Received: 5 June 2019 Revised: 7 January 2020 Accepted: 13 January 2020 DOI: 10.1002/ldr.3558 RESEARCH ARTICLE Live barriers and associated organic amendments mitigate land degradation and improve crop productivity in hillside agricultural systems of the Ecuadorian Andes Mark Caulfield1,2,3 | Jeroen C. J. Groot1 | Stephen Sherwood4 Pablo Tittonell6,7,8 | Pedro Oyarzun2 Ross Mary Borja2 1 Farming Systems Ecology, Wageningen University and Research, Wageningen, The Netherlands | Steven J. Fonte3 | | Sam Dumble5 | Abstract Land degradation caused by erosion and nutrient depletion in the Andes poses 2 Research and Development, Fundación EkoRural, Quito, Ecuador 3 Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO, USA 4 Knowledge Technology and Innovation, Wageningen University & Research, Wageningen, The Netherlands serious existential threats to small-scale farming. Although the potential of hedgerows to decrease water erosion is well recognised, their potential dual-use as a source of organic amendments to supplement farmer inputs is much less studied. The objective of this investigation was therefore to explore locally developed options for hedgerows that address these twin challenges. Experimental plots were installed to assess water erosion control by hedgerows and the effect of organic amendments 5 Statistics for Sustainable Development, Reading, UK harvested from the hedgerows on soil productivity, soil moisture, and soil fertility 6 over the course of 2 years and three crop cycles (two of barley and one of rye). The Agroecology, Environment and Systems Group, Instituto de Investigaciones Forestales y Agropecuarias de Bariloche (IFAB), San Carlos de Bariloche, Río Negro, Argentina 7 Agroécologie et Intensification Durable (AïDA), Centre de coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), Université de Montpellier, Montpellier, France 8 Groningen Institute of Evolutionary Life Sciences, Groningen University, Groningen, The Netherlands Correspondence Mark Caulfield, Farming Systems Ecology, Wageningen University and Research, Wageningen, 6700, The Netherlands. Email: markcaulfield11@gmail.com Funding information McKnight Foundation experiment was conducted in two sites within the community at distinct elevations and associated biophysical contexts. At each site, four treatments were established, comparing a control treatment versus three types of hedgerows: (a) Andean alder, (b) canary grass strips, and (c) mixed canary grass and Andean alder. Results demonstrated that hedgerows and associated organic inputs comprised canary grass, and mixed canary grass and Andean alder reduced water erosion by 50–60% and increased biomass production by up to 1.1 Mg ha−1 and grain yield by up to 0.5 Mg ha−1. We conclude that although hedgerows are unlikely to produce sufficient quantities of organic resources to satisfy all nutrient input requirements, their potential to decrease erosion and supplement existing organic matter inputs indicates that they should be strongly considered as an option for improved agricultural management within this and similar resource constrained contexts. KEYWORDS Andean alder, Andes, canary grass, Ecuador, erosion, nutrient depletion This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. © 2020 The Authors. Land Degradation & Development published by John Wiley & Sons Ltd Land Degrad Dev. 2020;1–12. wileyonlinelibrary.com/journal/ldr 1 2 1 CAULFIELD ET AL. | I N T RO DU CT I O N farmers are unable to replace the degraded SOM and nutrients exported in the harvest of crops (Bahr et al., 2014; De Koning et al., Small-scale farming in the Andean highlands often takes place in small 1997; Vanek & Drinkwater, 2013). Not only are the nutrient balances indigenous communities with each family usually managing a number of the macronutrients nitrogen (N), phosphorus (P), and potassium of fields dispersed across diverse topography and microclimates (K) often observed to be negative in these farming systems, but SOM (Buytaert et al., 2007; Zehetner & Miller, 2006). Mixed crop-livestock has also been observed to decrease as a result of agricultural manage- farming systems tend to dominate regions below 3,800 m above sea ment (due to accelerated degradation of SOM as a result of increased level (masl). Potatoes (Solanum spp.) have long been the staple crop in aeration of soils through ploughing). In a study from the southern the region, although other important crops include cereals, legumes, Ecuadorian Andes, SOM levels under crop lands were observed to be and native tubers. Most farming families own at least one or two 15% lower than those of nearby forest sites, which was attributed to heads of cattle (often used for draught power), whereas sheep, land-use conversion and unsustainable soil management (Bahr et al., chickens, and guinea pigs are also important livestock. Critically, 2014). SOM plays a critical role in maintaining soil health, supporting in addition to the constraints caused by the biophysical environment biological activity and diversity (Moore et al., 2004), and regulating soil (climate and topography), many farmers have restricted access to processes linked to agroecosystem functions such as nutrient cycling, basic agricultural inputs such as organic amendments, fertilizers, pesti- plant growth, soil aggregation (structure), and water storage (Barrios, cides, and irrigation (Fonte et al., 2012). 