Food Sec. (2012) 4:103–114
DOI 10.1007/s12571-012-0165-4
ORIGINAL PAPER
Effects of light environment on maize in hillside agroforestry
systems of Nepal
Thakur Prasad Tiwari & Robert M. Brook &
Paul Wagstaff & Fergus L. Sinclair
Received: 22 October 2011 / Accepted: 2 January 2012 / Published online: 28 January 2012
# Springer Science+Business Media B.V. & International Society for Plant Pathology 2012
Abstract Maize (Zea mays L.) is the most important staple
food in the mid-hills region of Nepal. The mid-hills are
characterized by steeply sloping land and complex farming
systems where crops, livestock and trees are inseparable
components, and maize has to compete with trees grown
for fodder, fuel wood, building materials and other purposes
in a landscape severely constrained for agricultural purposes. This paper reports the effects of the presence of trees
growing on crop terrace risers on bari (upper-slope, rainfed)
land on growth and yield of maize grown on terrace
benches. Maize performance was compared with and without tree and artificial shade to determine its responses above
and below ground to such limiting factors. Mean photosynthetic photon flux density (PPFD) incident on maize in farm
conditions was lower than 700 μmol m-2 s-1, well below the
light saturation point for maize (1,500 μmol m−2 s−1). Grain
yield was reduced by 33% under tree shade and by 43%
under artificial shade compared with natural (unshaded)
conditions. As the light environment is sub-optimal for
maize, the crop rarely achieved maximum rates of
T. P. Tiwari (*)
CIMMYT,
Dhaka, Gulshan, P.O. Box 6057, Bangladesh
e-mail: [email protected]
R. M. Brook : F. L. Sinclair
School of the Environment, Natural Resources and Geography,
College of Natural Sciences, Bangor University,
Bangor, Gwynedd LL57 2UW, UK
P. Wagstaff
Concern Worldwide 52/55 Lower Camden Street,
Dublin 2, Ireland
F. L. Sinclair
World Agroforestry Centre,
Nairobi, Kenya
photosynthesis. Farmers claim that local landraces are better
adapted to shade than station-bred genotypes, but there was
no evidence of varietal effects upon rates of photosynthesis.
However, there was some evidence that there were varietal
adaptations to shade for other factors such as greater numbers of leaves and more competitive rooting patterns. Maize
varieties with deeper root systems and adapted to low light
conditions are required if productivity in these complex
systems is to be improved. The findings of this study should
be useful to breeders in developing maize genotypes suitable for the complex hillside systems of Nepal, thereby
improving food security.
Keywords Maize . Zea mays . Agroforestry .
Photosynthesis . Hillside systems . Shade
Introduction
Maize (Zea mays L.) is a key staple in the mid-hills of
Nepal, second only to rice (Oryza sativa L.) in terms of
national food security. Finger millet (Eleusine coracana
Gaertn.) is relay cropped with maize on the terraces where
fodder trees grow on the risers of bari land (upper slopes,
rain-fed, often terraced with fodder trees on the risers) in the
hillside systems of Nepal. More than 90 (Thapa 1994) and
111 (Carter 1992) species of trees for fodder and fuel have
been recorded on the farmlands of the eastern and central
mid-hills of Nepal, respectively. These authors recorded a
number of positive as well as negative aspects concerning
the hillside bari land system where maize is grown. The
negative aspects identified include competition between
trees and crops for nutrients, water and light. The positive
aspects include increased productivity of the whole system,
largely through fodder and fuel wood provision and meeting
104
farmers’ multiple objectives of erosion control and maintenance of soil organic matter through leaf litter decomposition and the application of farm compost. Previous workers
have reported that shade affects maize growth and development negatively (Earley et al. 1966; Midmore et al. 1988;
Reed et al. 1988; Andrade et al. 1993; Ephrath et al. 1993;
Chamshama et al. 1998); and that there were varietal differences in adaptation to shade (Duncan 1980) and rate of
photosynthesis (Duncan and Hesketh 1968; Gaskel and
Pearce 1981). Characterization of the climatic and agronomic context in which farmers grow maize in the hillside
systems revealed a complex and heterogeneous environment, dominated by variation in farmers’ practices (Tiwari
et al. 2004). Farmers in the mid-hills of Nepal appear to be
prepared to trade off maize and finger millet yield penalties
against tree products such as fodder and fuel wood.
This study formed a component of a programme
designed to improve maize production in the mid-hills zone
of Nepal. Previous papers have described farmers’ agronomic growing practices which are peculiar to this zone
(Tiwari et al. 2004) and the participatory variety selection
programme conducted with farmers, using farmers’ own
selection criteria (Tiwari et al. 2009b). In response to farmers reporting that some maize landraces were more tolerant
of shade than newer, research station bred genotypes
(Thapa 1994; Tiwari et al. 2009a,b), this paper reports
research which sought to characterise the light environment
experienced by maize on bari terraces and test the
responses of differing maize genotypes to shade, both
induced by artificial shade material and by trees growing
along terrace risers.
Materials and methods
Site description
Three locations were selected for on-farm micro-climatic
studies, at Marga and Patle in Dhankuta district and
Fakchamara in Tehrathum district. They were chosen as
representative of the range of conditions used for maize
cultivation in the eastern mid-hills of Nepal and were located
between 1,200 and 1,500 m altitude (Table 1). Measurements
were carried out in five farmers’ fields at each site in 1999.
The sample fields were widely distributed throughout the
villages and were of variable sizes, ranging from 500 m2 to
2,000 m2. They were located on terraces with trees being
grown on the risers and captured the full range of biophysical
environments that farmers use to grow maize. Six quadrats
measuring 3×3 m within the selected fields were selected
immediately after maize was sown to represent the full range
of light environments experienced by maize in this farming
system.
T.P. Tiwari et al.
