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Revista mexicana de ciencias pecuarias

versión On-line ISSN 2448-6698versión impresa ISSN 2007-1124

Rev. mex. de cienc. pecuarias vol.12 no.2 Mérida abr./jun. 2021  Epub 15-Nov-2021

https://doi.org/10.22319/rmcp.v12i2.4918 

Articles

Cowpea [Vigna unguiculata (L.) Walp] herbage yield and nutritional quality in cowpea-sorghum mixed strip intercropping systems

Muhammad Aamir Iqbala 

Asif Iqbalb 

Zahoor Ahmadc 

Ali Razad 

Junaid Rahime 

Muhammad Imrane 

Umer Ayyaz Aslam Sheikhe 

Qaiser Maqsoodf 

Walid Soufang 

Nesma M.A. Sahloulh 

Sobhy Sorourh 

Ayman El Sabaghh 

a University of Poonch Rawalakot (AJK). Faculty of Agriculture, Department of Agronomy, Pakistan.

b University of Agriculture Faisalabad, Department of Agronomy, Pakistan.

c University of Central Punjab, Bahawalpur Campus, Department of Botany, Pakistan.

d Fujian Agriculture and Forestry University, Fujian Provincial Key Laboratory of Crop Molecular and Cell Biology, China.

e University of Poonch Rawalakot (AJK). Faculty of Agriculture, Department of Entomology, Pakistan.

f Government College University Faisalabad, Layyah University, Department of Botany, Pakistan.

g King Saud University. Plant Production Department, Saudi Arabia.

h Kafrelsheikh University. Faculty of Agriculture, Department of Agronomy, Egypt.


Abstract

In traditional row and strip cowpea-sorghum intercropping systems, cowpea forage yield reduces significantly due to intense competition and dominance of sorghum in acquiring growth resources. This field study evaluated novel mixed strip intercropping systems of forage cowpea and sorghum having different number of crops rows arranged under different spatial arrangements. Cowpea was intercropped with sorghum in 8, 12 and 16 rows strips with row-row spacing of 30, 45 and 60 cm. In each strip, equal number of rows of cowpea and sorghum were maintained. Factorial arrangement of randomized complete block design with three replicates was used to execute the field trials during summer seasons of 2013 and 2014. Strips having 12 rows and 60 cm row-row spacing positively affected all agronomic variables of cowpea which led to maximum forage yield (22.2 and 23.7 t ha-1 during 2013 and 2014 respectively) and dry matter biomass (6.63 and 6.94 t ha-1 during 2013 and 2014 respectively). In contrast, 8-rows strips having line spacing of 30 cm outperformed other intercropping systems by yielding the maximum herbage yield and dry matter biomass of sorghum. The intercropping system comprising of 12-rows strips with 60 cm row-row spacing remained superior in recording the maximum crude protein, fats and total ash along with the minimum fiber content of cowpea. In addition, this intercropping system under rest of spatial arrangements also remained unmatched, while 16-rows strips under all planting geometries remained inferior to other intercropping systems. Thus, cowpea intercropping with sorghum in 12-rows strips having 60 cm spacing offers biologically viable solution to improve biomass and forage quality of cowpea in intercropping with sorghum.

