Improved Pastures Support Early Indicators of Soil Restoration in Low-Input Agroecosystems of Nicaragua
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Environmental Management (2019) 64:201–212 https://doi.org/10.1007/s00267-019-01181-8 Improved Pastures Support Early Indicators of Soil Restoration in Low-input Agroecosystems of Nicaragua 1 1 2,3 4 5 Emily Webster ● Amélie C. M. Gaudin ● Mirjam Pulleman ● Pablo Siles ● Steven J. Fonte Received: 28 February 2018 / Accepted: 7 June 2019 / Published online: 18 June 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract Pasture degradation hinders livestock production and ecosystem services that support rural smallholder communities throughout Latin America. Silvopastoral systems, with improved pasture cultivars (especially Brachiaria spp.) and multipurpose trees, offer a promising strategy to restore soils and improve livelihoods in the region. However, studies evaluating the impact of such systems on pasture productivity and soil health under realistic smallholder constraints are lacking. We evaluated the impact of improved pasture grass and tree establishment on a suite of soil health indicators in actively grazed, low-input, farmer-managed silvopastoral systems. In August 2013, paired pasture treatments (improved grass with trees vs. traditional pastures) were established on nine farms with similar land-use histories near Matagalpa, 1234567890();,: 1234567890();,: Nicaragua. On each farm, one treatment was left as traditional pasture with naturalized grass (Hyparrhenia rufa), while the adjacent treatment was sown with the improved grass (Brachiaria brizantha cv. Marandu) and planted with tree saplings without fertilizer. In August 2015, we measured standing biomass and a suite of chemical, biological, and physical soil health variables. Improved silvopastoral systems with B. brizantha produced more standing grass biomass and supported higher levels of earthworm populations and permanganate oxidizable carbon (POXC) compared to the traditional control. Correlations suggest that earthworms and POXC were associated with incipient improvements to soil aggregate stability and water holding capacity. We report measurable improvements to soil health just two years following the establishment of improved pasture systems under common smallholder management practices and suggest that these systems, even with minimal fertility inputs, have the potential to enhance regional sustainability. Keywords Brachiaria brizantha ● Earthworms ● Pasture degradation ● Permanganate oxidizable carbon ● Silvopastoral systems ● Soil health Introduction Pastures and grassland systems occupy an estimated 70% of Supplementary information The online version of this article (https:// the global agricultural land area (FAO 2008) and contribute doi.org/10.1007/s00267-019-01181-8) contains supplementary material, which is available to authorized users. to 40% of the global gross domestic product (GDP) from agriculture (Galdino et al. 2015). In Central America, 73% * Steven J. Fonte of agricultural land is dedicated to livestock production on [email protected] pastures (Holman et al. 2004). Livestock production ’ 1 Department of Plant Sciences, University of California Davis, accounts for 39% of Nicaragua s agricultural GDP (Hol- Davis, CA 95616, USA mann et al. 2014). However, pastures in the dry corridor 2 Centro Internacional de Agricultura Tropical (CIAT), Soils region, where 40% of the national cattle herd is maintained, Research Area, AA 6713 Cali, Colombia face high levels of degradation (Szott et al. 2000) primarily 3 Department of Soil Quality, Wageningen University, PO Box 47, due to overgrazing and sub-optimal nutrient management 6700 AA, Wageningen, The Netherlands (Dias-Filho et al. 2001; Martinez and Zinck 2004). 4 Centro Internacional de Agricultura Tropical (CIAT), Soils Pasture degradation is characterized by reduced pasture Research Area, Apartado Postal LM-172, Managua, Nicaragua grass productivity, discontinuous grass cover, invasion by 5 Department of Soil and Crop Sciences, Colorado State University, weeds, and deterioration of soil biological, chemical, and Fort Collins, CO 80523, USA physical properties (Martınez and Zinck 2004). For 202 Environmental Management (2019) 64:201–212 example, Müeller et al. (2004) found that pasture degrada- intensification strategies for pasture systems that can tion was closely related to decreased forage production and simultaneously increase input use efficiencies and pro- increased soil bulk density, while Alegre and Cassel (1996) ductivity per unit of land while minimizing soil erosion, found that overgrazing pastures decreased earthworm creating positive SOM budgets, enhancing the activity and abundance. Others have suggested pasture degradation to diversity of soil life, and improving soil structure