 |
| About Bioline | All Journals | Testimonials | Membership | News |
|
||||||
|
||||||
African Crop Science Journal, Vol. 10. No. 3, 2002, pp. 251-261 RESOURCE UTILISATION IN SOYBEAN/MAIZE INTERCROPS S.A. Ennin, M.D. Clegg1 and C. A. Francis1 Crops Research Institute, P.O.Box 3785, Kumasi, Ghana (Received 16 January, 2001; accepted 7 June, 2002) Code Number: cs02025 ABSTRACT Field studies were conducted in 1994 and 1995 at Mead, Nebraska, to investigate management practices that will improve solar radiation capture and use, and to explore the nitrogen economy of legume/ nonlegume intercropping systems. There were five soybean (Glycine max L. ) /maize (Zea mays) intercrop row arrangements at two nitrogen application rates (0 and 160 kg N ha-1) and three sole crops. Percent PAR intercepted by intercrops was 4% greater in closer row arrangements of soybean and maize than in equally spaced 2 rows soybean: 2 rows maize, and increased 2 to 5% by N application. Dry matter productivity of the intercrops was more than sole crops, and up to 38 % more by close association of soybean and maize, N application, and limited moisture availability. Grain yield increase of intercrops over sole crops was not significant (P < 0.05). Soybean and maize may be planted as intercrops in alternating single rows in forage production systems to take advantage of available solar radiation and greater dry matter yields. Key Words: Nitrogen, row arrangement, photosynthetic active radiation, productivity RÉSUMÉ Des études des champs étaient conduites en 1994 et 1995 à Mead, Nebraska, pour examiner les pratiques de gestion améliorant l’interception de la radiation solaire et son utilisation, et explorer l'économie d'azote dans l’association des légumes et des non légumes. Il avait cinq lignes de soja (Glycine max L.) et de maïs (Zea mays) et deux taux d’application de l’azote (0 et 160 kg N ha-1) et trois monocultures. Le pourcentage de PAR intercepté par l’association était de 4% plus élévé dans un arrangement à forte densité des plantes du soja et le maïs que dans un arrangement de 2 lignes de soja et 2 lignes de maïs, et a augmenté de 2 à 5 % par l’application de N. La production en matière sèche dans l’association était plus élévée par rapport aux monocultures, et jusqu’à 38% de plus pour l’association à forte densité, à l’application de N, et la disponibilité limitée de l’humidité. L’augmentation du rendement due à l’association n’a pas été significative (P<0,05). Le soja et le maïs peuvent être plantés en association dans des lignes alternées dans un système de production du fourrage pour bénéficier de l’avantage de la radiation solaire et les rendements en matière sèche élévés. Mots Clés: Azote, arrangement en lignes, radiation photosynthétique active, productivité INTRODUCTION Increased productivity of intercropping over sole cropping has been attributed to better use of solar radiation, nutrients and water (Willey, 1990; Keating and Carberry, 1993; Morris and Garrity, 1993). Better use of solar radiation by intercrops was attributed to increased interception and /or greater radiation use efficiency (RUE ). Spatial arrangement of intercrops is an important management practice that can improve radiation interception through more complete ground cover (Reddy et al., 1989) However, Keating and Carberry (1993) have suggested that increased radiation interception due to better ground cover of intercrops may be due to sub-optimal sole crop population densities used in comparisons. The availability of nutrients and water enhances exploitation of available solar radiation for greater crop productivity. There is potential for higher productivity of intercrops when interspecific competition is less than intraspecific competition for a limiting resource (Francis, 1989). The inclusion of legumes in intercrops has been reported to reduce interspecific competition for N due to symbiotic N fixation (Clement et al., 1992a). Reduced competition for N due to greater N fixation efficiency of the intercropped legume compared to sole legume (Rerkasem and Rerkasem, 1988; Sangakkara, 1994) and transfer of the fixed N to the associated non-legume component (Fujita et al., 1990; Clark and Myers, 1994) have also been reported. There have been conflicting reports on the effect of increasing N availability through application of fertiliser N on the productivity of the legume/non-legume intercrops. Midmore (1993) reported that addition of N fertiliser to legume intercrops raises yield of both components but reduces the relative advantage of intercropping. Similar reports describe effects in soybean/cereal intercrops ( Searle et al., 1981; Chui and Shibles, 1984). However, productivity of legume intercrops has been reported by others to increase with N fertilization (Rerkasem and Rerkasem, 1988; Clement et al., 1992a). Recent reviews emphasize a need for research on how to optimize radiation capture and