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The effect of mixture proportions and fertilizer nitrogen on morphology, insect pest damage, competition and yield advantages in a maize/bean intercrop
M.A. UGEN and H.C. WIEN^1 Namulonge Agricultural and Animal Production Research Institute, P.O. Box 7084, Kampala, Uganda ^1 Fruit and Vegetable Science Department, Cornell University, Ithaca, New York, 14853, USA. (Received 4 January 1995; accepted 18 October 1995)
Code Number: CS96038
Sizes of Files:
Text:33.7K
Graphics: Line Drawings (gif) - 7.7KABSTRACT
A field experiment was conducted at Cornell University, New York, USA during 1990 and 1991 growing seasons to determine the effect of the proportions of beans and maize and of nitrogen on insect pest damage, morphology, competition and yield advantages of the two crops grown in mixtures. Inter- cropping reduced the incidence of Japanese beetles (Popillia japanica) and Mexican bean beetles (Epilachna varivestis Mulcant) compared to sole beans. Both bean beetles decreased with decrease in bean proportion in the mixtures. Sole maize tasseled and matured earlier than intercropped maize in both years. Nitrogen application resulted in earlier maize tasseling. Bean vegetative growth was greater and maturity delayed the higher the nitrogen rates. Competitiveness of either maize or beans increased with decrease in crop proportions and maize competitiveness increased with increasing N level. Land Equivalent Ratios (LERs) were greater for intercropping than for sole cropping in both years. LERs were also higher without N application suggesting better utilisation of soil nutrients by intercrops. Key Words: Bean beetles, competitive ratio, intercropping, land equivalent ratio, replacement series, sole cropping RESUME Un champ experimental etait conduit a l'Universite de Cornell, New York aux USA au cours de 2 saisons culturales en 1990 et 1991 pour determiner l'effet des proportions de haricot et de mays et de l'azote sur l'attaque des insectes, la morphologie, la competition et les avantages en rendement de 2 cultures plantees en association. La culture mixte reduisait l'incidence de coleopteres "Japanese beetles" (Popillia japanica) et de coleopteres d'haricot "Mexican" (Epilachna varivestis Mulcant) comparee au haricot en monoculture. Les deux insectes decroissaient avec la reduction de l'haricot dans la culture mixte. Le mays plante en monoculture fleurissait et arrivait plus tot en maturite que le mays en culture mixte au cours de 2annees. L'application de l'azote entrainait une floraison precoce du mays. La croissance vegetative de haricot etait plus grande et la maturite etait retardee par les taux d'azote tres eleves. La competitivite de mais ou de l'haricot croissait ou decroissait selon les proportions culturales tandis que la competitivite de mais croissait avec le niveau d'azote. Les rapports d'utilisation de la terre ou Land Equivalent Ratios (LERs) etaient plus grands pour la culture mixte que pour la culture pure dans les 2 saisons. Les LERs etaient egalement plus grands, en absence d'application d'azote, ce qui suggere la meilleure utilisation des nutriments du sol par la culture mixte. Mots Cles: Coleoptere d'haricot, rapport de competitivite, culture mixte, rapport d'utilisation de la terre, serie de remplacement, monoculture INTRODUCTION Intercropping non-legumes with legumes is one of the many cropping systems prevalent in the tropics and sub-tropics. This is due to the system's increased productivity per unit area; efficient use of limited resources such as land, labour, nutrients, light, time and water; greater yield stability due to reduced risks; and economics of better use of scarce resources for mixtures (Lamberts, 1980; Francis, 1986). Willey (1979) noted the objectives of proper crop selection being to reduce intercrop competition, and maximise complementary effects between the different intercrop components in order to increase yield of the components. Pests can cause significant yield losses depending on environmental conditions, cultivar susceptability and croppping system. Risch et al. (1983) discussed aspects of 198 insects that attack crops and reported that 53% showed lower abundance in multiple cropping than sole crops, 18% were more abundant in mixtures, 9% showed no difference and 20% were variable in their responses. The low levels of insect pests in intercrops could be attributed to presence of other non-host plants, camouflage of the preferred host, changes in texture or colour of the total background, masking of a chemical attractant, or presence of a repellant from a non-host plant (Risch et al.,1983). In legumes-cereals intercropping systems, the associated crops usually have different