Abstract
Exploiting native soil phosphorus (P) and the large reservoirs of residual P accumulated over decades of cultivation, namely “legacy P”, has great potential to overcome the high demand of P fertilisers in Brazilian cropping systems. Long-term field experiments have shown that a large proportion (> 70%) of the surplus P added via fertilisers remains in the soil, mainly in forms not readily available to crops. An important issue is if the amount of legacy P mobilized from soil is sufficient for the crop nutritional demand and over how long this stored soil P can be effectively ‘mined’ by crops in a profitable way. Here we mapped the spatial–temporal distribution of legacy P over the past 50 years, and discussed possible agricultural practices that could increase soil legacy P usage by plants in Brazil. Mineral fertiliser and manure applications have resulted in ~ 33.4 Tg of legacy P accumulated in the agricultural soils from 1967 to 2016, with a current annual surplus rate of 1.6 Tg. Following this same rate, soil legacy P may reach up to 106.5 Tg by 2050. Agricultural management practices to enhance soil legacy P usage by crops includes increasing soil pH by liming, crop rotation, double-cropping, inter-season cover crops, no-tillage system and use of modern fertilisers, in addition to more efficient crop varieties and inoculation with P solubilising microorganisms. The adoption of these practices could increase the use efficiency of P, substantially reducing the new input of fertilisers and thus save up to 31.8 Tg of P fertiliser use (US$ 20.8 billion) in the coming decades. Therefore, exploring soil legacy P is imperative to reduce the demand for mineral fertilisers while promoting long-term P sustainability in Brazil.
Highlights
Exploiting native soil phosphorus (P) and the large reservoirs of residual P accumulated over decades of cultivation, namely “legacy P”, has great potential to overcome the high demand of P fertilisers in Brazilian cropping systems
Estimates of global soil P budgets have suggested that most of Brazilian croplands are accruing a P surplus over time[12,13]. This has been confirmed by long-term field experiments, which have shown that a large proportion (> 70%) of the surplus P added to Brazilian soils by fertilisers remains in the soil mainly in forms not readily available to c rops[8,14]
Our findings revealed that soil legacy P quantified in Brazil is lower than results reported for other regions of the world with older legacies of agricultural exploitation
Summary
Exploiting native soil phosphorus (P) and the large reservoirs of residual P accumulated over decades of cultivation, namely “legacy P”, has great potential to overcome the high demand of P fertilisers in Brazilian cropping systems. The use of soil legacy P by plants is potentially attractive because it provides financial savings on inputs of inorganic P fertilisers, as well as reducing pressure on phosphate rock reserves and reducing the risk of P transfers to water, and eutrophication of freshwater and coastal regions Relevant questions, such as: Is sufficient P mobilized from the soil ‘legacy’ to satisfy crop nutritional needs? We use empirical data to: (i) investigate how agricultural area, P fertiliser consumption and P use efficiency of main crops has evolved over the last 50 years in Brazil; (ii) estimate the total amount of legacy P (agricultural P surplus) accumulated in Brazilian soils over the last 50 years based on P inputs from fertilisers and P outputs by crop harvests, (iii) map the spatial–temporal distribution of soil legacy P across the country; and (iv) forecast the future agricultural P balance and savings up to 2050, considering potential management strategies to explore more efficiently the use of modern phosphate fertilisers, and soil legacy P for crop production
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