versatile emerging crops with wider adaptability under
varied agro-ecological conditions in India. Following intensive rotations over the past
four decades exhaustive depletion of soil micronutrients has occurred in India (Singh,
2008). Approximately one third of the cultivated soils in India are deficient in boron
(B) (Gupta et al., 2008), with highly leached calcareous sandy soils (>15% CaCO3 )
with pH more than 7.0 being more prone to B deficiency (Alloway, 2008a). In fact,
low B availability is widely spread in calcareous soils, hill and sub-mountainous soils
of north-eastern Indian states and in red/lateritic soils. In the Indian agriculture,
B application is then essential in a wide range of soils. B deficiency leads to low
productivity and nutrient use efficiency, which ultimately accord less profit to farmers.

§Corresponding author. Email: ysshivay@hotmail.com

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 2 V I J AY P O O N I YA et al.

To date no scientific information is available on graded levels of boron-coated urea

(BCU) for maize.
Application of diammonium phosphate (DAP) has reduced sulphur (S) application
to soil. However, S deficiency has been reported in USA (Dick et al., 2008), Europe
(Messick, 2003), Australia (Hocking et al., 1996), Central America (Raun and Baretto,
1992), China (Messick, 2003), India (Biswas et al., 2004) and Pakistan (Rashid et al.,
1992). Agricultural grade commercial sulphur, gypsum, pyrites and phospho-gypsum
are common sources of sulphur in India (Oo et al., 2007), as well as bentonite
sulphur (Shivay et al., 2014). India has limited sulphur deposits in the form of
calcium sulphate (gypsum) and elemental sulphur has to be imported by the fertilizer
industry. The Sulphur Institute at Washington, DC has played a major role in focusing
on sulphur deficiency in soils. Initially, sulphur-coated urea (SCU) was developed
by Tennessee Valley Authority (TVA) researchers for controlled release of nitrogen
besides its popularity as turf fertilizer in USA (Prasad et al., 1971). Currently, different
companies in Canada, USA, China and Japan are manufacturing controlled release
urea materials (Trenkel, 1997) with sulphur content ranging from 4 to 15%. As results,
SCU increased grain yield by about 15% over prilled urea (PU) in a rice–wheat
system at Delhi (Prasad, 2013), less SCU is needed for rice production as compared
to PU in the Philippines (Flinn et al., 1984); and SCU improved productivity and
protein yields of wheat significantly in multi-location trials in Iran over PU fertilization
(Malkouti et al., 2008). However, SCU with graded doses has so far not been tried
in maize and our efforts were, therefore, directed towards evaluating the effect
of SCU on grain yield, nutrient use efficiency and input economics in the maize
crop.
Cereal grains such as rice, wheat, maize are inherently low in Zn content and
bioavailability when grown in Zn-deficient soils (Cakmak et al., 2010; Prasad, et al.,
2014). Gibson (2006) estimated that ∼60–70% of the human population in Asia
and sub-Saharan Africa could be at risk due to low Zn intake (IRRI, 2006). Zn
deficiency is also responsible for ∼4% of the burden of morbidity and mortality in
below 5 year age children and for the loss of ∼16 million global disability adjusted life
years (Black et al., 2008; Walker et al., 2009). The major issues for improving dietary
composition with Zn in developing countries are money and poor purchasing power.
Considering these facts, agronomic-biofortification of cereals through Zn fertilization
(e.g., agronomic biofortification/ferti-fortification) is an economically feasible option,
which aims at keeping sufficient amount of available Zn in the soil solution
for maintaining adequate Zn transport to the sink during reproductive growth
stages.
The major aim of this study was to evaluate the relative performance of different
coated urea materials (BCU, SCU and ZnCU) for increasing maize productivity
in an acceptable economically manner. The field experiments were set up with
the objectives to assess the response of maize to varying Zn, B and S-coated urea
levels, estimate use efficiencies of applied coated urea/fertilizers by maize, and
computation of the comparative economics of different coated fertilizer materials in
maize.