2007; Bronick & Lal, 2005; Lavelle et al., 2006). Land degradation caused by erosion, soil organic matter (SOM) A major reason for the pervasive trend of negative nutrient bal- depletion, and negative nutrient balances represents a pervasive ances within the rural Andes is that the smallholder farmers generally long-term threat to these small-scale farming systems (Vanek et al., have limited access to agricultural inputs, due to both a low financial 2016; Vanek & Drinkwater, 2013). The steep slopes of these moun- resource base to invest in agricultural inputs and their remoteness tainous agroecosystems mean that the landscapes are inherently from population centres (Fonte et al., 2012). Although overall inputs susceptible to erosion. For example, a study in the southern Ecua- are low, there appears to be great variability in the spatial allocation dorian Andes found sediment loss in rural landscapes to range of the available nutrient and organic matter inputs. For example, from 0.26 to 151 Mg ha−1 yr−1 with an overall average soil loss of farmers commonly allocate fewer agricultural inputs to fields that are 22 Mg ha−1 yr−1 (Molina et al., 2008). Another study in a water- further from their homestead or that are perceived to be less fertile shed located close to the site considered here, found similar ero- (Caulfield et al., submitted; Vanek & Drinkwater, 2013). The fact that sion losses, averaging 27 Mg ha near fields can often receive high quantities of inputs relative to outer −1 yr −1 , with estimates in some sites as high as 150 Mg ha−1 yr−1 (Henry et al., 2013). fields suggests that the negative nutrient balances (in the outer fields) Soil degradation, however, not only involves the loss of important are not simply a result of constrained resources but likely result from soil nutrients, but also the loss of soil biological activity and associated labour and logistical limitations as well. This could indicate that alter- structure, which play a critical role in soil water capture and retention, native, in situ mechanisms for addressing the negative nutrient bal- soil erosion, nutrient recycling, root penetration, and the overall pro- ances of distant fields are required (Caulfield et al., submitted; Fonte ductivity of agricultural lands (Bronick & Lal, 2005; Lal, 2001). et al., 2012). Although the loss of soil fertility can be partly compensated for One of the criticisms levelled at physical soil conservation struc- through the addition of fertilizers, the rehabilitation of overall soil tures, such as terraces, has been that they provide poor immediate health and productivity is a much slower process (Fonte et al., 2012). economic returns given their focus on soil conservation and therefore In response to the challenges posed by erosion, farmers in the often are not easily adopted by farmers (Erenstein, 2003; Post- Andes have long employed soil conservation structures such as ter- humus & De Graaff, 2005). Organic amendments, green manures, and races, both bench terraces, which are constructed by farmers, and mulches on the other hand, given the right conditions, appear to show slow-forming terraces, which develop overtime as soil accumulates some important potential both in terms of improving soil conservation behind vegetative barriers such as grasses, shrubs, and trees (Dercon and agricultural productivity (Babalola et al., 2007; Félix et al., 2018). et al., 2003). Although bench terraces are becoming less common Moreover, such techniques may be applied in situ, providing impor- nowadays due to their higher labour requirements for maintenance, tant sources for nutrient and organic matter inputs in areas that may slow-forming terraces are still frequently used by farmers in the Ecua- be less accessible to farmers such as distant fields. dorian highlands (Dercon et al., 2003). Slow-forming terraces have Some promising findings in this regard have been observed with been shown to be effective (e.g., Kagabo et al., 2013; Sánchez-Bernal vetiver grass (Vetiveria nigritana). In two similar studies, one under- et al., 2013; Tesfaye et al., 2018), but these techniques can also taken in the Central Highlands of Kenya, the other in Southern Nige- accentuate spatial variability in soil fertility, where the fertile topsoils ria, mulching with vetiver grass was shown to both increase yields and from the upper part of the field accumulate at the lower part of the decrease run-off (Babalola et al., 2007; Okeyo et al., 2014). Another field leaving strong field-level fertility gradients (Dercon et al., 2006). recent study in Burkina Faso investigated the harvesting of natural In addition to the inherent erosion processes of these mountain- resources in situ (ramial wood from Piliostigma reticulatum shrubs) as ous landscapes, land degradation in the rural Andes is also being soil amendments (Félix