use in intercrops (Keating and Carberry, 1993) and factors influencing N transfer from legumes to associated species in intercrops. The objective of this study was to investigate the effect of row spacing and applied N on % PAR interception, dry matter and grain productivity from soybean to maize in a soybean/maize intercrop. MATERIALS AND METHODS A soybean/maize intercropping experiment was established on 18 May, 1994 and repeated on 25 May, 1995. Field experiments were conducted at the University of Nebraska Agricultural Research and Development Center, near Mead. The soil at the experimental site is a Sharpsburg silt clay loam (fine montmorillonitic, mesic Typic Argiudoll). The soil was N-depleted with no fertiliser application for six years with continuous wheat prior to planting on the 1994 site, and continuous sorghum prior to planting on the 1995 site. Maize hybrid 3417IR was intercropped with soybean cultivar Hobbit 87'. Nitrogen was band applied near the maze rows at rates of 0 and 160 kg N ha-1. There were four row arrangements of soybean (S) and maize (M) intercrops: 1rowS: 1rowM (SM); 2rowsS: 1rowM (SSMa); 3rowsS: 1rowM (SSSM); and 2rowsS: 2rowsM (SSMM), (Fig. 1). Sole maize with 0 and 160 kg applied N ha-1 and sole soybean treatments (No added fertiliser) were included. An additive model was used and plant population density was kept constant on a total plot area basis, set at the optimum for sole crops and kept the same in intercrops. Maize was planted at 55,000 plants ha-1 and soybean at 562,000 plants ha-1 by adjusting within row spacings of the intercrops. Rows were spaced 75 cm apart in sole maize (M) and soybean (S) plots. Intercropped soybean rows were 75 cm from soybean to soybean and 37 cm from maize row to soybean row except in SSMM where it was 75 cm from maize to soybean row. Intercropped maize rows were 75 cm from maize to maize in SM and SSMM, 150 cm in SSMa, and 225 cm in SSSM row patterns with increasingly closer within row maize spacings (Fig.1). In the second year, a fifth spatial arrangement SSMb was included to give a wider spacing of 56 cm between maize row and soybean row with maize at 70% of sole maize population (38,500 plants ha-1). Treatments consisted of 2 x 4 factorial (N-rate x spatial arrangement) of intercrops in 1994, and 2 x 5 in 1995. Three sole crop treatments were included in both years. The experimental design was a randomized complete block with six replications per year. Plot size was 4.5 m wide and 9 m long. Soybean seed was coated with commercial Bradyrhizobia inoculant, Nitragin. Planting was done mechanically using a John Deere 71 flex planter. Weeds were controlled by post-emergent herbicide application of a mixture of Pursuit (Imazethapyr, 240 g L-1) at 0.29 L ha-1, 28% UAN at 4.67 l ha-1, and surfacant at 1 l 400 l-1. Further weed control was achieved by hand weeding during the growing season. Supplementary irrigation (5 cm) was applied during drought in 1995 when soybean was at full bloom stage (R2) (Fehr et al., 1971) and 5 cm applied when soybean was at podding stage (R3/R4.) and maize at 50% silking to minimise the effect of drought and high temperatures (Fig. 2). Soil was sampled in each replication at planting at 0-15 cm, 15-30 cm, 30-60 cm, 60-90 cm, and 90-120 cm. Soil was analyzed for baseline data on total mineral nitrogen (Lachat QuickChem Methods # 12-107-06-1-B (NH4-N) and # 12-107-04-1-A (NO-3-N), phosphorus (Bray P-1), potassium (1M NH4OAc Ext.), organic matter (Walkley Black method), and pH (North Central Regional Publication No. 221 (Revised), 1988). Incident photosynthetic active radiation (PAR) was measured using a line quantum sensor with LI-1000 DataLogger (Li-Cor Inc 1987) at six points in a plot. Readings were recorded about midday at 41, 69, and 110 days after sowing (DAS) at the top of the maize and soybean canopies, and at ground level in 1994. In 1995, PAR readings were taken on 42, 56, 74 and 108 DAS at the same positions. The average % PAR interception levels by the crop canopies were then calculated by difference. After taking PAR readings, leaf area index (LAI) was determined non-destructively using LAI-2000 Plant Canopy Analyzer with LAI-2050 optical sensor (Li-Cor Inc, 1991) . Plant heights were measured from five random plants in the central rows after 100% silking for maize and at harvest for soybean. Two rows 1m long of each component crop were harvested from each plot at physiological maturity (116 DAS for soybean and 130 DAS for maize) except in the SSSM plots where 3 rows soybean and 1 row maize were harvested. Plants were oven dried at 80oC to constant weight for dry matter measurements of grain and plant residue. Nitrogen content was determined for seeds and plant residue using a Tecatur Infratec Near Infrared Transmittance (Model 1255) instrument (AOAC International, 1994). Grain yield data were obtained by manually harvesting 3 m rows. Total numbers