1 Introduction

Livestock production is an important component of agriculture worldwide, providing a high-value protein and several essential micronutrients such as iron and zinc and vitamins. Additionally, livestock provides an important source of draft power, farm manure, and income which helps in poverty alleviation (Wanapat et al. 2015). Thus, livestock production is vital to livelihood subsistence and socio-economic development and plays a crucial role in meeting the goals set out in the UN 2030 Agenda for Sustainable Development, especially Goal 1 (End poverty in all its forms everywhere) and Goal 2 (End hunger, achieve food security and improve nutrition, and promote sustainable agriculture) (Johnston 2016).

Domestic cattle including yak, bison, cow, and buffalo rearing is a major livestock production system across the globe. Cattle are kept as possessions, ceremonial objects, and source of meat, milk, leather, and manure for fertilizer (Oduniyi et al. 2020). Globally, cattle population is reported to have increased from around 989 million in 2019 to over one billion in 2020 (Shahbandeh 2022). In China, cattle production is widely practiced particularly in arid and semi-arid areas. The cattle herd in China was estimated to be ~ 61 million in 2020 (Liu et al. 2019). Production largely depends on the quality and quantity of feed (Mengistu et al. 2019). Cattle fed with high-quality forage deliver better milk and meat, which could benefit the nutritional health of consumers.

Alfalfa (Medicago sativa L.) is a long-lived perennial legume fed to a wide range of livestock as hay or silage. Alfalfa has a high tolerance for warm and cold climates, and cultivation provides other benefits such as improving soil fertility and physical quality. Though the importance of alfalfa and other forages is gaining popularity, acreage and productivity are reported to have been stagnated or declined in some regions over the past two decades (Pereira 2018). This has been attributed to high competition for land for crops and construction to meeting the demands of the increasing population. More importantly, land degradation and climate change–related constraints like high temperatures, prolonged droughts, rainfall variability, and water scarcity have adverse effects on the productivity of alfalfa and other fodder (forage) plants (Ranjan et al. 2017). Consequently, at present, a large fraction of pasture fields, particularly in arid and semi-arid regions, are unable to produce sufficient fodder to meet the nutritional needs of livestock (Özköse 2018).

Given the importance of forage plants like alfalfa production to the livestock sector, it is important to improve yield to ensure sustainable livestock production. Addressing challenges such as poor soil fertility could be achieved by increasing the use of mineral fertilizers. However, the option can be costly and can have several environmental problems if applied inappropriately or excessively (Khan et al. 2020). Rainwater harvesting and the use of organic amendments such as biochar have been suggested as sustainable ways of addressing plant water stress and improving soil quality for crop production, respectively (Agegnehu et al. 2017). Biochar is a stable carbon-rich material produced when the feedstock is heated in a closed container with little or no oxygen (Reddy et al. 2015). Though biochar characteristics differ depending on factors such as feedstock and pyrolysis temperature, the presence of hydrophilic domains, large specific surface, and high porosity characterizing biochar can improve soil physical, chemical, and biological properties for plant growth (Hossain et al. 2020). For example, Liu et al. (2017) reported that the addition of 20 and 40 t ha−1 wheat straw biochar increased the productivity of maize (Zea mays L.) by 6.1% and 6.9%, peanut (Arachis hypogaea L.) by 6.6% and 11.2%, and soybean (Glycine max L.) by 7.2% and 7.6%. However, Ye et al. (2020) argued that biochar addition to soil can promote crop productivity in tropical and subtropical climates more than in other types of climates.

Until now, the potential of combining rainwater harvesting technologies and biochar to improve the productivity and economy of alfalfa for livestock fodder in drought-stricken regions is under-studied. Such information is relevant to increase forage plant production for animal nutritional security. The objective of this study was to examine whether yield, nutritional quality in terms of concentrations of crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF), and net economic benefit of alfalfa herbage are affected by the integration of maize straw biochar application and ridge-furrow rainwater harvesting methods in Northwestern China. We hypothesized that the amendment of maize straw biochar to ridge-furrow rainwater harvesting methods increases alfalfa fodder yield and economic returns more than the no-biochar amendment and/or flat planting.