To discriminate between effects of shade alone and that
of trees, which would include shade but confounded with
below ground competition, both artificial and natural shade
experiments were established in 2000. These were conducted at the Agricultural Research Station, Pakhribas
(ARSP) in 2000, at 1,740 m altitude, located 27° 17′ N
and 87° 17′ E.
For the artificial shade experiment, a split-plot design
was adopted with two shade regimes: no shade (unshaded)
and artificial shade (shaded) as main plots, and three Nepalbred maize varieties (PM-1, PM-3, Manakamana-1) and
Madi white (a local landrace) in sub-plots, randomized
within the main plots and replicated four times. The whole
terrace was sown to maize to create a continuous canopy,
within which treatment plots were demarcated. Sub-plot size
was 2×2 m, and main plots were 8×2 m. Seeds were primed
to help ensure good germination (Harris et al. 1999) and
were sown on 4 April, 2000 at 50×50 cm spacing, giving 16
maize plants in each sub-plot (40,000 plants ha −1 ).
Manakamana-1 maize was first introduced as a maize variety for the mid-hills zone in 1986, and is widely cultivated
in this region, although much of the crop is established from
seed saved on the farms, which has experienced several
generations of cross-pollination with local varieties (Tiwari
et al. 2004). Madi white is one such local ‘variety’, and this
genotype was regarded as being the local check. PM1 and
PM3 were preliminary selections as part of a programme to
develop new composites for testing by farmers. Chemical
fertilisers, N as urea and P as P2O5, each at the rate of 30 kg
of element ha−1 plus 15 tha−1 farm yard manure (FYM)
were applied as a basal dressing. Another 30 kg ha−1 N
was added as a top dressing on 31st May, 2000 (when the
maize was at about knee high). Shade was imposed using
green, loose-woven polypropylene, suspended over a bamboo frame 10 m long×4.5 m wide, which allowed 60%
transmission of photosynthetically active radiation (PAR).
The frame was suspended from vertical poles at just above
crop canopy maximum height and was raised as the crop
grew, up to a maximum height of 2.5 m. To limit ingress
of lateral solar radiation, shade material was also hung
down each side as a 500 mm curtain. Finger millet was
transplanted at a rate of 100 seedlings m−2 on 5 July
under the maize to simulate the relay cropping used by
farmers, but no recordings were made on this crop. This
experiment was established on a wide, treeless terrace,
which at the steeply sloping ARSP is at a premium, in
constant use for agronomic experiments and thus subject
to regular fertilization.
For the natural shade experiment, narrower terraces more
representative of hillside bari land and the maize agroforestry systems (Plate 1) were used, one bounded by mixed
fodder tree species and two adjacent terraces without trees.
The same maize varieties, degree of replication and fertilizer
Effects of light environment on maize in hillside agroforestry
105
Table 1 Description of study sites
Biophysical parameters\sites Marga
Patle
Fakchamara
On-station (ARSP)
Altitude (m asl)
Aspect
1,250 to 1,400
South-east
1,300 to 1,500
South-east
1,200 to 1,400
North-east
1,740
South
Major cropping patterns
Maize/finger millet
followed by fallow,
or
Maize/finger millet
followed by fallow
or
Maize-finger millet
followed by fallow
or
Maize/finger millet
followed by fallow
or
Maize/finger millet
followed by mustard
Maize/finger mille
followed by mustard
Maize-finger millet
followed by mustard
or
Maize/finger millet
followed by wheat
or mustard
Maize-finger millet
intercrop followed
by potato
Size of terraces
Tree species on terrace
rises
Soils
Contour terraces across Contour terraces across Contour terraces across
9–10 m wide and
slopes typically 5–7 m
slopes typically 6–8 m
slopes typically 7–10 m
40–50 m long
wide and 50–70 m
wide and 50–70 m
wide and 70–100 m
long
long
long
Patches or lines of mixed timber (Alnus nepalensis, Schima wallichii, Pinus wallichiana) and fodder tree species
(typically Bauhinea perpurea, Ficus nerifolia, Ficus semicordata, Albizia julibrissin, Celtis australis, Litsea
polyantha, Bambusa spp.)
The top soils are medium to The top soils are brown
The soils are deep on moderately steep slopes
and strongly acidic to
deep and dark brown to
developed on sloping terraces; dark to reddish
medium, the pH ranges
reddish brown and sandy
brown in colour and the texture sandy loam
from 5.0 to 6.0. The majority
loam to loam in texture.
to loam whilst the sola are deep and clay loam
of soils are shallow to
Soil pH ranges from 5.9
in texture. The organic matter is at medium
medium in depth developed
to 6.5. The organic matter
level.
on bench terraces. They
content varies from 1.6 to
are sandy loam and well
3.14%. The soils are
drained. Organic matter
underlain by reddish soil
and total nitrogen content
with sandy loam to sandy
are at medium level.
clay loam.
The available phosphorus (Olsen-P) and potassium (Ammonium Acetate Extraction) varies from medium to very
high and high to very high at all the sites, respectively.
In the cropping patterns sign (/) denotes relay crop
applications were used as for the artificial shade trial. Due to
the land constraints on the research station, blocks were
nested within sites.
On-farm light environment
Photosynthetic photon flux density (PPFD) was measured
on five of the sample farms at each of the Patle and Marga
sites using a Sunscan Canopy Analyser (Delta-T Devices,
Burwell, Cambridge, UK). Measurements were taken from
the central part of each 9 m2 quadrat, above and at the base
of the maize canopy. Measurements started 1 month before
maize sowing and then at 30 day intervals until the maize
reached physiological maturity, with five measurement
times during each sampling day at two-hourly intervals
commencing at 8 a.m. The fractional interception of PPFD
by maize (ƒ) was calculated using the following formula:
f ¼ 1 ðI=OÞ
Plate 1 Typical hill terraces where maize is commonly grown
Where: I0PPFD measured below the maize canopy and O0
PPFD measured above the canopy.