Key words Animal nutrition; Planting geometries; Row intercropping

Resumen

En los sistemas tradicionales de cultivo intercalado de frijol caupí y sorgo en franjas y filas, el rendimiento de forraje del frijol caupí se reduce significativamente debido a la intensa competencia y al dominio del sorgo en la adquisición de recursos para el cultivo. Este estudio de campo evaluó novedosos sistemas de cultivo intercalado en franjas mixtas de frijol caupí forrajero y sorgo con diferente número de filas de cultivo en diferentes disposiciones espaciales. El frijol caupí se intercaló con el sorgo en franjas de 8, 12 y 16 filas con un espaciamiento de 30, 45 y 60 cm entre las filas. En cada franja se mantuvo igual número de filas de frijol caupí y sorgo. Para la ejecución de los ensayos de campo durante las temporadas de verano de 2013 y 2014 se utilizó un diseño factorial en bloques completos aleatorizados con tres repeticiones. Las franjas con 12 filas y un espaciamiento de 60 cm entre las filas afectaron positivamente a todas las variables agronómicas del frijol caupí que condujeron al máximo rendimiento forrajero (22.2 y 23.7 t/ha en 2013 y 2014, respectivamente) y de biomasa de materia seca (6.63 y 6.94 t/ha en 2013 y 2014, respectivamente). En cambio, las franjas de 8 filas con un espaciamiento de 30 cm superaron a otros sistemas de cultivo intercalado al obtener el rendimiento máximo de hierba y de biomasa de materia seca del sorgo. El sistema de cultivo intercalado compuesto por franjas de 12 filas con un espaciamiento de 60 cm entre las filas siguió siendo superior, al registrar el contenido máximo de proteína bruta, grasas y cenizas junto con el mínimo contenido de fibra de frijol caupí. Además, este sistema de cultivo intercalado bajo el resto de las disposiciones espaciales también permaneció incomparable, mientras que las franjas de 16 filas bajo todas las geometrías de siembra permanecieron inferiores a otros sistemas de cultivo intercalado. Por lo tanto, el cultivo intercalado de frijol caupí con sorgo en franjas de 12 filas con un espaciado de 60 cm ofrece una solución biológicamente viable para mejorar la biomasa y la calidad del forraje del caupí en cultivo intercalado con sorgo.

Palabras clave Nutrición animal; Esquemas de plantación; Cultivos intercalados en filas

Introduction

Food security of rapidly increasing human populace demands proportionate increment in milk and meat production globally1,2. Under changing climate, production of forages with acceptable nutritional quality occupies central place for obtaining milk production on sustainable basis3. Although, many cereals including sorghum provide huge tonnage of biomass but these are unable to provide balanced nutrition to dairy animals4,5,6. Resultantly, expensive protein supplements need to be provided which result in slicing of economic returns. In addition, ruminants population is increasing globally which necessitate producing huge quantities of nutritional and cheaper forage throughout the year7,8. Thus, intercropping cereals with legumes might lead to achieve the dual purpose of obtaining higher quantities of forage with improved nutritional quality.

Row, mixed and strip intercropping of cereals with legumes have been practiced since long9,10. Intercropping forage legumes with cereals diversified the farm resources, preserved and restored soil fertility and improved the efficiency of soil and environmental resources11,12. However, serious consideration must be done in choosing the legume intercrops with respect to their compatibility in utilizing resources in spatial and temporal dimensions. Among legume intercrops, cowpea [Vigna unguiculata (L.) Walp] could be a good option for having potential to yield considerably higher quantity of nutritious forage in intercropping with sorghum13,14,15. In addition, cowpea holds potential to tolerate shade and sustain moderate drought along with fixing atmospheric nitrogen which favor its utilization as an intercrop with cereals16,17.

However, cowpea intercrop suffered losses in forage yield and nutritional quality owing to dominance of cereals in acquiring growth resources18,19. In this way, the type of intercropping becomes pivotal for achieving the added advantage of cowpea intercropping with cereal forages20. Thus, in sorghum-cowpea intercropping systems, the real challenge lies in preventing the drastic reduction in the yield and quality of forage cowpea. Various studies have reported contrasting results about the efficacy of strip intercropping system where separate strips of component crops were maintained 8,21,22. But, there have rarely been any field investigation regarding mixed strip intercropping system entailing rows of component crops in the same strip. In addition, spatial arrangement of component crops also determined the complementarity and competition in cereal-legume intercropping systems2,14. However, spatial arrangements must be optimized with respect of intercropping type especially for boosting the productivity of legumes.

Thus, it was hypothesized that optimization of strip intercropping systems and spatial arrangements might lead to improved yield and nutritional value of cowpea forage. The present study aimed primarily to investigate the influence of mixed strip intercropping (strips having rows of both cowpea and sorghum in the same strip) and planting geometries on forage yield of cowpea sown with forage sorghum. Furthermore, another objective was to test the agro-qualitative traits of forage cowpea as influenced by different strip intercropping systems as well as spatial arrangements.