nutritional demands, their peak periods of nutrient demands may not coincide, and their responses to the various nutrients tend to vary (Donald, 1963). Intercropping systems, therefore, have to take advantage of these factors in order to improve yields. In case of increased removal of nutrient by the intercrops, this may lead to soil nutrient depletion unless it is alleviated by additional nutrient application (Dalai, 1974). The objective of this study was to determine whether by altering proportions and populations of maize (Zea mays L.) and field beans (Phaseolus vulgaris L.) under different 1ertilizer regimes, a cropping system could be recommended for use under limiting conditions of rural farmers. This was done by determining the effects of intercropping and fertilizer N levels on growth morphological changes, insect pest damage, competition and yield advantages of the intercrops. MATERIALS AND METHODS Field experiments were conducted at Cornell University, New York, USA during the 1990 and 1991 growing seasons. The soils were Arkport, sandy loams (weak gray-brown podzolic soils) having chemical properties indicated in Table 1. Soil samples (0-30 cm) were taken prior to planting during both seasons. Soil pH, available nutrients, organic matter (OM) and cation exchange capacity (CEC) were determined. The same field was used for the experiments in both years. Soil samples taken before planting in 1991 were for determination of the status of residual N after the 1990 treatments. Results of the analysis (not included) confirmed no significant difference between the different blocks that received N fertilizer in 1990 growing season. The experiment consisted of three nitrogen levels applied as ammonium nitrate at 0,80 and 160 kg N ha^-1 to simulate low, medium and high fertility levels, respectively, and five crop proportions. TABLE 1. Chemical properties of the soil used in the maize/bean intercropping study in 1990 and 1991 growing seasons
Soil chemical properties 1990 1991 ---------------------------------------- pH in 0.01 M CaCl2 (1:1) 6.65 6.32 Organic matter (%) 2.42 1.94 Available NO3 (mg kg^-1) 4.63 6.41 Available P (mg kg^-1) 30.05 23.90 Exchangable K (mg kg^-1) 187.05 156.00 Exchangable Ca (mg kg^-1) 722.25 675.00 Exchangable Mg (mg kg^-1) 37.80 32.30 Exchangable Fe (mg kg^-1) 1.03 1.90 Exchangable AI (mg kg^-1) 11.33 13.20 Exchangable Mn (mg kg^-1) 5.83 15.00 CEC, cmol kg^-1 6.45 These were arranged in a split-plot design with N levels as main plots and crop proportions as sub-plots. The sub-plots were 8 x 4.5 m in both years. The five crop proportions in 1990 were sole maize crop at 37,037 plants ha^-1 (90 x 30 cm spacing), sole bean crop at 166,667 plants ha^-1 (60 x 10 cm spacing), 75% of sole maize + 25% of sole beans, 50% of sole maize + 50% of sole beans and 25% of sole maize + 75% of sole beans. These were combined in a replacement series to maintain the same total land area use. The assumption was that the sole crop populations of the two crops were the maximum populations of the two crops for the area. In 1991,50% of sole maize + 50% of sole beans was excluded but the rest of the 1990 crop proportions were included. In addition to the four crop proportions of 1990, a new set of crop proportions involving sole maize population of 55,556 plants ha^-1 (90 x 20 cm spacing) was included but maintaining the same population of beans as was for 1990 treatments. The sets of crop proportions in 1991 were sole maize at 55 556 plants ha^-1 (high maize population), sole maize at 37,037 plants ha^-1 (low maize population), sole planting in both years to achieve the desired plant populations. Weed control was by pre-emergence herbicide application, metalachlor (Dual) four days after planting. A rate of 1.68 kg active ingredient ha^-1 was used. Hand weeding was done once concurrently with second fertilizer application in both years. Insect pest damage of the crops was recorded by counting the number of infected plants as percentage of total number of plants in the two central rows. This was done at flowering time. Other records included time to 50% tasseling and maturity (drying) for maize and time to 50% flowering and maturity (drying) for beans. Beans and maize plants from the two central rows of 7 m each were harvested for grains. Beans were harvested by uprooting whole plants from each plot. Dry maize cobs from the field were husked in the field leaving the stalks behind. Both beans and maize were machine threshed and shelled, respectively. Determination of yield ha^-1 were made at 8% moisture content for beans and 12% moisture content for maize. Analyses of variance were performed on all the variables for both years and treatment means and graphs are used in beans at 