and impact soil organic matter (SOM) pools and overall soil hydraulic properties (Rao et al. 2015; Lerner et al. 2017). fertility (Fonte et al. 2014). Therefore, soil degradation For example, silvopastoral systems feature multipurpose limits economic returns and important ecosystem services tree species incorporated with improved pasture grasses provided by grassland systems such as carbon (C) seques- such as Bracchiaria or Panicum spp., which exhibit faster tration, soil and water conservation, and biodiversity habitat growth rates and higher biomass production potential than provision (Sala and Paruelo 1997). naturalized grass species, such as Hyparrhenia rufa that was Soil health has been defined as the capacity of a soil to introduced from Africa in the 1800’s and spread throughout function in maintaining (or enhancing) water and air qual- the region (Garcia et al. 2018; Parsons 1972). In addition to ity, and promoting plant and animal health (Doran 2002). their production value, the vigorous root systems of This concept integrates a range of physical, chemical and improved grasses aerate soils, increase SOM accumulation biological soil properties that vary with soil type, climate, (Fisher et al. 1994) and help improve soil aggregation land use, and management (Karlen et al. 2001; Lal 2015). In especially through root-derived aggregates and biopores tropical pasture systems, soil physical health can be mea- (Velasquez et al. 2012). Trees within silvopastoral systems sured via aggregate stability, compaction, infiltration and can provide multiple benefits including production of tim- water holding characteristics. Chemical properties asso- ber and non-timber products, increased shade for enhanced ciated with soil health include pH, cation exchange capacity animal welfare (Broom et al. 2013), improvements in soil C (CEC), and nutrient availability of key limiting macro- storage and biological activity (Rousseau et al. 2013; Casals nutrients (N, P, K). Additionally, SOM is a widely recog- et al. 2014) and provision of high-quality fodder, which can nized and important driver of soil health, affecting increase meat and milk production and quality (Murgueitio chemical, biological and physical soil qualities and a range et al. 2011). While fertilization is often recommended to of soil-based ecosystem services (Cardoso et al. 2013), and maintain pasture productivity and cover (Vilela et al. 2001; may be especially relevant for long-term nutrient manage- Santos et al. 2015), these recommendations are seldom ment in tropical pastures (Fonte et al. 2014). However, the followed by smallholder farmers (Vera et al. 1998). functionality of SOM depends on the contribution of dif- Therefore, assessing the ability of improved pasture systems ferent soil C pools. For example, labile (or active) C pools to restore degraded land under typical management sce- commonly change more rapidly than total soil C (Culman narios (i.e., active grazing and low-inputs) is highly relevant et al. 2012) and are closely associated with nutrient to understand if such practices still offer benefits to soil mineralization and availability, making them sensitive health and overall farmer livelihoods. indicators of short-term SOM stabilization and mineraliza- The objective of this study was to utilize an on-farm tion dynamics (Hurisso et al. 2016). approach to measure the impact of low-input, improved Soil macrofauna are also sensitive to soil management pasture system establishment (including the planting of and ecosystem engineers (e.g. earthworms, termites, and multipurpose, agroforestry tree species) on pasture pro- ants), in particular, can greatly influence SOM turnover, ductivity and soil health indicators within working small- nutrient cycling, and soil physical properties (Lavelle 1997; holder systems of the region. We sought to improve our Rousseau et al. 2013). Their responsiveness to alterations in understanding of linkages between soil biological, physical, plant cover and other disturbances make macrofauna and chemical properties in these systems and their value as abundance and diversity valuable indicators of tropical soil early restoration indicators. We hypothesized that improved health (Rosenberg et al. 1986; de Valença et al. 2017). pasture systems would support increased aboveground Monitoring the response of such indicators to changes in pasture grass biomass and that this would be reflected in soil management is valuable for providing early assess- improvements to soil health. ments of a land use system’s capacity to improve soil health and reverse degradation. As regional and global demand for livestock products Methods continue to increase (McDermott et al. 2010), developing low-input management practices that promote pasture and Site Characteristics livestock productivity while reversing