1. Introduction
Mixed crop-livestock farming systems are the backbone of farmers’ livelihoods in developing countries [
1,
2]. In these systems, the use of crop residues is important for various uses that include soil mulching and livestock feeding [
3]. In cereal-based crop-livestock systems, residues include stover and straw from cereal crops after harvesting the grain. The retention of such residual biomass in crop fields has the potential to improve soil quality by reducing surface runoff, enhancing soil moisture, improving soil structure and potentially suppressing weed growth [
4]. However, mixed crop-livestock farming systems typically use crop residues for livestock feed. This often becomes increasingly important due to the expansion of cropland, low productivity of natural pasture and prevailing livestock feed scarcity [
5]. In the Ethiopian highlands where crop-livestock systems are prevalent, the contribution of straw to the total dry matter fed to livestock ranges from 10% to 70% [
5]. The efficient utilization of straw resources will decrease soil erosion, enhance soil fertility, improve livestock feed supply, decrease pollution, produce biofuels and create jobs in rural societies. In Ethiopia, the barley-livestock farming system is predominantly found in the Central Highlands [
6].
Barley is a major food crop in the highland areas of Ethiopia. The annual main season area covered by barley crop is 0.92 million ha, making up 13% of the total area in the country [
7]. This system includes tree crop production with the emergence of apples and small backyard garden patches. Sheep are the dominant livestock type, with one or two cattle for milk production and equines for the transportation of goods. Livestock is fed mainly on natural pasture, rangelands and barley straw. Agricultural activities and petty trade are important sources of income. Poverty is severe in these systems with deteriorating food security [
6]. The pressure on the barley-livestock farming system is increasing due to the increase in human and livestock populations, income and rate of urbanization [
1]. These challenges tend to intensify land use, which results in the continuous cultivation of cropping lands without fallowing [
8,
9]. Without suitable investments in agricultural land management, this may contribute to land degradation and the deterioration of productivity [
10]. It has been reported that leaving 30% of the straw on crop farm plots decreases soil erosion by up to 80% [
11]. Barley straw is a key resource in mixed crop-livestock systems in the country. Production of 1 metric ton of barley grain is accompanied by 1.2 metric tons of straw. Barley straw has a better nutritive value compared to wheat straw with an average of 90.9% dry matter, 3.8% crude protein and 6 MJ metabolizable energy per kg of dry matter [
12]. However, it is rich in lignocellulose and poor in calcium and phosphorus. Ruminant animals have the ability to utilize barley straw since the ruminal microbes have the ability to ferment cell walls. Caecal microbes in equines also have the ability to digest fiber [
12,
13].
Maize crop residue (i.e., stover) is also used for soil mulching and livestock feeding in Ethiopia. Extension outreach has been shown to encourage farmers to leave more maize stover on crop plots. Farmers who keep more livestock in the household were more likely to use more maize stover for feed and less for soil amendment. Cropping pattern, farm size, agro-ecology and crop residue production affect maize stover use in the mixed farming systems of Ethiopia [
14]. The use of cereal and pulse straw by smallholder farmers in mixed farming systems in Ethiopia has also been studied [
15]. The use of cereal and pulse straw for soil amendment was positively influenced by the education level of the farmer, the distance between the homestead and the cropping plot, extension service, awareness about soil amendment, the cropping plot slope, farmer-to-farmer extension and the stock of crop residue [
15].
Farming at higher slopes without leaving crop residues as mulch can accelerate soil erosion [
16]. One of the impacts of soil erosion is the loss of soil productivity over time. Therefore, the cost of soil erosion can be conceptualized as the monetary value of reduced crop yield(s) resulting from lost soil productivity. In Ethiopia, the estimated cost of soil erosion assuming a soil loss rate of about 20 metric tons per hectare per year is an average of a 0.4% annual decline in value for all cereals [
17]. The impacts of soil erosion are not just for one year but can continue over multiple years until erosion is reduced through soil conservation measures such as mulching of crop residues [
18].
While prior research has identified factors that encourage or discourage Ethiopian farmers from using crop residues for soil conservation, the focus so far has been on pulses, corn grain and other cereals. No studies have evaluated straw use exclusively for barley-livestock systems in Ethiopia. Therefore, this study aims to fill this knowledge gap around the challenges to using the optimal proportion of barley straw as mulch and as livestock feed/bedding by Ethiopian highland farmers. The objectives of our research are to (1) determine the relative values of use of barley straw as mulch for reduced erosion compared to use as livestock feed/bedding and (2) identify the characteristics of farmers more or less likely to use barley straw as mulch for soil conservation and as feed for livestock feeding. This can help agricultural extension and other stakeholders design more targeted approaches to encourage farmers to use the optimal proportion of barley straw as mulch and as livestock feeding.