2 Materials and Methods

2.1 Experimental Site Description

The study was conducted at Anjiagou Catchment experimental station from 2020 to 2021. For decades, the experimental site has been subjected to severe water erosion. The average annual precipitation from 1971 to 2018 was approximately 404.5 mm. The average annual pan evaporation was 1515 mm. According to the USDA soil taxonomy, the soil at the experimental station is Calcic Cambisol. The permanent wilting point of the site was 5.16% and the field water holding capacity was 21%. The distance between the soil surface and the water table ranges from 30 and 100 m (Wei et al. 2015).

2.2 Experimental Design

The experimental design was a split-plot in three replications. Biochar application was the main treatment and rainwater harvesting methods were the sub-treatment (Fig. 1). There were two biochar treatments, 0 ha−1 and 30 t ha−1. The biochar used was maize straw biochar produced with residence time up to 2 h at 400 ℃. The properties of the biochar are presented in Table 1. A detail of soil property characterization before and after growing seasons is presented in supplementary Table S1. The rainwater harvesting treatments were flat planting (FP), tied-ridging (TR), and open-ridging (OR). In total, there were six treatments (two biochar treatments and three rainwater harvesting methods). Except for treatments with FP, each treatment field had nine ridges and ten furrows. Each treatment field was 52.5 m2 (5 × 10.5 m) in size. The rainwater harvesting scheme ridge width was 45 cm with height varying from 15 to 20 cm, and a furrow width of 60 cm for TR and OR treatment. The width of the ties was 15 cm, and the height was 20 cm. The space between two ties that were not staggered was 2.5 m. Ridges were mulched with biodegradable film (Ecoflex FS; BASF Co Ltd, Germany), 1.4 m in width and 0.008 mm in thickness, while ties in TR were naturally compacted through wetting and drying cycles. The ridges were used for runoff collection, whereas the furrow was employed for planting and for infiltration. Eighteen treatment plots were constructed 1.5 m apart by two cement adjacent borders, buried 20 cm in the soil and 15 cm above the ground.

Fig. 1
figure 1

Schematic representation of ridge-furrow rainwater harvesting system with maize straw biochar application on sloped land. VS = versus (against)

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Table 1 Characteristics of the maize straw biochar
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2.3 Field Management

The field site was cleared and raked on March 20, 2020. The plots were marked on April 2, 2020. On April 12, 2020, the treatment ridges and furrows for the rainwater harvesting treatments were constructed by molding the soil into ridges and furrows across the length of the fields. The ridges were immediately covered with biodegradable film and secured beneath 3 cm of soil. In 2021, the procedure was repeated from March 20 to March 24. Before sowing, the field site was harrowed, and the furrows were leveled. The maize straw biochar was ground and sieved to 5 mm before it was amended to the soil. The biochar was mixed with the soil on April 14, 2020, using a hoe. On April 15, 2020, a native alfalfa variety (No. 3 Gannong) was sown at 22.5 kg ha−1. For the OR- and TR-treated plots, four rows, 20 cm spaced were sown in a 60 cm furrow width on an area of 30 m2 with 40 alfalfa-planted rows. The FP treatment field was 50.25 m2 with 66 alfalfa sown rows. Approximately 2 months after seeding, the ties in tied-ridging treatments were manually banked and reinforced with soil. Before, during, or after alfalfa cultivation, neither fertilizer nor irrigation was used because alfalfa is a nitrogen-fixing legume and it is sensitive to excessive soil water.

2.4 Sampling and Measurements

2.4.1 Fodder Yield and Forage Quality

Alfalfa was manually harvested (first cutting) at the beginning of flowering (between the first bloom and when 25% of the plants were in bloom), 42 days after first cutting (second cutting), and at the end of senescence (third cutting). In 2020, alfalfa was harvested three times, whereas in 2021, it was harvested twice. Alfalfa was not harvested at the third cutting in 2021 because of weather and growth-related challenges. Alfalfa’s actual fodder yield (AFY) was quantified from the samples collected on ridges and in furrows (including tied-ridge areas) while net fodder yield (NFY) was determined from the samples harvested in furrow areas (excluding tied-ridges) only. The harvested crop was weighed immediately after harvest. Leaf samples were dried at room temperature and ground into fine powder to estimate fodder yield. The Kjeldahl method was used to estimate total nitrogen (total N) (Sadeghpour et al. 2013), and crude protein (CP) was measured by multiplying the nitrogen content by the constant factor of 6.25 to convert nitrogen values to crude protein (CP) (Rodrigues et al. 2018) and determined by AOAC procedures (2005). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were evaluated using heat-stable amylase and VS-acid detergent fiber, respectively, as described by Grzegorczyk et al. (2017). Total digestible nutrients (TDN), relative feed value (RFV), digestible dry matter (DDM), and net energy for lactation (NEl) were calculated following equations adapted from Sadeghpour et al. (2013), and Holman et al. (2016):

