Effects of conservation agriculture maize-based cropping systems on soil health and crop performance in New Caledonia
Introduction
Agricultural practices are key drivers of agroecosystem functions and their negative impacts have increased in recent decades. Land use changes, intensive use of chemical inputs, and fragmentation of habitats have contributed to the depletion of soil fertility, biodiversity, water quality and availability, and to the magnitude of climate change (Foley et al., 2011; Rockström et al., 2017). These rapid changes have also had positive effects including increasing food production at global scale, but significant trade-offs have been observed, to preserve environmental integrity (Tilman et al., 2011). Soil is one of the key components of ecosystems and is under serious pressure from human activities. To mitigate the negative impacts of agricultural systems, some approaches promote agronomic technical levers such as soil conservation practices or agroforestry (Altieri and Nicholls, 2013; Wezel and Soldat, 2009).
Agriculture represents less than two per cent of the gross domestic product of New Caledonia where the economy is mainly driven by the nickel industry and the service sector (ISEE, 2016). However, islands in the South Pacific need to increase their agricultural production to respond to population growth and to increasing demand from the commercial sector (Murray, 2001; Naidu, 2010). Like in many developing countries, agricultural intensification in these islands has had positive impacts on agricultural production and food security (Naidu, 2010; van der Velde et al., 2007). Unfortunately, agricultural intensification has also had detrimental impacts on soil and water resources, including significant soil erosion (Dugain, 1953; Losfeld et al., 2015), especially in New Caledonia, a hotspot of biodiversity (Myers et al., 2000).
Conservation agriculture (CA) is a farming system that promotes minimum soil disturbance (i.e., no tillage), maintenance of a permanent soil cover, and diversification of plant species (FAO, 2014). Through the application of these three principles, the maintenance and improvement of soil functioning is driven by (i) high and continuous production of above and belowground biomass, (ii) a permanent soil cover which supports a continuous flow of nutrients and organic compounds and improves the water balance, and (iii) enhanced soil biological activity which regulates carbon transformation, soil structure maintenance, and improved nutrient cycling (FAO, 2014; Hobbs et al., 2008; Scopel et al., 2013). CA is being promoted to improve the resilience of cropping systems and reduce their negative externalities (Hobbs et al., 2008; Lal, 2015a; Séguy et al., 2006). CA can help reduce physical, chemical and biological soil depletion and production costs (Palm et al., 2014; Scopel et al., 2013; Sithole et al., 2016; Thierfelder and Wall, 2012). CA practices could thus be a promising way to reduce the negative impacts of agriculture, especially on soil, while conserving production and ecosystem services (Pittelkow et al., 2015; Verhulst et al., 2010).
The relationships among soil and crop management practices, soil health, crop performance and ecosystem services under CA practices are poorly described in the literature (Palm et al., 2014; Ranaivoson et al., 2017; Verhulst et al., 2010). Appropriate and sensitive indicators should be selected to assess agrosystem multifunctionality. Soil health is defined as “the capacity of a soil to produce a good quantity and quality food and fibre together with the delivery of other ecosystem services” (Kibblewhite et al., 2008). Although many approaches are available to assess soil health, Thoumazeau et al. (2019b) proposed an integrative, multifunctional, and easily transferable approach, named Biofunctool®. Biofunctool® makes it possible to assess the three main soil functions linked to soil biological activities identified by Kibblewhite et al. (2008): (i) carbon transformation, (ii) nutrient cycling, and (iii) soil structure maintenance with a core set of ten in-field and low-tech indicators. Weeds and crop development are key aspects to assess cropping system performance. Weeds are indeed a major factor affecting yields (Teasdale et al., 2007) and weed control is one of the farmer’s main concerns in agricultural systems (Hobbs, 2007; Nichols et al., 2015; van Heemst, 1985). On the other hand, grain yield is the main indicator used by farmers to assess the performance of their system. Combining these measurements should help understand the synergies and trade-offs between the components that may affect cropping system performance.
We hypothesise that CA practices have both direct and indirect effects on weeds and crop productivity by influencing soil health, thereby increasing the performance of CA compared to that of CT. The overall objective of the study was to conduct an integrative and quantified assessment of the relationships between contrasted maize-based cropping management (i.e., conventional plough-based tillage (CT), and CA with a diversity of cover crops and managements), soil health and cropping system performance in New Caledonia.
Section snippets
Site description
The study site is located at the Adecal Technopole Ouenghi experimental station in Boulouparis, South province, New Caledonia (21°53′50″ S, 166°06′45″ E). The west coast of New Caledonia is characterised by a semi-arid subtropical climate with a cool, dry season from May to September, and a warm, wet season from December to April. Intense rainfall associated with thunderstorms peaking in austral summer are usually followed by recurrent drought periods from October to November. Data from the
Effects of the cropping systems on soil health
For carbon transformation, labile fraction of the soil organic carbon (POXC), basal soil respiration (SituResp®) values as well as bait lamina scores were significantly higher under the two CA cropping systems than under CT (Table 1). The GTB score was significantly higher under CA-DM (0.46 ± 0.03) than under CT (0.43 ± 0.02) but did not significantly differ from CA-LM (0.45 ± 0.02).
Concerning structure maintenance, the same trend was recorded for the three indicators (Table 2). Mean VESS
Discussion
It is worth noting that the results are based on the cumulative effects of the two distinct periods linked to changes in the experiment management strategy. The results of CT compared to CA are linked to a relatively long-term change (2011–2018), whereas the results that compare CA practices are linked to short-term changes (2017–2018).
Conclusions
The effects of three annual cropping systems (i.e., CT, CA-DM and CA-LM) on soil functioning were evaluated using an integrative assessment of soil health. Higher structure maintenance (i.e., soil aggregation, water infiltration, VESS) and nutrient cycling functions (i.e., NO3−, NH4+) were recorded under CA-DM and CA-LM, and a higher carbon transformation function (i.e., labile-C, soil respiration, baits lamina, GTB) was assessed under CA-DM. Overall, the soil health index (SHI) was 1.3-fold
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors thank DDR Province Sud NC, Adecal Technopole, and IAC for funding the project, Adecal Technopole for technical assistance, and LAMA laboratory (LAMA-US IMAGO-IRD, NC) for laboratory work. We thank Joséphine Peigné (UR AE, ISARA-Lyon) for comments on an earlier version of this manuscript.
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