et al., 2018). They found that although the driven by negative SOM and nutrient balances, where small-scale ramial wood chips did not contain sufficient nutrients to replace those 3 CAULFIELD ET AL. lost from crop production, soil organic carbon (SOC) increased signifi- quality and crop productivity, a prerequisite for farmers to adopt cantly, and biomass and grain yields were higher in the high ramial these soil conservation techniques more widely. wood treatments compared with the control with no organic inputs. Finally, it is worth noting that leaf litter from N-fixing Alder trees (Alnus rubra Bong.),which are common in many parts of the high 2 M A T E R I A L S A N D M ET H O D S | Andes, can provide significant amounts of N to the soil and to support crop growth (Swanston & Myrold, 1997; Visscher, 2018). 2.1 | Study site description Although some notable research has been conducted into the effects of slow-forming terraces (e.g., Dercon et al., 2003; Kagabo et al., The research took place from July 2015 to July 2017 in the rural indige- 2013; Sánchez-Bernal et al., 2013), more research is required in differ- nous community of Naubug, Flores Parish, Chimborazo Province, Ecua- ent socioecological contexts to assess their efficacy in decreasing water dor (1
510 24.00 S, 78
390 15.60 W), with around 640 inhabitants erosion. More critically, however, the sparse research into the potential (120 families). Annual precipitation is approximately 400–500 mm, with of hedgerows to act as supplemental sources of organic amendments most rain falling between November and May (wet season) and a drier, appears to be an important gap in the scientific literature. This dual-use windier period from June to October (dry season). Average annual tem- potential for hedgerows is particularly important to explore as farmers peratures range between 12
and 16
C, with minimum temperatures do not easily adopt improved land management techniques that do not rarely falling below zero and maximum temperatures rarely rising above provide immediate returns on investment(Erenstein, 2003; Post- 22
C. The community is characterised by steep topography (slopes are humus & De Graaff, 2005). By exploring the potential of hedgerows to typically between 10
and 25
) with elevation ranging from 2,850 to act as sources of organic amendments, such barriers to adoption may 3,600 masl (Gobierno Autónomo Descentralizado Parroquial Rural de be overcome because this may offer a relatively short-term benefit for Flores, 2015). The long-term pedogenic processes of the region have increased productivity. been dominated by volcanic activity with pyroclastic deposits giving rise The objective of this research was therefore to work with an to the formation of volcanic (Andosol) soils rich in SOM, especially at the indigenous community in the Ecuadorian Andes to explore locally higher elevations (De Noni et al., 2001; Zehetner & Miller, 2006b). At developed options for dual-use hedgerows to address the twin lower elevations and in areas that have experienced high erosion the challenges of erosion and nutrient depletion in rainfed small-scale subsoils are exposed revealing thick layers of compacted volcanic ash farming systems. Based on consultation with community members, known locally as ‘cangahua.’ The soils of these areas are roughly classi- subsequent laboratory analyses of vegetative material present in fied as entisols or inceptisols. the community, and according to the decision tree developed by As a result of these soil patterns and the climate gradients associated Palm et al. (2001), the species identified for inclusion in the hedge- with the elevation range, local farmers have delineated the landscape into rows were Andean alder and canary grass (Phalaris tuberosa; three agricultural ‘management zones,’ broadly defined along elevation Figure 1). lines—the upper, middle, and lower zones. The lower zone has sandier Specifically, we studied the influence of hedgerow barriers and soils with a low nutrient content, coupled with a climate that is associated organic matter amendments on soil water erosion, topsoil characterised by a lower precipitation:evapotranspiration ratio. The upper moisture content, SOC and nutrient stocks, as well as on crop produc- and middle zones have soils higher in clay and nutrients and a cooler, tion in two different locations within the same landscape. As per more moist climate (Caulfield et al., submitted). Soil texture in the field Kagabo et al. (2013), we hypothesised that the hedgerows would considered here in the upper zone comprised 26% sand and 16% clay, significantly reduce water erosion in different biophysical contexts whereas soil in the field of the lower zone had 34% sand and 12% clay. within the same community. Moreover, based on Babalola et al. The main sources of income in Naubug include the sale of very mod- (2007), Félix et al. (2018), Okeyo et al. (2014), and Visscher (2018), we est amounts of agricultural products to local markets, monthly govern- postulated that incorporating organic amendments from these hedge- ment subsidies, and remittances from temporary