$$\mathrm{TDN}=4898+(\left[1.044-\left(0.119\times \mathrm{\% ADF}\right)\right]+\left(89.796\right)$$
(1)
$$\mathrm{RFV}=\mathrm{\% DDM}\times \mathrm{\% DMI}\times 0.775,$$
(2)
$$\mathrm{DDM}=88.9-\left(0.779\times \mathrm{\% ADF};\mathrm{dry matter basis}\right),$$
(3)
$${\mathrm{Ne}}_{1}=\left[1.044-\left(0.0119\times \mathrm{\% ADF}\right)\right]\times 2.205$$
(4)

2.5 Cost–Benefit Analysis

Total costs, revenue from hay sales, and net economic benefit (NEB) were considered in the cost–benefit analysis. The total production costs included seed and biodegradable film costs. The term “income” refers to the amount of money from the sale of fodder. The calculations, however, did not account for fixed costs such as land value, depreciation, or interest on capital. Labor was self-provided at zero cost for ridging, cross ties, weeding, application of biodegradable films, and other sampling operations. The major output considered in this analysis was alfalfa fodder yield. The net economic benefit was calculated as the difference between revenue from fodder yield and input costs (Guo et al. 2019). Total input (TI), total output (TO), and net profit (NP) were calculated using the following equations:

$$\mathrm{TI}=\mathrm{PFI}+\mathrm{SI}$$
(5)
$$\mathrm{TO}=\mathrm{AFY}\times \mathrm{Pr}$$
(6)
$$\mathrm{NP}=\mathrm{TO}-\mathrm{TI}$$
(7)

where Y is the fodder yield; Pr is the local price of alfalfa fodder yield; PFI is the PF input and SI is the seed input.

2.6 Statistical Analysis

All statistical analyses were done with SPSS version 26 statistical software. Before statistical analyses, the data were statistically tested for normality using the Shapiro–Wilk test and variance homogeneity using the Levene test. Thereafter, a two-way analysis of variance (ANOVA) was used to examine variations between treatments. When the treatment effect was found to be significant, Tukey’s pairwise comparison was performed to isolate which treatment means were significantly different at a 5% significance level.

3 Results

3.1 Fodder Yield and Crude Protein

Maize straw biochar addition led to considerably higher yield throughout alfalfa growing seasons in comparison with the no-biochar application (Table 2). The OR and TR significantly (p < 0.05) increased alfalfa fodder yield in biochar-amended plots as compared to the FP. Net fodder yield (NFY) in 2020 ranged from 806 to 4101 kg ha−1 for the no-biochar application, and from 907 to 4461 kg ha−1 for the biochar-amended plots. Annual total net fodder yield increased by 7.96% with biochar addition compared to the no-biochar application. Actual fodder yield (AFY) ranged from 545 to 2089 kg ha−1 for the no-biochar application, and from 552 to 2411 kg ha−1 for the biochar-amended treatment. Total annual yield for the OR and TR without biochar amendment increased by 38.63 and 34.06% compared to the FP, respectively, while for the OR and TR with biochar amendment, total annual fodder yield increased by 41.09 and 44.39%, respectively, compared to the FP. Overall, alfalfa fodder yield increased by 11.12% with biochar addition compared to the no-biochar application during the alfalfa growing season in 2020.

