Intercropping wheat (Triticum aestivum) with faba bean (Vicia faba) combined with vermicompost and NPS fertilizer application increases crop yields and agronomic efficiency in the humid mid-highlands of Ethiopia

Abstract

A field study was conducted in Dire and Legedadi watersheds in the humid mid-highlands of Ethiopia to determine the effect of intercropping and application of vermicompost (VC) on crop yield. Eight treatments (two treatments included 100% recommended NPS and urea fertilizer treatment versus 100% recommended VC application. The four other treatments are combinations of 50% of recommended NPS and urea and the 50% of VC rate of applications) were studied on farmers’ fields using a randomized complete block design (RCBD) with three replications. The assessment of these treatments relied on a range of intercropping and agronomic performance metrics, including the land equivalent ratio (LER), crowding coefficient (K), marginal rate of return (MRR). Results revealed that the highest total wheat yield of 4000 kg ha⁻¹ in Dire and 4151.7 in Legedadi site, achieved from the application of 100% recommended NPS + urea fertilizers. Wheat–faba bean intercropped with 50% NPS + Urea and 50% VC added treatment resulted in higher agronomic and recovery efficiency (RE) of N (41.0% and 41.9%) and (124.8% and 126.7%), K (2.91 and 2.38), LER (1.89 and 1.49), system productivity index (5672.02 and 4423.80) and net benefits (US$ 5598.1 ha⁻¹, 5690.8 ha⁻¹) values in Dire and Legedadi sites, respectively. Wheat–faba bean intercropped with half dose NPS + urea and VC added treatment was cost-effective and had the biggest yield advantage in both research locations.

Keywords:

• Agronomic efficiency
• crop productivity
• intercropping
• vermicompost
• yield

REVIEWING EDITOR:

• Manuel Tejada, Universidad de Sevilla, Spain

SUBJECTS:

• Agriculture & environmental sciences
• Soil Sciences
• Agronomy

Introduction

In Sub Saharan Africa, around 30% of the population remains food insecure and economically poor (FAO, 2012). Low agricultural productivity is a major cause of food insecurity and poverty. Over 80% of Ethiopia’s population relies on agriculture, contributing to over 50% of the nation’s gross domestic product (GDP) and accounting for over 80% of its export revenue (Alemu et al., 2010). Agriculture plays a central role in propelling economic development, but it is characterized by low productivity caused by declining soil fertility (Elias, 2017; Mubarak et al., 2021; Salem et al., 2022). This decline in soil fertility is attributed to factors such as severe soil erosion, extensive nutrient depletion, salinization, limited use of external inputs, hence poor crop yields are gained (Tamene et al., 2017).

Efforts have been exerted to enhance soil fertility mainly through the application of blanket recommendation of 100 kg NPS (19 N-38P₂O₅ + 7S) and 100 kg urea per ha since 2015. In the past decades, 100 kg diammonium phosphate (DAP: 18%N, 46% P₂O₅) and 100 kg urea were used as blanket recommendation (Elias et al., 2019). However, a comprehensive approach combined use of organic and inorganic fertilizer as well as crop-soil specific fertility management recommendations have been lacking in Ethiopia. Integrated soil fertility management (ISFM) practices are considered a more realistic approach to addressing soil nutrient depletion, low agricultural production and poverty in Africa (Teklewold et al., 2013).

Individual ISFM trials were conducted and encouraging results were reported in different regions of Ethiopia. For instance; ‘effect of plant density of sweet lupine intercropping on teff crop in Northwest Ethiopia (Hunegnaw et al., 2022)’, ‘adoption of intercropping and ISFM practices by smallholder farmers in Northwestern Ethiopia (Nigussie et al., 2017)’ and ‘evaluation of intercropping legume covers with maize on soil moisture improvement in Southern, Ethiopia (Bekele et al., 2021)’. The findings of all these studies suggested that an increase in agricultural productivity is believed to result from the application of ISFM approaches. Farmers conventionally practice cereal legume rotation and chemical fertilizer and combined use of mineral fertilizer, compost and intercropping of legume with cereals has not been well established in study sites.

In Dire and Legedadi watersheds, smallholder farmers are facing difficulties as a result of declining soil fertility. The Central Statistical Agency (CSA) reported that, in 2021, the average Ethiopian farmers hold 0.72 hectares of land and decline over time. One of the primary advantages of intercropping is the efficient utilization of land and other valuable resources (Sheha et al., 2023). Farmers practice mono-cropping of wheat-barley rotation in the main season while lentil and chick pea are planted as catch crops and adoption of ISFM practices is modest (personal observation). This is mainly due to lack of informational and technology awareness, limitations in resources and climate-related factors, that affect the adoption of ISFM practices in most parts of Ethiopia (Negera et al., 2022; Teklewold et al., 2017). In the study areas, information is particularly lacking regarding the relative contribution of these practices to crop productivity and soil health. Therefore, it is important to investigate the impacts of selected ISFM practices on crop productivity, yield and recommend the ISFM practice that performs better in the study areas. As the study site is in close proximity to the Addis Ababa City, production of legumes such as faba bean intercropped with bread wheat which is the dominant cereal is of high economic importance.

Intercropping with combined application NPS + urea and vermicompost (VC) were selected to study their impacts on crop productivity and yield. The study areas are known for production of wheat, barley and faba bean. Cereals (wheat and barley) are the most significant field crops in the study areas. Because of the faba bean’s adaptability, stability and practicality of production, it was chosen as the first legume to intercrop with wheat in the study areas. Legume and cereal intercropping is essential to promote sustainable food production systems, especially in agricultural systems that rely on minimal external inputs and dispersed land use (Saudy & Mubarak, 2015).