In order to determine whether the light quality environment was similar under tree canopies and under artificial
shade, the red:far-red ratio (r:fr) was measured using an
106
SKR 110; 660:730 nm sensor (Skye Instruments, Llandrindod
Wells, Powys, UK). The measurement schedule and procedure were the same as those used for the PPFD measurements
in farmers’ fields in 1999, and the same procedures were used
to measure PPFD and r:fr ratio in the artificial shade experiment in 2000.
Photosynthesis
Farmers contend that local maize varieties are more stress
tolerant (e.g. tolerant to competition from trees, etc.) than
introduced varieties. To determine whether there was a
physiological basis for this, net photosynthesis was measured on maize plants grown at ARSP using a portable infrared gas analyser (IRGA) model LCA3 (Analytical Development Co. Ltd., Hoddesden, Herts., UK) at a wide range of
natural photosynthetic photon flux densities, resulting from
the mixed sunny and cloudy conditions that often prevail
during the rainy season. Due to equipment and time constraints, recordings of photosynthesis were concentrated on
the artificial shade experiment in 2000, supplemented by
photosynthesis data collected from maize grown on a treelined terrace in 1999. A Parkinson leaf chamber with a
cuvette window of dimensions 20 mm × 60 mm was
clamped over the uppermost fully expanded maize leaf,
taking care to fill the leaf chamber window but to avoid
the mid-rib. The leaf chamber was held horizontally. Air to
both the IRGA and the leaf chamber was supplied by an
integral air supply unit which drew its reference air down a
tube with its orifice positioned above the shades and crop
canopies, well away from the zone of measurement. The air
was dried by passing it through two columns of silica gel.
Once the leaf chamber was clamped over the leaf, the
differential mode of the IRGA was used, which compared
the volumetric concentrations of CO2 and H2O in the reference and measurement streams of air (in volumes per million). When a steady reading for the differential in CO2
concentrations was obtained (normally after about 1 min),
it was recorded.
Readings were taken when the maize in the experiment was
at approximately the seven leaf stage, on 28 and 29 June, 1999
and 16 to 18 May, 2000 (due to severely delayed onset of
rains, the crop was established 6 weeks later in 1999 than in
2000). In 1999, two maize genotypes, Madi white (local
landrace) and Manakamana-1, growing on a 10 m wide terrace
with mixed fodder tree species established along one side,
were recorded. Forty randomly selected plants of each genotype, divided equally into shaded and non-shaded sample
groups, were used for measurements; thus, 80 plants were
sampled. Recordings were made between 11.30 am and
2.10 pm, when the sun was at or close to its zenith. In the
event, conditions were predominantly overcast and photon
flux densities rarely approached those close to light saturation.
T.P. Tiwari et al.
In 2000, plants from the artificial shade experiment only
were measured, because shading conditions were less variable than natural tree shade. Eleven plants of four varieties
were sampled with and without shade; thus 88 plants in all
were measured. Recordings were made between 11.30 a.m.
and 2.10 pm.
The Mitscherlich model, an exponential curve rising to
an asymptote often fitted to photosynthesis curves (Peek et
al. 2002) was fitted to the PPFD response curve obtained
from the non-shaded plants, using Sigma Plot v. 8 (SPSS
Inc.). This took the form:
y ¼ a 1 ebx
where a is the maximum rate of net photosynthesis (the
asymptote), b is the initial slope of the curve (the initial
quantum efficiency) and x is PPFD. In the case of overcast
conditions in 1999 and shaded plants in 2000, PPFD never
approached light saturation for maize, a plant with the C4
pathway of carboxylation. Thus, where appropriate, a linear
response was fitted instead.
Maize growth
From both the artificial and natural shade experiments, time
from sowing to 50% tasseling, 50% silking and 95% maturity
were recorded. At maturity, plant height, number of nodes per
plant, number of ears per plant and grains per ear, degree of
turcicum blight (Exserohilium turcicum (Pass) Leonard and
Suggs) infection, lodging and barrenness were recorded. Plot
grain yields were weighed at 15% moisture content. Residuals
from data for degree of turcicum blight infection, lodging and
barrenness were not normally distributed, so were square root
transformed prior to statistical analysis.
In the artificial shade experiment five randomly selected
plants per sub-plot were tagged for recording of number of
leaves, Aleaf (leaf area) and plant height at 10 day intervals
starting from 45 DAS until vertical extension ceased. For
consistency plant height was measured from the ground
level to the tip of the longest leaf. Leaf numbers 4, 7, 10,
13 and 16 from the five randomly selected plants were
measured.
Aleaf was calculated using the following formula:
Aleaf ¼ 0:75 L B
where L0length from base to the tip of a leaf, B0breadth
from the widest point of a leaf, and 0.750constant (Maddoni
and Otegui 1996).
Maize root systems
Maize root development was monitored only in the artificial
shade experiment. Due to resource limitations, roots were
Effects of light environment on maize in hillside agroforestry
sampled only twice, at 48 DAS and at 68 DAS using a
6.3 cm internal diameter mild steel corer, made locally using
2 m long plumbing pipe sharpened at one end and reinforced
with a wooden anvil at the other end for hammering. A hole
was drilled towards the upper end of pipe to insert a rod
used to remove it from the soil with a twisting motion. Soil
cores were pushed out from the corer using a 1.5 m length of
bamboo in increments of 10 cm for four rooting zones 0–10,
10–20, 20–30 and 30–40 cm at 48 DAS. The sampling
depth was extended to 40–50 cm depth at 68 DAS. The soil
cores were stored at 4°C until they could be washed. The
roots were separated from the soil cores by the flotation
technique using a root washer. Organic material washed out
of the soil cores was preserved in dilute acetic acid and
refrigerated at 4°C until it could be analysed. The roots were
then hand sorted to separate maize roots from those of other
plants and organic material, with the help of a binocular,
×10 dissecting microscope. The number of intersections
between lines on a grid and living roots were counted.
