search
for
 About Bioline  All Journals  Testimonials  Membership  News


African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 5, Num. 4, 1997, pp. 351-357
African Crop Science Journal,Vol. 5. No. 4, pp. 351-357, 1997

COWPEA INTERCROP GROWTH AND YIELD AS AFFECTED BY TIME OF PLANTING RELATIVE TO MILLET

K.C. REDDY and P.L. VISSER1

Alabama A & M University, P. O. Box 1208, Normal, AL 35762, USA
^1 National Agronomic Research Institute of Niger (INRAN), B.P. 429, Niamey, Niger

(Received 31 December, 1996; accepted 25 August, 1997)

Code Number:CS97041
Sizes of Files:
      Text: 17.4K
      Graphics: Line drawings and tables (gif) - 35.8K

ABSTRACT

Cowpea growth and yield performance in intercrop system with millet was compared on seven relative sowing dates in a field experiment over a three year period in the Sahelian zone of Niger. Cowpea growth period decreased by the same number of days as the delay in sowing, and light interception level of same stage cowpea decreased progressively with the delay in sowing. Delaying sowing from simultaneous sowing with the millet to 7 weeks after millet led to significantly lower crop growth rates (19 to 10 kg ha^-1 d^-1), and lower grain (1110 to 100 kg ha^-1) and dry matter (2110 to 560 kg ha^-1) yields of cowpea. However, intercrop millet grain yield did not vary significantly with cowpea interplanting times. Contrary to the recommendations made in the long rainy season areas of Africa, in the Sahel zone, intercrop cowpea needs to be sown simultaneously or soon after sowing the cereal for maximum grain yield performance.

Key Words: Growth, intercrop, light interception, planting time, Vigna unguiculata

RESUME

La croissance des niebes et le rendement de culture dans le systeme de culture derobee avec le mil etaient compares sur sept dates relatives des semis au champ d'experience, pendant une periode de trois ans, dans une zone sahalienne du Niger. La periode de la croissance des niebes a baisse par les memes nombres des jours que le retard des semis, et l'interception de rayons de la lumiere par les niebes au meme stade de la croissance a baisse progressivement en fonction du retard des semis. Differer les semis de ceux qui devraient etre effectues simultanenent avec le mil jusqu'l sept semaines apres les semis du mil, a entraine aux taux des croissances inferieurs de la culture (19 a 10 kg ha^-1 d^-1), et au rendement mediocre en graines (1110 a 100 kg ha^-1) et en matieres seches (2110 a 560 kg ha^-1) rendement de niebe. Par contre, le rendement en graines du mil sous un systeme de culture derobee n'a pas varie, d'une maniere considerable, avec les dates des intersemis des niebes. Contrairement a ce qu'il est exigi en recommendations, dans les zones a longues saisons de pluies de l' Afrique, dans les zones sahaliennes, le systeme de la culture derobee avec les niebes devrait etre effectue simultanement ou peu de temps apres les semis des cereales pour pouvoir realiser le rendement eleve en graines.

Mots Cles: Croissance, culture derobee, interception d'eclairage, dates des semis, Vigna unguiculata

INTRODUCTION

Intercropping of cowpea (Vigna unguiculata (L.) Walp) with pearl millet (Pennisetum glaucum (L.) R. Br) under rain-fed conditions is common in Niger and in other Sahelian countries (Reddy and Buckner, 1991). For example, in Niger in 1990, 93% of the total cowpea area and 69% of the total millet area (the two dominant crops of the country) were intercropped. In the traditional intercrop system, millet is the priority crop. As a consequence, the legume or cereal intercrop is usually planted after millet is established. Depending on the year and location, this may take from three weeks to two months after millet planting and places cowpea in a competitive disadvantage.

The Sahelian region is characterised by a unimodal and short summer rainy season (about 60-110 days) with erratic rainfall (300-600 mm). The onset of the rains is quite variable across years. Usually, the rainy season starts in June and rainfall probabilities reach a maximum in August, but the season often ends abruptly by the first fortnight of September (Sivakumar et al ., undated). Soils in this region are sandy and low in nutrients (Ouattara and Persaud, 1986).