Numerous studies have validated the remarkable benefits of intercropping with cover legumes when compared to sole cropping (Bekele et al., 2021; Hunegnaw et al., 2022; Kherif et al., 2021). VC application increases plant productivity, maintains soil health and shows promising potential for soil physicochemical improvement (Piya et al., 2018). Besides, VC has low cost and environmental friendly (Jemal & Abebe, 2020). Thus, the objective of this research was to explore effects of intercropping and application of VC on crop productivity and yield that would help to improve management practices to enhance productivity.

Materials and methods

Study areas

The study site encompasses the Dire and Legedadi watersheds, situated within the Bereh woreda of the Oromia regional state in Ethiopia’s humid-mid highlands. Dire site is 37 km north east of Addis Ababa city. It is geographically located between 9°8.9″ to 9°13.7″N and 38°50″ to 38°57.9″E covering a total area of 7807 ha. The elevation ranges between 2491 and 3248 m.a.s.l. Legedadi watershed is located between 9°3′0″ to 9°13′30″N and 38°60′30″ to 39°02′30″ E, covering a total area of 20,318 ha (Figure 1). The elevation of Legedadi watershed ranges from 2346 to 3216 m.a.s.l. Legedadi and Dire are the two water reservoir sites located in the area that supply the bulk of the drinking water for the Addis Ababa city inhabitants.

Figure 1. Dire and Legedadi watershed map.

Climate

The area falls within the tepid sub-moist mid highlands receiving average annual rainfall 1103 and 1120 mm, respectively, for Dire and Legedadi reservoir areas. In the Dire watershed, the mean annual maximum temperature was 25.5 °C, while the minimum temperature was 11.3 °C, whereas Legedadi’s were 25.5 °C and 16.1 °C, respectively (Figure 2). The rains fall during the main rainy season (June–October) with monomodal peak in August. In 2021 and 2022, the study areas experienced more rain during the months of July and August compared to the rest of the year.

Figure 2. Monthly rainfall distribution of the study areas (data source: NMSAE, 2023).

Soil

The predominant soil categories within the Dire and Legedadi watersheds consist of Cambisol, Leptosol, Luvisol and Vertisol (Figure 3). Vertisols and Leptosols are most dominant in both watersheds with Leptosols occupying the extensive areas in the severely dissected high relief mountains while Vertisols occupying the low-lying plains and foot hills.

Figure 3. Soil type map of Dire and Legedadi watersheds.

Treatments and experimental design

Intercropping, the application of VC, their combination and a control were used as treatments in the field trials. Two sole crops of wheat (variety Danda’a) and faba bean (variety Gabelcho) without any soil amendment were used as control. Two treatments included 100% recommended NPS and urea fertilizer treatment versus 100% recommended VC application.

The four other treatments are combinations of 50% of recommended NPS and urea and the 50% of VC rate of applications (Table 1). These eight treatments were arranged in a randomized complete block design (RCBD) with three replications planted in two farm fields in Dire and Legedadi sites (Figure 4).

Figure 4. Field management of wheat–faba bean intercropping in Dire and Legedadi site.

Table 1. Treatments at Dire and Legedadi watersheds, humid-mid highlands of Ethiopia during 2021 and 2022 cropping seasons.

Code	Description of treatments
T1	Sole wheat without fertilizer application
T2	Sole faba bean without fertilizer application
T3	Wheat with100% recommended NPS + urea fertilizer rate
T4	Wheat with100% recommended vermicompost rate
T5	Wheat with 50% recommended rate NPS + urea fertilizer and half rate VC rate
T6	Wheat and faba bean intercropping with 50% recommended rate NPS fertilizer + urea and half rate VC
T7	Wheat and faba bean intercropping with 50% recommended rate NPS + urea fertilizer
T8	Wheat and faba bean intercropping with 50% recommended rate VC

Field experiments

Field trials were carried out during the primary cropping seasons from June to December in both 2021 and 2022. The same farm fields were used for both cropping seasons. In each watershed, a farm field were selected to layout the trials; selection criteria’s were representation of typical field conditions and the willingness of farmers to actively participate in the experiments. The crops were arranged in rows, with faba bean and wheat having an inter row spacing of 40 and 20 cm, respectively. Sole wheat was planted in 20 cm inter-row spacing. Faba bean rows were sown at an intra-row spacing of 20 cm and an inter-row spacing of 40 cm, positioned in the center of the wheat rows. Similarly, in sole planting of faba bean was made at seeding rate of with spacing of 40 cm between rows and 10 cm between plants. The space between the replications and the plots was 1 m and 50 cm, respectively. The plot size for all treatments was 2.6 m × 3 m (7.8 m²).

Vermicompost application

VC was applied one month prior to sowing at a rate of 3.3t ha⁻¹ for both plants (MoA, 2016). The sowing of faba bean seeds took place on 17 and 18 June 2021 and 2022, while wheat seeds were sown on 21 and 22 July 2021 and 2022 at Dire and Legedadi sites, respectively. Wheat seeds were sown by hand drilling. Wheat and faba bean seeds were applied at a rate of 150 and 350 kg ha⁻¹, respectively (EIAR, 2018). The recommended rate of application blended NPS fertilizer (19 N-38 P₂O₅ +7% S) was 100 kg ha⁻¹ for faba bean at planting while 100 kg/ha urea (46% N) was split applied in two halves. The recommended approach is to apply half of the blended NPS fertilizer (100 kg ha⁻¹) during planting and the other half during the tillering stage, in accordance with the wheat’s recommended application rate. Fertilizers were purchased from Bereh district Farmers’ Cooperative Union.

During the growing periods of both cropping seasons, plants were hand weeded three times and cultivated once. All agronomic procedures were applied uniformly throughout all treatments (EIAR, 2007). The moisture content of VC was 55%. The chemical properties of VC are shown on Table 2.

Table 2. Chemical properties of vermicompost.