Material and methods

Description of experimental site

To evaluate the impact of mixed strip intercropping and planting geometries on the productivity of cowpea intercrops, a field experiment was conducted during summer months of 2013 and 2014 at the research area of University of Agriculture, Faisalabad (30.35-41.47°N and 72.08-73.40°E) situated at an attitude of 184 m14. The climate of the experimental area falls into Koppen’s class of semi-arid, while the soil of the experimental site is classified as Haplic Yermosols as per FAO soil classification system. The meteorological data for crop growing seasons of cowpea were obtained from the meteorological center located closer (about 1 km) to research fields (Table 1).

Table 1 Meteorological data for crop growing seasons of cowpea in 2013 and 2014 along with 10 years mean (10YM) values 

Month Temperature (°C) Rainfall (mm) Relative humidity
(%)
2013 2014 10YM 2013 2014 10YM 2013 2014 10YM
June 40.3 41.5 40.1 44 40 40 60 64 59
July 39.5 38.6 41.0 106 102 101 65 72 62
August 35.0 37.8 34.7 77 68 72 58 69 65
Mean/Total 38.2 39.3 38.6 227 210 213 61.0 68.3 65.3

Experimental treatments and design

Cowpea and sorghum were sown in different strip intercropping systems and three spatial arrangements as follows: T1A1= 8 rows strips (cowpea-sorghum in 4-4 rows in the same strips) with 30 cm row-row spacing, T1A2= 8 rows strips (cowpea-sorghum in 4-4 rows in the same strip) with 45 cm row-row spacing, T1A3= 8 rows strips (cowpea-sorghum in 4-4 rows in the same strip) with 60 cm row-row spacing, T2A1= 12 rows strips (cowpea-sorghum in 6-6 rows in the same strip) with 30 cm row-row spacing, T2A2= 12 rows strips (cowpea-sorghum in 6-6 rows in the same strip) with 45 cm row-row spacing, T2A3= 12 rows strips (cowpea-sorghum in 6-6 rows in the same strip) with 60 cm row-row spacing, T3A1= 16 rows strips (cowpea-sorghum in 8-8 rows in the same strip) with 30 cm row-row spacing, T3A2= 16 rows strips (cowpea-sorghum in 8-8 rows in the same strip) with 45 cm row-row spacing, T3A3= 16 rows strips (cowpea-sorghum in 8-8 rows in the same strip) with 60 cm row-row spacing.

In this way, a total of 9 treatment combinations were tested in factorial arrangement of randomized complete block design (RCBD) with three replications. The strip × strip distance for all intercropping systems was kept at 70 cm. Cowpea rows were adjacent to sorghum rows in subsequent strips. There was no consideration for plant × plant distance. In total, there were 27 experimental plots which were homogeneously maintained for testing the proposed treatments.

Agronomic management plan

In order to formulate the soil fertility management plan, pre-sowing physico-chemical analysis was performed from soil samples collected from 15 and 30 cm depth (Table 2). The seedbed preparation was started with a pre-sowing irrigation of 12 cm and 3 tractor mounted cultivations each followed by planking was done. Cowpea (cv. P-51840 at kg ha-1) and sorghum (cv. Hegari at 80 kg ha-1) were intercropped in 30 cm spaced rows using a hand drill. Recommended dose of nitrogen (50 kg ha-1) (urea) was applied in two splits (at the time of sowing and with first irrigation 12 d after sowing) while total phosphorous (single super phosphate) (40 kg ha-1) was applied as basal dose. Three flood irrigations were applied at 12, 33 and 50 d after sowing. Manual hoeing was done thrice (12, 22 and 32 d after sowing) to keep weed infestation at bay. Cowpea intercrops were harvested using hand sickle at complete flowering.