166,667 plants ha^-1, 75% of maize + 25% of sole beans (under both high and low maize proportions), 50% of sole maize + 50% of sole beans (under high maize population), 25% of sole maize + 75% of sole beans (under both high and low maize population) giving a total of eight crop proportions. This was arranged in a split-plot design with N levels as main plots and crop proportions as sub-plots. The early-maturing maize cultivar (Pioneer 3925), and bush red kidney beans (cultivar Ruddy), were used in the experiment in both years. Nitrogen treatments remained the same in both years. Half the nitrogen (40 or 80 kg N ha^-1) was applied at planting as broadcasts. Maize was machine planted at 90 x 30 cm in 1990 and 90 x 20 cm in 1991 while beans were hand planted at 60 x 10 cm between two maize rows in both years. Bean rows were 15 cm from each maize row on either side. The second fertilizer application was side-dressed by broadcasting when maize plants were at knee height. The fertilizer material was incorporated in the soil concurrently with weeding. Thinning was manually done three weeks after reporting the results. Mean yields of both sole and intercropped systems were used to calculate Land Equivalent Ratio (LER) and Competitive Ratio (CR) following Mead and Willey's (1980) approach. RESULTS AND DISCUSSION Growth morphological changes. Sole maize tasseled and matured much earlier than intercropped maize in both years (Table 2). As the maize proportion reduced, tasseling and maturity of the crop (maize) delayed. This could have been due to early interspecific competition in maize/bean intercrop compared to intraspecific competition in sole maize. There were no significant effects of crop proportions on days to flowering and maturity of beans. Nitrogen application resulted in early maize tasseling (Table 3). Intercropping could have subjected the maize to competition for the available N thus slowing maize growth. Low N level in the soil slowed maize growth with eventual late tasseling. Bean vegetative growth was high and maturity was delayed with high N rates (Table 3). Wahua (1983) also noted that competition for nutrients between legumes and cereals in intercrops may delay development and productivity of the crops. Our result seems to support this statement as there was delayed maturity in intercropped maize. Insect pest damage on beans. Pest damage was significantly reduced by intercropping beans with maize, with lowest bean proportion resulting in the least damage in both 1990 and 1991 (Table 4). This was due to shading effect of maize on beans. Stoop (1986) noted a similar response of insect pests in cowpea and cereal intercrops where an increase in cowpea intercrop density increased the incidence of pests in the system. The presence of maize in the system seems to have been a barrier to pest movements further reducing damage in intercrops. More reduction in pest damage under the high maize proportion cropping system of 1991 (Table 4) further indicates that shading might be a greater determining factor in the control TABLE 2. Effect of crop proportions on number of days to tasseling and maturity in sole and intercropped maize systems in 1990, 1991
Maize 1990 1991 (A)^a 1991 (B)^b
proportion
Tasseling Maturity Tasseling Maturity Tasseling Maturity
(days) (days) (days) (days) (days) (days)
--------------------------------------------------------------
25% 55.9 d 107.7b 52.7b 92.8c 53.2b 91.5c
50% 54.8 c 106.8b - - 53.3b 88.5b
75% 53.8 b 100.8a 52.9b 88.3b 52.6ab 86.3a
Sole 51.9 a 103.4a 50.7a 84.8a 52.1a 85.4a
crop
--------------------------------------------------------------
Linear *** *** *** *** *** *
Quadratic * NS NS NS NS
NS
a, b, c, d: means followed by the same letter are not
significantly different (P>O.05) (LSD) TABLE 3. Effect of N fertilisation on days to tasseling in maize and maturity in beans in sole and intercropped systems
Nitrogen 1990 1991 (A) 1991 (B)
(kg ha-1)
Maize Bean Maize Bean Maize Bean
tasseling maturity tasseling maturity tasseling maturity
(days) (days) (days) (days) (days) (days)
------------------------------------------------------------
0 55.7b 80.3a 53.0b 71.4a 53.4 72.3a
80 53.7a 83.9b 52.5ab 78.3b 52.9 78.8b
160 52.9a 86.5b 51.4a 84.2c 51.9
83.1c
a, b, c: Means followed by the same letter are not
significantly different (P
Effects of crop proportions and N fertilisation on intercrop
seed yield. Maize and bean yield varied from one crop
proportion to another and decreased as crop proportions
increased, with high bean yield variability in 1991 compared
to 1990 (Table 5). Nitrogen fertilisation significantly
affected maize yield in 1990 and not in 1991 (Table 6). Bean
yield ha^-1 was not significantly affected by N fertilisation
in both years.