Tennant’s Modified Line Intersect Method (Tennant 1975)
was used to determine the total root length of each sample,
where
Root length ¼
11 grid size number of intersections
14
where 11 and 14 are constants. Two grid sizes were used,
depending on number of roots in the sample, 4.5×4.5 mm
and 10.5×10.5 mm.
Statistical analyses
Analyses of variance were performed using Genstat v. 3.2
(Lawes Agricultural Trust, Harpenden, UK), data from the
artificial shade experiment being treated as a split plot
design, whilst for the natural shade experiment, blocks were
nested within each site (shaded or non-shaded). Thus, it was
not possible to conduct a combined analysis of the two
shading experiments. To compare treatment means, the
standard error of the difference (s.e.d.) was computed.
Results and discussion
Light environment
Mean diurnal PPFD incident (IPPFD) throughout the day upon
the maize averaged over the season was 693 μmol m−2 s−1 onfarm in 1999 (Fig. 1) and 788 μmol m−2 s−1 in the open and
455 μmol m−2 s−1 under artificial shade on-station in 2000
(Fig. 2). In all cases, about 50% of IPPFD was intercepted by
the crop. IPPFD values were well below the light saturation
point of maize leaves of about 1,500 μmol m−2 s−1 (Stirling et
al. 1993), and were similar to those recorded by Prasad and
107
Brook (2005) in the rainy season in the central mid-hills of
Nepal. Even in the open, mean incident light (IPPFD) levels on
farms was well below the saturation point for maize, due to
cloudy conditions during the rainy season, and was further
reduced by farmers growing fodder trees on crop terrace risers.
It is the red:far red ratio (r:fr) rather than total radiation
that controls photomorphogenetic responses in plants
(Morgan and Smith 1981; Smith 1986). However, studies
of r:fr per se upon maize are very few, and none has been
reported from field conditions. The mean r: fr ratio recorded
in the 1999 season under on-farm conditions was 1.07 in
1999. In the 2000 season, it was 1.11 in the open and 1.06
under artificial shade. Thus, the environment created by the
netting was close to that created by the natural shade with
respect to quality of the light. McCalla et al. (1939) cited by
Earley et al. (1966) reported that shade treatments alter the
quality of incident light and this in turn might alter hormonal
balances which could alter plant height and other attributes.
In this experiment, artificial shade significantly reduced
plant height (Table 2), so there was no evidence of etiolation. Therefore the evidence suggested that the reduction of
total incident PPFD exerted a greater effect upon maize
growth than any change in r:fr ratio.
In addition to effects upon PPFD, shade, either artificial
or natural, exerts other effects upon the crop including
humidity within the canopy and temperature of leaf surfaces. During significant dry periods, tree roots will also
compete with the crop for water, although in the seasons
during which the present work was conducted, rainfall was
abundant.
Photosynthesis
The net photosynthesis rate of maize leaves rose with increasing PPFD, reaching a plateau at approximately
1,500 μmol m−2 s−1 for those unshaded. All regressions,
fitted with the Mitscherlich model were highly significant
(P<0.001) and yielded a coefficient for maximum rate of
photosynthesis of 29.3 μmol CO2 m−2 s−1 for maize growing in association with natural shade in 1999, and 28.2 μmol
CO2 m−2 s−1 for non-shaded maize in the artificial shade
experiment in the year 2000 (Fig. 3). This model yielded
low values for initial quantum efficiency (0.0013 and
0.0011 μmol CO2/μmol photons for 1999 and 2000 respectively). CO2 exchange rates measured on leaves of shaded
maize plants never reached light saturation. For the sake of
consistency, the Mitscherlich model was fitted to data from
shaded maize leaves in 1999, but in the case of artificial
shade in 2000, a linear regression provided a better fit (r2 0
0.91) and the quantum efficiency for the linear phase of the
response to PPFD was estimated to be 0.024 μmol CO2/
μmol photons (Fig. 3). Ephrath et al. (1993) also reported
similar findings. When PPFD was recorded in farmers’
108
T.P. Tiwari et al.
Fig. 1 Incident photosynthetic
photon flux density (PPFD)
recorded in on-farm condition
under mixed fodder tree species
(natural shade) and level of
interception at different stages
of maize growth, mean of ten
farms, 1999. BS before sowing
fields, mean light levels were sub-optimal for maize, regardless of whether or not they were growing under tree shade.
The implications of this finding, interpreted alongside the
light response curves of maize, are that even small reductions due to tree shading would have a large impact on
photosynthesis because the maize leaves are operating in
the linear portion of their light response curve. The results
also showed that there were no varietal differences in photosynthesis in maize, so any indication of adaptation to
shade, such as occurs in some species (Johnson et al.
1995; Peek et al. 2002) was absent. However, others have
reported evidence of genotypic variation in rates of photosynthesis at light saturation in maize (Duncan and Hesketh
1968; Gaskel and Pearce 1981), but this variation was not
apparently exhibited in the genetic material tested in the
experiments described here. Therefore, any varietal adaptation to shade as reported by farmers must be due to other
factors.
Maize growth
Leaf area (or its integral over land area, leaf area index) is an
important determinant of productivity in maize (Prasad and
Brook 2005), particularly in the light limited environment
Fig. 2 Incident photosynthetic
photon flux density (PPFD)
recorded in open and under
shade (artificial shade) and
level of interception at different
stages of maize growth, mean
of four varieties, 2000. BS
before sowing
experienced during the rainy season in Nepal and especially
under tree canopies. Therefore, the development of leaf area
to capture solar radiation is important. The components of
leaf area per plant are area per leaf (Aleaf) and number of
leaves per plant. Despite the lack of shade adaptation in
photosynthetic response in maize, the development of leaf
area was not affected by natural shade (Table 3) (P>0.05),
but was by artificial shade (Table 4) (P<0.05). Under artificial shade, mean Aleaf per leaf was about 10% lower than
in plants grown in the open. Except for a few cases (var.
