Participatory design of improved forage/fallow options across soil gradients with farmers of the Central Peruvian Andes

Highlights

• 3-year Andean fallows seeded with forages increased soil cover and forage supply.

• Forage was of higher quality than in unseeded control fallows during year one.

• After three years yield of potato was not reduced in forage-based fallows.

• Soil carbon trajectories in these fallows depend on the intensity of forage removal.

• Farmers’ evaluations prioritized forage and potato yields and healthy potato tubers.

Abstract

Land use intensity is increasing in Andean smallholder systems, and innovations are needed to sustain soil fertility and productivity of potato-cereal rotations with shortening fallow periods. In collaboration with farmers in central Peru, we assessed forage-based fallows in 58 fields across three production zones over three years. Fallow treatments selected with farmers tested grass-legume mixtures with different combinations of Vicia Sativa (vetch), Avena sativa (oats), Lupinus mutabilis (Andean lupine), Trifolium pratense (red clover), Medicago sativa (alfalfa), and Lolium multiflorum (ryegrass) compared to an unseeded control fallow with natural revegetation. The ability of fallows to quickly cover soil was tested, as was their biomass production in years one and three. Following the incorporation of fallow vegetation in a sub-set of nine fields, we also tested fallows’ effects on soil pH, available phosphorus (P), permanganate-oxidizable carbon (POXC) and potato yield. In year one managed fallows produced from 1.9 to 5.4 Mg ha⁻¹ of forage biomass compared to 0.5 to 1.1 Mg ha⁻¹ in unseeded controls. Managed fallows also exceeded controls in nutrient uptake, soil cover, and forage quality (lower lignin and higher protein content). First-year biomass of vetch and Andean lupine responded differently to soil pH in fields, indicating that appropriate fallow options likely depend on soil context. After three years, total biomass did not differ among treatments. However, legumes had greater biomass in treatments employing perennial species (0.79–1.18 Mg ha⁻¹ of legumes) than in controls (0.15 Mg ha⁻¹). Potato yield and soil fertility was not reduced in managed fallows compared to the control, and an alfalfa + liming treatment yielded higher than the control (p < 0.05). Diseased tubers were also less prevalent in fallows containing ryegrass and clover, versus other treatments (2.7 % vs. 4.7 % diseased; p = 0.05). In a post-hoc analysis considering 41 treatment plots with contrasting cutting regimes, plots that were cut repeatedly throughout the fallow period had more negative changes in POXC than those cut initially and then left to regrow (p = 0.04). In evaluation workshops, farmers emphasized forage production, potato yield, and potato tuber health as evaluation criteria for the fallows, and ranked the alfalfa + liming treatment as the best. In Andean communities with shortening fallow periods, forage-based fallows represent a promising, multi-functional option to maintain soil health and productivity while generating additional sources of high-quality forage. However, future research should examine long-term nutrient and carbon balances under different forage removal scenarios, as well as designing fallows for varied agroecological contexts.

Introduction

Increasing intensity of land use among smallholder farmers is a global trend that threatens the productive base of food systems in many developing countries (International Fund for Agricultural Development (IFAD, 2013; Vanlauwe et al., 2014). With land use intensification there is often a decline in the ability of these farmers to replenish soil fertility and soil organic matter (SOM), due to a lack of fertilizers and/or organic residue inputs. The shortening or elimination of fallow periods often accompanies this intensification process (Bosma et al., 1999; Hervé and Beck, 2006; Mponela et al., 2016; Ollenburger et al., 2016; Sitko and Chamberlin, 2016).