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 Maize yield as affected by coated urea 3
M AT E R I A L S A N D M E T H O D S

Experimental site
Field experimentation was conducted during rainy (July–October) seasons of 2013
and 2014 at the Experimental Farm of Indian Agricultural Research Institute (IARI),
New Delhi, India (28°38’N, 77°10’E, 228.6 m above mean sea level). The sandy
loam (Typic Haplustepts) soil had 0.43% organic carbon (Walkley and Black, 1934),
142.5 kg ha–1 of oxidizable N (Subbiah and Asija, 1956), 12.5 kg ha–1 available P
(Olsen et al., 1954), 275.1 kg ha−1 exchangeable K (Hanway and Heidel, 1952) and
pH 7.9 (1:2.5 soil and water ratio; Prasad et al., 2006). The DTPA extractable Zn
(Lindsay and Norvell, 1978), the soluble sulphate estimated turbidimetrically (Chesnin
and Yien, 1950) and available boron (Berger and Troug, 1939) in the experimental
field were 0.36, 8.0 and 0.36 mg kg–1 soil, respectively. The critical level of DTPA
extractable Zn for rice grown in alluvial soils in rice–wheat belt in north India varies
from 0.38 to 0.90 mg kg−1 while the critical limits of hot water extractable B and
CaCl2 extractable S in soil is 0.58 and 8–10 mg kg−1 (Katyal and Rattan, 2003; Rego
et al., 2007).

Experimental details
Three different coated urea materials, Zn-coated urea (ZnCU), SCU and BCU,
were tested in three different experiments. The experiments were laid out in a
randomized block design with three replications for two years. The experiment I
consisted of seven fertilizer treatments: absolute control (no N and no B), PU, 0.1,
0.2, 0.3, 0.4 and 0.5% BCU (the amount of boron applied was 0.28, 0.56, 0.84, 1.12
and 1.40 kg ha–1 , respectively). The experiment II also had seven fertilizer treatments:
absolute control, PU, 1, 2, 3, 4 and 5% SCU and the amount of S applied was 3.1,
6.3, 9.42, 12.6 and 15.7 kg ha–1 , respectively. The experiment III consisted of 10
combinations of two coating materials, zinc sulphate hepta hydrate (ZnSHH) and
zinc oxide (ZnO), with five levels of Zn coating (0.5, 1.0, 1.5, 2.0 and 2.5% w/w of
PU) and an absolute control (no Zn and no N). The amount of Zn applied was 1.4,
2.8, 4.2, 5.6 and 7.1 kg ha–1 with 0.5, 1.0, 1.5, 2.0 and 2.5% ZnCU, respectively. The
experimental field was ploughed twice with a tractor drawn disc plough following
planking and ridge making on 67.5 cm spacings. Phosphorus at 26 kg P ha–1 as
single super phosphate and potassium at 41.6 kg K ha–1 as muriate of potash were
broadcasted at final ploughing. However, N at 130 kg ha–1 as PU or coated fertilizer
materials was applied in two equal splits; half at sowing and the other half at the
knee height stage. Maize (Zea mays L.) variety ‘HQPM 1’ (HKI 193–1 × HKI 163)
was sown in the second week of July with recommended practices and harvested in
the last week of October in both 2013 and 2014. The plot size was 5.4 × 3.0 m for
each treatment. Herbicide atrazine (Atrataf 50 WP) was applied at 1.0 kg a.i. ha−1
as a pre-emergence spray one day after sowing. In addition, earthing up was done at
45 days of growth. The gap filling was accomplished immediately after germination
in order to maintain uniform plant population. Irrigation was scheduled based on
the crop water requirement and gap in rainfall. The irrigations were applied through

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 4 V I J AY P O O N I YA et al.

open channels at critical crop growth stages, i.e., young seedling, knee high stage,
flowering, cob development to dough stage. The plots were irrigated separately with
60–70 mm depth of water.

Coating prilled urea with boron, sulphur and zinc

BCU with 0.1, 0.2, 0.3, 0.4 and 0.5% B coating onto PU was prepared in
laboratory using borax (12% B) and 1:1 aqueous solution (water:gum) of gum–acacia
as a sticker. Gum is natural plant origin adhesive material of Acacia tree. Boron
coating of PU was done in lots of 5 kg PU in a manual rotating seed treatment
drum. Five kg of PU was added to the drum then the required quantity of gum–
acacia solution was added and the drum was rotated for 15 minutes to provide a
fine coating of gum–acacia on urea prills. The required amount of borax was then
added to the drum and the contents were thoroughly mixed by rotating the drum for
15 minutes. BCU was then transferred to plastic trays, which were dried overnight
at room temperature (25 ± 5 °C) using air blowing fans. The amount of borax and
gum–acacia required for 0.1, 0.2, 0.3, 0.4 and 0.5% coating onto 5 kg PU was 41.2,
82.4, 123.8, 164.9 and 206.1 g and 30, 40, 50, 60 and 70 g, respectively. SCU was
prepared like BCU. The amount of sulphur (bentonite sulphur dust) required for 1,
2, 3, 4 and 5% coating onto 5 kg PU was 55.6, 111.1, 166.7, 222.2 and 277.8 g,
respectively. Coating more than 5% S onto PU using the present technique was not
possible. ZnCU was also prepared following the same procedure as for BCU. The
amount of ZnSHH and ZnO required for 0.5, 1.0, 1.5, 2.0 and 2.5% Zn coating onto
5 kg PU was 125, 249, 374, 499 and 624 g and 31, 62, 93,125 and 156 g, respectively
(Table 1). The quantity of gum–acacia needed was same as used in preparation of
BCU. Coated urea was made about 3–4 days before application in the field. Total
cost involved in coating of urea (cost of B/S/Zn + coating) based on prevailing prices
(US $ ha−1 ) in the Indian market during the cropping season is given in Table 1.

