Open Access

Jakob Vögerl

• Over the past years, nitrogen (N) fertilisation has been identified as an issue that has a major negative impact on the environment. Therefore, sustainable agricultural practices aim to reduce external fertiliser inputs and focus more on naturally available resources and sustainable cropping practices. One example of that is the ancient milpa polyculture which is practised by traditional small-scale farmers in Central America. It consists of climbing bean (Phaseolus vulgaris var. vulgaris), maize (Zea mays), and squash (Cucurbita moschata) that are said to represent a holistic symbiosis in which beans assume the task to accumulate additional nitrogen via N2-fixation and subsequently transfer it to its companions. The potential of intercropping, and thus nitrogen transfer to level out and reduce nitrogen fertiliser inputs compared to monocultures has not been assessed yet and little is known about the resulting practical implementation for small-scale farmers. Therefore, a pot trial with monoculture treatments (100 kg N/ha) of each crop and milpa treatments with varying levels of nitrogen fertilisation (0, 25, 50, 75, and 100 kg N/ha) was established. The intercropped beans were labelled with the 15N isotope using the cotton wick method to track nitrogen transfer in the system. Further, the Land Equivalent Ratio (LER) was used to determine the productivity of the system. Results showed that all polyculture treatments performed similarly or significantly better than the pure stands in terms of total dry matter content per pot. Milpas provided with 100 and 25% of the recommended nitrogen rate were most productive and achieved a total LER of 1.25 and 1.30, respectively. Also, the non-fertilised milpa was still as productive as the respective plants grown in a monoculture. Due to external reasons, the importance of nitrogen transfer and the related microorganisms could not be evaluated. However, growing a milpa instead of monocultures enables farmers to greatly reduce N fertiliser inputs and provides higher yields in the growing season, while other intercropping benefits are also present. It further has the potential to maintain yields and enhance natural nutrient cycling even if no fertiliser is applied.