Table 2 Alfalfa fodder yield in ridge-furrow rainwater harvesting with biochar application
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In 2021, alfalfa NFY largely ranged from 3101.87 to 6064.80 kg ha−1 with the no-biochar application, and from 5000 to 9490.73 kg ha−1 for the biochar-added plots (Table 2). Annual total net fodder yield increased by 51.10% with biochar addition compared to the no-biochar application. Alfalfa AFY ranged from 2155.9 to 3620.8 kg ha−1 with the no-biochar application, and from 3874 to 5666.1 kg ha−1 for the biochar-amended treatment. Total actual fodder yields were higher for the TR with no-biochar amendment compared to the counterpart FP treatment. Total annual AFY for the OR and TR increased by 9.80 and 11.62%, respectively, in the no-biochar-treated plots, while in the biochar-amended plots, AFY significantly (p < 0.05) increased by 16.00 and 21.09%, respectively. Overall, biochar application increased alfalfa fodder yield by 52.71% during the alfalfa growing season in 2021.

The OR and TR treatments with biochar increased the annual total CP concentration of alfalfa by 4.72 and 4.44%, respectively, compared with the OR and TR treatments with no-biochar addition. Overall, biochar addition in the FP slightly increased CP of alfalfa by 0.83% in 2020 compared with the FP with no biochar. In 2021, the biochar-amended plots tended to increase CP concentrations of alfalfa more than the no-biochar-treated plots irrespective of the rainwater harvesting method. As in 2020, there were significant variations in CP between the cuts. For first and second cuts, CP concentration of alfalfa significantly (p < 0.05) increased in biochar-amended plots by 10.55 and 8.75%, respectively, compared to the no-biochar-treated plots (Table 3).

Table 3 Seasonal crude protein concentrations and acid detergent fiber in alfalfa fodder yield in 2020 and 2021
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3.2 Acid Detergent Fiber and Neutral Detergent Fiber

In 2020, acid detergent fiber (ADF) concentrations of alfalfa, on average, tended to increase in the biochar-amended plots than in the no-biochar-treated plots (Table 3). The TR treatment with maize straw biochar increased the annual total ADF concentration of alfalfa by 1.62% compared to the TR with the no-biochar application. The acid detergent fiber of alfalfa significantly (p < 0.05) increased by 4.16% in the FP with biochar compared to the FP without biochar. Contrary to the results in 2020, the maize straw biochar-amended plots, on average, marginally increased ADF concentrations of alfalfa compared to no-biochar-treated plots in 2021. Specifically, the FP, OR, and TR with maize straw biochar increased the annual total ADF concentration of alfalfa by 8.40, 9.28, and 14.66%, respectively, compared to the counterpart plots without biochar. In 2020, the neutral detergent fiber (NDF) concentration of alfalfa cultivated on the biochar-amended plots was slightly lower than the no-biochar-added plots for both first and second cuts. However, in 2021, biochar addition to FP and OR significantly (p < 0.05) increased the total annual NDF content of alfalfa cultivated on the FP and OR treatments by 7.46 and 6.04%, respectively, compared to the corresponding plots without biochar.

3.3 Total Digestible Nutrients

Total digestible nutrients (TDN) of alfalfa grown on the no-biochar-treated plots slightly increased in 2020 than in the biochar-amended plots (Table 4). The OR with biochar amendment increased the annual total TDN of alfalfa by 0.60% compared to the no-biochar application. However, in 2021, the TDN of alfalfa cultivated on the biochar-amended plots marginally increased compared with the no-biochar treatment. The TR with biochar amendment increased the annual total TDN of alfalfa by 18.51% compared to the no-biochar application.

Table 4 Seasonal neutral detergent fiber and total digestible nutrients in alfalfa fodder yield in 2020 and 2021
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3.4 Digestible Dry Matter and Net Energy for Lactation

In 2020, the digestible dry matter (DDM) concentrations of alfalfa cultivated on biochar-amended plots generally tended to decrease than that cultivated on the no-biochar-treated plots (Table 5). However, in 2021, a higher DDM of alfalfa was recorded in the biochar-amended plots, particularly towards the end of the growing season compared with the no-biochar-amended plots. Specifically, the DDM of alfalfa cultivated on the TR with biochar amendment increased by 12.75% compared to the counterpart plots with no-biochar addition.