and permanent migrant row species into the soil would have beneficial impacts on both soil family members. Limited financial resources mean access to agricultural F I G U R E 1 Photos of existing hedgerows in the community used to control erosion. Andean alder (Alnus acuminata) trees interspersed with canary grass (Phalaris tuberosa) hedgerow (left); canary grass strip (right) 4 CAULFIELD ET AL. inputs and markets are also heavily restricted. Land is privately owned, established at the bottom of the plots, located within the experimental and most farmers own between 12 and 18 fields dispersed throughout plot area, just uphill from the erosion trenches with six A. acuminata the landscape amounting to between 2 and 3 ha of land managed by saplings (1-cm diameter) planted in the pure alder hedgerows and three each farming family. There is no access to irrigation water. saplings in the mixed hedgerows. Canary grass tussocks (30 cm in height and 20–30 cm in width) were planted adjacent to one another 8 months before beginning the first crop cycle and data measurements (Figure 2). 2.2 | Experimental design Canary grass was cut every 3 months to a height of 20–30 cm. To measure erosion, the run-off and sediment were emptied from the sediment A workshop was held with community members to identify existing capture trenches after each significant precipitation event using a plastic and alternative improved agricultural techniques that have the poten- jug. The run-off was filtered twice through cotton cloth. The remaining tial to decrease land degradation and also ‘aggrade’ (improve) soils sediment was then dried in an oven at 60
C until no weight change was (Figure 1). Dual-use hedgerows were identified as having potential to observed and the weight recorded. Measurements were taken from July reduce water erosion and provide sources of soil organic amendments 2015 until July 2017. to supplement the small amounts of organic resources currently avail- To understand the effects of the organic amendments harvested able to community members. Three types of hedgerows were selected from hedgerows, 40 kg of fresh grass and/or alder leave residues to meet these objectives: (a) grass strips of canary grass (P. tuberosa), (equivalent of around 16.5 Mg ha−1 fresh weight, harvested from (b) ‘native’ tree hedgerows of Andean alder (A. acuminata), and nearby the plots) were applied to the soils in each plot and incorporated (c) mixed hedgerows of both Andean alder and canary grass. A control 2 weeks before the planting of each crop with equal weight of seed. with no live barrier or organic inputs was also included in the experi- The organic amendments incorporated into the soils reflected the mental design. Subsamples of these organic resources were assessed hedgerow composition of the experimental plots such that the experi- for nutrient content and quality (Table 1) at the laboratory of the mental plots with Andean alder received 40 kg of Andean alder leaves, Ecuadorian National Institute for Agricultural Research. the grass strips received 40 kg of canary grass amendments, and the 2 Twelve closed experimental plots (8 × 3 m ) were installed in each upper and lower zones of the landscape (24 plots total), representing the mixed hedgerows treatment received 20 kg each of canary grass and Andean alder leaves. The control treatment received no inputs. greatest contrasting biophysical contexts found within the landscape. At harvest, the total fresh crop biomass of each plot was weighed These plots were oriented vertically and placed side-by-side along the and recorded. A subsample of 100 tillers was then collected, weighed, contour. Plots in the upper zone were located at approximately 3,600 and dried in an oven at 60
C until no change in weight was recorded. masl and had a slope of around 20 , whereas plots in the lower zone The subsample was then separated into component parts (grain and were at around 3,100 masl and with a slope of around 13
(with minimal stalk) and reweighed. The first experimental crop cycle was planted variation in slope between plots ±1
). Given the objective of this research with barley (Hordeum vulgare) in October 2015 and harvested in was to compare the different hedgerow treatments in controlling erosion March 2016 (subsequently referred to as Barley 2016); the second processes, as well as improving soil fertility and productivity through crop cycle was planted with rye (Secale cereale) in September 2016 associated organic amendments, a relatively small, closed experimental and harvested in January 2017 (subsequently referred to as Rye plot design was selected, as such plot designs enable easy comparison 2016); and the last crop cycle was planted with barley in February among different responses at the same spatial scale, with exactly the 2017 and harvested in July 2017 (subsequently referred to as Barley same size of drainage area (Boix-Fayos et al., 2006). Furthermore, plot 2017). In the lower zone, this last crop failed, and therefore, no data size was chosen to allow for significant overland flow, although also were collected for Barley 2017 in this zone.