Parameters	Result
TN (%)	1.35
Organic carbon	8.7
Pav (mg kg^−1)	16.37
K (cmol^+kg^−1)	0.64
CEC (cmol^+kg^−1)	58.01

TN: total nitrogen; Pav: available phosphorus, K: potassium CEC: cation exchange capacity

Plant laboratory analysis

A total of 48 composite samples, consisting of both grain yields and crop residues, were collected for the purpose of analyzing their nitrogen (N) and phosphorus (P) content. These samples underwent analysis at the Holeta Agricultural Research Center’s soil and plant analysis laboratory, following established standard procedures. To assess the N and P composition of these samples, a laboratory process involving wet oxidation was employed. For plant P content analysis, the dry ashing method was utilized, followed by measurement using a spectrophotometer and atomic absorption techniques. Total nitrogen (TN) analysis, on the other hand, was conducted through a series of steps, including Kjeldahl digestion, distillation and titration (Sahlemedhin & Taye, 2000).

Analysis of indices for intercrop efficiency

Several important crop performance metrics were assessed during the study. These metrics provide valuable insights into the advantages and competitiveness of intercropping. Here are the details of the calculations and formulas used:

The land equivalent ratio (LER) quantifies the amount of land needed in an intercropping system to attain an equivalent yield compared to that of sole cropping. It is calculated following (Mead & Willey, 1980). $$\text{Land Equivalent Ratio}=\frac{\mathit{\text{Ya}}}{\mathit{\text{YA}}}+\frac{\mathit{\text{Yb}}}{\mathit{\text{YB}}}$$ where Ya is seed yield of faba bean in intercrop with wheat, YA seed yield/ha of sole faba bean; Yb is grain yield/ha of wheat in intercrop with faba bean YB is grain yield/ha of sole wheat.

Competitive ratio (CR) provides a measure of crop competitiveness (Dhima et al., 2007). $$\text{CR}=\text{LER Wheat}-\text{LER faba bean}$$ where LER wheat and LER faba bean, CR values greater than 1 indicate that the first crop is the dominant competitor, while values less than 1 suggest that the second crop has a competitive advantage.

The crowding coefficient: assesses the degree of one crop’s dominance over another within the intercropping system, each crop has a unique K value in the intercropping system (Willey, 1979a, 1979b). The crop component with a higher K value is dominant, while the yield component with a lower K value is dominated. Relative crowding coefficient was calculated as follows (Willey 1979a, 1979b): $$K=K\hspace{0.17em}\mathit{\text{wheat}}*K\hspace{0.17em}\mathit{\text{faba}}\mathit{\text{bean}}$$ $$\text{Crowding coefficient of Wheat}=\frac{\mathit{\text{YIW}}\text{\hspace{0.33em}*\hspace{0.33em}}\mathit{\text{ZIF}}}{\left(\mathit{\text{YW}}-\mathit{\text{YIW}}\right)X\mathit{\text{ZIW}}}$$ $$\text{Crowding coefficient of faba bean}=\frac{\mathit{\text{YIF}}\text{*}\mathit{\text{ZIW}}}{\left(\mathit{\text{YF}}-\mathit{\text{YIF}}\right)X\mathit{\text{ZIF}}}$$ where K total relative crowding coefficient; K wheat, relative crowding coefficient of wheat; K faba bean, relative crowding coefficient of faba bean; YIW, wheat yield in intercropping system; YW, wheat yield in sole planted; YIF, faba bean yield in intercropping system; YF, faba bean yield in sole planted; ZIW, proportion of wheat in intercropping system; ZIF, proportion of faba bean in intercropping system. If K > 1, there is a yield advantage; if K = 1, there is no yield benefit; and if K < 1, there is yield disadvantage.

Partial budget analysis

It assists in evaluating the economic benefits of intercropping and different fertilizer applications in the context of grain and straw yield. To address the yield difference observed between experimental plots and actual farmer fields, grain and straw yields were reduced by 10% (CIMMYT, 1988). The prices (USD/Kg) of wheat, faba bean, faba bean straw and wheat straw were 0.74, 0.92, 0.04 and 0.15, respectively. Labor expenses vary and were regarded a variable cost while other costs were assumed to be constant. Labor costs per man-day were estimated at 5.58 USD. The indicies were calculated using the formulae given below:

Gross average yield (kg/ha) (Yav) was computed by converting the average yield for each treatment into hectares.

Adjusted yield (AjY) was derived by reducing the average yield by 10% to align it with the difference between experimental and farmers’ yields: $$\text{AjY}(\mathrm{t}/\text{ha})=\text{Yav}\times (1-0.1)$$

Gross field benefit (GFB) (USD/ha) was calculated by the following formula $$\text{GFB}=\text{AjY}\times \text{field}/\text{farmgate\hspace{0.33em}price\hspace{0.33em}for\hspace{0.33em}the\hspace{0.33em}crop}$$

Total variable cost: covers labor cost, fertilizers cost (NPS, urea and VC)

Net benefit (NB) (USD/ha) was determined by deducting the overall costs from the GFB s $$\text{NB}=\text{GFB}-\text{totalcost}$$

Marginal rate of return (MRR %) was calculated by dividing the change in net benefits by the change in costs (CIMMYT, 1998). $$\mathrm{\text{MRR}}=\frac{\text{Marginal benefit}}{\text{marginal cost}}\times 100$$

Nutrient use efficiency

• Nutrient uptake: determined by the multiplication of the grain or straw yield (kg ha⁻¹) with the nutrient concentration (%).

1. Nutrient (N, P or K) uptake by grain or straw (kg ha⁻¹) = [Yield of grain or straw (kg ha⁻¹ × Nutrient (N, P or K) concentration of grain or straw (%) × 10⁻².