Yield attributes and yields

The crop was harvested when cob sheaths turned brownish and grains became
hard. Five cobs were randomly selected from each plot during harvest and their length
from base to tip of the cob was measured and the mean value was recorded. The
cobs were harvested manually and grains were separated from cob by hand operated
shelling machine. The total number of grains from the five cobs were counted and
averaged out to get number of grains cob−1 . The grains obtained from five cobs were
weighed and averaged to compute grain weight cob−1 . The border rows around the
experimental plots were harvested first and the net area was harvested for yields. After
separating from stalk and shelling of husk and silk, all the cobs from each plot were
dried naturally and threshed by a mechanical thresher. The grain yield was adjusted
to 15% moisture content and the stover yield was determined after air drying. Stover
yield was obtained by subtracting grain yield from respective total biomass yield (grain
+ dry stover). Grain and stover yields were expressed in Mg ha−1 . The cultivation cost
and economics (US $ ha−1 ) of maize is shown in Table 1.

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Table 1. Cost involved in the coating of boron, sulphur and zinc onto prilled urea and economic evaluation for one hectare maize crop. Means in a column with at least one
letter common are not statistically significant using Fisher’s least significant difference.

Cost involved Economic evaluation

Quantity Amount of borax/ Cost of borax/ Cost of coating Total cost of Cultivation Gross Net Benefit:
(kg) of B/S/Zn sulphur/Zn product sulphur/ of urea with coating urea cost returns returns cost
Treatments required∗ (kg) required∗ Zn (US $ ha−1 ) B/S/Zn∗∗ of (US $ ha−1 ) (US $ ha−1 ) (US $ ha−1 ) (US $ ha−1 ) ratio

Absolute control – – – – – 496.4 687.7c 191.3c 0.39c

Prilled urea – – – – – 571.5 1334.7b 763.3b 1.34b
0.1% BCU 0.28 2.33 4.67 2.08 6.75 578.2 1347.4b 769.2b 1.33b
0.2% BCU 0.56 4.66 9.32 2.40 11.72 583.1 1350.5b 767.4b 1.32b
0.3% BCU 0.84 7.00 14.0 2.73 16.73 588.1 1408.2a 820.1a 1.39a
0.4% BCU 1.12 9.32 18.63 3.05 21.68 593.0 1409.9a 816.9a 1.38a

Maize yield as affected by coated urea

0.5% BCU 1.40 11.65 23.30 3.38 26.68 597.9 1413.5a 815.6a 1.36a

Absolute control – – – – – 496.4 873.8e 377.4d 0.76c

Prilled urea – – – – – 571.5 1088.2d 516.7c 0.90b
1.0% SCU 2.83 3.14 1.57 1.85 3.42 574.9 1164.5c 589.6b 1.03a
2.0% SCU 5.65 6.28 3.13 1.97 5.10 576.5 1179.4bc 602.9ab 1.05a
3.0% SCU 8.48 9.42 4.72 2.08 6.80 578.2 1202.7ab 624.5a 1.08a
4.0% SCU 11.30 12.56 6.28 2.18 8.47 579.9 1210.7ab 631.0a 1.09a
5.0% SCU 14.13 15.70 7.85 2.30 10.15 581.5 1214.0a 632.4a 1.12a