ensuring a similar slope across plots and an acceptable amount of area by To measure the effect of the organic amendments on soil moisture, participating farmers. In each of the zones, the four treatments (three we used a soil moisture probe with a SM300 sensor (https://en. hedgerow treatments and the control) were assigned randomly to repli- eijkelkamp.com/products/field-measurement-equipment/soil-moisture- cate blocks. The tops and the sides of each experimental plot were measuring-system-with-sm300-sensor.html). fenced off using corrugated zinc-metal sheets inserted vertically into the taken every 2 weeks from July 2015 to July 2017 at three different soil to a depth of 45 cm and supported by wooden stakes. At the bottom points in each plot, 1.5 m in from the side and 2, 4, and 6 m down from of each plot, an erosion trench was dug and lined with thick plastic sheet the top of the experimental plot, at a depth of 10 cm. An average of into which the run-off and sediment would collect. The hedgerows were each of these measurements per plot was used for data analysis. Measurements were T A B L E 1 Moisture content and chemical composition of the organic amendments applied to the experimental plots (phenols, lignin C, N, P, K, Ca, and Mg presented as % of dry matter) Property (%) Organic amendment Water Phenols Lignin C N P K Ca Mg Canary grass 74.95 1.04 6.58 51.10 4.23 0.25 3.18 0.34 0.32 Andean alder leaves 59.17 3.65 11.67 48.98 3.17 0.2 1.18 0.86 0.36 5 CAULFIELD ET AL. F I G U R E 2 (a) Photo showing experimental plots and sediment capture trenches located in the lower agricultural management zone. Near: Andean alder hedgerow treatment; Left: canary grass strip treatment. (b) Schematic representation of the experimental plot dimensions and components To assess overall impacts of the organic amendments on the control treatment. Although the Andean alder treatment exhibited chemical composition of the soils, composite soil samples were greater erosion than the canary grass and mixed treatments, it also taken from each experimental plot at the beginning of the study, in displayed significantly less erosion than the control treatment July 2015, and following the harvest of the last crop cycle, in July (Figure 3, Table S1). 2017. Twenty subsamples (0–20 cm) were combined to create a composite sample of around 2 kg. All soil samples were air-dried and transported to the laboratory of the Ecuadorian National Insti- 3.2 | Biomass production and yield tute for Agricultural Research for analysis of SOC (Walkley & Black, 1934), total N (Kjeldahl, 1883), as well as available P (Olsen The statistical analyses revealed significant differences among treat- method; Olsen et al., 1954), and exchangeable K, Ca, and Mg (modi- ments for biomass production and grain yield (Table S2). The canary fied Olsen method, pH 8.5). Plant and other organic debris were grass and the mixed canary grass and Andean alder treatments dis- removed, and soil was ground and sieved (2 mm) before chemical played significantly greater crop biomass production and grain yield analysis. Net changes in soil chemical properties were then calcu- compared with the control treatment for all crop cycles (Figure 4). The lated for each plot by subtracting the pre-experiment soil values Andean alder treatment did not display improved biomass production from the postexperiment soil chemical composition results. or grain yield compared with the control (Figure 4). 2.3 3.3 | Statistical analysis | Soil moisture A repeated measures analysis of variance was applied with fixed effects Soil moisture measurements displayed significant differences among for location (zone) and for each year measured (2015/2016 and treatments. A significant interaction between treatments and date of 2016/2017) with random block effects to test for differences in erosion measurements (time) was also observed (Table S3). Soil moisture among the four experimental treatments. A Fisher's least significant dif- under the control treatment was significantly lower than for the treat- ference test was applied to test which treatments were different at 5% ments receiving amendments (hedgerows). The canary grass treat- significance level. The same structure of statistical model was also ment exhibited the greatest soil moisture content among treatments applied to test for differences among treatments for biomass produc- (Figure 5). In general, soil moisture tended to remain higher under the tion, grain yield, soil moisture, and net changes in soil chemical proper- treatments receiving organic amendments compared with the control ties (SOC, total N, available P, exchangeable K, Ma, and Ca) from the condition throughout the research period (Figure 6). It is noteworthy, start of the trial to after the last harvest. All analyses were carried out that although during the first extensive period of low soil moisture within the RSTUDIO environment version 1.2.1335 for R (version levels (around January 2016), differences between treatments did not 3.6.1) using ade4, agricolae, lmerTest, and emmeans packages. appear to be large; in the second period of lower soil moisture levels (around August–September 2016), differences between treatments were more pronounced (Figure 6). 