2. Total uptake (kg ha⁻¹) = Nutrient uptake grain + Nutrient uptake straw

• Recovery Efficiency (RE) the amount of nutrient uptake per unit of nutrient applied $$\text{RE\%}=\frac{\text{Un}-\text{Uo}}{n}x100$$

where Un rate of N and P fertilizer uptake, Uo nutrient absorption without any fertilizer application and n for amount of fertilizer used.

• Agronomic efficiency (AE) Assesses the economic production achieved per unit of nutrient applied $$\text{AE}\left(\text{kg/kg}\right)=\frac{\text{Gf}-\text{Gu}}{\overline{Q}\dot{A}}$$

where Gf, grain yield from fertilized plots at ‘n’ rates, $$\begin{array}{c}\text{Gu},\text{grain yield from unfertilized plots},\\ \text{QA},\text{nutrient used}.\end{array}$$

Data analysis

The yield, yield components, marginal rates of return and intercropping indices subjected to analysis of variance using SAS version 9.1 (SAS Inc., Cary, NC) (SAS, 2008) to determine the different treatment effects. Comparisons between means of the treatments were assessed using analysis of variance (ANOVA) at confidence intervals of 95% (p < 0.05). Treatment differences were assessed through Fisher’s least significant difference (LSD) test at a significance level of 5%.

Results

Effect of treatments on crop growth parameters

Plants height varied amongst the various treatments. Intercropping, addition of NPS + urea fertilizer and VC either alone or their combination significantly (p < 0.05) affected plant height (PH) of wheat and faba bean related to the control in both sites. Highest faba bean PH was obtained at wheat and faba bean intercropped with 50% recommended rate NPS + urea fertilizer and half rate VC fertilizer added treatment (Table 3). This treatment had 17.81% in Dire site and 31.1% in Legedadi site higher faba bean PH than the control treatment.

Table 3. Treatments effect on growth and yield parameters of faba bean in 2021 and 2022 cropping seasons (combined over years) in Dire and Legedadi site.

	PH (cm)	SC (no)	PPP (no)	SPP (no)	PH (cm)	SC (no)	PPP (no)	SPP (no)
Treatments	Dire				Legedadi
T2	79.7^c	19.5^b	3.9^c	2.1^c	90.0^c	21.4^b	4.6^c	2.4^b
T6	93.9^a	23.4^a	6.5^a	3.3^a	118.0^a	24.2^a	7.7^a	2.9^a
T7	92.0^a	21.7^ab	6.1^a	2.6^b	111.0^ab	22.8^ab	7.4^a	2.56^b
T8	89.7^ab	21.2^b	5.3^b	2.5^b	96.0 ^bc	22.5^ab	5.9^b	2.5^b
Mean	88.8	21.5	5.45	2.63	103.7	22.7	6.88	2.61
Standard error	1.29	0.72	0.275	0.09	1.01	1.02	1.45	0.09
p Value	0.01	0.060	0.004	0.002	0.027	0.137	0.002	0.008
F value	47.2	4.32	33.52	45.45	6.3	5.45	15.18	55.42
Level of significance	*	ns	**	**	*	^ns	**	**

In the notation used, ^∗ and ^∗∗ indicates significance at p < 0.05, 0.01 and 0.001, respectively,

ns: not significant at p < 0.05.

Means in a column with the same letter signifies that they are not significantly different from one another at a significance level of p < 0.05; Plant Height (PH), stand count (SC), pods per plant (PPP), seed per pod (SPP) of faba bean grown in Dire and Legedadi site.

Wheat height was highest at 100 cm and 97.4 cm in wheat–faba bean intercropped with half dose of each VC, NPS + urea fertilizers in Dire and Legedadi sites, respectively. The average height of wheat plants was greater at the Legedadi site than at the Dire site. The mean PH of wheat decreased from T5 > T6 > T3 > T7 > T8 > T1 treatments (Figure 5) in both study sites.

Figure 5. Treatments effect on growth and yield parameters of wheat in 2021 and 2022 cropping seasons (combined over years) in Dire and Legedadi site.

Growth and yield

The results of the analysis of variance demonstrated that the applications of NPS + urea fertilizer and VC either alone or in combination significantly (p < 0.05) affected grain yield and total biomass of wheat in both sites. The maximum wheat yield (4000.3 and 4151.7 kg ha⁻¹) was gained from the application of full dose recommended rate of mineral fertilizers in Dire and Legedadi sites, respectively. Similarly, highest wheat biomass yield was recorded on the same plot in both sites. As shown on Figure 6 biomass yield and grain yield showed positive relationship.

Figure 6. Interrelationships of biomass yield and grain yields (kg ha⁻¹) of wheat and faba bean intercropping in Dire and Legedadi sites (combined over years).

Intercropping with addition of 50% VC and 50% NPS fertilizer gave highest total intercrop yield of wheat 2647 kg ha⁻¹ in Dire and 2510 kg ha⁻¹ in Legedadi site. The average yield from half dose VC and 50% NPS + urea added treatment was higher by 89.1% and 76.8% compared to average yield of the control in Dire and Legedadi sites, respectively. Increasing the recommended VC rate from 50% to 100% increased wheat yield by 79% and 80.3% in Dire and Legedadi sites, respectively. Intercropping effects were significant (p < 0.001) for wheat yields on both sites. Wheat intercrops with faba bean, with half dose VC and half dose NPS + urea fertilizers added treatment had obtained highest (4104.18 and 5495 kg ha⁻¹) wheat equivalents yields than the total intercrops yields in Dire and Legedadi sites, respectively (Table 4).

Table 4. Treatments effect on yield and yield components of wheat in 2021 and 2022 cropping seasons (combined over years) in Dire and Legedadi sites.