4. Discussion
Soil erosion is a key limitation to soil fertility and thus crop production in developing countries. Up to 30% of soil cover by crop residue mulch can reduce soil erosion by 80% [
23]. Half of the households in the study did not leave any barley straw for soil mulch. Only 14% adhered to the soil mulching recommendations issued by extension services. In line with our results, previous studies reported on farmers’ low interest in applying crop residue soil amendment [
14,
15]. Thus soil fertility and biomass productivity of crop plots can be prone to gradual deterioration from soil erosion. To avoid that, farmers should be encouraged to mulch adequate amounts of barley straw to preserve the fertility of their cropping plots.
One tropical livestock unit requires roughly 7.5 kg of dry matter daily [
27]. In the current study, the households thus required a total of 13.1 metric tons of dry matter to feed their livestock. However, barley straw production per household was only 7.1 metric tons of dry matter. If barley straw is the main forage available for livestock, the demand for barley straw for both livestock production and soil conservation is far higher than the production, especially in the case of deterioration in biomass and nutritive value of natural pastures. The strong correlation between the use of barley straw for livestock feeding and soil mulch in the current study confirms this high pressure. The high pressure on crop residues for livestock feeding and soil mulching was reported for maize-livestock systems in Ethiopia [
4,
14]. Given the limited resources of most farmers in the region, optimization of the use of barley straw for soil mulch and livestock feeding is warranted.
4.1. Soil Erosion Loss
The overall soil loss in the study area was 46.7 metric tons (t)/hectare (ha)/year (yr), which is a severe soil loss area according to [
28]. Our soil erosion estimates were lower than the range of 84 to 300 t/ha/yr reported by some studies [
29,
30,
31,
32,
33]. They were consistent with soil losses of 42 to 47.3 t/ha/yr reported by others [
28,
34,
35,
36], yet higher than other measurements of 10 to 31 t/ha/yr [
17,
37,
38,
39,
40,
41,
42,
43,
44]. This may be due to the intensification of agricultural production in the study area. The mean annual soil loss for those farmers that did not use barley straw for soil mulching in the study area was 49.2 t/ha/yr, which is higher than the overall soil loss, whereas the mean annual soil loss for farmers using barley straw as mulch was 31.5 t/ha/yr. This means that using barley straw for soil mulch is associated with a reduction in soil loss of 17.7 t/ha/yr, or 36%, compared to not using barley straw for mulching in our study. Factors such as heavy concentrated rainfall, steep topography, deforestation, over-grazing, use of marginal land and agricultural intensification can accelerate soil erosion in mixed crop-livestock farming systems in Ethiopia [
27,
45].
In the first scenario, by considering the short-term impact of soil mulch, most farmers would prefer using barley straw for feeding rather than mulching, which is the case of our study. If the farmers left 30% of straw yield on the plot, they would indirectly lose USD 35.81 (Etb 1479)/ha/yr, or 30%, of the total value of barley straw when it is used for feeding since the estimated value of barley straw when used for feeding is USD 119.37 (Etb 4930). That amount is much higher than the cost reduction of USD 4.55 (Etb 188)/ha/yr from using barley straw for soil mulch. That figure is valid when only the present value is considered but when the future value is considered, the value of using barley straw for mulch would become USD 70.56 (Etb 2914).
In the second scenario, the long-term effect of using barley straw for mulching was not valued by the farmers in the study area. This is clearly because the farmers are not fully aware of the long-term cost of soil deterioration on grain yield and straw yield.
4.2. Empirical Analysis
Female-headed households were more likely to mulch less barley straw in the cropping land. In addition to that, the increasing education of the household head lowered the probability of optimal mulching. This is in agreement with the authors of [
14,
15] who found an effect of household socioeconomic characters on crop residue use in the mixed farming systems.
4.2.1. Distance
According to a previous study [
46], the ability of farmers to carry materials to and from the cropping land affects the probability of optimal mulching. Farmers economize their labor by using barley straw as feed/bedding only when the fields are close enough. Our results deviate from prior research that has reported that farmers mulched crop fields less for fields that were farther from their homesteads [
4,
14,
15] or shown that there is no significant effect of distance on soil mulching [
47]. Unlike past studies, our results suggest that soil erosion may be more aggravated closer to farm homesteads since soil mulching there is less compared to more remote fields. Such an imbalance in the distribution of crop residues highlights the need for more even spreading of barley straw residues in the Ethiopian highlands for better carbon cycling and soil conservation. The farms that are closer to the homestead thus tend to have less barley straw as soil mulch and are, therefore, more prone to erosion. Farmers with more remote plots tend to leave excess amounts of barley straw as mulch, which is a wastage of biomass.
