Evaluation of biodegradable mulch films as alternatives to plastic mulching in sustainable agriculture

Introduction

On one hand, polyethylene mulch films have transformed vegetable farming by raising soil temperature, cutting water loss, and blocking weeds lifting yields by 20-60% in tropical systems [1] . On the other hand, these films persist in soil for decades, fragmenting into microplastics that reduce porosity and contaminate water [2,3] . Nigeria generates roughly 18,000 tonnes of agricultural plastic waste annually with limited disposal options [4] . Biodegradable alternatives made from PLA, PBAT, starch, PHA, or cellulose paper have entered markets in Europe and East Asia [5,6] , but most performance data come from temperate climates and their behavior in warm, humid West African conditions is largely untested [7,8] . Key unknowns include whether tropical temperatures accelerate degradation so fast that films lose function before crop maturity, and whether moisture conservation matches PE during critical early growth [9,10] . This research compared four biodegradable films against PE in a 24week okra trial in southwestern Nigeria.

Climatic conditions during the trial

The trial ran March-August 2023 at the University of Ibadan (7.44° N, 3.90° E, 227 m), spanning the dry-to-wet season transition. Total rainfall was 847 mm, peaking in June (194 mm) and July (178 mm) [11] . Mean air temperature ranged 26.3-29.7 °C. Soil temperature at 5 cm under mulch averaged 27.8-31.4 °C, 2-4 °C above bare soil, creating conditions for accelerated microbial decomposition [12] .

Materials and Methods

Materials

Four biodegradable films were tested: PLA/PBAT blend (15 µm thickness, BASF ecovio®), starch-based (20 µm, Novamont Mater-Bi®), cellulose paper mulch (80 g m⁻², Weedguard Plus®), and PHA-based film (18 µm, Danimer Scientific). Conventional black PE film (25 µm, local supplier) served as the control. Okra (cv. Clemson Spineless) was the test crop. Compound NPK fertilizer (15:15:15) was applied at 200 kg ha⁻¹ at transplanting. The soil is a ferric Luvisol (Alfisol) with 62% sand, 21% clay, 17% silt, pH 6.4, and organic carbon 1.34% [13] .

Methods

A randomized complete block design with six treatments (four biodegradable films, PE, and bare soil) and four replicates gave 24 plots of 12 m² each. Mulch was laid manually on raised beds (1.0 m wide, 0.2 m high) with transplanting holes cut at 50 × 40 cm spacing. Soil moisture was recorded weekly at 15 cm depth using TDR probes (Campbell CS616). Weed biomass was harvested from a 0.5 m² quadrat per plot at 6, 12, and 18 weeks. Film degradation was assessed by retrieving buried meshenclosed strips (10 × 30 cm) at 6-week intervals and measuring dry mass loss. Okra pods were harvested twice weekly from week 8 to week 22 and weighed fresh [14] . Data were analyzed by one-way ANOVA with Tukey's HSD (p<0.05) in R 4.3.2. Discussion: The near-equivalent yield of PLA/PBAT (14.8 vs 15.3 t ha⁻¹ for PE) matches temperate trials where PLA-based films performed within 5% of PE [5,6] . Faster degradation here (63.4% at 24 weeks vs 40-50% in Mediterranean trials) reflects higher soil temperatures (28-31 °C) stimulating microbial enzymatic activity [7] . Paper mulch failed beyond 12 weeks, consistent with humid subtropical reports of cellulose disintegrating within 8-10 weeks under heavy rainfall [8] , allowing weed incursion that cut yield by 21%. PHA film showed the slowest degradation (41.7%) and secondhighest yield, balancing longevity with eventual soil incorporation. But PHA's price roughly three times PLA/PBAT limits adoption among Nigerian smallholders [15] .

Results

Limitations

This research covered a single site and one growing season; year-to-year rainfall variation could shift degradation rates. The trial did not assess microplastic residues from partial PLA/PBAT or PHA degradation, which is an emerging concern for certified biodegradable materials [16] . Economic cost-benefit analysis was not performed, and only one crop species was tested results may differ for shorter or longer growing cycles.

Conclusion

PLA/PBAT blend films emerged as the most promising alternative to conventional PE mulch for humid tropical vegetable production. They maintained soil moisture and weed suppression comparable to PE through the first 12 weeks and delivered equivalent okra yield (14.8 vs 15.3 t ha⁻¹, p>0.05) while degrading by 63% in soil over 24 weeks. PHA-based films also performed well agronomically but degraded more slowly and cost more. Paper mulch broke down too quickly for a 22week crop cycle. Tropical soil temperatures accelerated biodegradation relative to temperate benchmarks, a factor that should be built into product development for West African markets. Future work should test these films across multiple seasons, assess microplastic residues from partial degradation, and evaluate cost-effectiveness under smallholder conditions.

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