Absolute control – – – – – 496.4 886.6g 390.1g 0.79h

Prilled urea – – – – – 571.5 1365f 793.5f 1.39fg
0.5% ZnCU (ZnSHH) 1.41 7.07 3.50 1.98 30.20 577.0 1411.5e 834.5ef 1.45de
1.0% ZnCU (ZnSHH) 2.82 14.1 6.98 2.23 33.91 580.7 1433.3cde 852.6cdef 1.47bcde
1.5% ZnCU (ZnSHH) 4.23 21.15 10.48 2.46 37.66 584.4 1463.8ab 879.4abc 1.50abc
2.0% ZnCU (ZnSHH) 5.64 28.2 13.96 2.71 41.39 588.2 1483.4a 895.3a 1.52a
2.5% ZnCU (ZnSHH) 7.05 35.25 17.46 2.95 45.13 591.9 1487.6a 895.7a 1.51ab
0.5% ZnCU (ZnO) 1.41 1.76 2.61 1.91 29.24 576.0 1373.4f 797.4g 1.38g
1.0% ZnCU (ZnO) 2.82 3.52 5.23 2.10 32.05 578.8 1410.5e 831.7f 1.44e
1.5% ZnCU (ZnO) 4.23 5.28 7.84 2.28 34.83 581.6 1426.1de 844.5def 1.45de
2.0% ZnCU (ZnO) 5.64 7.04 10.46 2.46 37.64 584.4 1452.2bcd 867.8abcd 1.48abcde
2.5% ZnCU (ZnO) 7.05 8.81 13.09 2.64 40.45 587.2 1442.7bcd 855.5bcdef 1.46cde
∗ For coating of 282.6 kg urea (kg ha−1 ); ∗∗ At the rate of 7% of fertilizer prices (US $ ha−1 )
Prevailing prices of fertilizer materials during 2013&14: (i) Borax (12% boron) at the rate of US $ 2.0 kg–1 , (ii) Sulphur dust (90% S) at the rate of US $ 0.50 kg–1 , (iii) ZnSO4 .7H2 O
(20% Zn) at the rate of US $ 0.50 kg−1 ; (iv) ZnO (80% Zn) at the rate of US $1.49 kg−1 , (v) Prilled urea at the rate of US $ 0.087 kg−1 , (vi) Price of one US $ = 60.6 INR [Note:

5
Prilled urea at the rate of US $ 883 tonne–1 ; US $ 24.97 for an application of 130 kg ha–1 ]
 6 V I J AY P O O N I YA et al.

Chemical analysis of plant samples

Above ground maize samples (three plants per plot) were collected 10 days before
harvesting and washed with tap water followed by dilute hydrochloric acid (0.05 N),
deionized water and finally with double distilled water. The samples were dried in an
oven at 60 ± 5 °C, separated into grain and stover, ground and sieved to pass 40 mesh
sieve in a Macro–Wiley Mill. Three samples per plot were analysed for total N using
a Kjeldahl digestion unit as described by Prasad et al. (2006). From each plot, 0.5 g
dry matter samples of grain and stover were taken for Zn analysis. The Zn content
in grain and stover was determined by wet digestion (di-acid digestion) procedure on
an atomic absorption spectrophotometer (Prasad et al., 2006). Finally, the uptake of
N or Zn was determined by multiplying maize biomass (grain and stover) and N or
Zn concentration in the respective parts. Total N or Zn uptake was calculated by
summing up the two values, i.e., grain + stover uptake of N or Zn. N uptake (grain,
stover and total) was calculated by using the following expression: N uptake (kg ha−1 )
in grain/stover = [% N in grain/stover × grain/stover biomass (kg ha−1 )]; Total N
uptake (kg ha−1 ) = N uptake in grain + N uptake in stover. The Zn uptake was also
calculated following the same procedure as in N uptake.

Nitrogen use efficiencies

In general, four terms are used in relation to nitrogen use efficiency: Agronomic
Efficiency (AEN ), Recovery Efficiency (REN ), Partial Factor Productivity of nitrogen
(PFPN ) and N Harvest Index (HIN ). The following expressions were used to determine
these efficiencies as suggested by Pooniya and Shivay (2013):

AEN (kg grain increased per kg N applied) = (Yf − Yc)/Na (1)

REN (% of N taken up by a crop) = [(NUf − NUc)/Na] ∗ 100 (2)

PFPN (kg grain per kg N applied) = Yf/Na (3)

HIN (Nitrogen harvest index as %) = (NUg/NUg + s) ∗ 100 (4)

Where, Yf and Yc are the yields (kg ha–1 ) in fertilized and control (no fertilizer)
plots, respectively. NUf and NUc are the amounts of N taken up by a maize crop in
fertilized and control plots, respectively and Na refers to the amount of N applied
(kg ha–1 ). NUg and NUg + S are the amounts of N uptake in maize grain and grain
+ stover, respectively.

Statistical analysis
Analysis of variance (ANOVA) was done to determine treatment effects (Gomez
and Gomez, 1984). Fisher’s least significant difference was used as a post hoc mean
separation test (p < 0.05) using Proc GLM in SAS 9.3software. The Fisher’s procedure
was used when the ANOVA was significant.

