Biodegradable plastic film mulch increases the mineralisation of organic amendments and prevents nitrate leaching during the growing season in organic vegetable production
Samphire, M., D. R. Chadwick and D. L. Jones. 2024.
Abstract
ntroduction: Organic vegetable production relies on inputs of organic forms of nitrogen
(N). This presents a challenge as it needs to be mineralised by the soil microbial com-
munity. Difficulties matching the timing and rate of organic N amendments to crop
demand could potentially lead to high rates of nitrate leaching. The use of plastic film
mulch (PFM) has the potential to increase crop yield, accelerate N mineralisation, reduce
rainfall infiltration and therefore N leaching. Biodegradable PFM reduces the risk of
contaminating soil with plastics. Although these positive effects have been proven in
major conventionally grown commodity crops, the effects of PFMs are poorly under-
stood in organic vegetable crops, particularly in moist temperate climates prone to N
losses via winter leaching.
Materials & Methods: Our plot-scale field experiment attempted to quantify the effect
of biodegradable PFM on N leaching and N mineralisation in organic lettuce production
in the presence and absence of biodegradable PFM. It took place in one season within a
longer-term experimental organic vegetable rotation.
Results: We used two methods to measure the rate of carbon and N mineralisation: the
buried bag method showed biodegradable PFM resulted in no additional N miner-
alisation; however, the ion exchange membrane method indicated an increase in N
mineralisation of 30%. During heavy rainfall at the end of the growing season, nitrate
leaching was observed only in the non-PFM plots, leading to N losses equivalent to
6.3 g N m-2 . This led to surplus mineral N at harvest of 18.1 g N m-2 in the PFM treat-
ment and 8.6 g N m-2 in the corresponding unmulched plots. This did not lead to more
leaching in the mulched plots in the following 6 months.
Conclusion: In conclusion, our evidence supports the use of biodegradable PFMs to
enhance the sustainability of organic vegetable production systems in temperate
climates.
Key Words
nitrogen dynamics, organic horticulture, organic residues, sustainable production
