Using Si-Rich Compounds to Facilitate the Economic and Water Quality Aspirations of Māori Landowners
The leaching of nutrients can have a significantly negative effect on the quality and biodiversity of natural waters (Liu et al., 2019). The leaching of nutrients applied to farmland as fertiliser is a leading cause of reduced water quality and biodiversity in the freshwater ecosystems of Aotearoa-New Zealand (Gluckman, Bardsley, et al., 2017). Of the rivers that are located in the pastoral areas of Aotearoa-New Zealand up to 90.0% exceed the Australian and New Zealand Guidelines for Fresh and Marine Water Quality standards (Statistics, 2019). In an attempt to reduce nutrient leaching from farmland more than 50 nutrient leaching mitigation strategies have been used in Aotearoa-New Zealand (McDowell, 2013). Despite the use of these mitigation strategies, nutrient leaching trends for both nitrogen (N) and phosphorus (P) have been worsening over the last decade (Ministry for the Environment & Stats NZ, 2020). Some of the strategies used in Aotearoa-New Zealand have inherent problems. These problems can be summarised as the high cost, the length of time it takes to achieve water quality objectives and the harm that can be caused to other features of the environment (McDowell, 2013).
The leaching of nutrients is a significant cultural issue for Māori landowners due to the responsibilities and obligations of kaitiakitanga. The inherent problems with many of the mitigation strategies make them incompatible with the social and economic imperatives of kaitiakitanga (Forster, 2012; Morgan, 2008). This incompatibility heightens the issue for Māori by limiting their ability to reduce nutrient leaching from within a culturally appropriate framework. The kaitiakitanga practices of early Māori were developed through experience and observation of the natural environment (Marsden & Henare, 1992). Among them was the use of silicon (Si) rich compounds in their food growing and land management practices (Burtenshaw, 2010, Roskruge, 2011). Because early Māori did not experience nutrient leaching at the volume of contemporary farming these traditional practices do not address nutrient leaching. However, the use of Si-rich compounds in modern agriculture has been shown to improve farming productivity and reduce environmental harm including the leaching of N and P (Laing et al., 2006; Matichenkov et al., 2005; Snyder et al., 2016).
A series of pot trials, column experiments and financial analyses were used to determine the suitability of Si-rich compounds for mitigating N and P leaching and their compatibility with the principles and values of kaitiakitanga. Pot trials were used to determine the physical and economic effect of Si-rich compounds on crop yield, fertiliser efficiency, P fixation, soil pH and aluminium (Al) toxicity. The column experiments were used to determine the ability of the Si-rich compounds to reduce N and P leaching and to hold these nutrients in the soil in a plant-available form.
The data collected from the analysis, trials and experiments showed that Si-rich compounds reduced ammonium-N and nitrate-N leaching by up to 72.0% and 85.0% respectively. Phosphorus leaching was also reduced by up to 95.0%. The economic and social imperatives of kaitiakitanga were also met through increased crop yield, reduced expenditure, and no environmental harm.