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 Maize yield as affected by coated urea 7
R E S U LT S

Maize yield and its components

Application of uncoated PU significantly increased the yield attributes i.e., grain
weight cob−1 and cob length over the absolute control (Table 2). Application of 0.5%
BCU (supplying 1.4 kg B ha–1 ), 0.4% BCU (supplying 1.12 kg B ha–1 ) and 0.3% BCU
(supplying 0.84 kg B ha–1 ) caused the highest grain weight cob−1 and cob length. SCU
recorded significantly higher values for grain weight cob−1 and cob length over PU
and absolute control, regardless SCU concentrations. Coating of urea with 2% and
2.5% ZnSHH produced significantly more grain weight cob−1 than 0.5% ZnO, PU
and absolute control and was the similar in the other coating treatments. Cob length
of ZnCU (ZnSHH and ZnO) treatments was very close to each other and significantly
superior to the absolute control.
BCU did not increase the grain and stover yields significantly over PU (Table 2).
However, the application of PU and BCU increased maize yield as compared to the
absolute control. Application of 2 to 5% SCU increased grain yield significantly over
PU. For stover yield, SCU and PU were similar and significantly higher than the
absolute control (Table 2). Among the ZnCU treatments, 2.5% ZnSHH recorded the
highest grain yield though it did not differ from the rest of the ZnCU treatments, with
the exception of 0.5% ZnO and PU. Coating of urea with ZnSHH and ZnO and
use of PU caused similar stover yields, which were significantly superior to absolute
control (Table 2).

Nitrogen concentration and uptake

Increasing concentration of boron in BCU (0.1 to 0.5%) and PU improved N
concentrations and uptake in grain and stover over absolute control (Figure 1). A
significant increase in total N uptake (grain + stover) was recorded with 0.5% BCU
over PU, 0.1% BCU and absolute control. On average, application of 0.5% BCU
resulted in 7.6% higher total N uptake than the PU treatment (Figure 1). Application
of 5% SCU significantly increased N concentration and uptake in grain as well as total
N uptake compared to PU, 1% SCU and absolute control (Figure 2). Application of
N as 2 or 2.5% ZnSHH registered the highest N concentrations and uptake in grains
(Figure 3). Considering the stover, 2.5% ZnSHH gave the maximum N concentration
and uptake closely followed by 2.0 or 1.5% ZnSHH or ZnO. Likewise, the highest
total N uptake was recorded in 2.5% ZnSHH treatment (Figure 3). In the current
study, total N uptake with 2.5% ZnSHH was enhanced by 14.6% over PU (Figure 3).

Zinc concentration and uptake

The highest Zn concentration and uptake by maize grain and stover was recorded
with 2.5% ZnSHH closely followed by 2% ZnSHH and 2.5% ZnO (Figure 4). For
total Zn uptake (grain + stover), 2.5% ZnSHH was also superior and remained on
par with 2.0% ZnSHH and 2.5% ZnO treatments. Per cent increase in total Zn
uptake with 2.5% ZnSHH was 26% over PU. In general, coating of PU with ZnSHH
caused more benefits to Zn uptake than coating with ZnO.

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8
Table 2. Effect of boron-coated urea, sulphur-coated urea and Zn-coated urea materials on yield attributes and nitrogen use efficiencies in maize. Means in a column with at
least one letter common are not statistically significant using Fisher’s least significant difference.

Amount of Grain Cob Grain Stover Partial factor Crop recovery Agronomic efficiency Nitrogen
B/S/Zn weight length yield yield productivity efficiency (kg grain increased harvest
Treatments added (kg ha−1 ) cob−1 (g) (cm) (Mg ha−1 ) (Mg ha−1 ) (kg grain kg–1 N applied) (%) kg–1 N applied) index (%)

Absolute control – 57.6c 10.6c 2.56b 4.07b – – – 60.6b

Prilled urea – 79.0b 12.8b 5.15a 6.71a 39.6a 46.5c 19.9a 65.1a
0.1% BCU 0.28 79.1b 12.9b 5.21a 6.70a 40.1a 47.1c 20.4a 65.3a
0.2% BCU 0.56 80.2b 13.2ab 5.22a 6.73a 40.2a 48.3bc 20.5a 65.0a
0.3% BCU 0.84 85.6a 13.8a 5.47a 6.84a 42.1a 52.1b 22.4a 65.9a
0.4% BCU 1.12 85.4a 13.9a 5.49a 6.76a 42.2a 52.5b 22.5a 65.9a
0.5% BCU 1.40 86.1a 13.8a 5.49a 6.87a 42.2a 58.6a 22.5a 65.7a

