Legume-Modified Rotations Deliver Nutrition With Lower Environmental Impact

Abstract

Introducing legumes to crop rotations could contribute toward healthy and sustainable diet transitions, but the current evidence base is fragmented across studies that evaluate specific aspects of sustainability and nutrition in isolation. Few previous studies have accounted for interactions among crops, or the aggregate nutritional output of rotations, to benchmark the efficiency of modified cropping sequences. We applied life cycle assessment to compare the environmental efficiency of ten rotations across three European climatic zones in terms of delivery of human and livestock nutrition. The introduction of grain legumes into conventional cereal and oilseed rotations delivered human nutrition at lower environmental cost for most of the 16 impact categories studied. In Scotland, the introduction of a legume crop into the typical rotation reduced external nitrogen requirements by almost half to achieve the same human nutrition potential. In terms of livestock nutrition, legume-modified rotations also delivered more digestible protein at lower environmental cost compared with conventional rotations. However, legume-modified rotations delivered less metabolisable energy for livestock per hectare-year in two out of the three zones, and at intermediate environmental cost for one zone. Our results show that choice of functional unit has an important influence on the apparent efficiency of different crop rotations, and highlight a need for more research to develop functional units representing multiple nutritional attributes of crops for livestock feed. Nonetheless, results point to an important role for increased legume cultivation in Europe to contribute to the farm and diet sustainability goals of the European Union's Farm to Fork strategy.

Transition to legume-supported farming in Europe through redesigning cropping systems

“…Our indicators on protein and energy yield reflect the nutritional opportunities of legume systems for animal nutrition as well as for human consumption and the potential contribution on the plant protein deficit in Europe. This is only a proxy in terms of human nutrition and specific livestock classes and did not consider differences in varieties and management as well as other nutritional properties (Costa et al 2021). Our results indicate that protein selfsufficiency can be increased through legume integration with a trade-off for energy production.…”

Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems

“…While poorly timed application of synthetic N results in a mismatch between flushes of N supply and crop N demand which greatly increases the susceptibility of the surplus fertilizer N to loss processes, the slower availability of N derived from BNF sources such as legumes might be expected to better synchronize supply with demand, as the rate of N release from organic residues and the N requirements for crop growth are both regulated by available water and temperature ( Crews and Peoples, 2005 , Ladha et al, 2020 ). Certainly, this proposition is supported by numerous studies that have demonstrated lower losses of the N derived from legume systems than N fertilized cropping and intensive forage systems ( Peoples et al, 2004b , Crews and Peoples, 2005 , Jensen et al, 2012 , Jeuffroy et al, 2013 , Schwenke et al, 2015 , Costa et al, 2021 ). However, it should also be acknowledged that in some climates, soil types and farming systems can be an elevated risk of leaching or volatile losses of N mineralized from the N-rich legume residues following the end of the growing season ( Fillery, 2001 , Watson et al, 2017 , Williams et al, 2017 ), although often there are opportunities for this to be managed with the use of cover crops ( Kaye and Quemada, 2017 , Plaza-Bonilla et al, 2017 , Watson et al, 2017 ).…”

“…Such endeavors could utilize simulation models that integrate the effect of climate variability, the retention of the legume and non-legume residues, and changes in the soil water balance and N dynamics and their effects on yield and economic returns from different rotations ( Hochman et al, 2020 ). Simulations models provide the ability to undertake life-cycle analyses of fossil energy consumption, or to design, predict and compare long-term requirements for inputs of N fertilizer and the implicit environmental costs (NO 3 leaching, greenhouse gas emission outcomes) of different alternative cropping sequences ( Costa et al, 2021 , Hochman et al, 2021 ). This would enable the identification of where the N benefits are likely to be the greatest, and provide information on cropping systems and sequences most suited for different agroecological zones ( Smith and Chalk, 2020 , Tagliapietra et al, 2021 ).…”

“…However, it should also be acknowledged that in some climates, soil types and farming systems can be an elevated risk of leaching or volatile losses of N mineralized from the N-rich legume residues following the end of the growing season ( Fillery, 2001 , Watson et al, 2017 , Williams et al, 2017 ), although often there are opportunities for this to be managed with the use of cover crops ( Kaye and Quemada, 2017 , Plaza-Bonilla et al, 2017 , Watson et al, 2017 ). The added advantage of N being supplied from the organic residues of N 2 -fixing food or fodder legumes substantially lower fossil energy C costs associated with their production than N fertilized systems ( Erismann et al, 2008 , Jensen et al, 2020 , Costa et al, 2021 ).…”

Climate change impacts on European arable crop yields: Sensitivity to assumptions about rotations and residue management

“…S13). However, the rotations generated also did not consider legume crops, grass leys or fallows as rotation components that are well known to diversify cropping systems (Hufnagel et al, 2020), affect yields and environmental impacts (Costa et al, 2021). The assumptions about residues retained would not be representative of the actual farmers' practices as the residues management will depend on crop rotations and soil tillage.…”