3 3.1 RESULTS | | Erosion 3.4 | Net changes in soil chemical fertility Erosion was significantly lower in the canary grass and mixed Soil chemical analyses of the experimental plots taken before canary grass and Andean alder treatments compared with the the first crop cycle (Barley 2016) and after the last crop cycle 6 CAULFIELD ET AL. F I G U R E 3 Annual soil erosion by treatment (control, Andean alder, mixed canary grass, and Andean alder and canary grass hedgerows). Error bars indicate standard error of the mean; letters above bars indicate results from Fisher's least significant difference test, such that treatments with different letters have significantly different means F I G U R E 4 Production of total dry crop biomass (a) and grain yield (b) by treatment (control, Andean alder, mixed canary grass, and Andean alder and canary grass amendments). Error bars indicate standard error; letters above bars indicate results from Fisher's least significant difference test, such that treatments with different letters have significantly different means (Barley 2017; Table S4) revealed significant increases in SOC, as well compared with the control condition. It is noteworthy that total N, and exchangeable K in the grass treatment compared with although not always significant, the canary grass amendments the control treatment. The mixed amendments and Andean alder treatment displayed the highest net increases in all soil chemical treatments both displayed significant increases in exchangeable K properties except exchangeable Ca and Mg (Table 2). 7 CAULFIELD ET AL. F I G U R E 5 Mean soil moisture content measurements by treatment (control, Andean alder, mixed canary grass and Andean alder, and canary grass amendments). Error bars indicate standard error of the mean; letters above bars indicate results from Fisher's least significant difference test, such that treatments with different letters have significantly different means F I G U R E 6 Timeline displaying mean soil moisture content measurements by treatment (control, Andean alder, mixed canary grass and Andean alder, and canary grass amendments), with key dates indicated T A B L E 2 Mean net changesa and standard errors (in parentheses) to soil chemical properties measured before (July 2015) and after the research period (July 2017) presented by treatment (control, Andean alder, mixed canary grass and Andean alder, and canary grass) Treatment Soil chemical property Control Alder Mixed Grass SOC (%) 0.24b (0.06) 0.34ab (0.06) 0.37ab (0.06) 0.46a (0.06) Total N (%) 0.03b (0.03) 0.03ab (0.03) 0.06ab (0.03) 0.06a (0.03) Available P (mg kg ) 4.76a (1.11) 4.90a (1.13) 4.90a (1.13) 5.59a (1.13) Exchangeable K (cmol kg−1) 0.05d (0.04) 0.21c (0.04) 0.34b (0.04) 0.43a (0.04) −1 Exchangeable Ca (cmol kg ) 1.58a (0.70) 2.55a (0.70) 2.57a (0.70) 1.58a (0.70) Exchangeable Mg (cmol kg−1) −0.42a (0.08) −0.42a (0.08) −0.44a (0.08) −0.49a (0.08) −1 Note: Fisher's least significant difference test results are presented to the right of the mean net changes, with different letters different at the 5% significance level. a Net changes are calculated based on the soil chemical component measurement before starting the experimental treatments and after the last experimental treatment was conducted (Barley, 2017). 8 4 CAULFIELD ET AL. | DISCUSSION It is therefore important to use caution in extrapolating erosion data from plot level studies, such as this one, to the landscape scale 4.1 | fields Hedgerows impacts on erosion in agricultural (Boix-Fayos et al., 2006). Instead, the erosion measurements in this study should be taken as a relative measure of the potential for different types of hedgerows to control erosion in this particular context. The hedgerows comprised canary grass and canary grass combined Further research is necessary to assess the hedgerows' potential with Andean alder displayed significant potential to decrease soil for controlling other types of erosion processes such as gully erosion water erosion (Figure 3). Canary grass strips reduced soil loss by about and erosion induced by animal-powered tillage. Tillage erosion has 60%, whereas the mixed canary grass and Andean alder hedgerow been shown to be particularly important in the region of study with reduced soil loss by about 50% compared with the control. Our results soil loss figures in the southern Ecuadorian Andes reported to be corroborate past research demonstrating that grass strips can be between 30 and 186 Mg ha−1 yr−1 (Dercon et al., 2007). With regard highly effective in controlling erosion (e.g., Donjadee et al., 2010; to this type of erosion, another study conducted in Ecuador suggests Tesfaye et al., 2018; Wu et al., 2010; Xiao et al., 2012). that grass hedgerows similar to the ones assessed here do have the Perhaps more surprisingly, our results exhibited considerably potential to reduce erosion, through the development of slow-forming less erosion than observed in other studies from the region. For terraces (Dercon et al., 2003). However, it should be pointed out that example, Henry et al. (2013) using 137Cs to estimate erosion at land- the development of such terraces cause important within field spatial scape level found average erosion rates of 27 Mg ha−1 yr−1, whereas variability in fertility, which implies the need for enhanced fertility Molina et al. (2008) using direct measurements of accumulated sedi- management practices (Dercon et al., 2003). ment at ‘checkdams’ at the catchment level found similarly high ero- It has been suggested that climate change will expose Andean sion rates of 22 Mg ha−1 yr−1. Erosion found in this study barely agroecosystems to more extreme weather events, which in turn could reached levels above 1 Mg ha−1 yr−1 in the control condition, which potentially increase water erosion rates (Fonte et al., 2012; Kohler is similar to the estimated global average rate of soil formation et al., 2014). In this event, erosion control techniques such as those (Pimentel, 2006). assessed in this study may be important for building greater resilience Part of the reason why the levels of erosion observed in this to the effects of climate change. Furthermore, notwithstanding the study may have been low could be due to the fact that erosion was low levels of erosion measured here at the agricultural plot level, it is assessed at the plot level rather than at the landscape or catchment clear that at the landscape level and under other land uses, the region scale where greater slope lengths can contribute substantially to the is highly susceptible to erosion given findings from other studies erosive energy of overland flow (Kearney et al., 2017b), and water (Harden, 2001; Harden, 1996; Henry et al., 2013; Molina et al., 2007, and