PM-1, leaf numbers 13 and 16) unshaded plants always
produced larger leaves (data not shown). Ephrath et al.
(1993) found that shading decreased leaf size, but the effect
was minimal. Wilson et al. (1998) also found a similar result
in sorghum (Sorghum bicolor), where green leaf and stem
mass of shaded plants were significantly lower than those of
semi-shaded or those in the open. Leaf size increased until
leaf 13 in all varieties and above this point leaf size decreased. Varietal differences were observed in mean Aleaf
and this demonstrated that variety and shade affected leaf
size, as also found by Maddoni and Otegui (1996).
In the artificial shade experiment, number of leaves until 85
DAS were fewer under shade but they caught up by 95 DAS
and shaded plants had more leaves at 105 DAS (P<0.05)
Effects of light environment on maize in hillside agroforestry
Table 2 Effect of artificial shade
on plant height (cm) in the year
2000. Shade consisted of green,
loose-woven polypropylene,
which allowed 60% transmission
of light, hung over a bamboo
frame 10 m long×4.5 m wide.
Shade material hung down each
side in a 50 cm curtain, and the
shade was raised as the crop grew
Statistical results
Days after sowing (DAS)
45 DAS
55 DAS
65 DAS
75 DAS
85 DAS
95 DAS
105 DAS
No shade (Unshaded)
93
151
207
250
292
316
318
Artificial shade (Shaded)
68
112
159
200
243
274
296
Mean
F-test
81.0
***
131.0
***
183.0
**
225.0
**
268.0
**
295.0
**
307.0
*
s.e.d.
1.7
2.5
4.7
6.1
8.2
6.9
5.1
86
81
139
132
192
184
237
227
285
271
316
299
334
313
V30Mana-1
V40M/local
70
86
115
139
161
194
196
238
233
282
249
316
263
319
F-test
**
***
***
***
***
***
***
s.e.d
4.0
5.4
6.4
6.5
6.5
8.2
7.9
Variety effect, V10PM-1
V20PM-3
***0P<0.001; **0P<0.01;
*0P<0.05. Interaction effects
were not significant, so no data
presented
109
(Fig. 4). Conversely, Midmore et al. (1988) found that the leaf
numbers in maize were not modified by shade. There were
significant variety effects (P < 0.001) (as also found by
Duncan 1980; Robertson 1994), where Manakamana-1, an
early maturing variety had fewer leaves in both no shade and
shade treatments, followed by PM 3 (Fig. 5). Early maturing
varieties generally have fewer leaves and are shorter plants
(Duncan and Hesketh 1968; Maddoni and Otegui 1996). In
the context of maize culture in the mid-hills of Nepal, the
stover of maize has the significance of being an important
fodder supply for livestock (Tiwari et al. 2004), so identification of any varietal traits to maintain a higher leaf area under
shade may be important and might have been one criterion
used by farmers to assess shading tolerance of maize (Tiwari
et al. 2009a,b). Unlike many less determinate crops, maize
does not exhibit plasticity in development of leaf area in
response to population density (Prasad and Brook 2005), so
Fig. 3 Relationship between
net assimilation rate and
photosynthetic photon flux
density (PPFD) in maize, 1999
and 2000
establishment of a denser population at harvesting time
appears to be one means to increase total maize productivity per unit land area. However, in the hill farming systems
of Nepal, maize is usually under-cropped with finger millet
or soybean, and denser maize establishment has a negative
effect upon these (Prasad and Brook 2005). Therefore,
proper or suitable plant populations for each crop combination needs further investigation. Nepali hill farmers also
progressively thin maize crops throughout the season to
provide livestock fodder and to optimize plant population
(Tiwari et al. 2004).
Agronomic attributes
The two main attributes of interest to Nepali farmers are
grain yield and fodder production, the stover being fed to
livestock after grain harvest. Mean grain yield under natural
0.82
s.e.d.
† original data transformed before analysis of variance, therefore s.e.d. presented are from transformed data. Transformed data are in parentheses. There were no significant interaction effects
ns
16.5
1.7
ns
***
9.5
11.7
ns
ns
0.07
0.344
ns
***
11.0
17.07
ns
ns
0.686
0.0867
ns
ns
0.94
ns
F-test
ns
146
82
M/local (V4)
90
143
88
81
Mana-1 (V3)
1.6
407
395
415
409
12.1
333
211
0.90
2.76
285
5,625 (62.1)
8.0 (2.17)
2.5 (1.577)
11.4
269
235
0.95
2.78
227
3,438 (53.5)
4.0 (1.38)
2.4 (1.556)
10.9
15.1
316
297
224
230
0.93
0.89
2.51
2.75
289
268
6,875 (68.3)
3,438 (49.8)
7.0 (2.45)
6.5 (1.73)
2.6 (1.596)
2.1 (1.435)
144
144
92
82
90
82
PM-3 (V2)
Varieties
PM-1 (V1)
ns
11.6
1.2
ns
ns
6.7
8.3
***
*
0.05
0.243
***
ns
7.7
12.1
**
ns
0.0434
ns
***
***
0.58
1.2
***
s.e.d.
149
94
85
140
87
78
No shade
(Unshaded)
Tree shade
(Shaded)
F-test
Shades
0.67
12.1
298
199
0.86
2.16
261
6,719 (76.2)
7.6 (1.21)
309
251
0.97
3.24
273
2,969 (40.7)
5.0 (1.63)
2.4 (1.546)
2.4 (1.536)
416
12.7
Biomass
t ha−1
1,000 grain
weight (g)
No. of grains
ear−1
No. of ears
plant−1
Grain yield t ha−1
Plant height
(cm)
† barren
plants ha−1
† lodging
(%)
†Turcicum blight
(1–5 scale)
95% maturity
(DAS)
50% silking
(DAS)
50% tasseling
(DAS)
Characters
treatments
Table 3 Effect of natural shade on maize varieties and their agronomic attributes in the year 2000
397
T.P. Tiwari et al.