V I J AY P O O N I YA
Absolute control – 61.6c 11.4c 3.32c 4.73b – – – 63.1b
Prilled urea – 68.1b 12.2b 4.13b 5.92a 31.8b 20.5d 6.2b 62.9a
1.0% SCU 3.14 73.9a 13.1a 4.48ab 5.94a 34.5a 25.8c 8.9a 64.6a
2.0% SCU 6.28 74.4a 13.3a 4.54a 6.00a 34.9a 27.9b 9.4a 64.6a
3.0% SCU 9.42 76.3a 13.6a 4.64a 6.05a 35.7a 29.8abc 10.2a 65.1a
4.0% SCU 12.56 76.5a 13.7a 4.66a 6.16a 35.8a 31.6ab 10.3a 64.7a
5.0% SCU 15.70 76.8a 13.6a 4.66a 6.26a 35.8a 33.0a 10.3a 64.1a

et al.
Absolute control – 66.8d 11.2c 3.35d 4.92b – – – 63.1b
Prilled urea – 79.8c 12.9b 5.27c 6.84a 40.5c 35.9f 14.8g 65.5a
0.5% ZnCU (ZnSHH) 1.41 85.7ab 13.4ab 5.47abc 6.94a 42.1abc 40.4def 16.3efg 66.0a
1.0% ZnCU (ZnSHH) 2.82 86.6ab 13.6ab 5.56abc 7.01a 42.8abc 43.5bcde 17.0abe 66.3a
1.5% ZnCU (ZnSHH) 4.23 87.4ab 13.6ab 5.68abc 7.15a 43.7a 47.0abcd 17.9abe 66.2a
2.0% ZnCU (ZnSHH) 5.64 89.2a 13.6a 5.76ab 7.22a 44.3a 49.7ab 18.5ab 66.3a
2.5% ZnCU (ZnSHH) 7.05 89.3a 13.7ab 5.79a 7.15a 44.5a 51.2a 18.8a 66.5a
0.5% ZnCU (ZnO) 1.41 82.7bc 12.8b 5.30bc 6.90a 40.8bc 37.3ef 15.0fg 65.7a
1.0% ZnCU (ZnO) 2.82 85.1abc 13.3ab 5.47abc 6.91a 42.1abc 40.7cdef 16.3efg 66.3a
1.5% ZnCU (ZnO) 4.23 85.8ab 13.4ab 5.53abc 6.99a 42.5abc 42.7bcde 16.8bef 66.1a
2.0% ZnCU (ZnO) 5.64 86.9ab 13.6ab 5.64abc 7.06a 43.4ab 45.1abcd 17.6abe 66.3a
2.5% ZnCU (ZnO) 7.05 86.1ab 13.4ab 5.59abc 7.10a 43.0ab 46.2abcd 17.2abe 66.2a
 Maize yield as affected by coated urea 9

Figure 1. N concentration and uptake in maize as influenced by boron-coated urea. Means for each parameter with
at least one letter common are not statistically significant using Fisher’s least significant difference.

Figure 2. N concentration and uptake in maize as influenced by sulphur-coated urea. Means for each parameter with
at least one letter common are not statistically significant using Fisher’s least significant difference.

Nitrogen use efficiency

BCU treatments (0.1–0.5%) did not differ significantly from PU with respect to
PFPN and AEN (Table 2). The highest REN was found with 0.5% BCU and all BCU
treatments were similar to PU with respect to HIN but significantly superior to the
absolute control (Table 2). REN increased from 20.5% with PU to 33.0% with 5%
SCU, while the highest HIN was similar in SCU treatments and PU (Table 2). With
respect to PFPN , all SCU treatments recorded similar values, which were significantly

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 10 V I J AY P O O N I YA et al.

Figure 3. Effect of zinc-coated urea materials on N concentrations and uptake in maize. Means for each parameter
with at least one letter common are not statistically significant using Fisher’s least significant difference.

Figure 4. Effect of zinc-coated urea materials on zinc concentrations and uptake in maize. Means for each parameter
with at least one letter common are not statistically significant using Fisher’s least significant difference.

higher than PU. SCU at 5% recorded significantly higher REN than PU, 1 and 2%
SCU. All the SCU treatments were similar with respect to AEN but significantly
superior to PU. Among ZnCU treatments, the highest PFPN was registered with 2.5%
ZnSHH and it was equal to the rest of the treatments except 0.5% ZnO and PU
(Table 2). REN and AEN also increased with 2.5% ZnSHH, but this treatment did not

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 Maize yield as affected by coated urea 11

differ significantly of 2.0, 1.5% ZnSHH and 2.5, 2.0% ZnO treatments. On average,
coating of urea with 2.5% ZnSHH increased the REN and AEN by 29.5 and 21.3%
over PU. The coated urea materials, either with ZnSHH and ZnO, did not differ from
each other with respect to HIN but were significantly superior to the absolute control
(Table 2).