Table 2 Pre-sowing physico-chemical analysis of experimental soil in 2013 and 2014 

Soil characteristics 2013 2014
Mechanical analysis:
Sand, % 57.0 54.5
Silt,% 17.5 19.3
Clay, % 25.5 26.2
Textural class Sandy clay loam Sandy clay loam
Chemical analysis:
Ph 7.9 7.6
EC, dSm-1 1.68 1.64
Organic matter, % 0.75 0.78
Available nitrogen, ppm 6.1 6.4
Available phosphorous, ppm 0.96 0.91
Available potassium, ppm 117 112

Data recordings

All agronomic attributes of cowpea were recorded at the time of harvesting by following the prescribed methods. Ten plants were harvested from middle rows of each replication and then their average was taken. Plant height was recorded with the help of tailor’s measuring tape from base of the plant to the tip of the highest leaf. Stem girth was taken by using vernier caliper. Electric balance was used to take fresh weight per plant while spring balance was used to record green forage yield per plot which was then converted into tons per hectare. The agro-qualitative attributes of forage cowpea were determined by using methodologies given in Table 3.

Table 3 Procedure adopted for measuring agro-qualitative traits of cowpea as suggested by AOAC (2003) 

Quality attributes Methodology
Crude protein Macro-KJeldahl method and subsequently multiplying nitrogen percentage with a constant of 6.25
Crude fiber H2SO4 and NaOH digestion method
Ether extractable fat Soxhlet extraction method
Total ash Ashing at 600 °C using muffle furnace technique

Statistical analysis

Statistical analyses of the recorded data were done through employing analysis of variance (ANOVA) using the statistical program “Statistix 8.1”. The means were grouped for conducting orthogonal contrasts on following basis; (a) intercropping system versus year, (b) spatial arrangement versus year, (c) intercropping system versus spatial arrangement and (d) intercropping system versus spatial arrangement versus year at 5% probability level. The data were also subjected to correlation analysis in order to sort out the relationship (linear or inverse) between yield attributes and forage yield of cowpea.

Results and discussion

Plant height and stem diameter

The agronomic variables of forage cowpea were significantly improved during 2014 probably owing to higher precipitation and moderate temperatures in comparison to 2013. The interactive effect of strip intercropping systems and spatial arrangements was significant for plant height (189** and 203** during 2013 and 2014 respectively) and stem girth (88* and 98** during 2013 and 2014 respectively) of cowpea (Table 4). The tallest cowpea plants (110.3 ± 0.57 and 117.9 ± 0.83 cm during 2013 and 2014 respectively) with greatest stem girth (2.87 ± 0.67 and 2.94 ± 0.69 cm during 2013 and 2014 respectively) were recorded by cowpea sown in 12-rows strips with 60 cm spaced rows (T2A3), while 16-rows strips having 45 cm line-line spacing (T3A2) resulted in the lowest plant height (78.0 ± 0.38 and 83.1 ± 0.82 cm during 2013 and 2014 respectively) as well as stem girth (2.32 ± 0.81 and 2.53 ± 0.41 cm during 2013 and 2014 respectively) (Table 5). Correlation analysis revealed that there was linear correlation between plant height and stem girth of cowpea as depicted in Figure 1. These results are in complete confirmation with another study23, where legumes plant height and stem diameter were influenced planting geometries of cereal-legume intercropping systems. Simultaneous cultivation of component crops in row and mixed intercropping systems intensified inter-species competition for farm applied resources which led to reduced plant height and stem girth of legumes compared to their monocultures. But when cowpea was sown in 12-rows strips (cowpea-sorghum in 6-6 rows), it might have reduced sorghum dominance in acquiring growth resources. Varied root lengths of cowpea and sorghum might be attributed as the probable reason for reducing competition for growth resources which was further supported by wider strip spacing24.

