Zizania aquatica–duck ecosystem with recycled biogas slurry maintained crop yield

The Chinese government recently adopted the concept of ecological circular agriculture in a bid to increase recycling of agricultural waste and reduce chemical fertilizer input. Field experiments were conducted in 2015 and 2016 to determine the effects of a Zizania aquatica–duck ecosystem supplemented with recycled biogas slurry and no chemical fertilizers on Z. aquatica yield, plant nitrogen (N) and phosphorus (P) uptake, and NP concentrations in the surface water. Compared with Z. aquatica monoculture plus chemical fertilizer (Zcf treatment), the Z. aquatica–duck ecosystem with biogas slurry and no chemical fertilizer (Zbs–D treatment) maintained yield (approximately 24.48 t ha−1) and N and P uptake (approximately 3.15 and 0.98 g plant−1, respectively). Although N and P concentrations in the surface water were approximately 3.11 times higher under Zbs–D than Zcf treatment, concentrations in the draining surface water (4.54 mg N L−1 and 0.74 mg P L−1) met the discharge standard (5.00 mg N L−1 and 1.00 mg P L−1). These findings suggest that the Zbs–D ecosystem could be used to completely substitute chemical fertilizers in Z. aquatica production without yield losses via safe application of biogas slurry. In turn, this system would also increase the sustainability of Z. aquatica crop production in an environmentally-friendly manner. Simple and efficient methods for determining the NP content of biogas slurry are now required in addition to further long-term monitoring.