Leaf size
plant−1 (cm2)
110
tree shade both on-farm in 1999 (Tiwari et al. 2004) and onstation in 2000 were the same (2.16 tha−1), and represented
yield decreases of 37% in 1999 and 33% in 2000, compared
to maize plants growing further away from trees (Tables 3
and 4). On the other hand, whereas there was a large penalty
in biomass production under trees on-farm in 1999 (Tiwari
et al. 2004), the difference on-station in 2000 was small and
non-significant (Table 3). Farmers trade-off lower maize
yield for the fodder supplied by trees. To compensate for
this loss, other work as part of this research programme
showed that farmers exhibited a preference for higher yielding maize, even though these types were longer in duration,
as long as they exhibited a degree of tolerance to tree shade
(Tiwari et al. 2004).
Grain yield and biomass production in unshaded treatments in the artificial shade experiment were much greater
(Table 4) than the natural shade experiment (Table 3), both
conducted in 2000. The only terraces on the research station
wide enough for an artificial shade experiment away from
the influence of trees had been used intensively in previous
seasons for horticultural experiments, and had a long history
of heavy fertilization, whereas narrower terraces influenced
by tree shade were used less and consequently fertilized
moderately. Therefore, it was perhaps more appropriate to
compare proportional response to shade than absolute grain
yields. Artificial shade reduced grain yield by 43%, a figure
in proportion to the 40% of light intercepted by the shade
netting, whilst shade due to trees reduced on-station maize
yields by 33%. However, leaving aside the issue of below
ground interactions, the nature of tree shade is rather different from that of artificial shade cloth, so explaining such
differences in proportional response is difficult.
Natural shade on-farm (except at Marga) in 1999 (data
presented in Tiwari et al. 2004) and artificial and natural
shade on-station in 2000 significantly delayed tasseling (P<
0.001), silking (P<0.001) and maturity (P<0.001) (Tables 3
and 4). There were no varietal effects in the 2000 season on
time to 50% tasseling, neither was there an interaction
effect, showing that varieties displayed the same trend in
both the open and under shade. Unlike tasseling, variety did
have an effect on time to 50% silking (P<0.05) and maturity
(P<0.01) under artificial shade. Manakamana-1 was the
earliest, but this only differed significantly from PM-1
(Table 4) with respect to days to silking. There were no
interaction effects for these traits either.
Shade, both natural and artificial, resulted in fewer grains
per ear. There might have been floret or kernel abortion due
to insufficient plant assimilates under shade after fertilization. Tollenaar (1977, cited by Andrade et al. 1993) reported
that the amount of intercepted radiation at flowering stage is
critical for kernel set. If it is limited at flowering, ear abortion occurs immediately, whereas kernel abortion can continue up to 20 days after pollination.
Effects of light environment on maize in hillside agroforestry
111
Table 4 Effect of artificial shade on maize varieties and their agronomic attributes, 2000
Characters
treatments
50% tasseling
(DAS)
50% silking
(DAS)
95% maturity
(DAS)
Grain yield
(t ha−1)
Plant population
(ha−1)
No. of ear
plant−1
No. of
grain ear−1
1,000 grain
weight (g)
Biomass
(t ha−1)
Leaf size
plant−1 (cm2)
Main plot (shade)
No shade
(Unshaded)
Under shade
(Shaded)
F-test
82
88
142
5.31
39,800
1.2
319
332
26.0
521
92
99
153
3.01
39,800
0.9
242
310
16.9
470
***
***
***
**
NS
*
**
ns
***
**
s.e.d.
0.32
0.64
0.33
0.381
255.2
0.05
12.0
10.8
0.66
8.69
506
Sub-plot (variety)
PM-1 (V1)
87
95
147
4.21
40,000
1.11
268
327
22.5
PM-3 (V2)
86
94
148
4.38
39,688
1.12
287
326
21.8
501
Mana-1 (V3)
86
92
145
3.99
39,688
1.03
295
285
16.6
479
M/local (V4)
87
93
149
4.08
40,000
1.08
274
346
25
498
F-test
ns
*
**
ns
ns
ns
ns
***
***
ns
s.e.d.
0.74
0.99
0.90
0.279
312.5
0.07
15.9
7.5
1.22
16.2
ns not significant
Maize root systems
The non-shaded treatment had greater root length than the
artificial shade treatment on both recording dates (48 DAS
and 68 DAS) (Fig. 6), which is consistent with findings of
other researchers (Ephrath et al. 1993; Huxley et al. 1994).
Found that under light limited conditions (50% of the normal light, which is almost equivalent to the artificial shade
treatment in the present study) the growth of roots was
reduced, which led to a decrease in the root/shoot ratio.
Mean root length density (RLD) was greatest in the 10–
20 cm horizon, followed by 0–10 cm at the first recording
(48 DAS), and 10–20 cm, followed by 20–30 at the second
(68 DAS) (data not shown). This pattern of higher root
biomass in upper soil layers has been well documented in
maize by Jose et al. (2001).
A common problem with root coring studies are large
errors arising from sampling, combined with the considerable
Fig. 4 Mean number of leaves
at specific time intervals as
affected by artificial shade.
Error bars smaller than the point
size are not visible
amount of effort and time needed to acquire data by this
means, which necessarily reduces sample size. Therefore,
trends will be discussed here as indicators of genotype and
shading effects, in line with what is known from local knowledge. Although not significant, Manakamana-1 had greater
root length than other varieties (Madi local, PM-3 and PM-1)
at 48 DAS, but less at 68 DAS. The higher root length at 48
DAS was mainly due to the fact that Manakamana-1 matured
earlier and therefore roots grew more quickly than in other
later maturing counterparts. In contrast, later maturing varieties showed slow initial root development but overtook
Manakamana-1 by 68 DAS. The root distribution patterns
confirmed the results obtained in 1999 from local knowledge
acquisition that local maize varieties have deeper rooting
systems than more recently released varieties, and in Bangor,
UK where five Nepalese varieties (Manakamana-1, Local
white, Local yellow, Manakamana-3 (formerly called
Population-22, Tiwari et al. 2009b) and Gadbade (a mixed
112
T.P. Tiwari et al.