Economics
Total cost involved in coating of PU with boron ranged from US$6.75 for 0.1%
BCU to US$26.7 for 0.5% BCU (Table 1). Among treatments, 0.5% BCU was
the costliest cultivation treatment, which was 4.6% higher than the PU treatment
(Table 1). Applications of 0.3, 0.4 and 0.5% BCU recorded significantly higher gross
and net returns as well as benefit: cost ratio than the PU, 0.1% and 0.2% BCU.
The cost of sulphur required for 1% SCU was 6.25% of the cost of PU whereas for
5% SCU was 31.4%. The total cost of coating PU with sulphur ranged from US$3.42
for 1% SCU to US$10.2 for 5% SCU (Table 1). Data on economics of SCU showed
that significant improvements in gross and net returns were obtained with 3, 4 or 5%
SCU (Table 1). However, the benefit:cost ratio was similar among SCU treatments.
Input cost of 2.5% ZnSHH was US$17.5 and 2.5% ZnO US$13.1 per ha. Cost of
urea coating with Zn ranged from US$1.98 to US$2.95 for ZnSHH and US$1.91 to
US$2.64 per ha for ZnO. Thus, total cost involved in coating of PU with ZnSHH or
ZnO varied from US$30.2 to 45.1 (0.5 to 2.5% ZnSHH coated urea) and US$29.2
to 40.5 (0.5 to 2.5% ZnO coated urea) ha–1 (Table 1). Economics of ZnCU revealed
that significant improvement in gross and net returns was obtained when 2.5 or 2%
ZnSHH was coated onto PU. However, a significant benefit:cost ratio was obtained
with 2% ZnSHH (Table 1).

DISCUSSION

Boron-coated urea
BCU (0.1–0.5%) supplying 0.28–1.4 kg B ha–1 improved maize yield, N
concentration and its uptake, as well as N use efficiencies (PFPN , REN , HIN and AEN )
as compared to PU and control. However, the highest net returns and benefit:cost
ratio occurred with 0.3–0.5% BCU (Table 1). The amount of B supplied by 0.3%
BCU (0.84 kg B ha–1 ) is within the recommended range of 0.30 to 2 kg B ha–1
for B deficient Indian soils (Singh, 1999). Our experiment also indicated that N
concentration in both grain and stover of maize increased due to urea application
whether with or without B, while total N uptake was significantly increased with
0.2–0.5% BCU (Figure 1). Accordingly, Singh (2013) reported that boron application
helped in increasing uptake of N in cereal crops, indicating a positive interaction
between B and N. Positive effects of B and N are likely associated with accumulation of
metabolites in the reproductive organs, which would increase protein or carbohydrate
synthesis and improve crop yield. Our data revealed that application of 0.5% BCU is
a promising strategy for maize production in boron deficient soils, allowing farmers
to apply boron to maize and other cereals along with nitrogen.

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 12 V I J AY P O O N I YA et al.

Sulphur-coated urea
Previously, SCU was evaluated mainly in rice and wheat crops to enhance efficiency
of nitrogen fertilization but studies did not evaluate economic aspects of different
graded levels. Combined use of N or sulphur through SCU in intensive cereal–cereal
rotations will assure regular/controlled supply of sulphur in deficient soils. Response
to nitrogen and sulphur in cereal crops have been reported by a number of researchers
but the literature on response of SCU to maize is limited. There was a significant
improvement in PFPN , REN and AEN with SCU as compared to PU (Table 2) and
this is in accordance with earlier findings (Shivay et al., 2016). Nitrogen application
through SCU might have increased N as well as S concentrations due to positive
N × S interactions, which ultimately enhanced their uptake in grain and stover.
Prasad (2005) reported that heavy N fertilization depletes native S in intensive cereal-
based rotations in Asian countries.
Herein, application of SCU not only improved S status of the soil but also increased
maize productivity. The elemental sulphur is slightly costlier than calcium sulphate
and phosphogypsum and for that reason coating of sulphur onto urea prills is
an important strategy. Combined application of N and sulphur through 5% SCU
(supplying 15.7 kg S ha–1 , at an N application of 130 kg N ha–1 ) was adequate to bring
out the benefits of sulphur supplying to the soil and to enhance maize productivity.
Generally, the sulphur recommendation to cereals ranges from 10 to 40 kg ha–1
(Morris, 2007), thus 5.0% SCU would help to meet the sulphur requirements in most
situations and is also economically viable. The use of 5% SCU supplied ∼45% crop
sulphur needs and increased REN by 60% over PU (Table 2). Also, the highest net
returns and benefit:cost ratio were found with 5% SCU.