The short and erratic rainy season of the region does not allow any classic temporal complementary between intercrops. Further, in the millet/cowpea association, cowpea is at a disadvantage for light interception as it is low growing (about 0.25 m in height) compared to millet (about 2 m). These limitations and the current trend of decreasing rainfall in the region (Lamb, 1982) have resulted in extremely low cowpea grain yields in intercrop systems. In 1990, cowpea grain yield in Niger in an intercrop system was 70 kg ha^-1, whereas its yield in a sole crop system was 412 kg ha^-1 (Anonymous, 1991).

Because of these particulars, the limited rainy season and the growth habit of intercrops, the time of planting of a short statured intercrop plays a critical role in determining final grain yield. Hence, the objective of this study was to determine the effect of relative time of interplanting cowpea on its performance and that of the associated millet.

MATERIALS AND METHODS

This study was conducted at the Regional Agricultural Research Center, Kolo, Niger (13 degrees 15'N, 2 degrees 18'E) during 1986-1988. Soils at the experimental site are deep sands (Psammentic Paleustalf) with 964 g kg^-1 sand, 0.7 g kg^-1 organic C, 1.21 cmol kg^-1 CEC, 0.1 g kg^-1 total N, 9 mg kg^-1 (Bray 1) extractable P, and 6.4 pH (1:2.5 H2O).

Treatments included the millet and cowpea sole crops and seven intercrop treatments of varying cowpea sowing dates. The sole crops and first intercropped cowpea were sown on the same day. The same treatments were sown on the same plots each year. The cultivars were millet cv. CIVT and cowpea cv. TN 5-78 and were recommended for the area (Reddy et al., 1990). TN 5-78 is early maturing with a spreading but determinate growth habit and cv. CIVT is early maturing and of intermediate height. Treatments were arranged in four replications in a randomised complete block design.

Millet was sown at 1.5 x 0.75 m spacing (8889 hill/ha^-1) in sole and intercrop treatments. Cowpea was sown at 0.75 x 0.375 m spacing (35,556 hill/ha^-1) in sole crop and at a 0.75 x 0.75 m (17,778 hills/ha) in intercrop. Intercropped cowpea was arranged in twin rows, 0.75 m from each other and 0.375 m away from millet rows. Thus, a row pattern of millet-cowpea-cowpea-millet was created representing 100% of sole millet and 50% of sole cowpea plant density (Reddy, 1988).

Millet was planted on 10, 2 and 11 June in 1986, 1987 and 1988, respectively, after the first 20 + mm rain of the growing season. Cowpea interplanting dates varied between years depending on the occurrence of a rain of 12 mm or more to ensure cowpea germination. These were 0, 8, 15, 26, 31, 42, and 56 days after millet planting in 1986; 0, 30, 37, 44, 57, 61, and 67 in 1987; and 0, 14, 20, 28, 36, 47, and 56 in 1988. Two to three weeks after planting, millet was thinned to three plants per hill and cowpea to two plants per hill. Each year, 45 kg N ha^-1 was point applied to millet in two equal split-applications (at planting and tillering) as urea. Nine kg P ha^-1 was basally applied each year by broadcast method. Fields were kept weed free by manual hoeing. Cowpea was sprayed three times with a mixture of Delmethrine and Dimethoate at flowering, early-podding and late-podding stages to control thrips (Megalurothrips sjostedti), pod borers (Maruca testulalis), and aphids (Aphis craccivora).

Plot size was 12 by 10 m. The central 9 by 6 m area was manually harvested at maturity. Millet stems were left standing until the final cowpea harvest to avoid damage to the associated cowpea. Millet leaves had dried and dropped by the time millet had matured causing little shading of cowpea. After cowpea harvest, millet and cowpea stalks were removed, imitating farmers' practice.