sediment fluxes are interconnected leading to the possibility of 2008). As such, we would argue that the use of mixed hedgerows and greater erosion losses through gully erosion (Boix-Fayos et al., 2006). grass strips under agricultural land uses could play an important role Furthermore, the current study also focuses on agricultural land uses, in addressing land degradation caused by erosion, especially when as opposed to other land uses also present in rural landscapes or employed more strategically, for example, by considering the overall catchments. In studies examining the effect of different land uses on landscape mosaic and interconnections between land uses. Further erosion, it has been found that surface run-off on agricultural land is research in this regard would be particularly welcome to assess the often low to minimal compared with other land uses, because high efficacy of these hedgerows in controlling erosion in other contexts infiltration rates are often associated with cultivated soils (Harden, or land uses with greater susceptibility to erosion. 2001; Harden, 1996; Molina et al., 2007). In a study in the Ecuadorian Andes using rainfall simulators, the compacted surfaces of paths and roads generated much greater run-off volumes, initiated greater runoff at lower rainfall intensities, and produced run-off sooner during a 4.2 | Influences of organic amendments on soil fertility and productivity rain event compared with cultivated areas (Harden, 2001). Similarly, Molina et al. (2007), also working in the Ecuadorian Andes, found As hypothesised, our results indicate that canary grass and mixed degraded and abandoned land to generate surface run-off within a canary grass and Andean alder hedgerows and their associated few minutes after the start of the rainfall event, whereas surface run- organic amendments have the potential to increase soil productivity off on arable land was rare. Another reason may be that the cotton fil- in terms of both overall biomass and grain yield when incorporated tration method used to remove the soil from the water in the sedi- into the soil before planting (Figure 4a,b). This is an important, novel ment catchment trenches was not fine enough to trap all soil particles. finding in this socioecological context as it suggests that resource- Therefore, soil loss measurements may have been slightly lower from constrained farmers may be able to supplement limited organic agri- the erosion plots than the actual losses experienced. Notwithstanding cultural inputs with amendments from canary grass strips to improve this potential experimental bias, it is unlikely that any under- their productivity and overall resilience to climate change. The results measurement can account for the magnitude of difference in soil ero- reflect previous studies with vetiver grass in Africa, which was also sion measured in the current study compared with those referenced shown to increase yields when used as a mulch (Babalola et al., 2007; above. Okeyo et al., 2014). 9 CAULFIELD ET AL. In contrast, alder-based organic amendments alone did not signifi- grass strips may not produce sufficient quantities of organic amend- cantly improve soil productivity in the time frame of this study. This is ments to satisfy all carbon and nutrient input requirements (Félix surprising given that the scarce research on the use of alder leaf mate- et al., 2018). Indeed, it is unlikely that the quantities of the OM inputs rial as organic amendments suggests that it has the potential to used in this experiment (16.5 Mg ha−1 fresh weight) would be feasibly increase soil nutrient levels and a range of other soil properties produced by hedgerows grown around an agricultural field, with a (de Valença et al., 2017; Swanston & Myrold, 1997). Moreover, chem- recent study suggesting that a different species of canary grass pro- ical composition of the leaf material indicated that it was high quality duced between 4.5 and 9.5 Mg ha−1 yr−1 dry matter (or around (i.e., low C:N) and was composed of suitable levels of lignin (<15%) 30 Mg ha−1 yr−1 fresh weight; Pocienė et al., 2013). Instead, our and phenols (<4%; Table 1), according to Palm et al. (2001). It is note- results should be placed within the context of identifying farming worthy, however, that phenols were at the high end (3.65%) of the practices that have the potential to increase overall access to carbon acceptable levels for direct incorporation with annual crops. In cases and nutrient resources as mechanisms to supplement rather than with levels of phenols higher than 4% the decision-support tool of replace current input patterns. This potential is particularly useful in Palm et al. (2001) suggests mixing the organic resources with fertil- mountainous landscapes where the development of soil conservation izers or high-quality materials. Indeed, when the Andean alder leaves practices such as slow-forming terraces can lead to important soil fer- were mixed with canary grass, biomass production and grain yield tility gradients at the field level (Dercon et al., 2003). An increased were not significantly different to the canary grass alone treatment access to organic amendments means that less fertile parts of the field (Figure 4a,b), although it cannot be discounted that this effect was may be targeted with additional inputs, although still being able to simply a result of the canary grass amendments included in the provide lower level inputs to the other areas. Moreover, the potential mixed amendments treatment. More research is needed to better to harvest the amendments in situ may be able to address some com- understand this effect and the minimal quantities of organic amend- monly observed landscape scale fertility gradients, where far-fields ments necessary to achieve significant improvements in soil produc- receive fewer inputs than fields located closer to homesteads (Fonte tivity. Additionally, future research should consider the potential et al., 2012; Vanek & Drinkwater, 2013). trade-offs with loss of productivity due to the use of hedgerows on agricultural land. Finally, although our results indicate that out of the three experimental conditions, canary grass strips performed the best both in Although it is not possible with the current experimental design terms of erosion control, soil humidity, and for improving soil produc- to assess whether the soil productivity improvements observed under tivity; on other metrics, it is likely that the other hedgerows would the canary grass and mixed organic amendment treatments (Figure 4) perform better. For example, mixed hedgerows and other agroforestry were a result of the hedgerows themselves (e.g., through decreased techniques with important ligneous components have been shown to erosion or additional belowground organic matter inputs from roots) be particularly valuable for C sequestration (Albrecht & Kandji, 2003; or the organic amendments incorporated, it is likely that the additional Palma et al., 2007; Takimoto et al., 2008), vegetative richness and nutrients these amendments provide (Tables 1 and 2 and Table S4) diversity (Deckers et al., 2004; Kearney et al., 2017a; Smukler et al., coupled with their ability to increase soil moisture (Figures 5 and 6, 2010), and for supporting macrofauna abundance and diversity (Pauli Table S4) are at least partly responsible for these improvements. et al., 2011; Rousseau et al., 2013). When factoring in these ecosys- With regard to soil moisture levels average soil moisture levels tem components, it would appear that mixed hedgerows with canary were significantly higher in all three treatments receiving organic grass and Andean alder may be optimal, providing the potential for amendments compared with the control (Figures 5 and 6). In moun- erosion control, sources of organic amendments, C sequestration, and tainous rain-fed agricultural systems, which are expected to experi- improved biodiversity. Furthermore, although it was not explicitly ence more erratic precipitation patterns in the coming years (Kohler assessed in the current research, it would be important to investigate et al., 2014), application of such amendments may help resource- the possible competition between the hedgerows and crops grown constrained farmers further build resilience to climate change beyond for nutrient and water resources. For example, given that Andean the use of the hedgerows as techniques to control erosion. Given the alder trees have the potential to fix N, mixed hedgerows may perform critical relationship between soil water storage, soil aggregation, and better in the long term. SOC (Bronick & Lal, 2005), the increased levels of soil moisture in the experimental conditions are likely a result of the increased levels of SOC incorporated through the organic amendments. SOC levels 5 | CONC LU SIONS tended to increase in all treatments compared with the control, significantly so for the canary grass alone treatment (Table 2). These Our results demonstrate that hedgerows comprised canary grass, and increased levels of SOC following the incorporation of in situ sourced canary grass together with Andean alder have the potential to provide organic amendments reflects the findings of Félix et al. (2018) who important benefits for small-scale farmers by minimising land degrada- found that although the ramial woody amendments that they incorpo- tion due to water erosion and by aggrading soils through the incorpo- rated did not provide sufficient nutrients to balance the nutrient out- ration of organic amendments harvested from these hedgerows. The flows, they did lead to higher yields and levels of SOC than the erosion control potential of canary grass strips and mixed canary grass control condition. It is important to highlight that hedgerows and and Andean alder hedgerows decreased water erosion in the plots by 10 CAULFIELD ET AL. between 50% and 60%. However, we also found that annual erosion at the plot scale in agricultural fields was rather low suggesting that water erosion may not be the greatest driver of land degradation for agricultural land uses in this landscape or at this scale. Nevertheless, we argue that erosion control structures such as those tested in this study may be effective for other types of erosion, such as tillage or gully erosion, or adjacent to other land-use types that may experience greater erosion rates, although more research is necessary to assess these possibilities. Canary grass and mixed canary grass and Andean alder leaf amendments increased both biomass production and grain yield in this study. Canary grass appears to be a particularly high-quality organic amendment being able to boost soil productivity by itself. Andean alder leaf amendments on the other hand, appear to be less effective, needing to be incorporated with higher quality organic material or composted. It is likely that the agricultural production benefits were, at least partly, a result of the nutrient inputs from the organic amendments as well as their ability to improve soil moisture levels by increasing SOC. In conclusion, although hedgerows may not be able to produce sufficient quantities of organic resources to satisfy all nutrient input requirements, their potential to supplement existing inputs in a resource constrained socioecological context mean that they should be strongly considered as an option for improved agricultural management. Not only can these extra resources enable farmers to target additional inputs to low fertile areas within fields, but the potential to harvest the amendments in situ is an additional benefit to address commonly observed landscape scale soil fertility gradients where distant fields receive fewer inputs than fields located closer to homesteads. ACKNOWLEDGMENTS The research was funded by the McKnight Foundation's Collaborative Crop Research Program, USA and executed under the auspices of Fundación EkoRural, Ecuador. 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