Complex rice systems to improve rice yield and yield stability in the face of variable weather conditions.

Extreme weather events and pest outbreaks decrease rice yields and increase their variability, presenting challenges for the agricultural agenda to increase rice productivity and yield stability in Asia. The integration of azolla, fish and ducks has been shown to create robust systems that maintain high yields under heavy rainfall, but no clear evidence exists that rice yields in these systems are stable across locations and throughout time under divergent weather conditions. We show that the introduction of additional elements into the rice cropping system enhanced the adaptive capacity to extreme weather events across four locations and three cropping cycles. The complex system showed both static and dynamic stability, and had the highest reliability index, thereby outperforming the conventional and organic monoculture systems. The complex rice system design provides a promising example for resilience towards the impacts of climate change on rice production and for safeguarding food security in Asia and beyond.

Variable responses of the depth of tree nitrogen uptake to pruning and competition.

Trees in cropped fields may improve nitrogen (N) use efficiency by intercepting leached N, but crop yield will be reduced if the trees compete strongly with crops for N. Ideal trees for intercropping will take up N from deeper soil layers not accessed by the crop species. Spatiotemporal aspects of tree nitrogen capture niches were investigated within a hedgerow intercropping system by placing 15N at three depths and monitoring 15N uptake by trees pruned either 25 or 4 days before application of 15N. Trees with contrasting rooting patterns (Gliricidia sepium L. and Peltophorum dasyrrachis (Miq.) Kurz) were grown in mixed hedgerows and intercropped with maize (Zea mays L.). Neither species showed significant N uptake during the 5-14 days after pruning, even though some shoot regrowth occurred during this time. Mean topsoil (0-5 cm depth) root length density of G. sepium was 520% greater than that of P. dasyrrachis, whereas total root length (0-100 cm depth) of G. sepium was only 450% greater. On average, G. sepium recovered 15 times as much 15N as P. dasyrrachis, following application of 15N at 5 cm depth, but the two species recovered a similar amount following application at 80 cm depth, suggesting that P. dasyrrachis had better niche complementarity with shallow rooting crops. However, both species showed strong plasticity in vertical N uptake pattern in response to competition from establishing maize plants. The species differed in their response: N uptake activity by G. sepium shifted down the soil profile in response to increasing competition from a growing maize crop (uptake from 80 cm depth changed from 4 to 9% of uptake from 5 cm depth), whereas N uptake by P. dasyrrachis became relatively shallow (uptake from 80 cm depth changed from 305 to 25% of uptake from 5 cm depth). Niche avoidance and increased competitiveness within the topsoil represent alternative responses to competition. The response displayed may be related to soil fertility in the species' natural habitats.