Nitrogen fertilizer rate increases plant uptake and soil availability of essential nutrients in continuous maize production in Kenya and Zimbabwe

Abstract

Low fertilizer application rates for several decades have depleted soil nutrients in Sub-Saharan Africa (SSA) and contributed to relatively stagnant maize (Zea mays L.) yields. As maize is a staple crop, nutrient depletion has resulted in major food insecurity. While one potential solution is to apply more nitrogen (N) fertilizer, previous studies in SSA have found maize yield responses to be variable, likely because N is often not the only limiting nutrient. This study aimed to determine the impact of consecutive N fertilizer applications on plant uptake and available soil reserves of non-N nutrients. Maize was grown continuously in 3 sites that were representative of the ecosystem variability found in East/Southern Africa (Embu, Kenya; Kiboko, Kenya; Harare, Zimbabwe) at 4 different N fertilizer rates (0-160 kg N ha -1 ) from 2010 to 2015. Following the final season, grain, stover, and soil (sampled at different depths to 0.9 m) samples were analyzed for essential plant nutrients. Nitrogen fertilizer increased plant uptake of P, S, Cu, and Zn by up to 280%, 320%, 420%, and 210%, respectively, showing potential for mitigating non-N nutrient deficiencies in 2 of the 3 sites. Cumulatively, however, there was a net negative effect of higher N rates on the P, K, and S soil-plant balances in all sites and on the Mn and Cu soil-plant balance in Kiboko, indicating that applying N fertilizer depletes non-N soil nutrients. While N fertilizer enhances the uptake of non-N nutrients, a balanced application of multiple essential nutrients is needed to sustainably increase yields in SSA.

Nitrogen rate impacts on tropical maize nitrogen use efficiency and soil nitrogen depletion in eastern and southern Africa

“…As was the case with grain yield, plant N content did not plateau within the applied N rate range in Kiboko. Plant N content did not differ consistently among hybrids from season to season at any site (Pasley 2018).…”

“…The data reported in this paper are averaged over all hybrids, but detailed hybrid data is reported in Pasley (2018). Unless otherwise noted, there were no significant interactions between hybrid, N rate, and/or depth effects for any of the plant-soil N dynamics reported in this paper.…”

“…In the 5 years preceding the initiation of this experiment, continuous maize (in Embu and Harare) and sorghum ( Sorghum bicolor L.) (in Kiboko) were cultivated continuously without any inorganic or organic inputs to simulate the N depleted conditions of the average small-holder farm in SSA. More details about the site conditions can be found in Supplementary Table 1 and in Pasley et al ( 2019 ).…”

“…In our study, the only site in which NRE increased when N rate decreased was Harare. Embu and Kiboko's stagnant NRE values suggest that while N uptake was likely restricted by drought stress in Embu and sub-optimal N rates in Kiboko (Pasley et al 2019), these constraints lessened with increased fertilizer N supply (Vanlauwe et al 2001;Betrán et al 2003). Meanwhile, P deficiency in both Embu and Harare likely equally limited N uptake at all N rates (Pasley et al 2019).…”

Growing out of hunger: towards an improved understanding of the water and nutrient limited yield of cassava

“…Under imbalanced supply of nutrients, plants take up more of the omitted nutrients (Pasley et al, 2019) due to improved soil exploration by more developed root systems and/or root functioning. This plantsoil interaction is not modelled, we used input values for indigenous nutrient supply and fertilizer recovery derived from experimental measurements (Table 5.2) as parameter in the LINTUL-Cassava-NPK model.…”