T	Dire site					Legedadi site
	TB kg ha^−1	GY kg ha^−1	WEY kg ha^−1	SY kg ha^−1	GMV (USD ha^−1)	TB kg ha^−1	GY kg ha^−1	WEY kg ha^−1	SY kg ha^−1	GMV (USD ha^−1)
T1	5073^f	1400.3^g	1400.3^e	3684.0^c	1174.1^g	5104^g	1420.0^g	1420.0	3684.0^f	1260.2^g
T3	12883^a	4000.3^a	4656.3^a	8227.0^a	3354.1^d	12700^a	4151.7^a	4691.7	8548.3^a	3481.0^d
T4	9433^c	3140.3^c	3140.3^d	6293.0^b	2633.0^f	9510^c	3285.3^c	3285.3	6224.7^c	2754.6^f
T5	11500^b	3827.3^b	3645.3^c	6756.0^b	3207.3^e	10317^b	3927.3^b	3560.7	6389.3^b	3291.1^e
T6	8483^d	2647.0^d	4104.2^b	5836.3^c	6150.9^a	7658^d	2510.0^d	5495.0	5148.0^d	6553.9^a
T7	6133^e	2023.7^e	3656.9^c	4109.7^d	4575.5^b	6171^e	2128.3^e	3928.3	4042.7^e	4467.6^b
T8	5767^ef	1754.0^f	3101.8^d	4012.7^d	4340.1^c	5754^f	1821.7^f	4348.8	3932.3^ef	4305.5^c
Mean	8324.4	2734.9	2963.1	5476.6	82573	8044.8	2749.2	3818.5	5424.2	3686.9
Standard error	326.03	437.6	125.3	185.8	262.3	215.6	75.6	35.2	272.6	56.8
P value	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
F value	93.04	377.7	36.52	83.9	586.45	368.9	390.9	143.7	83.3	566.5
Level of significance	***	***	***	***	***	***	***	***	***	***

***significant at p < 0.05.

Means in a column with the same letter signifies that they are not significantly different from one another at a significance level of p < 0.05.

T: treatment; TB: total biomass; TY: total yield, SY: straw yield; GMV: gross monetary value; USD: 53.67 Ethiopian birr.

Competition indices

The application of 50% NPS + urea and 50% VC had the highest wheat LER 1.89 and 1.49 at Dire and Legedadi sites, respectively. The lowest LER 1.25 and 1.26 was found in 50% VC rate added treatment in both study sites (Figure 7). All intercrops had LER value greater than a unit.

Figure 7. The effect of treatments on LER of wheat and faba bean at Dire and Legedadi sites in 2021 and 2022 (combined over years) cropping seasons.

According to the analysis result shown on Table 5, for all treatments wheat was the dominant crop with a higher K value than faba bean with a lower K value. The highest relative crowding coefficient of wheat 2.91 in Dire site and 2.38 in Legedadi site was recorded in the wheat–faba bean intercropping treatments where 50% NPS + urea and 50% VC were applied. The product of relative crowding coefficient was greater than one in all treatments and in both sites.

Table 5. Relative crowding coefficient (k), aggressivity value (A) and system productivity index (SPI) of wheat and faba bean grown in intercrops in 2021 and 2022 (combined over years) in Dire and Legedadi sites.

	Relative crowding coefficients						Aggressivity				System
Treatments	Dire			Legedadi			Dire		Legedadi		Productivity index
	Wheat	FB	K	Wheat	FB	K	Wheat	FB	Wheat	FB	Dire	Legedadi
T6	2.21	1.32	2.91	2.14	1.11	2.38	0.09	−0.09	0.19	−0.19	5672.02	4423.80
T7	3.15	0.84	2.64	3.42	0.68	2.33	0.02	−0.02	0.16	−0.16	4122.53	3751.54
T8	3.88	0.72	2.81	3.8	0.56	2.13	0.05	−0.05	0.13	−0.13	4088.59	3535.12
Mean	3.08	0.96	2.79	3.12	0.78	2.28	0.05	−0.05	0.16	−0.16	4627.71	3903.49

Nutrient use efficiency of wheat

The average (2021 and 2022 cropping seasons) grain yield, nutrient uptake, nitrogen and phosphorus harvest index, nitrogen and phosphorus use efficiency data exhibit variation among the treatments. Wheat nutrient intake was considerably impacted by the application of either sole or combined NPS + urea and VC fertilizers in different rates (Figure 8). It is noteworthy that the grain exhibited higher nitrogen content than the straw in Dire and Legedad sites.

Figure 8. Nitrogen and phosphorus content of wheat in 2021–2022 cropping seasons (combined over years) at Dire and Legedadi sites (nitrogen content of straw [SN], nitrogen content of grain [GN], total nitrogen [TN], phosphorus content of straw [SP], phosphorus content of grain [GP], total phosphorus [TP]).

The maximum nitrogen uptake by the grain 47.2 and 48.5 kg N ha⁻¹ in Dire and Legedadi sites, respectively, was recorded in a plot treated with combined NPS + urea and VC fertilizers. Similarly, the maximum p uptake was recorded in full dose NPS + urea plot in both sites. These findings indicate that combined application of NPS + urea and VC fertilizers increased N uptake by 197.6%, 102.2% and 154.3% in the grain, straw and in the whole plant compared with the control.

AE and RE of N and P significantly influenced by rates and types of fertilizers applied (Figure 9). Application of 50% NPS + urea and 50% VC produced maximum AE (41.0 and 41.9 kg grain per kg N) in Dire and Legedadi sites respectively. Conversely, the control plots in both sites exhibited the lowest AE values. The highest RE of N (124.8% and 126.7) was obtained from the treatment involving 50% NPS + urea and 50% VC addition in Dire and Legedadi sites, respectively.

Figure 9. Treatments effect on nutrient use efficiency of wheat at Dire and Legedadi sites in 2021 and 2022 (combined over years) cropping seasons (recovery efficiency of phosphorus [REP], recovery efficiency of nitrogen [REN], agronomic efficiency of phosphorus [AEP] and agronomic efficiency of nitrogen [AEN]).