Fig. 5 Effect of artificial shade
and genotype upon average
maximum number of leaves of
maize, Pakhribas 2000
type)) were grown in a rhizotron experiment in a glasshouse
over an 8 week period in 1998 showed similar trends (data not
shown).
In summary, this work has shown that there was no
evidence for a difference in photosynthetic adaptation to
shade amongst the varieties tested but there were indications
that local germplasm developed a longer (possibly deeper)
root system early in the growth cycle under shade than more
recently released varieties. This could confer drought tolerance, which might explain farmers’ perceptions that local
varieties are drought tolerant. However, this hypothesis
requires further testing. Additionally, there was evidence
that some genotypes can compensate for sub-optimal light
conditions by growing more leaves.
This work reinforced findings that environments in which
maize is grown in the hillside systems are variable and very
different from the conditions on research stations where new
germplasm is usually selected and recommendations are
generated. Conventional maize breeding programmes are
often based in non-stressed environments and therefore give
results that are frequently not representative of target enviFig. 6 Effect of artificial shade
and genotype on root length
density of maize verieties, at
two growth stages, Pakhribas
2000
ronments. Given the heterogeneity in conditions on farms,
flexibility in both the germplasm available to farmers and
the recommendations that accompany it are necessary to
cater for the diverse environments in which the crop is
grown. The selection of better root morphology, if feasible,
could improve both lodging and drought tolerance. As there
appears not to be any capacity of the maize photosynthetic
apparatus to compensate for low levels of incident light then
selection for a larger leaf area per plant, so increasing the
opportunity to capture solar radiation, appears to be a more
promising strategy. This also has the benefit of producing
more fodder for livestock.
Conclusions
Maize is the principal staple food of the population of the
mid-hills of Nepal. Yet, this study has shown that farmer
practices and the marginal environment of the hillside systems impose significant constraints on maize productivity,
and indicate that presently available maize germplasm is
Effects of light environment on maize in hillside agroforestry
poorly adapted to them. The implications for food security
in the mid-hills in particular is that because the growing
environment is so different from that which is optimal for
maize production, breeding and agronomy programmes
need to be conducted in the agro-climatic conditions experienced by the crops if locally adapted and robust planting
material is to be developed.
Acknowledgements We thank the farmers of Marga, Patle and
Fakchamara for their co-operation and inputs in running on-farm trials.
Help from Messrs P. B. Baruwal, P. P. Poudel, R. B. Katuwal, D.P.
Sherchan and P. P. Khatiwada is gratefully acknowledged. We also
benefited from interactions with Dr Joel Ransom, a CIMMYT Agronomist based in Nepal at the time of this research. We would also like to
thank Drs. Kevin Pixley, and Marianne Banziger CIMMYT, for their
encouragement and guidance in preparing this paper. The authors
appreciate the assistance of Mr. Surath Pradhan in editing figures.
Thanks are also due to SDC for the support of maize research
and development in the hills of Nepal. This publication is an output
from a research project partly funded by the United Kingdom
Department for International Development (DFID) for the benefit
of developing countries (Project No. R7281, Plant Sciences Research Programme). The views expressed are not necessarily those
of DFID.
References
Andrade, H. F., Uhart, S. A., & Frugone, M. I. (1993). Intercepted
radiation at flowering and kernel number in maize: shade versus
plant density effects. Crop Science, 33, 482–485.
Carter, E. J. (1992). Tree cultivation on private land in the middle hills
of Nepal: lessons from some villages of Dolakha district. Mountain Research and Development, 12(3), 241–255.
Chamshama, S. A. O., Mugasha, A. G., Kloustad, A., Haveraaen, O.,
& Maliond, S. M. S. (1998). Growth and yield of maize alley
cropped with Leucaena leucocephala and Faidherbia albida in
Morogoro, Tanzania. Agroforestry Systems, 40, 215–225.
Duncan, W. G. (1980). Maize. In L. T. Evans (Ed.), Crop physiology
(pp. 23–50). UK: University Press Cambridge.
Duncan, W. G., & Hesketh, J. D. (1968). Net photosynthetic rates,
relative leaf growth rates and leaf numbers of 22 races of maize
grown at eight temperatures. Crop Science, 8, 670–674.
Earley, E. B., Miller, R. J., Reichert, G. L., Hageman, R. H., & Seif, R.
D. (1966). Effects of shade on maize production under field
conditions. Crop Science, 6, 1–7.
Ephrath, J. E., Wang, R. F., Terashima, K., Hesketh, J. D., Huck, M.
G., & Hummel. (1993). Shading effect on soybean and corn.
Biotronics, 22, 15–24.
Gaskel, M. L., & Pearce, R. B. (1981). Growth analysis of maize
hybrids differing in photosynthetic capability. Agronomy Journal,
73, 817–821.
Harris, D., Joshi, A., Khan, P. A., Gothkar, P., & Sodhi, P. S.
(1999). On-farm seed priming in semi-arid agriculture: development and evaluation in maize, rice and chickpea in India
using participatory methods. Experimental Agriculture, 35,
15–29.
Huxley, P. A., Pinney, A., Akunda, E., & Muraya, P. (1994). A treecrop interface orientation experiment with a Grevillea robusta
hedgerow and maize. Agroforestry Systems, 26, 23–45.
113
Johnson, I. R., Riha, S. J., & Wilks, D. S. (1995). Modelling
daily net canopy photosynthesis and its adaptation to irradiance and atmospheric CO2 concentration. Agricultural Systems, 50, 1–35.
