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Pongamia pinnata (L.) Pierre (Pongamia) is a tree native to Southeast Asia. Recently, interest in Pongamia focused on its potential as a biofuel source as its seeds contain around 40% oil. However, Pongamia has multiple applications beyond biofuel production. It is a legume, can form symbiotic associations with mycorrhizal fungi, has been shown to be tolerant to drought, salinity, and heavy metals in soil, and has potential to mitigate climate change. Additionally, Pongamia oil has medicinal properties, can be used as biopesticide, insect repellent, to produce soap, and as a source of edible grade vegetable oil. The seed cake can be used as a source of bioenergy, food and feed protein, and organic fertiliser, and the flowers are a good source of pollen and nectar. Pongamia can also bring socio-economic benefits as its ability to restore degraded and contaminated land provides opportunities for local communities through novel valorisation pathways. These multiple applications have potential to form part of a circular bioeconomy in line with sustainable development goals. Although research on the multiple applications of Pongamia has grown considerably, knowledge gaps remain and these need to be addressed so that the full potential of Pongamia can be achieved. Further understanding of the mechanisms underlying its resilience to abiotic stresses, phytoremediation potential and biotic interactions should be a priority, and co-ordinated breeding efforts will be key. Here, we critically review the available literature on Pongamia and highlight gaps in knowledge in which future research should focus on to ensure that the full potential of this versatile tree can be achieved. We conclude that Pongamia can potentially form part of a circular bioeconomy and that harnessing the multiple applications of Pongamia in a holistic manner, with collaboration among key stakeholders, is crucial for the successful application of its benefits far beyond biofuel production.

Integrated farming systems are promising strategies towards land-use efficiency and sustainable agriculture. The integrated crop-livestock-forestry (ICLF) system stablish complex interactions were synergies or competition depend on the arrangements throughout time and space. Fine root (≤2 mm) growth dynamics of crops, pasture and trees remains unclear when these species are integrated. We aimed to assess root growth dynamics after Eucalyptus urograndis introduction into an integrated crop-livestock (ICL) system. Previous ICL area was used as a reference. We assessed ICLF 1.9, 4.3 and 7.5 m distances from tree rows, starting the study when trees had three years of age. Eucalyptus rows were spaced 15 m apart and integrated to annual crops and pasture. We evaluated the root growth under two different successional periods: (i) corn cultivation interspaced with palisade grass (Urochloa brizantha); and (ii) a pasture, when palisade grass was grazed. We tracked fine root length using the minirhizotron technique, capturing 3200 images scanning up to 70 cm soil depth. Data of photosynthetically active radiation (PAR) transmission, soil bulk density, rainfall and air temperature were used as complementary information to support the discussion. Our results showed that Eucalyptus trees impaired root growth of annual crops cultivated in the interrow position, regardless of distance from the row. From 31 to 80 days after corn germination, root length production in ICLF was reduced by 120–179 cm m−2.d−1 along the tree interrow space. For the pasture period, total produced root length density reduced 6% at 1.9 m but increased 25% at 4.3 and 7.5 m, when compared to ICL. Shade of Eucalyptus trees at ICLF 1.9 m position, with PAR transmission mainly below 60%, sharply impaired root growth. Eucalyptus roots represented 12% from total root length produced in ICLF system, and 38% of these roots had positive ectomycorrhizal status. In conclusion, under Eucalyptus trees higher than 20 m, pasture of palisade grass is more adaptable than corn when considering the root growth dynamics of our studied ICLF arrangement. Based on our findings, corn intercropped with palisade grass should not be introduced in future management of the ICLF system, unless part of the trees is chopped to reduce light competition. However, implemented pasture of palisade grass showed belowground synergies with Eucalyptus, increasing root growth in intermediary interrow positions and emerging new fungal symbiosis, which could be playing important functions in soil, as soil carbon storage and nutrient cycling.

Brazil is the world's largest sugarcane producer. This crop leaves huge amounts of straw behind which have to be managed with innovative approaches. In this study, a field experiment was carried out over six successive years of sugarcane harvests to evaluate the effect of straw maintenance on the field on changes in soil phosphorus (P) fractions. Four straw maintenance rates were tested: (i) maintaining 15 Mg ha−1 (SM15); (ii) maintaining 10 Mg ha−1 (SM10); (iii) maintaining 5 Mg ha−1 (SM5), and (iv) maintaining 0 Mg ha−1 (SM0). Our results showed that low maintenance of straw (SM5) resulted in the highest amount of P extracted by anion exchange resin and inorganic P extracted by 0.5 mol L−1 NaHCO3 in 0−5 and 5−10 cm soil depths. While total removal of residues resulted in soil P deficiency after six crop cycles, keeping straw on the soil surface at the rate of 5 Mg ha−1 supports plant growth without the need for P fertilizer application. We detected inorganic P extracted by 0.1 mol L−1 NaOH as the sink of P derived from straw since it was the only P fraction which increased with increasing straw on the soil surface. Non-labile P fractions were not influenced by straw maintenance rates in all depths. This is a promising result since it shows that P derived from straw does not accumulate in non-labile P fractions which are not plant available. Inorganic P was not influenced by straw removal rates and total P was only changed in 0−5 cm soil layer, while organic P was affected in all depths. We observed that organic P is available to sugarcane plants under SM0, SM5, and SM10, while under SM15, organic P does not play a role in sugarcane nutrition.