In 1987, photosynthetically active radiation waveband (0.4-0.7um; PAR) interception was measured on 89, 96, 103, 110, 117, 124, 131, and 138 days after millet planting using LICOR 191 SB line Quantum Sensor (LICOR, Lincoln, NE 68504, USA) together with a LI-1776 Solar Monitor; cowpea was in its reproductive stage during this time. PAR was measured during the morning and afternoon. Crop rows were oriented east-west, and solarimeters were placed east-west and north-south at the centre of the rows. Incoming PAR was measured at the top of the canopy (I0) at the same time as measurements were taken above the cowpea canopy (I1) and on the soils surface (I2) in two replications. Intercepted PAR was expressed as a mean percentage of I1/I0 or (I1 - I2)/I0. For analytical purpose, the mean values of the two placements and two sampling times were used since the treatment differences were consistent across these variations.

Crops were solely rain-fed and rainfall distribution varied across years (Table 1). The potential crop growing season was calculated for each treatment. The end of the season was determined as the last significant rain depleted at a rate of 4.5 mm per day (Virmani et al., 1980). When the last harvest occurred before the estimated end of the season (1988), the harvest date was taken as the end of the season. The final cowpea harvests of cowpea pods were carried out when the crop looked completely dry due to physiological maturity or desiccation. In general, the final harvest of cowpea occurred on the same day in each season. The difference between the planting date and the estimated end of the season was considered as the cowpea growth period.

Millet panicles/m^2, mean length and circumference (3 positions) of five panicle were determined each year for all treatments. Harvest index (HI) (grain yield/total above-ground dry matter yield) and crop growth rate (CGR) (total dry matter yield per m^2 per day) were calculated. In 1987, the millet stalks and cowpea stover were partially grazed by animals after grain harvest and those data have been excluded.

SAS General Linear Models procedure (GLM) was used for analyses of variance and regression analyses. Differences between means were compared by the LSD test at the 0.05 probability level.

RESULTS AND DISCUSSION

Millet yields. Treatment effects were not significant for millet grain yield (570 kg ha^-1; Table 2), final plant stand (94%), and panicle size (52 cm length and 6.5 cm circumference) and number (26m^2).

Unlike grain yields, the millet total dry matter yield under intercropping was significantly lower than the sole crop yield for the first to third dates of cowpea planting in 1986. In these treatments, the millet grain yield was maintained as in sole crop by significant improvement in harvest index (HI) (Table 2). However, this trend was not observed in 1988 probably due to higher rainfall (616 mm) compared to 1986 (454 mm) (Table 1).

Cowpea yields. The cowpea growth period varied from 111 to 55 days in 1986, 133 to 66 days in 1987, and 107 to 51 days in 1988 for various intercrop treatments following the order of planting dates; the longest growing season being with the first planting date. The cowpea planted at the same time as millet in 1987 had the longest growing season due to the virtual dormancy or cessation of cowpea growth during the 30-day drought following planting. The delay in cowpea planting caused a corresponding decrease in the cowpea growth period due to the cessation of rains and due to the determinate type of the cowpea variety used in the study.

Mean cowpea grain yield in the intercrop systems was 503 kg ha^-1 which was significantly less than the sole crop yield of 1866 kg ha^-1 (Table 3). Simultaneous millet and cowpea planting gave the highest cowpea grain yield. The best-fit quadratic regression model of intercrop cowpea grain yield (CGY) over the difference in millet and cowpea planting dates (PD) is CGY =1137-27.1PD + 0.16PD^2; R^2 = 0.93; P = 0.0001. Misbahulmunir et al. (1989) reported highest intercrop peanut yield when maize and groundnuts were simultaneously planted compared to other planting dates. Like grain yields, cowpea total dry matter yields were significantly higher in sole systems compared to intercrop systems (Table 3).

Any delay in cowpea planting compared to millet caused a corresponding decrease in cowpea growth period and reduced plant survival probably due to increased shading by millet plants. For example, in 1986 the mean survival rate of cowpea in sole crop and the first three planting dates was 97%, in dates 4 to 6 was 87%, and in date 7 was 75%.

Cowpea sown 0 and 30 days after millet intercepted similar amounts of PAR during the season (Fig. 1). Late planted cowpea intercepted significantly less PAR than early planted cowpea (Table 4). Theoretically, early introduction of cowpea in millet causes a longer overlapping period between the two crops and consequently a longer period of shading. However, the advantage of maximum overlapping in this case was due to the completion of the cowpea vegetative phase before millet reached its highest leaf area index, as reported by Nouri and Reddy (1991).