Table 4 Analysis of variance (ANOVA) for all experimental variables under study of cowpea sown with sorghum under different spatial arrangements during 2013 and 2014 

SOV Plant height
(cm)
Stem girth
(cm)
Leaves per
plant
Leaf-stem ratio Fresh weight
per plant (g)
Dry weight
per plant (g)
Cowpea green forage
yield (t ha-1)
2013 2014 2013 2014 2013 2014 2013 2014 2013 2014 2013 2014 2013 2014
T 213** 288** 73* 85* 109* 100* 74* 89* 287** 234** 166** 183** 244** 280**
A 134** 111** 66* 71* 81* 123* 33* 57* 132** 141** 211** 137** 112* 89*
T×A 189** 203** 88* 98** 93* 112* 83* 96* 274** 297** 187** 257** 266** 287**
SOV Cowpea DMY
(t ha-1)
Sorghum GFY
(t ha-1)
Sorghum DMY
(t ha-1)
Crude protein
(%)
Crude fiber
(%)
Ether
extractable fat
(%)
Total ash (%)
2013 2014 2013 2014 2013 2014 2013 2014 2013 2014 2013 2014 2013 2014
T 123** 116** 97 110** 88* 104** 91** 109** 237** 250** 233** 240* 134* 103*
A 91* 75* 132 103* 145* 74* 51* 74* 88* 122** 75* 111* 90* 87*
T×A 134** 120** 114 139* 137* 92* 120*** 135** 142* 169** 200** 225* 101* 109*
T×Y=NS A×Y=NS T×A×Y=NS

SOV= source of variance; T= Type of strip intercropping, A= Spatial arrangements, Y=Year. *(P<0.05) ** (P<0.01).

Table 5 Plant height (PH), stem girth (SG), number of leaves (NL), leaf-stem ratio (LSR), fresh weight (FW) and dry weight (DW) per plant of cowpea sown with sorghum under different planting times and spatial arrangements 

IS 2013 2014
PH (cm) SG (cm) NL LSR FW (g) DW (g) PH (cm) SG (cm) NL LSR FW (g) DW (g)
T1A1 94.5±0.27c 2.60±1.16d 22.7±0.55cd 0.50±0.18bc 172.5±0.83cd 50.8±0.21cd 96.2±0.67d 2.63±0.33e 24.3±0.27d 0.52±1.19c 173.0±0.65d 52.6±0.66de
T1A2 90.7±0.64cd 2.64±0.51cd 21.2±0.67d 0.44±0.27d 170.1±0.67d 48.4±0.37d 94.7±0.51de 2.67±0.57d 23.0±0.53de 0.50±0.35cd 173.9±0.25d 50.8±1.15e
T1A3 94.3±0.37c 2.68±0.94c 24.0±0.34c 0.52±0.30b 174.5±0.31c 52.3±0.25c 97.2±0.28d 2.71±1.17c 26.5±0.49cd 0.55±0.82bc 177.0±0.37c 54.1±0.96d
T2A1 102.7±0.29b 2.74±0.56b 28.9±0.67ab 0.53±0.28b 185.1±0.44ab 58.5±0.50a 108.4±0.19b 2.87±0.94b 29.0±0.72b 0.57±0.93b 186.2±0.24b 61.4±0.67b
T2A2 100.0±0.33b 2.70±0.42bc 26.6±0.90b 0.52±0.64b 181.5±0.58b 55.9±0.41b 101.6±0.43c 2.73±0.35c 27.3±0.60c 0.55±0.24bc 184.6±0.51b 58.3±0.29c
T2A3 110.3±0.57a 2.87±0.67a 29.1±0.57a 0.59±0.19a 188.6±0.67a 59.1±0.67a 117.9±0.83a 2.94±0.69a 29.9±0.31a 0.69±0.21a 190.5±0.61a 66.3±1.19a
T3A1 83.5±0.41d 2.35±0.31ef 21.5±0.87d 0.45±0.22cd 169.9±0.29d 44.9±0.59ef 89.9±0.67ef 2.58±0.52g 22.5±0.29e 0.48±0.17d 171.2±0.20de 46.0±0.88fg
T3A2 78.0±0.38e 2.32±0.81f 18.8±0.66e 0.41±0.37e 164.2±0.21e 41.7±0.32f 83.1±0.82f 2.53±0.41h 21.9±0.40f 0.45±0.29e 165.3±0.19f 43.8±0.60g
T3A3 91.1±0.24cd 2.39±0.92e 21.4±0.37d 0.48±0.40c 166.0±0.34de 46.2±0.19e 92.4±0.97e 2.60±0.60g 24.4±0.69d 0.51±0.33cd 170.9±1.11e 48.7±0.37f
LSD0.05 3.80 0.06 2.93 0.04 4.23 3.89 5.29 0.15 0.47 0.03 4.01 3.87