Table 5 Seasonal digestible dry matter of alfalfa fodder yield in 2020 and 2021
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In 2020, when averaged across the two growing seasons investigated, the net energy for lactation (NEl) of alfalfa was slightly increased for the no-biochar-added plots than the biochar-amended plots in the 2020 growing season (Table 6). In terms of rainwater harvesting treatment and biochar application, the OR with maize straw biochar increased NEl of alfalfa by 0.65% compared to the no-biochar application. On the contrary, in 2021, when averaged across the two growing seasons, NEl increased for the biochar-amended plots more than the no-biochar-treated plots. Overall, the TR with biochar increased the annual total net energy for lactation of alfalfa by 20.44% compared with the no-biochar-amended plots.

Table 6 Seasonal net energy for lactation and relative feed value in alfalfa fodder yield in 2020 and 2021
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3.5 Relative Feed Value and Economic Benefit

Results showed that in 2020, irrespective of the rainwater harvesting method, alfalfa relative feed value (RFV) marginally increased for the biochar-treated plots compared to the no-biochar plots (Table 6). The OR and TR with biochar addition increased the annual total RFV of alfalfa by 17.29 and 15.35%, respectively, compared to the counterpart treatment with the no-biochar application. However, in 2021, alfalfa relative feed value tended to increase for the no-biochar-treated plots compared to the biochar-amended plots. The OR and TR with biochar addition decreased the annual total RFV of alfalfa by 24.80 and 7.55%, respectively, compared to the no-biochar application.

Because different rainwater harvesting methods were used during the investigation years, input costs varied. The average input cost for rainwater harvesting methods for the 2-year growing season was OR > TR > FP, with the output values in the order: TR > OR > FP. However, in 2020, the FP with biochar significantly (p < 0.05) increased the cost–benefit ratio (15) compared to 11 for the FP without biochar amendment. In terms of rainwater harvesting methods, the TR had a higher cost–benefit ratio of 37 compared to the OR treatment (22) in 2021 (Table 7).

Table 7 Cost–benefit analysis of flat planting, open-ridging and tied-ridging in 2020 and 2021
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4 Discussion

The study demonstrated that compared to the no-biochar treatment, tied-ridge-furrow rainwater harvesting (TR) with biochar amendment resulted in higher fodder yield during the 2-year alfalfa growing seasons investigated. High alfalfa fodder yield in the biochar-amended soil could be ascribed to biochar’s ability to improve soil health for plant growth. For example, improve soil water retention due to the addition of maize straw biochar might have stimulated the release of nutrients from organic or insoluble forms to the root zone for alfalfa uptake. In other words, the findings suggest that the better soil condition induced by biochar addition might have improved the physical traits and physiological mechanisms of the alfalfa plant, e.g., the development of more resilient root architecture for better water and nutrient uptake under semi-arid conditions characterized by water deficit and poor soil quality. In China’s Loess Plateau, Mak-Mensah et al. (2021) reported that combining biodegradable film with biochar in a ridge-furrow rainwater harvesting system increased maize yield by 23% compared to flat planting (FP). In areas with an annual rainfall total of 549 mm, soil water conservation technologies such as TR and mulching increased maize yield by 65% (Enfors et al. 2011). Conversely, Jensen et al. (2003) found that TR in a maize-cowpea intercropping system in a semi-arid climate was very beneficial when rainfall amounts were 500 to 600 mm. The authors attributed the lower yield recorded for the TR to waterlogging when rainfall amounts were 700 to 900 mm. Biochar applications to agricultural soils have been shown in several studies to significantly improve vegetative growth and crop productivity (E.gs., Liu et al. 2017; lulu et al. 2020; Nguyen et al. 2017; Sarfraz et al. 2020; Vaccari et al. 2011; Zhang et al. 2010, 2012). According to Liu et al. (2013), biochar soil applications of less than 30 t ha−1 increased crop productivity by 11% on average. However, it is important to mention that biochar amendment could lead to a decrease in plant yield due to for example soil toxicity caused by toxic elements and a high percentage of the volatile content of biochar, which reduces nutrient uptake by plants (Peiris et al. 2019).