4.2.2. Role of Extension
Our results highlight the significance of agricultural extension in encouraging the use of barley straw as mulch in mixed farming systems. Similar results were found by other researchers [
14,
15,
19,
48,
49,
50,
51,
52] on the importance of extension when it comes to farmer adoption of conservative agricultural practices. Extension outreach can also help encourage more efficient use of equines to transport crops and crop residues. Our current study shows that the farmers who have more equines, which is the only way to efficiently transport farm products in Ethiopia, were better at optimizing the use of barley straw for soil mulch.
Extension workers thus could improve the profile of barley straw use by encouraging the culture of equine exchange within mixed farming systems. This would help the farmers with remote cropping plots to carry more straw to the household to feed the livestock and leave the optimal amount on the plot as soil mulch. Plot slope did not influence farmers’ intention to increase the use of barley straw as soil mulch. This is in contrast with other studies [
14,
15], which found a positive association between plot slope and the use of crop residues for soil mulch. Steeply sloped plots in barley-livestock systems in Ethiopia are prone to severe soil erosion as they do not receive optimal amounts of straw mulch. Households with fields on greater slopes need more extension service outreach on the importance of soil mulching when it comes to reducing soil erosion. An efficient extension approach to optimizing the use of barley straw should consider the differences in household characteristics. Households with steep plots close to the homestead should be warned that they may be leaving too much barley straw. Households with more remote plots or that have more equines should be made aware by the extension service that they might be leaving too much barley straw in the field.
Currently, extension services discourage farmers from using more than 15% of their barley straw for soil mulching. This could be due to the limited feed options in these systems. The mission of the formal extension service to encourage optimal soil mulching could be facilitated by improving the feed supply. The current study indicates that higher barley straw biomass production may allow for the enhanced use of barley straw for soil mulch. This is in line with previous studies [
14,
15,
17], which reported that easing the pressure on crop residues, by providing new feed resources to livestock, would encourage farmers to leave more crop residues in fields; therefore, improving barley straw biomass in terms of yield. Improving feed nutritive value through genetic selection may have important long-term effects of increased mulching as a strategy against soil erosion. In addition, other management practices that might improve barley straw biomass utilization include optimizing animal bedding, mulching of the soil with non-edible residues and optimal timing of harvest to avoid the decrease in the nutritive value of straw as a result of over-maturity [
53]. Most Ethiopian households store crop residues in exposed heaps [
15], which might lead to heavy loss in biomass and nutritive value due to feed spoilage. Consequently, improved crop residue storage may improve the nutritive value of straw, thus avoiding wastage. This may result in an increased supply of straw for soil mulching and livestock feeding on farms. However, future research considering the feasibility of these solutions is important and would enhance the design of efficient biomass utilization and appropriate intensification strategies.
5. Conclusions
There is pressure to use barley straw as livestock feed in barley-livestock mixed farming systems in Ethiopia due to low straw yield, which is further constrained by competing uses and low nutritive value. Generally, farmers tended to use barley straw for livestock feeding rather than for soil mulching. This is because farmers allocate barley straw to different uses based on the short-term benefits. Farming land in barley-livestock farming systems is, therefore, expected to deteriorate, leading to a decrease in grain and straw production.
Agricultural extension in the Ethiopian highlands should focus more on the long-term benefit of soil mulching to preserve soil health. Formal extension outreach had a statistically significant effect on farmers’ greater use of barley straw as soil mulch. Interventions, training and extension services promoting context-specific crop residue management for both agriculture and livestock components are imperative to facilitate the optimal utilization of barley straw in Ethiopian mixed farming systems.
Introducing new feed resources in barley-livestock farming systems would increase the feed supply to livestock. This would increase the use of barley straw as soil mulch. Improving straw yield besides grain yield via breeding would increase the supply of straw to not only meet livestock feed needs but also provide enough crop residues for soil mulching. More studies on decreasing post-harvest loss in barley straw should be undertaken. In order to discourage the excessive application of barley straw as mulch, agricultural extension workers should focus on farmers with remote crop fields and with limited access to equines. This can be part of a process that could evenly distribute and effectively utilize crop residues in mixed farming systems in Ethiopia as well as other regions of the world.