The impact of phosphorus on projected Sub-Saharan Africa food security futures

Sub-Saharan Africa must urgently improve food security. Phosphorus availability is one of the major barriers to this due to low historical agricultural use. Shared socioeconomic pathways (SSPs) indicate that only a sustainable (SSP1) or a fossil fuelled future (SSP5) can improve food security (in terms of price, availability, and risk of hunger) whilst nationalistic (SSP3) and unequal (SSP4) pathways worsen food security. Furthermore, sustainable SSP1 requires limited cropland expansion and low phosphorus use whilst the nationalistic SSP3 is as environmentally damaging as the fossil fuelled pathway. The middle of the road future (SSP2) maintains today’s inadequate food security levels only by using approximately 440 million tonnes of phosphate rock. Whilst this is within the current global reserve estimates the market price alone for a commonly used fertiliser (DAP) would cost US$ 130 ± 25 billion for agriculture over the period 2020 to 2050 and the farmgate price could be two to five times higher due to additional costs (e.g. transport, taxation etc.). Thus, to improve food security, economic growth within a sustainability context (SSP1) and the avoidance of nationalist ideology (SSP3) should be prioritised

Efficiency of phosphorus resource use in Africa as defined by soil chemistry and the impact on crop production

By 2050 the global population will be 9.7 billion, placing an unprecedented burden on the world’s soils to produce extremely high food yields. Phosphorus (P) is crucial to plant growth and mineral fertilizer is added to soil to maintain P concentrations, however this is a finite resource, thus efficient use is critical. Plants primarily uptake P from a labile (available) P pool and not from the stable solid phase; transfer between these pools limits bioavailability. Transfer is controlled by soil properties which vary between soil types. The dynamic phosphorus pool simulator (DPPS) quantifies crop production and soil P relationships by utilising the transfer. This approach effectively models crop uptake from soil inputs, but it does not quantify the efficiency use. This study incorporates geochemical techniques within DPPS to quantify the efficiency of fertilizer-P use based on soil chemistry

Soil chemistry aspects of predicting future phosphorus requirements in Sub-Saharan Africa

Phosphorus (P) is a finite resource and critical to plant growth and therefore food security. Regional‐ and continental‐scale studies propose how much P would be required to feed the world by 2050. These indicate that sub‐Saharan Africa soils have the highest soil P deficit globally. However, the spatial heterogeneity of the P deficit caused by heterogeneous soil chemistry in the continental scale has never been addressed. We provide a combination of a broadly adopted P‐sorption model that is integrated into a highly influential, large‐scale soil phosphorus cycling model. As a result, we show significant differences between the model outputs in both the soil‐P concentrations and total P required to produce future crops for the same predicted scenarios. These results indicate the importance of soil chemistry for soil‐nutrient modelling and highlight that previous influential studies may have overestimated P required. This is particularly the case in Somalia where conventional modelling predicts twice as much P required to 2050 as our new proposed model. Plain language summary Improving food security in Sub‐Saharan Africa over the coming decades requires a dramatic increase in agricultural yields. Global yield increase has been driven by, amongst other factors, the widespread use of fertilisers including phosphorus. The use of fertilisers in Sub‐Saharan Africa is often prohibitively expensive and thus the most efficient use of phosphorus should be targeted. Soil chemistry largely controls phosphorus efficiency in agriculture, for example iron and aluminium which exist naturally in soil reduce the availability of phosphate to plants. Yet soil chemistry has not been included in several influential large‐scale modelling studies which estimate phosphorus requirements in Sub‐Saharan Africa to 2050. In this study we show that predictions of phosphorus requirement to feed the population of Sub‐Saharan Africa to 2050 can significantly change if soil chemistry is included (e.g. Somalia with up to 50% difference). Our findings are a new step towards making predictive decision‐making tool for phosphorus fertiliser management in Sub‐Saharan Africa considering the variability of soil chemistry

Monitoring winter wheat growth performance at sub-field scale using multitemporal Sentinel-2 imagery

A crop growth monitoring system should objectively and reproducibly reflect changes in crop biophysical properties during the growing season. By monitoring crop growth and performance at specific crop development stages, the farmer can obtain reliable information for timely crop management to achieve optimum crop production. This work aimed to evaluate crop development using five winter wheat (Triticum aestivum L.) biophysical properties (shoots number, green area index, plant height, leaf N content, and aboveground dry biomass) predicted from Sentinel-2 data compared with benchmarks representing target growth from emergence to harvest. Data were collected for four principal phenology stages (tillering, stem elongation, heading, and fruit development) in 35 winter wheat fields in the Republic of Ireland and 40 in the United Kingdom in 2020 and 2021. A total of 1500 plots were selected for crop sampling over two growing seasons. The models were generally good, but phenology-specific models performed better (R2 between 0.72 and 0.87) than models for the entire season (R2 between 0.13 and 0.84). To assess the low-performance zones in fields, the predicted biophysical properties were compared to benchmarks taken from agronomic advice. Spatial analysis was then used to identify low-performance areas in fields, which were validated using farmers’ feedback. It was concluded that the approach taken could be reliably used to monitor winter wheat over a wide area and through time

A multi-level analysis of China's phosphorus flows to identify options for improved management in agriculture

Phosphorus (P) is a finite natural resource and is essential for food production. The amount of P involved in food production in China relative to the increase of food production has increased dramatically over the past decades, which has led to serious environmental pollution. Because of China's enormous share in global P fertilizer production (30%) and consumption (37.5%), it evidently plays a crucial role in developing a more sustainable use of this essential resource for agriculture. We performed an integrated analysis of the P flows, P stocks, P utilization efficiencies (PUE) and environmental implications at the national level in China for the year 2010, complemented with an analysis at regional, county and farm levels. The static Material Flow Analysis approach based on the law of mass balance was used. We found that P accumulation in the arable land and P losses in the livestock raising industry are the major contributors to environmental pollution. Improving the PUE in arable land and the livestock raising industry, on the basis of the actual demands combined with efforts to promote the use of residual soil P on arable land and the recycling of organic manure and wastes, will significantly reduce the consumption and losses of P from the food chain, and will slow down the depletion of this finite natural resource.</p