It could be theorised that in the Sahelian zone (at about 13 degrees latitude), the early cowpea inter-planting resulting in longer overlap time are required to obtain higher cowpea yields. Our millet/groundnut and millet/sorghum association studies from the region indicate similar results (unpublished data). This is contrary to the optimum cowpea dates of planting proposed in the relatively southern zone as in Nigeria (about 12 degrees latitude), where the greater the duration of overlap of maize/cowpea, the smaller the yield of the intercropped cowpeas. Hence, as reported by Wien and Smithson (1979), the appropriate cowpea interplanting dates may very much depend on the geographical location and consequent rainy season length.

ACKNOWLEDGEMENTS

The authors wish to thank the USAID for financial support for this research through the Niger Applied Agricultural Research Project N. 683-0226 and Dr. J.H. Williams (ICRISAT) for his valuable suggestions in preparing this manuscript.

REFERENCES

Anonymous. 1991. Definitive Agricultural Statistics of Niger, 1990 Cropping Season. (In French). Agricultural Statistics Service., Department of Agriculture, Ministry of Agriculture and Livestock, Niger.

Lamb, P. 1982. Persistence of sub-Saharan drought. Nature 299:46-48.

Misbahulmunir, M.Y., Sammons, D.J. and Weil, P.R. 1989. Corn-peanut intercrop performance in relation to component crop relative planting dates. Agronomy Journal 81:184-189.

Nouri, M. and Reddy, K.C. 1991. Water use of millet and cowpea in association and sole crop. (In French). In: Proceedings Inter-national workshop on Soil Water Balance in the Sudano-Sahelian Zone. Sivakumar, M.V.K., Wallace, J.S., Renard, C. and Giroux, C. (Eds.), pp. 421-429. Niamey, Niger, 18-23 Feb. 1991. IAHS Publ. 199.

Ouattara, M. and Persaud, N. 1986. Soil and water constraints and adaptations to these constraints by farmers in rainfed cereal production. In: Niger Sorghum and Millet Workshop, Niamey, Niger, 13-17 Oct. 1985. Axtell, J.D. and Clark, J.W. (Eds.), pp. 95-103. INTSORMIL/IPIA, Purdue University, West Lafayette, Indiana.

Reddy, K.C. 1988. Alternative Pearl Millet and Cowpea Rainfed Production Strategies. (In French). Handbook 1. National Agricultural Research Institute, INRAN, Niamey, Niger and Purdue University, West Lafayette, Indiana.

Reddy, K.C. and Buckner, P. 1991. Exploratory studies for mechanisation of millet/cowpea intercropping (In French). Agronomie Africaine 3:87-95.

Reddy, K.C., Van Der Ploeg, J. and Maga, I. 1990. Genotype effects in millet/cowpea intercropping in semi-arid tropics of Niger. Experimental Agriculture 26:387-396.

Sivakumar, M.V.K., Virmani, S.M. and Reddy S.J. Undated. Rainfall Climatology of West Africa: Niger. Information Bulletin 5. ICRISAT, Patancheru, India.

Virmani, S.M., Reddy, S.J. and Bose, M.N.S. 1980. A Handbook on the Rainfall Clima-tology of West Africa: Data for Selected Locations. Information Bulletin 6. ICRISAT, Patancheru, India.

Wien, H.C. and Smithson, J.B. 1979. The evaluation of genotypes for intercropping. In: Proceedings International Workshop on Intercropping. ICRISAT, Hyderabad, India.

Copyright 1997, African Crop Science Society


The following images related to this document are available:

Line drawing images

[cs97041e.gif] [cs97041a.gif] [cs97041b.gif] [cs97041d.gif] [cs97041c.gif]
Home Faq Resources Email Bioline
© Bioline International, 1989 - 2024, Site last up-dated on 01-Sep-2022.
Site created and maintained by the Reference Center on Environmental Information, CRIA, Brazil
System hosted by the Google Cloud Platform, GCP, Brazil