Soils have been spotlighted for their central role in addressing global threats including climate change and food security. Soils play an important role in the cycling of elements essential to life. They supply all plant essential elements but the basic macro elements Carbon, Oxygen and Hydrogen, facilitating 95 per cent of global food production. However, not all soils provide all required elements at all times. Multiple threats to soils, such as erosion, acidity and nutrient imbalance, add layers of complexity to maintaining health, quality and supporting functions in food production and climate resilience.
Local soils have poor health, characterised mainly by low organic carbon content and acid pH. Traditionally, synthetic fertilisers and manures have been used to improve productivity. While these approaches have merit, little attention is placed on site conditions and best practices to optimise the expected positive response. The large variability in soil properties across the country warrants more detailed analysis of specific farmer and community growing conditions. The need for and use of soil testing is fundamental. Arguably, farmers are aware of the importance of testing to support cultivation but are reluctant to engage or are not confident in the outcome. The result, poor soil fertility practices, low productivity, low nutritional quality, nutrient mining, environmental pollution and soil degradation. It is not unusual to hear farmers complain of reduced productivity on soils even under intense fertilisation.
Managing soil fertility and, by extension, crop nutrition is complex and technically challenging for most farmers. Restoring confidence and ensuring quality in supporting institutions is fundamental to managing soil for nutrition. Evidence shows that average yields for many vegetable and field crops are < 50 per cent potential yields even under high input levels. Inadequate soil fertility and crop nutrition management contribute to low yields and nutritionally poor foods. Research at The UWI on cassava production showed that raising soil pH to 6 resulted in a 100 per cent increase in yield. When combined with targeted nutrient management (application of 100 kg N/ha) increased yield approximately 2.5 times greater and has a longer shelf life.
Liming is fundamental to addressing soil acidity and nutrient availability. With the larger portion of Trinidadian soils classified as moderately to strongly acid and noting the sugarcane plantation history, amelioration should be as routine as land preparation.
The 4Rs of nutrient stewardship include right source, right rate, right frequency and right placement and present a simple framework for using fertiliser and amendments. Source and rate considerations are linked to soil testing. The local norm is over application (often not measured) of nutrients weekly. This contributes to soil degradation and resource pollution. The timing of nutrient inputs should complement crop demand to encourage uptake and utilisation. Nutrient uptake patterns have not been determined for local crops, but the concept of “rooting”, “growing” and “bearing” salts is inadequate for optimising yield.
Adjusting fertiliser placement is the easiest win for farmers and perhaps the one with the greatest potential impact. Under local conditions, “top dressing” or other variations of fertiliser placement on the soil surface is very inefficient, particularly for phosphorus and potassium with low to moderate mobility in soils. Deep placement (10 cm below the propagule as a basal application) or spot application with incorporation (buried five to ten cm next to plant) is recommended to encourage early root establishment and vegetative growth.
Organic amendments have a special role in tropical soils, providing benefits beyond nutrient supply. Stable organic amendments (eg, composts) have the potential to feed the crop as well as the soil. Nourishing the soil is important, as tropical soils have poor health. Not only do composts recycle nutrients and facilitate circularity, they also keep carbon in the soil. Farmers produce tons of biomass per season that otherwise is loss to the atmosphere and contributes to greenhouse gas emissions. Programmes encouraging on-farm composting and biomass reuse are important elements of food and nutrition security.
The “one health” principle teaches better soils for better plants for better animals with final stage benefits to humans. The mantra recognises the multidimensional nature of connecting living systems. As the country expands its efforts at increasing food production and ensuring food and nutrition security, the role of institutions providing development support must be centre stage. A new model of cooperative extension and technology transfer is needed to attain these goals. The Faculty of Food and Agriculture at The UWI has responded to the need for diagnostic testing by establishing the Agro-environmental Services Unit and continues to focus on innovative and resilient soil management.
Dr Gaius Eudoxie
Dr Eudoxie is an advocate for soil and Senior Lecturer of Soil Science at the University of West Indies (St Augustine Campus) with responsibility for teaching and research in sustainable soil management and crop nutrition. Additionally, he serves as Deputy Dean, Teaching, Learning and Student Development at the Faculty of Food and Agriculture.