Jose, S., Gillespie, A. R., Seifert, J. R., & Pope, P. E. (2001). Comparison of minirhizotron and soil core methods for quantifying root
biomass in a temperate alley cropping system. Agroforestry Systems, 52, 161–168.
Maddoni, G. A., & Otegui, M. E. (1996). Leaf area, light interception and crop development in maize. Field Crops Research,
48, 81–87.
Midmore, D. J., Roca, J., & Berrios, D. (1988). Potato (Solanum spp)
in the hot tropics IV. Intercropping with maize and the influence
of shade on potato microenvironment and crop growth. Field
Crops Research, 18, 141–157.
Morgan, D. C., & Smith, H. (1981). Non-photosynthetic responses to
light quality. In O. L. Lange, P. S. Nobel, C. B. Osmond, & H.
Ziegler (Eds.), Encyclopedia of plant physiology: physiological
plant ecology. I. Responses to the physical environment (pp. 108–
134). Berlin: Springer Verlag.
Peek, M. S., Russek-Cohen, E., Wait, D. A., & Forseth, I. N. (2002).
Physiological response curve analysis using nonlinear mixed
models. Oecologia, 132, 175–180.
Prasad, R. B., & Brook, R. M. (2005). Effect of varying maize densities on intercropped maize and soybean in Nepal. Experimental
Agriculture, 41, 365–382.
Reed, A. J., Singletary, G. W., Schussler, J. R., Williamson, D. R., &
Christy, A. L. (1988). Shading effects on dry matter and nitrogen
partitioning, kernel number and yield of maize. Crop Science, 28,
819–825.
Robertson, M. J. (1994). Relationships between internode elongation,
plant height and leaf appearance in maize. Field Crops Research,
38, 135–145.
Smith, H. (1986). The perception of light quality. In R. E. Kendrick &
G. H. M. Kronenberg (Eds.), Photomorphogenesis in plants (pp.
187–216). Dortrecht: Martinus Nijhoff.
Stirling, C. M., Rodrigo, V. H., & Emberru, J. (1993). Chilling and
photosynthetic productivity of field grown maize (Zea mays);
changes in the parameters of the light-response curve, canopy
leaf CO2 assimilation rate and crop radiation-use efficiency. Photosynthesis Research, 38, 125–133.
Tennant, D. (1975). A test of a modified line intersect method of
estimating root length. Journal of Ecology, 63, 995–1001.
Thapa, B. (1994). Farmers’ ecological knowledge about the management and use of farmland tree fodder resources in the middle hills
of eastern Nepal. Ph.D. Thesis. Bangor: University of Wales.
Tiwari, T. P., Brook, R. M., & Sinclair, F. L. (2004). Implications of hill
farmers’ agronomic practices in Nepal for crop improvement in
maize. Experimental Agriculture, 40, 397–417.
Tiwari, T. P., Virk, D. S., & Sinclair, F. L. (2009). Rapid gains in yield
and adoption of new maize varieties for complex hillside environments through farmer participation. I. Improving options through
participatory varietal selection (PVS). Field Crops Research, 111,
137–143.
Tiwari, T. P., Ortiz-Ferrara, G., Urrea, C., Katuwal, R. B., Koirala, K.
B., Prasad, R. C., Gurung, D. B., Sharma, D., Hamal, B.,
Bhandari, B., & Thapa, M. (2009). Rapid gains in yield and
adoption of new maize varieties for complex hillside environments through farmer participation. II. Scaling-up the adoption
through community-based seed production (CBSP). Field Crops
Research, 111, 144–151.
Wilson, T. D., Brook, R. M., & Tomlinson, H. F. (1998). Interaction
between Nere (Parkia biglobosa) and under-planted sorghum in a
parkland system in Burkina Faso. Experimental Agriculture, 34,
85–98.
114
Dr. Thakur Prasad Tiwari
gained his PhD in Agronomy
from the University of Bangor,
UK, in 2001. He started his professional career in 1982 and
worked for many years in the hills
of Nepal. He is currently working
as a Cropping Systems Agronomist for CIMMYT, based in Bangladesh. He is an output oriented
person and believes in participatory research and development and
enjoys working closely with farmers to understand their social and
biophysical circumstances in order
to focus on targeted research and development interventions. He has
published several papers in national and international journals.
Dr. Robert M. Brook has taught
agroforestry, crop science and rural development in the School of
Environment, Natural Resources
and Geography, Bangor University, Wales, United Kingdom since
1993. Research on agroforestry
and tropical farming systems conducted at Bangor University has
been conducted in Nepal, India,
Bangladesh, Kenya, Nigeria,
Costa Rica and Guatemala. He
started his career in tropical agriculture working for the Papua
New Guinea government agricultural research service for 6 years, and for shorter periods in South Sudan
and Indonesia. His PhD was awarded in 1980 from Dundee University
whilst conducting research at the Scottish Horticultural Research Institute.
T.P. Tiwari et al.
Paul Wagstaff studied tropical
agroforestry at Bangor University
in 1999–2000, and carried out research at the Pakhribas Agricultural Research Centre, Nepal.
Paul started his career in tropical
agriculture as a Crop Protection
Officer with the Tanzanian Ministry of Agriculture and Livestock
Development in 1989 and has
since worked in smallholder agriculture and tropical forestry for a
wide range of local and national
NGOs, government departments
and bilateral development agencies in Africa and South Asia. He is currently the Agricultural Advisor
for Concern Worldwide, an Irish international development NGO, supporting agricultural programs in 27 countries in Africa, Asia and the
Caribbean.
Dr. Fergus Sinclair is the
Global Research Leader in Production Ecology, World Agroforestry Centre (ICRAF), Nairobi,
Kenya and the Director, Centre
for Advanced Research in International Agricultural Development (CARIAD), College of
Natural Sciences, Bangor University, Wales, UK. He has published
several scientific papers in peerreviewed international journals
and books.