High-quality fodder is essential for high milk and meat production because the essential nutrient elements for animal daily nutrient requirements depend on the fodder quality (Sandhu et al. 2020). Information on fodder quality is useful for fodder processing and animal feeding (Farooq and Pisante 2019). Crude protein (CP) is generally regarded as a key factor affecting the quality of fodder (Abbasi et al. 2018). Forage quality is also determined by the presence of neutral detergent fiber (NDF) and acid detergent fiber (ADF) (Khatiwada et al. 2021). Results from the present study showed that biochar amendment tended to increase alfalfa CP and ADF concentrations, but slightly decreased NDF concentrations compared with the no-biochar application. According to Sadeghpour et al. (2013), legumes have higher crude protein levels than cereal crops. The authors reported that the concentration of CP is higher in the leaves of legumes than in stems, while the concentrations of ADF and NDF were higher in stems than in the leaves (Santos et al. 2021). However, it is worth noting that drought degrades fodder quality and accelerates the loss of CP (Kamely et al. 2020). The application of ridge-furrow rainwater harvesting with biochar can improve forage quality by reducing alfalfa cell wall component production (Xiao et al. 2016). High fodder digestible dry matter (DDM) improved livestock voluntary intake (feeding), leading to increased nutrient intake. According to Sadeghpour et al. (2013), legumes have a higher intake than non-legumes, and immature forage has a higher intake than mature forage. Unlike DDM yield, results from the present study showed neither maize straw biochar acting solely or in combination with rainwater harvesting methods significantly affected CP, NDF, and ADF of alfalfa during the 2-year experimental period. The lack of significant effect is probably because of differences in response rate between DDM yield and the nutritional quality parameters. Improvement in alfalfa DDM yield is probably associated with soil moisture and nutrient availability in the biochar-amended soil, which might have enhanced chlorophyll fluorescence and the rate of photosynthesis of the alfalfa plant. Habermann et al. (2019) reported that water deficit under ambient temperature reduced photosynthesis rate, stomatal conductance, and maximum rate of carboxylation of Rubisco of forage grass Panicum maximum Jacq.

Regardless of whether alfalfa is used as pasture, hay, or silage, soil fertility has an impact on its quality. A forage farming system that supplies large quantities of adequate quality feed is required for profitable livestock production. However, the biggest challenge in recent years has been how to maximize profit from alfalfa production in semi-arid regions under rain-fed conditions (Mak-Mensah et al. 2022). Results of the present study showed that the highest net income throughout the 2 years of alfalfa cultivation was recorded in the TR with biochar amendment. Findings suggest that the integration of maize straw biochar and ridge-furrow rainwater harvesting method can provide additional benefits by increasing net economic returns to improve the income of farmers. The results are consistent with Zheng et al. (2019), who reported that plastic-mulched ridge plus bare furrow increased net income by 9.8% compared to plastic-mulched ridge plus straw-mulched furrow. Conversely, Mo et al. (2018) reported that mulched ridge-furrow rainwater harvesting increased net income for spring maize in Northwestern China. Furthermore, a study by Li et al. (2012) found that straw-mulched furrows had a higher net income than bare furrows. According to Fox et al. (2005) and Gang et al. (2019), a ridge-furrow rainwater harvesting system is economically viable when combined with mulching and improves soil nutrient management. The findings of the present study have practical relevance and lay a foundation for further research by showing TR with maize straw biochar amendment can be used to ameliorate the yield and quality of forage legumes, which are increasingly becoming key constraints to sustainable livestock production under arid and semi-arid conditions.

5 Conclusions

This study demonstrated that maize straw biochar amendment with a ridge-furrow rainwater harvesting method improved alfalfa fodder yield compared to the no-biochar application and flat planting. However, neither the individual effect of maize straw biochar and ridge-furrow rainwater harvesting methods nor their interactions significantly changed the nutritional quality of alfalfa fodder in terms of crude protein concentration, acid detergent fiber, and neutral detergent fiber contents. The insignificant treatment effect suggests that perhaps, the nutritional parameters of alfalfa responded slowly to the maize straw biochar amendment and/or with rainwater harvesting compared to fodder yield. Therefore, a longer time is probably required before any significant effect is observed. The highest net economic benefit during the 2 years of alfalfa cultivation was recorded in the tied-ridging with biochar amendment. Findings, thus, support the potential of adopting tied-ridging with maize straw biochar in smallholder agriculture to increase alfalfa fodder yield. Further studies investigating the long-term of tied-ridging methods with maize straw biochar amendment on the nutritional quality of alfalfa fodder are recommended to help make firm recommendations for farmers and ensure sustainable livestock production in semi-arid regions.