Data presented here is average of 3 replications. IS= Intercropping systems, T1= 8-rows strips (cowpea+sorghum in 4-4 rows), T2= 12-rows strips (cowpea+sorghum in 6-6 rows), T3= 16-rows strips (cowpea+sorghum in 8-8 rows)

A1= 30 cm spaced strips, A2= 45 cm spaced strips, A3=60 cm spaced strips.

abcdef Values followed by different letters within columns differ (P<0.05), ± represents standard deviation increase or decrease.

Figure 1 Correlation analysis for yield attributes with green forage yield and dry matter yield of cowpea (combined analysis of pooled data of 2013 and 2014) 

Number of leaves and leaf-stem ratio

The interactive effect of intercropping systems and spatial arrangements was significant for the number of leaves (93* and 112* during 2013 and 2014 respectively) and leaf-stem ratio (83* and 96* during 2013 and 2014 respectively) (Table 4). Sorghum and cowpea 12-rows strip intercropping in 60 cm spaced lines (T2A3) resulted in higher number of leaves per plant (29.1 ± 0.57 and 29.9 ± 0.31 during 2013 and 2014 respectively) and leaf to stem ratio (0.59 ± 0.19 and 0.69 ± 0.21 during 2013 and 2014 respectively) (Table 5). These results corroborate with the findings of other studies2,3,25, where it was concluded that closely spaced rows of legumes recorded minimum number of leaves and leaf-stem ratio despite exploring varied soil horizons for absorbing moisture and nutrients by sorghum and legumes, still the intra-species competition was severe enough to drastically reduce the growth of legume intercrops. Furthermore, shading effect rendered by sorghum was also found to be an important factor in reducing photosynthesis of legume plants particularly in adjacent rows with sorghum which leads to less number of leaves per plant.

Plants fresh and dry weights, green forage yield and dry matter biomass

The interactive effect of intercropping system and spatial arrangements was also significant for fresh weight (274** and 297** during 2013 and 2014 respectively) and dry weight (187** and 257** during 2013 and 2014 respectively) per plant of cowpea along with green forage yield (266** and 287** during 2013 and 2014 respectively) as well and dry matter yield (134** and 120** during 2013 and 2014 respectively). The highest fresh weight (188.6 ± 0.67 and 190.5 ± 0.61 g during 2013 and 2014 respectively) and dry weight (59.1 ± 0.67 and 66.3 ± 1.19 g during 2013 and 2014 respectively) per plant (Table 5) were rendered by 12-rows strip having 60 cm apart rows (T2A3). Correlation analysis depicted a linear relationship for fresh and dry weights per plant with green forage and dry matter yields (Figure 1). The same intercropping system (T2A3) was instrumental in yielding the maximum green forage yield (22.2 ± 0.28 and 23.7 ± 0.34 t ha-1 during 2013 and 2014 respectively) and dry matter biomass (6.63 ± 0.26 and 6.94 ± 0.19 t ha-1 during 2013 and 2014 respectively) of forage cowpea (Table 6), while it was followed by 12-rows strips sown in 45 cm spaced rows (T2A1). In contrast, sorghum-cowpea 8-rows strips having 30 cm row-row spacing (T2A1) remained superior as far as green forage biomass and dry matter yield of sorghum were concerned. It was followed by the same intercropping system having row-row spacing of 45 cm, while sorghum-cowpea intercropping systems comprising of 16-rows strips with 60 cm row-row spacing (T3A3) remained inferior to rest of intercropping systems and spatial arrangements (Table 6). The T2A3 intercropping system resulted in superior agronomic attributes including plant height, stem girth, fresh and dry weights per plant which ultimately enhanced green forage biomass as well as dry matter yield. These findings are in line with others22,26, who inferred that productivity of cowpea in narrowly spaced (30 and 45 cm) intercropping systems remained below-par to solo cowpea despite well-developed nodulation and fully functional biological nitrogen fixation (BNF). Similar findings were also reported by other researchers10,27, where cowpea remained recessive in acquiring nutrients and moisture compared to cereals. In addition, legume intercrops suffered losses in productivity owing to their dependence on soil solution for nitrogen before the initiation of BNF after 27-35 d of sowing. Moreover, in strip intercropping systems, cowpea rows adjacent to sorghum confronted lesser competition for growth resources by exploiting different soil horizons but had to face shading effect rendered by taller sorghum plants. Similarly, inner rows of cowpea faced lesser shading effect but competition for growth resources intensified owing to having same root length which led to reduced herbage yield28.