of maize plants and ears were recorded and ears were shelled and soybeans threshed mechanically. Statistical analysis was carried out with Statistical Analysis System (SAS) using General Linear Model (GLM) procedures. Analysis of variance (ANOVA) and contrasts (Steel and Torrie, 1980) were constructed to examine nitrogen, intercrop row spacing and their interactions and sole crop effects on the variables measured. RESULTS AND DISCUSSION The soils were initially low in N content due to the cropping history of continuous cereal production for six years with no N application. Nitrate-N ranged from 1.0 to 3.5 mg kg-1 and ammonium-N from 6.5 to 17.3 mg kg-1. Phosphorus levels in the top 15 cm soil profile were high (26.0) and decreased to a low level of 8.1 mg kg-1 at the 30-60 cm depth. Potassium levels throughout the 120 cm soil profile were high (201 to 436 mg kg-1). Soil organic matter were 23-26 g kg-1 in the top 15cm and decreased with soil depth to 4 g kg-1 at 90-120 cm. Soils were slightly acidic (5.8-6.1) throughout the 120cm profile. Photosynthetic active radiation (PAR) interception. Crop row arrangement had a significant (P < 0.05) effect on %PAR intercepted on the first two and the last two dates in 1994 and 1995, respectively (Table 1). During the vegetative seventh node stage of soybean (V7) at 41 DAS, sole soybean and sole maize intercepted the least amount of PAR. The greatest PAR was intercepted by the SM intercrop row arrangement in 1994 (Table 1). At full flowering/beginning of podding (R2/R3, 69 DAS), % PAR interception by sole soybean had rapidly increased and was intercepting as much as the intercrops. Sole maize with and without applied N was intercepting the least PAR. Percent PAR interception pattern remained fairly constant until R6 stage (110 DAS) when soybean leaves and pods had just begun to yellow. In 1995 (Table 1), rate of crop growth was less than in 1994 and % PAR interception remained low for both sole crops and intercrops. The %PAR interception by all sole crops of soybean and maize with or without applied N was lower than intercrops during all stages of crop growth through R6 (108 DAS). Results are similar to those reported by Clement et al. (1992b) where in the absence of moisture stress, sole crop of the faster growing legume intercepted as much incident solar radiation as intercrops after early vegetative stage, and the sole crop of the cereal intercepted the least. In 1995 when moisture was limiting, our results agree with the conclusion that one of the conditions under which intercrops intercepted more solar radiation than sole crops was moisture stress (Keating and Carberry, 1993). The application of 160 kg N ha-1 resulted in increased total interception at full flowering/beginning podding stages (P < 0.05) by 2% (95 to 97%) in 1994 and by 5% (79 to 84%) in 1995. In both 1994 and 1995, there was no N x row arrangement interaction on PAR intercepted by the soybean/maize intercrop throughout crop growth (Table 1). In 1994, intercrop row arrangement significantly (P < 0.05) affected PAR interception during the V7 and R2/R3 stages but not later when soybean pods had just begun to yellow. Row arrangements with close association of maize and soybean intercepted more PAR than the less closely associated maize and soybean arrangement (SSSM). In 1995, row arrangement and nitrogen application had significant effects on PAR interception later in the growth period (full flowering). At this stage, the SSMM arrangement intercepted less PAR than other row arrangements. Our results are similar to those of Reddy et al. (1989) who reported that PAR interception by the intercrop decreased with increasing distance between the taller component, pigeonpea, and the shorter component, peanut. When PAR interception by component crops was measured in 1995, the increase with N application could be attributed to the significant increase in the maize radiation interception (Fig. 3). Similarly, in the study reported by Searle et al. (1981), 100 kg N ha-1 increased PAR interception by maize from 57 to 68% in soybean/maize and peanut/maize intercrops. At all stages, soybean intercepted more radiation than maize (Fig.3). Radiation interception increased for both components with time to 74 DAS and then little change occurred. However, the rate of increase was faster in the soybean component than the maize component of the intercrop. Sole soybean intercepted similar amounts of radiation as soybean in the intercrops from early growth up to 74 DAS. At 108 DAS, sole soybean intercepted more radiation than soybean in the intercrops. Interception by soybean in SM + N and SSMM + N systems were the lowest. Sole maize with or without application of 160 kg N ha-1 intercepted the same amount of PAR at all stages. Unlike soybean, PAR intercepted by sole maize was significantly higher (P < 0.05) than the PAR intercepted by maize in the intercrops. Apparently, due