TABLE 4. Effect of bean proportion on bean damage by Japanese
and Mexican bean beetles in sole and intercropped systems
a, b, c: Means followed by the same letter are not
significantly different (P>O.05) (LSD)
This agrees with Chui's (1988) finding where N had no
significant effect on bean monocrop yield in Tanzania. But
Keya et al. (/982) reported monocrop bean response to
80 kg N ha^-1 of 2555 - 3482 kg ha^-1 increases at Embu in
Kenya but no bean response to N in Uganda. This suggests that
beans are capable of supplying their own N with yield equally
as high as plots that may receive N.
There was no significant response of maize to applied N in
1991 under both maize populations. In 1991, the weather was
very variable which could have caused the lack of response of
maize to applied N (Table 6). There was high variability in
maize yield in both years.
Competition between beans and maize. Competitive
abilities of maize and beans increased with decrease in the
crop proportions in both study years (Figs. 1 and 2). It seems
competition was more intense within crops than between crops.
Donald (1963) noted that yield per plant declined with
increase in plant density, while intraspecific interference
increased with increasing density.
TABLE 5. Effect of crop proportions on the yield of beans and
maize (kg ha^-~) in sole and intercropped system
a, b, c, d: Means followed by the same letter are not
significantly different (P>O.05) (LSD)
Increasing N level, at all crop proportions used in the
system, increased maize competitive ability while that of
beans decreased with N application (Figs. 1 and 2). Beans
competed less with maize as more N became available. At the
same time, maize growth was enhanced by N application which
might have enhanced better root development and, therefore,
nutrient uptake equipping the plant for better competition for
the available N. Russell and Caldwell (1989) reported similar
results for maize/soybean intercropping.
In 1991, however, the increase or decrease in competitive
abilities of maize or beans, respectively, due to N
application was slight compared to 1990 (Fig. 2). This
suggests that applied N was not effectively used in 1991
compared to 1990.
In the 1990 growing season, yield and number of pods per
plant of beans were positively correlated with competitive
ratings of bean (r=0.99).
Figure 2. The relationships between competitive ratios for
yield with change in crop proportions of bean and maize intercrops at (a) 0
kg N ha^-1, (b) 80 kg N ha^-1 and (c) 160 kg N ha^-1 under high maize
intercropping,
a, b: Means followed by the same letter are not significantly different
(P>O.05) (LSD) ***, *, NS - significant at 0.1%, 5% or not significant,
respectively.
Faris et al. (1983) reported similar results where the competitive
ratios of cowpeas were positively correlated with the number of pods and
seeds per plant in cowpeas/maize mixture. There was also high correlation
between maize ears and yield per plant with maize competitive ratios in
1990 (r=0.95 and r=0.82, respectively). For both beans and maize, yield per
plant and/or pods per plant and/or ears per plant increased with increase
in competitive abilities of the crops as the crop proportions were reduced
in the intercrops.
Yield advantages of mixing beans and maize. Relative yields (RY) of
beans at all crop proportions decreased with increasing N levels. The
reverse was, however, true for maize except for 25% maize proportions at 80
kg N ha^-1 where RY was lower than at 0 kg N ha^-1 in 1990 (Table 7). This
agrees with the trend noted by Russell and Caldwell (1989) in maize/soybean
intercrop. LERs for 25% maize +75% beans decreased with increasing N
application, indicating the effective use of the applied N by larger
component of the intercrop, in this case, the beans. The LER values of 50%
maize + 50% beans increased with increasing N application (Table 7). The
increase in LER of intercrops due to N application were mostly due to the
yield increase in maize in response to applied N fertilizer. Maize at 50%
proportion + 50% beans had higher LER values at all N levels indicating
some mutual sharing of resources or there was less interspecific and
intraspecific competition at the two crop proportions as indicated by their
competitive abilities and RY values in Figure 1 and Table 7, respectively,
for 1990 growing season. In 1991, the RY of bean under high maize
population cropping system decreased with increasing N application just as
for 1990, while under the low maize population cropping bean RY first
increased at 80 kg N ha^-1 then decreased at 160 kg N ha^-1 (Table 8).