Zinc-coated urea
Limited information is available on use of graded levels of Zn-enriched urea
(ZnEU) and Zn-coated fertilizers (ZnSHH or ZnO) in maize. Small scale land holders
of South Africa, Zimbabwe and other African countries are not using Zn fertilizers
due to their poor socio-economic conditions and non-availability of Zn fertilizers
(Prasad et al., 2014). However, soil Zn deficiency reduces plant performance and
decreases crop productivity in countries such as India, Pakistan, Australia and China
(Alloway, 2008b). Thus, ZnCU (ZnSHH or ZnO) has great potential for improving
productivity and Zn concentrations in maize (Shivay and Prasad, 2014) as well as
its nutritional quality. In this study, Zn-coated fertilizers (2.0% or 2.5% ZnSHH)
significantly improved grain yield of maize (Table 2) over absolute control (no N and
no Zn) and control (only PU). A similar positive response of applied Zn has been
reported by several workers in rice grown in Zn deficient soils of India (Pooniya and
Shivay, 2013; Pooniya et al., 2012; Shivay et al., 2008).
The 2.5% ZnSHH caused the highest total uptake of N and Zn, which was due
to increased grain and stover yields and increased concentration therein (Figures 3
and 4). Synergistic interaction between Zn × N in soil is mainly attributed to an
increased availability of Zn due to the acid forming effect of nitrogen (Prasad, 2006).

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 Maize yield as affected by coated urea 13

Although Zn coating onto PU had same Zn concentration from different sources

(ZnSHH and ZnO), the total uptake of Zn significantly differed between sources with
the same level of N input. This might be because the mobility of Zn in soil differs
among Zn sources, influencing Zn uptake. In fact, ZnSHH moves easier than the
relatively water insoluble ZnO in soil, affecting Zn uptake in maize grain and stover
(Pooniya et al., 2012).
ZnCU with 2.5% ZnSHH lead to the highest N concentration in maize and this
can be explained due to an increase in N uptake through slow released of N from
Zn-coated material (Mhaskar and Thorat, 2005; Pooniya and Shivay, 2013). Pooniya
and Shivay (2013) also reported that soil Zn application either as ZnSO4 or ZnEU
increased N concentrations and their uptake. The positive improvement in REN , AEN
and PFPN with ZnCU over PU (Table 2) was due to the positive effect of applied
ZnCU on maize yield and N uptake, leading to an increase in their use efficiency. Both
2.5 and 2% ZnSHH led to a respective significant enhancement in PFPN and AEN by
9.9 and 27.0% over PU plots owing to higher yield and total N uptake. In contrast, the
low N use efficiencies of uncoated PU plots are attributed to more N losses through
denitrification, leaching and runoff (Prasad, 2005) compared to ZnCU. An effort is
therefore being made by the fertilizer industries in India to produce ZnEU/ZnCU,
which would permit farmers to use Zn along with N where cereal–cereal rotation is
common practice under Zn deficient conditions. From the manufacturer’s viewpoint,
ZnO is easier to coat because it forms a good emulsion with oil (Prasad et al., 2014).
On the other hand, ZnSO4 is the most widely applied inorganic source of zinc for
soil or foliar applications due to its higher solubility, low cost and easier availability
in the market (http://www.zinc.org). Zn sources such as ZnO, Zn(OH)2 and ZnCO3
are ∼105 times more soluble than soil Zn and therefore these products could be used
as coating materials (Kiekens, 1995; Prasad et al., 2014). Although location specific
recommendations are not available with respect to Zn application, this study suggests
that ZnCU would be prescribed for soil application. Overall, 2.5% ZnCU (ZnSHH) is
an economically feasible option to meet the Zn requirement and increase productivity
over PU. However, 2.0% ZnCU (ZnSHH) is the best option for maximum benefit:cost
ratio.

C O N C LU S I O N

Our field study clearly demonstrated the beneficial effects of BCU, SCU and ZnCU
on maize productivity and economic feasibility. From an economic point of view, 0.3%
BCU, 5% SCU, 2% ZnCU (as ZnSHH) were the best choices for maximum benefits
to the farmers. These are important findings for environmental sustainability since
coating of urea presumably reduces N losses and increases N use efficiency in the
Indo-Gangetic plains of Northern India.

Acknowledgements. The authors duly acknowledge the partial financial support

received from the Matix Fertilisers and Chemicals Limited (MFCL), Mumbai,
Maharashtra, India. Our sincere thanks are due to Director, Joint Director Research

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 14 V I J AY P O O N I YA et al.

and Head, Division of Agronomy, Indian Agricultural Research Institute, New Delhi
for their advice and support.

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