Nutrient use efficiency of faba bean

The simultaneous use of VC and NPS + urea amendments significantly (p < 0.001) affected the N and P contents in the faba bean tissue. Specifically, the treatment involving 50% NPS + urea and 50% VC fertilizer demonstrated the highest N uptake (118.89 and 120.34 Kg ha⁻¹), followed by 50% VC added treatment in Dire and Legedadi sites, respectively.

The joint application of these treatments led to a significant enhancement in both phosphorus (P) content and uptake when compared to the control plots at both sites. The control plots (T2) exhibited the lowest AE in both sites. Additionally, the highest RE of nitrogen (165.4% and 167.6%) was obtained from 50% NPS + urea and 50% VC-added treatment in Dire and Legedadi sites, respectively (Figure 10).

Figure 10. Treatments effect on nutrient use efficiency of faba bean at Dire and Legedadi sites in 2021 and 2022 (combined over years) cropping seasons.

Economic analysis

In the partial budget analysis, the most substantial net benefits, amounting to US$ 5598.1/ha in Dire and US$ 5690.8/ha in Legedadi sites, were derived from wheat intercropped plots treated with a ­combination of 50% NPS + urea and 50% VC fertilizer.

Conversely, the sole faba bean plots generated the lowest net benefits, with US$ 1036.4 ha⁻¹ in Dire and US$ 1260.4 ha⁻¹ in Legedadi sites, ranking just above the control plots, which produced US$ 1449.9 ha⁻¹ in Dire and US$ 1464.5 ha⁻¹ in Legedadi sites (Table 6). The marginal rates of return for the most economically promising treatment, wheat–faba bean intercropped with 50% NPS + urea and 50% VC fertilizer, were notably high 4227.2 in Dire and 4890.4 in Legedadi sites.

Table 6. Economic efficiency of wheat–faba bean intercropping in 2021–2022 cropping seasons (combined over years).

Treatments	Adj. WY	Adj. SYW	Adj. SYF	Adj. FY	GFB WY	GFB FY	GFB SYW	GFB SYF	TC	NB	MRR
Dire site
T1	1400.3	3684.0	0.0	0.0	1036.2	0.0	552.6	0.0	138.9	1449.9	1066.8
T2	0.0	0.0	3326.5	1100.8	0.0	1012.7	0.0	133.1	109.4	1036.4	857.5
T3	4000.3	8227.0	0.0	0.0	2960.2	0.0	1234.1	0.0	507.8	3686.4	1299
T4	3140.3	6293.0	0.0	0.0	2323.8	0.0	944.0	0.0	220.4	3047.4	1043.6
T5	3827.3	6756.0	0.0	0.0	2832.2	0.0	1013.4	0.0	364.1	3481.5	1207.7
T6	2647.0	5836.3	9853.2	3107.4	1958.8	2858.8	875.4	394.1	489.1	5598.1	4227.2
T7	2023.7	4109.7	7769.2	1819.5	1497.5	1673.9	616.5	310.8	448.3	3650.4	1166.9
T8	1754.0	4012.7.0	8671.3	2314.1	1298.0	2129.0	601.9	346.9	304.6	4071.1	1451.0
Legedadi site
T1	1420	3684.0	0.0	0.0	1050.8	0.0	552.6	0.0	138.9	1464.5	1009.4
T2	0.0	0.0	4326.5	1300.8	0.0	1196.7	0.0	173.1	109.4	1260.4	915.7
T3	4151.7	8548.3	0.0	0.0	3072.3	0.0	1282.2	0.0	507.8	3846.7	1334.2
T4	3285.3	6224.7	0.0	0.0	2431.1	0.0	933.7	0.0	220.4	3144.4	1254.4
T5	3927.3	6389.3	0.0	0.0	2906.2	0.0	958.4	0.0	364.1	3500.5	1318.3
T6	2510	5148	10769.2	3390.8	1857.4	3119.5	772.2	430.8	489.1	5690.8	4890.4
T7	2128.3	4042.7	8971.3	2014.7	1574.9	1853.5	606.4	358.9	448.3	3945.4	1761.8
T8	1821.7	3932.3	8971.3	2014.7	1348.1	1853.5	589.8	358.9	304.6	3845.6	1761.8

Adj.: adjusted; WY: wheat yield, FY: faba bean yield; SWY: straw wheat yield; SFY: straw faba bean yield; GB: gross field benefit; TC: total cost; NB: net benefit; MRR: marginal rate of return.

Discussion

Growth and yield components

Plant productivity and growth rate are correlated with PH (Sritarapipat et al., 2014). In this study, there was a significant (p = 0.001) variation of PH of wheat between treatments in both sites. The highest faba bean PH was recorded in the wheat–faba bean intercropped plots with combined fertilizers, consisting of half doses of each VC and NPS + urea. This can be explained by the rise in the uptake of available nutrients and the variation in the major nutrient content among the different fertilizer sources (Armin et al., 2016). These findings align with previous studies (Demissie et al., 2017; Habtamu et al., 2015; Mahmud et al., 2016; MoA, 2016; Woldesenbet & Tana, 2014) which also reported that higher PH was observed in plots treated with combinations of compost and inorganic fertilizers.

Wheat/faba bean intercropped plot also had highest wheat PH than other treatments. This might be due to the integrated fertilizer application and intercropping effect. A similar result was also reported by (Ahmad & Maaroof, 2020; Biswas et al., 2020; Ginwal et al., 2019; Hailu, 2019; Ijoyah & Dzer, 2012) who noticed substantial differences in PH among intercropped plots, potentially attributed to the competition for light among the intercropped plants, resulting in an overall increase in PH. Moreover, simultaneous use of NPS + urea and VC fertilizers also exhibited significant (p < 0.001) difference on spike length, tiller number and number of seeds spike⁻¹. In this respect providing the plants by the appropriate amount and form of elements enhanced the crop growth (Noureldin et al., 2013; H. S. Saudy et al., 2020; H. S. Saudy & Mohamed El–Metwally, 2023).