to moisture stress in 1995, less %PAR was intercepted by the maize component of the intercrop allowing greater PAR availability and interception by soybean. Crop growth and dry matter productivity. Total leaf area index (LAI) increased from the vegeteative to early reproductive stage (R2/R3) but had dropped by the R6 stage of soybean growth due to leaf senescence (Fig. 4). In the drier year, 1995, maximum leaf area was reached at beginning of podding (R3), but the LAI was lower than 1994. The differences in leaf area development were similar to those of %PAR interception, with sole maize with and without N application having least leaf area and interception. Sole soybean attained highest leaf area of 4.3 in 1994, but was similar to intercrops in the drier 1995. Intercropping resulted in increased soybean plant height in both years (Fig. 5), especially in arrangements where soybean and maize were more closely associated (SM). In 1994 when rainfall favored good crop growth, soybean stems in SM were thin with less branching and the lower leaves began to shed by R3 leading to a greater decline in LAI than in the other intercrops. Maize height was reduced by intercrop, and the effect was greater in the drier 1995. These results confirmed the observations of Keating and Carberry (1993) in their review of solar radiation capture and utilisation in intercrops. Increased internode elongation, and a reduction in branching and leaf production of the lower component, were reported to be typical responses in intercrops due to increased far-red: red ratio at the lower levels of the intercrop canopy. Similarly, Carr et al. (1995) found that intercropping wheat and lentil increased lentil plant height, facilitating mechanical harvesting of intercropped lentil compared to sole lentil. Dry matter production of the maize and soybean components in intercrops were lower than their sole crop counterparts (Table 2). The reduction was greater in intercropped soybean in 1994 due to more shading by maize in this year when rainfall was not limiting crop growth. In both years, total dry matter production at a given N rate was highest in SM, but was not statistically different from sole maize. Total dry matter production was higher in all intercrops as compared to sole soybean. Productivity of the intercrops on a dry matter production basis measured by land equivalent ratio of dry matter production (LERd) increased by intercropping soybean and maize and was significantly higher than sole cropping in 1995 when rainfall was limiting (Table 2). This could be due to the combination of greater PAR interception by intercrops than sole maize and a greater efficiency of dry matter production by intercrops than sole soybean due to the presence of C4 maize (Table 3). Increased dry matter productivity of intercropping C3 species with a C4 as compared to a sole crop of C3 species has been established. The increase in dry matter productivity of C4 / C3 intercrops over C4 species have been reported to occur only when light interception or RUE of the intercrop is higher than the C4 species (Keating and Carberry, 1993). Fujita et al. (1990) reported total dry matter production by a soybean/sorghum intercrop to be greater than either sole crop due to increasing sorghum growth. Their total intercrop dry matter increased with closer proximity of maize and soybean rows, as confirmed in our study. A 36% increase in dry matter productivity and 25% in grain productivity of a millet/groundnut intercrop was attributed to efficiency of radiation interception with no increase in intercrop radiation interception over sole crops (Willey, 1990). However the author reported that greater intercrop dry matter and grain productivity of a sorghum/pigeonpea intercrop was due to greater total radiation interception in the intercrop. In our studies there was no N x row arrangement interaction or row spacing effect on LERd. Application of 160 kg N ha-1 increased the dry matter productivity of the intercrops, with SM +160 kg N ha-1 having the highest LERd of 1.38. This could be because this system had relatively high PAR interception by the maize component throughout the growing season (Fig. 3). The greater PAR intercepted by the maize resulted in the highest relative maize dry matter production, 77% in the intercrop as compared to sole maize. In general, these results indicate that the intercrops were more productive than sole crops of maize and soybean in dry matter production, with intercrop productivity enhanced by close association of soybean and maize, N application or limited moisture availability. Grain yield and grain productivity. Intercropping reduced maize grain yields by 53 to 88% of sole maize yields in 1994 and 31 to 60% of sole maize yields in 1995 as indicated by the relative yields (RY) (Table 3). Soybean grain yields had greater yield reductions than maize due to shading by maize; yields were 