Table 6 Green forage yield (GFY), dry matter yield (DMY), crude protein (CP), crude fiber (CF), ether extractable fat (EEF) and total ash (TA) of cowpea sown with sorghum under different planting times and spatial arrangements in 2013 and 2014 

IS 2013 2014
GFY
(t ha-1)
DMY
(t ha-1)
CP
(%)
CF
(%)
EEF
(%)
TA
(%)
GFY
(t ha-1)
DMY
(t ha-1)
CP
(%)
CF
(%)
EEF
(%)
TA
(%)
T1A1 18.4±0.18d 5.36±0.18e 18.8±0.41bc 26.2±0.72e 1.79±0.24cd 11.00±0.15d 18.8±0.58d 5.59±0.16d 18.9±0.33c 26.0±0.98d 1.82±0.18c 11.33±0.11c
T1A2 17.7±0.53e 5.29±0.37ef 18.6±0.22c 26.9±0.15cd 1.76±0.17d 11.07±0.37d 17.9±0.28e 5.51±0.34d 18.8±0.92c 26.6±0.62c 1.79±0.11cd 11.07±0.24e
T1A3 19.9±0.91c 5.52±0.25d 19.0±0.34b 26.6±0.37d 1.81±0.18c 11.13±0.17c 20.7±0.67cd 5.72±0.84c 19.3±0.53b 25.4±0.37e 1.84±0.23c 11.39±0.15bc
T2A1 21.0±1.23b 5.93±0.53b 19.6±0.55ab 26.1±0.51e 1.86±0.29b 11.29±0.28b 22.2±1.09b 6.09±0.50b 19.4±0.20b 26.0±0.90d 1.90±0.15b 11.45±0.37b
T2A2 20.4±0.44bc 5.78±0.47c 19.0±0.67b 26.7±0.18d 1.84±0.33bc 11.08±0.34d 21.0±0.77c 5.91±0.77b 19.3±.37b 26.7±1.17c 1.87±0.26bc 11.23±0.38d
T2A3 22.2±0.28a 6.63±0.26a 19.9±0.21a 25.9±0.91f 1.91±0.17a 11.78±0.16a 23.7±0.34a 6.94±0.19a 19.6±0.37a 21.5±0.32f 1.95±0.29a 11.78±0.21a
T3A1 17.8±0.37e 5.26±0.38ef 18.2±0.79d 27.6±0.27b 1.73±0.23de 10.93±0.28e 18.5±0.59d 5.29±0.61e 18.5±0.40d 27.3±0.67b 1.75±0.20d 11.05±0.16e
T3A2 16.1±0.41f 5.16±0.82f 18.1±0.62d 27.9±0.67a 1.70±0.29e 10.55±0.27f 16.7±0.44f 5.10±0.94f 18.0±1.11e 27.8±0.85a 1.71±0.10e 10.58±0.44f
T3A3 17.2±0.30ef 5.18±0.21f 18.6±0.63c 27.1±0.41c 1.74±0.37de 11.07±0.18d 17.8±0.69e 5.48±0.26d 18.9±0.91c 27.1±0.71bc 1.79±0.17cd 11.46±0.27b
LSD0.05 1.38 0.19 0.40 0.33 0.05 0.13 1.08 0.21 0.20 0.36 0.04 0.10

Data presented here is average of 3 replications. IS= Intercropping systems: T1= 8-rows strips (cowpea+sorghum in 4-4 rows), T2= 12-rows strips (cowpea+sorghum in 6-6 rows), T3= 16-rows strips (cowpea+sorghum in 8-8 rows) A1= 30 cm spaced strips, A2= 45 cm spaced strips, A3=60 cm spaced strips.

abcd Values followed by different letters within columns differ (P<0.05); ± represents standard deviation increase or decrease.