In the Andes, traditional fallows (typically >5 yr.) are a key soil regeneration practice in the mixed livestock/cropping systems of the region, where potatoes and cereal crops for grain and forage are major staples for consumption and sale, and legumes and minor tubers are important complementary crops. Andean long fallows establish expansive perennial root systems and vegetative cover, which restore soil structure and SOM, enhance biological activity, and control erosion, thus supporting soil productivity in the next cropping phase (Pestalozzi, 2000; Sarmiento and Bottner, 2002; Rolando et al., 2017a). Long fallows also represent ecological succession processes which begin to re-establish the biodiversity and ecological function present in undisturbed sites (Sarmiento et al., 2003; Ortuño et al., 2006). By contrast, shortened fallows (often less than 3 years) are associated with increased tillage frequency and reduced residue inputs from wild vegetation, and thus no longer contribute sufficiently to restoring soil fertility, or breaking pest and disease cycles (Mayer and Shea, 1979; de Haan and Juárez, 2010; Fonte et al., 2012). In addition, long fallows are often a vital source of feed for livestock, while shortened fallows can reduce forage supplies in smallholder systems as the global importance of livestock among smallholders continues to grow (Herrero et al., 2010; Thornton and Herrero, 2014).

One response to shortened fallows and the resulting challenges to soil quality has been “improved” or managed fallows, analogous to the strategy of cover crops in annual rotations, that incorporate plant functional traits to favor soil regeneration. Such traits include rapid soil cover, abundant organic residue production and biological nitrogen (N) fixation from legumes (Sanchez, 1999). Residues from managed fallows are incorporated directly to soils, left on the surface as mulch, or incorporated indirectly as manure resulting from increased supplies of animal forage. Such fallow practices include quick-growing shrub and tree species (e.g. Swinkels et al., 1997; Phiri et al., 2001) and grass and legume forage crops (e.g. Yanggen and Reardon, 2001; Ramos et al., 2010). Improved fallow species must be well adapted to local climates and soil types, and be useful to farmers, usually within a multipurpose framework that includes soil fertility impacts, forage provision, weed suppression, disease reduction, and other useful traits. These multiple levels of adaptation are reflected in so-called “socioecological niches” for soil-improving crops (Ojiem et al., 2006).

In smallholder farming contexts, one strategy for developing improved fallows and other sustainable management practices is a process of co-learning, where farmers and scientists both contribute technical expertise and farmers convey preferences, evaluations and proposed modifications to the tested options (Coe et al., 2014). Multi-location testing of options with farmers also contributes to the matching of innovative options to different contexts within local soil type and management gradients (see e.g. Vanek and Drinkwater, 2016) including differences in levels of intensification and fertility inputs across communities and landscapes (e.g. Wiegers et al., 1999; Tittonell et al., 2005; Zimmerer and Vanek, 2016). These participatory research approaches, along with strategic deployment of ecological mechanisms such as complementary species traits and residue recycling to maintain or increase productivity on a fixed land base, are key components within “agroecological intensification” of smallholder management strategies globally (Nelson and Coe, 2014).

In the research presented here we used a co-learning process with two smallholder communities in the central Peruvian Andes to test a range of managed fallow options in farmers’ fields using domesticated forages as an alternative to unmanaged fallows (hereafter, “unseeded fallows”) in three distinct production zones. Earlier diagnostic work in these communities indicated the perceived importance and scarcity of forage, which became a key consideration in developing fallow options of high functional diversity (legume/non-legume and annual/perennial) to create a wider and more stable range of benefits across sites. The detailed objectives of the study were to: (1) compare the potential of these managed fallows to provide vegetative cover and biomass for forage and direct residue incorporation to soils; (2) understand how fallow performance varies across gradients of elevation and soil characteristics; (3) assess the forage quality resulting from these fallows; (4) evaluate the practices with farmer focus groups at key stages during the fallow; and (5) assess the impacts of treatments on soils and potato production immediately after the fallow period. We hypothesized that at least one of the tested fallow options would enhance fallow productivity and soil cover compared to unseeded fallows with natural revegetation, as well as generate impacts on soil properties such as organic matter and available nutrients, and crop production that were equivalent to or better than natural revegetation (control plots) during a three-year period. Furthermore, we expected that performance of the fallow options tested would vary across differences in soil type and soil fertility (e.g. soil texture, pH, and nutrient availability), allowing better matching of the managed fallow practices to different soil contexts in the project area. Because women are typically responsible for livestock management in these communities and may have a distinct outlook from men on forage needs and soil management, we also anticipated gender differences in evaluating the different fallow practices and tradeoffs in prioritizing soil improvement versus forage provisioning from managed fallows.