In 1991, LERs were highest without N application suggesting that
beans/maize intercrops were advantageous even under low N and variable
weather as experienced during the growing season of 1991 (Table 8). This
could have also been due to large yields of intercrops or low yields of
corresponding sole crops due to competition. This confirms the finding of
Ahmed and Rao (1982) that intercropping advantage (LER) decreases with
increasing rate of applied N fertilizer. This contradicts the finding of
Waghmare and Singh (1984) that higher LERs and net returns were achieved at
a maximum N level (120 kg N ha^-1) than at low N level. Our results suggest
that intercropping maximises nutrient use even under low soil fertility
than at high soil fertility level.
TABLE 7. Effects of varied fertilizer N levels and crop proportions on bean
and maize relative yields and total land equivalent ratios (LERs)in sole
and intercropped systems, 1990
^a NO, N1, N2 represent 0, 80 and 160 kg N ha^-1 respectively, and B, M and
one percent proportions of beans and maize, respectively, in the
intercrops.
TABLE 8. Effects of varied N levels and crop proportions on bean and maize
relative yields (RY)and total land equivalent ratios (LERs)in sole and
intercropped systems under low and high maize population cropping systems,
1991
^a NO, N1, N2 represents O, 80 and 160 kg N ha^-1 respectively, and B and M
are percent proportions of beans and maize respectively in the
intercrops.
Low LERs were noted in 1991 under low maize proportion cropping (Table 8)
which were not significantly different. Fisher (1979) indicated that no
yield advantage from bean/maize mixture was apparent under low rainfall
conditions. Dry weather at maize's critical growth period coupled with low
maize population could have allowed less retention of moisture, low uptake
of nutrients and, therefore, low yield in 1991. LERs were significantly
affected by cropping system and no significant effect of N fertilisation on
LER values. There was higher LER values for intercropped than sole crops in
both years.
CONCLUSION
Intercropping is much more efficient in utilising the available resources
than sole cropping as indicated by the high LER values. Intercropping also
led to reduction in damage by Japanese and Mexican bean beetles compared to
sole crops.
This means reduction in cost of production under intercropping than
sole cropping, and therefore, increased yield of both crops per unit area.
Where the use of inorganic pesticides is limited as in developing
countries, intercropping may be a solution to reduce crop losses due to
pest attack.
Overyielding under intercrops compared to sole crops indicates better
and efficient utilisation of available resources by intercrops compared to
sole crops. Intercropping old beans and maize at low N level is effective
in utilising available resources. The advantage of intercropping seems to
be more expressed under low N level even when the weather conditions are
erratic.
Addition of N in the system increases the competitive ability of maize
and reduces that of beans. Therefore, a compromise in the crop combination
as well as population of the crops have to be carefully considered. In this
case, it would seem more appropriate to have equal amounts of beans and
maize (50% of each sole crop) as intercrop under good weather condition and
good N fertility as was for 1990. Where soil fertility is high, a farmer is
better off planting more maize than beans in the intercrop to take
advantage of soil resources and their efficient utilisation and the
reverse is true where soil fertility is low (more beans in the system than
maize). Therefore, as N level increases, the density of maize in the
intercrop may be increased for maximum yield of the intercrop, and as the N
level of the soil decreases the density of maize is reduced while that of
beans is increased for maximum yield in the intercrops.
ACKNOWLEDGEMENT
The first author acknowledges the help of Profs. Chris Wien and Tom
Scott who were his thesis advisers; Ass. Prof. Minotti Peter and the
Graduate Students of Fruit and Vegetable Science Department who helped with
the field work and whose positive criticisms of the paper made this work a
success.
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Copyright 1996 The African Crop Science Society
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