Grain yield

The application of 100% recommended NPS + urea fertilizers resulted in the highest wheat yields, with 4000.3 kg/ha in Dire and 4151.7 kg/ha in Legedadi sites. The simultaneous use of 50% VC and 50% NPS also resulted in high yields in both sites. This treatment gave grain yield advantage of 859.7 and 866.4 kg ha⁻¹ compared to application of 100% VC rate at Dire and Legedadi sites, respectively. This could be because nutrients from mineral sources are readily available (Hammad et al., 2020). These results corroborate earlier findings (Agegnehu et al., 2008; Hadis et al., 2018; Hammad et al., 2020; Mahmud et al., 2016) that, highest grain yield was recorded when the recommended rate of NPK fertilizer is applied.

Additionally, higher grain yield was also recorded in combined half dose of each VC and NPS fertilizer added treatment than the control. The different sources of nutrient effect on grain yield of the crop might be due to various concentrations of NPS in the applied organic fertilizer (Saudy et al., 2021). Similarly, Almaz and Tadesse (2018), MoA (2016), Tehulie and Eskezia (2021) and Woldesenbet and Tana (2014) reported that the concurrent application of both organic and inorganic fertilizers resulted in increased yields and provided soil and environmental advantages that contribute to sustainable production. The highest total intercrop yield of 2647 in Dire and 2510 kg ha⁻¹ in Legedadi sites were obtained from combined application of half dose each NPS + urea VC fertilizers added treatments than other intercropped plots.

Researches indicated the increment of total yield and economic return in intercropping system than sole cropping system (Girma et al., 2019; Hailu, 2019; Kumsa et al.; Negash & Mulualem, 2014). For instance, a 3-years study of ‘sorghum/groundnut and sorghum/soybean intercropping in Asosa (Ethiopia)’ demonstrated that the sorghum/groundnut intercrop consistently yielded the maximum sorghum yields across all growing seasons (Dereje et al., 2017). This may be due to intercropping of cereal and leguminous crops, as nitrogen can build up under nodule conditions. Such cooperation is expressed in a higher yield of the mixture than the yield of a single culture (Gao et al., 2014).

The main benefit of intercropping is its effective utilization of available resources, which ultimately results in higher productivity when compared to each crop individually within the mixture (Mobasser et al., 2014). In addition to yield, intercropping help to reduce disease incidence (Zhang et al., 2019).

Competition indices

In the intercropped plots of wheat and faba bean, the application of a combination of half-dose NPS + urea and 50% VC yielded the highest TLER of 1.89 in Dire and 1.49 in Legedadi sites. This indicates that the intercropping system achieved 89% (0.89 ha) and 49% (0.49 ha) higher yields compared to a sole cropping system, meaning that more land area would be required for sole cropping to match the yield of the intercropping (Midya et al., 2005). These results are in line with a study by Bekele (2022) that intercropping wheat and bean showed a yield advantage with LER values of 0.99 and 0.31, respectively.

LER values exceeding one, as evidenced in the wheat component of the intercropping systems at both research sites, signify the benefit of intercropping in terms of resource utilization for plant growth when compared to sole cropping. This implies that intercropping led to greater land use efficiency, where the positive interactions between different plant species outweighed any negative competition between them. The LER value revealed that wheat and faba bean intercropping produced yielded a higher total production per unit area in comparison to the control. The LER indices were greater in wheat component of the intercropping systems in both study sites which was greater than one, indicating an advantage of intercropping in terms of environmental resources use (Mead & Willey, 1980). This indicates that intercropping led to increased land utilization efficiency, with interspecific facilitation outweighing interspecific competition (Machiani et al., 2018). Similar results have been reported for various intercropping systems, such as wheat–pea (Pankou et al., 2021), wheat–maize (Gou et al., 2016), wheat–faba bean (Agegnehu et al., 2008; Xiao et al., 2021), teff–lupine (Hunegnaw et al., 2022), maize–soybean (Xu et al., 2020), and maize–peanut (Feng et al., 2021) that intercropping led to increased efficiency in land utilization.

The partial LER values also indicated that the land use efficiency of wheat seems to be more beneficial than faba bean in all mixtures. The appropriate selection of plants and cropping techniques, as well as the existence of mutualism symbiosis between intercropped plants, can boost land productivity (Hafid et al., 2021). Wheat was the dominant crop with higher K value than faba bean with lower K value in half dose each VC and NPS + urea fertilizer added treatment in both study sites.

The relative crowding coefficients of wheat were greater than a unit in all treatments and in both sites, indicated that making intercropping of faba bean had advantage in terms of competition.

Nutrient use efficiency

The use of varying levels of NPS + urea and VC fertilizers had a discernible effect on wheat’s nutrient uptake. It was observed that the grain had higher N and P content compared to the straw. The higher N uptake by the grain was 47.2 in Dire site and 48.5 kg N ha⁻¹ in Legedadi sites. The findings showed that the joint use of NPS + urea and VC fertilizers led to increased nitrogen (N) and phosphorus (P) uptake (both in straw and grain) compared to the control in both research sites. This resulted 80.8% and 131.3% higher total N and P uptake, respectively, over the control in Dire site. This implies that combined application of NPS + urea and VC had better agronomic value than the sole application of either VC or NPS + urea fertlizers. This finding aligns with the report of Qaswar et al. (2020) that simultaneous use of mineral fertilizer and manure increased N, P and K uptake. Additionally, Moe et al. (2017) found that the inorganic fertilizer and organic manure enhanced nitrogen uptake and nitrogen use efficiency in hybrid rice. This effect might be attributed to the combined fertilizers improving soil physical characteristics that support root growth and distribution while reducing nitrogen loss, leading to increased nutrient uptake by the crops. Elfstrand et al. (2007) also reported that green manure application increased plant nitrogen content by enhancing nitrogen availability to the plant. Similarly, Zhihui et al. (2016) reported that manure addition enhanced maize N uptake by 43% from a long-term (28-year) experiment in China. Grain’s content of nutrient was higher than the straw. These findings were corroborated by the results of Agegnehu et al. (2016) and Hadis et al. (2018) that grain and straw nitrogen (N) uptake showed an increase when a combination of organic and N fertilizer was applied, as compared to the use of either one individually. Similarly, combined use of NPS + urea and VC fertilizers resulted highest N uptake by grain and straw. The control showed the lowest nitrogen uptake on straw and total.