12 to 39% of the sole soybean yield in 1994. In 1995, soybean yield reduction in the maize intercrop was less, and relative yields ranged from 46 to 76% of sole soybean yields. This was due to less shading by maize in this drier year when maize growth was reduced. Thus LERs were generally greater than one, indicating that most intercrops were more productive than sole crops in the dry 1995. Little advantage in grain productivity by intercropping occurred in 1994 when rainfall was non-limiting to crop growth. The trend was for higher LERs, 1.15 and 1.20, when two rows of soybean were planted after one row of maize in SSMa, 0-N and SSMb +160 kg N ha-1. This implies that 15 to 20% more land would be needed under sole cropping of soybean and maize to obtain same yields as these intercrops. Maximum LERs were in intercrops with moderate yield reduction of maize as well as soybean, indicated by the moderate relative yields (Table 3). Unlike dry matter productivity, there was a need for a balance in %PAR intercepted by the maize and soybean components of the intercrop for maximum grain productivity to occur (Fig. 3). Trends in our study appear to be similar to the review reports on cereal/legume intercrops by Ofori and Stern (1987) and Clement et al. (1992a) which indicated that SSM arrangements resulted in more grain productivity than planting both crops in single alternate rows. In row arrangement studies where several rows of a legume alternate with several rows of a non-legume in strip intercropping, Pendleton et al. (1963) reported that four-row or six-row strips of maize alternating with strips of soybean had a 16 to 20% yield increase. However, shading by maize caused a proportionate 20% decrease in soybean yields, resulting in no increase in productivity by intercropping. Market price of each crop and relative yield on each farm were suggested as factors that determine the utilisation of strip cropping of maize and soybean. Crookston and Hill (1979) studied various row arrangements of soybean/maize intercrops in Minnesota and reported LERs of 0.97 to 1.02 with no significant increase in grain productivity of the intercrops. Ayisi et al. (1997) reported significant row arrangement effects on the productivity of canola/soybean. In the absence of applied N, narrower strips of 1 to 4 m width had LERs significantly greater than 1 (1.02 to 1.65), and with application of N wider strips of 1 m to 6 m also became significant. Among the intercrops, there was no significant (P<0.05) nitrogen x row arrangement interaction effects, row arrangement or nitrogen effect on grain LERs in this study. Although relative yield of intercrop maize increased with application of N in 1994, relative yield of intercrop soybean decreased, with no net effect of N on productivity of the intercrop. Reports from other studies on the effect of nitrogen application on intercrop productivity have been conflicting. There have been reports of increased intercrop productivity with N application in soybean/maize intercrops (Clement et al., 1992a) and maize/rice bean intercrops (Rerkasem and Rerkasem, 1988), and decrease in LER with N application (Searle et al., 1981; Chui and Shibles, 1984). The reported decreases in grain yield and productivity with N application were attributed to high soil N status. The lower intercrop advantage for grain as compared to dry matter production was probably due to less partitioning of assimilate to grain by the intercrop as compared to the sole crops. The high total plant population density of the intercrops, and an associated high interspecific and intraspecific competion may have contributed to the observed trend in grain and dry matter productivity of the soybean/maize intercrops. CONCLUSIONS Interception of PAR by soybean/maize intercrops was higher than either sole crop only under limiting moisture conditions. Although close row arrangement and N application significantly (P<0.05) increased spatial PAR interception by intercrops, the increase was minimal. The greater dry matter productivity of the soybean/maize intercrops than sole crops could be attributed to greater PAR interception by intercrops than sole maize. Soybean and maize may be planted in the alternate SM intercrop row arrangement in forage production systems to take advantage of available solar radiation and greater dry matter yields. In labor-intensive agricultural areas with limited rainfall, soybean may be grown in SSM intercrop systems to minimise the risk of crop failure. ACKNOWLEDGEMENT Financial support by the Canadian International Development Agency (CIDA) through the Ghana Grains Development Project is highly appreciated. REFERENCES
©2002, African Crop Science Society The following images related to this document are available:Photo images[cs02025t2.jpg] [cs02025t1.jpg] [cs02025f3.jpg] [cs02025f4.jpg] [cs02025f2.jpg] [cs02025t3.jpg] [cs02025f1.jpg] [cs02025f5.jpg] |
| |||||||||