Crude protein and crude fiber contents

All quality traits were significantly influenced by intercropping systems and spatial arrangements including crude protein (120** and 135** during 2013 and 2014 respectively), crude fiber (142* and 169** during 2013 and 2014 respectively), ether extractable fat (200** and 225*during 2013 and 2014 respectively) and total ash (101* and 109* during 2013 and 2014 respectively) (Table 4).

Protein content occupies vital position in determining the nutritional quality of forage while agronomists as well as animal nutritionist recommend protein-rich forages for boosting the performance of dairy animals. Cowpea-sorghum intercropping in 12-rows strips having 60 cm row-row spacing (T2A3) effectively improved crude protein (19.9 ± 0.21 and 19.6 ± 0.37 during 2013 and 2014 respectively) of cowpea forage with the minimum crude fiber (26.1 ± 0.51 and 26.0 ± 0.90 during 2013 and 2014 respectively) contents (Table 6). This was followed by 12-rows strips having 45 cm spacing (T2A1), while strips having 16-rows performed below par under all spatial arrangements. Earlier research works1,14 are in conformity with these findings, as it was reported that substantial enhancement in crude protein of mixed forage could be achieved by intercropping cowpea with cereal forages under optimized spatial arrangements. It was suggested that type of intercropping could influence nitrogen fixed by cowpea which might be attributed for improved crude protein content and reduced fiber as the absorbed nitrogen and protein content were linearly correlated. Type of intercropping and planting geometries as in our research have also been reported to improve the efficacy of applied nutrients which imparted a significant influence on protein and crude fiber contents of forages14,29.

Ether extractable fat and total ash contents

Fats are pivotal quality attribute of forages as these secrete higher amounts of energy during metabolism than proteins. Similarly, mineral constituents of forages required to perform various metabolic processes are measured as ash. The intercropping system (T2A3) resulted in the maximum fat (1.91 ± 0.17 and 1.95 ± 0.29 % during 2013 and 2014 respectively) and total ash (11.78 ± 0.16 and 11.7 ± 0.21 % during 2013 and 2014 respectively) (Table 6), 16-rows strips registered the minimum fat and ash contents without any regard to spatial arrangements. Strips having 8-rows under all planting geometries performed better in terms of forage quality than 16-rows strips but it remained below par to cowpea sown with forage sorghum in 12-rows strips. These findings also match with a previously conducted study30, which revealed that considerably higher herbage yield with improved quality attributes could be obtained by optimizing intercropping type and spatial arrangement of component crops.

Conclusions and implications

This study reports novel mixed strip intercropping systems to check the drastic reduction in forage yield cowpea while in intercropping with forage sorghum. As far as green forage yield and agro-qualitative traits of cowpea were concerned, it could be inferred that 12-rows strips (cowpea-sorghum in 6-6 rows) (T1A2) remained unmatched particularly when row-row spacing was maintained at 60 cm. Moreover, better growth of cowpea was observed in rows adjacent to sorghum rows in subsequent strips in comparison with cowpea rows adjacent to sorghum rows in the same strip. Strips having 16-rows irrespective of planting geometry could not come at par to rest of the strips probably due to higher intra-species competition for growth resources. However, these encouraging results necessitate further field investigations regarding mixed strip intercropping of cereal forages and legumes for boosting legumes yield under varied agro-climatic and agro-ecological conditions.

Acknowledgements

The research support under Researchers Supporting Project number RSP/2021/390, by King Saud University, Riyadh, Saudi Arabia, is thankfully acknowledged. Additionally, Higher Education Commission of Pakistan support Under Indigenous Fellowship (2AV1-215) is also acknowledged.

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Received: May 30, 2018; Accepted: August 31, 2020

*Corresponding author: muhammadaamir@upr.edu.pk

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