The rates and types of fertilizers applied also had a significant effect on the AE of nitrogen. Application of 50% NPS + urea and 50% VC produced maximum AE (41.0 kg grain per kg N in Dire site and 40.9 kg grain per kg N in Legedadi sites. The control plots in both locations exhibited the lowest AE. Higher values of AE from combined fertilizers application compared to the sole application either VC or NPS + urea suggested the greater soil health amelioration. The findings are compared to the results of Agegnehu et al. (2016) and Gadisa and Wakgari (2021) in Ethiopia, Dorsey (2014) in USA and Zheng et al. (2017) in North China that agronomic N efficiency was higher in combined application of organic and nitrogen fertilizers. This indicted that combined fertilizers application is effective for sustainable wheat cultivation.

The simultaneous use of VC and NPS + urea fertilizer not only enhanced wheat crop growth and yield but also increased the AE of nitrogen. This aligns with the findings of other authors, illustrating that high AE is attained when there is an increase in yield per unit of applied nitrogen, primarily due to an increase in nitrogen uptake (Agegnehu et al., 2016; Glaser et al., 2015; Klikocka et al., 2017; Yousefi & Sadeghi, 2014). Integrated fertilizers application had higher AE than full dose application of NPS + urea which had higher N content. Similarly, Solomon and Anjulo (2017) stated that the highest AE of nitrogen occurs at its lowest due to reduced losses. The wheat plant utilized a substantial portion of the provided nitrogen (N) for grain yield, especially at the lower N application rate (Saudy & Mubarak, 2015). Similarly, Daba (2017) also noted that there is a tendency for AE to decrease as nitrogen levels increase.

Economic analysis

The economic analysis revealed that wheat faba bean intercropped treatment with the application of 50% NPS + urea and 50% VC fertilizer was the most profitable (Table 6). The partial budget analysis indicated that the most substantial net benefits (US$ 5598.1 and 5690.8 ha⁻¹) were achieved with wheat–faba bean intercropped with a combination of 50% NPS + urea and 50% VC fertilizer.

Despite the increase in yield attributed to VC, it is important to highlight that the variable costs associated with VC treatments were higher. Consequently, this led to an overall lower economic benefit when compared to the combined use of NPS + urea and VC. Therefore, in Dire and Legedadi sites, the treatment combination involving 50% NPS + urea and 50% VC fertilizer, along with wheat–faba bean intercropping, emerged as the most economically advantageous choice with marginal rates of return (MRR) 4478.6% and 4278.6%, respectively.

The use of wheat-faba bean intercropping with the use of combined fertilizers is therefore promoted for farmers in Dire, Legedadi and other locations with similar agro-ecological conditions to increase crop yields. From this finding it was observed combined fertilizer application and intercropping was crucial for higher net benefit and MRR.

Conclusion

The study was conducted at Dire and Legedadi sites, humid mid-highlands of Ethiopia to evaluate effects of intercropping of wheat–faba bean and application of VC on crop productivity in 2021 and 2022 cropping seasons. The highest net benefits (US$ 5598.1 and 5690.8 ha⁻¹) was recorded at faba bean intercropped with 50% NPS + urea and 50% VC added treatment in Dire and Legedadi sites, respectively. In addition combined use of NPS + urea and VC fertilizers improved almost all growth and yield component parameters, nutrient uptake, agronomic, recover and use efficiency. Furthermore, this treatment resulted in higher crowding coefficient (2.91 and 2.38), LER (1.89 and 1.49), system productivity index (5672.02 and 4423.80) and MRR (4478.6% and 4278.6%) in Dire and Legedadi sites, respectively.

Wheat–faba bean intercropping with half rate of NPS + urea and half rate VC are recommended ISFM practices to increase yield agronomic, economic and nutrient use efficiency and fertilizer usage efficiency. Further study across seasons and places is required to verify the effects of the selected ISFM practices on crop productivity and yield.

Additional information

No additional information is available for this article.

Acknowledgments

The authors are thankful for the financial support provided by Addis Ababa University under the thematic research project on Integrated Landscape-based Management (ILM) Approach for Improving Ecosystem Services, Agricultural Productivity and Water Availability in the Central Highlands of Ethiopia (ILM-ESAW).

Disclosure statement

The authors declare no conflict of interest.

Data availability statement

Data will be made available on request.

Additional information

Funding

This work was supported by Addis Ababa University project on Integrated Landscape-based Management (ILM) Approach for Improving Ecosystem Services, Agricultural Productivity and Water Availability in the Central Highlands of Ethiopia (ILM-ESAW).

Notes on contributors

Meseret Habtamu

Meseret Habtamu is a PhD student at Addis Ababa University and a lecturer at Kotebe University of education.

Eyasu Elias

Professor Eyasu Elias is State Minister, Ministry of Agriculture, of FDRE and professor at Addis Ababa University Cenetr for environmental science.

Mekuria Argaw

Mekuria Argaw: is director for Horn of Africa and professor at Addis Ababa University Cenetr for environmental science.

Geberekidan Feleke

Gebrekidan Feleke is an agronomist at Debre zeyit agricultural researcg center and PhD student at university of Florence in Italy.