Journal Publication

Late-season fertilizer N applications in maize (Zea mays L.) is a tactical agronomic practice that seeks to improve the synchrony between plant N demand and soil N supply. While this management practice can increase yield and limit unintended environmental impacts, a quantitative synthesis of the effects of late N applications on grain yield and resource use efficiency is lacking.

A meta-analysis was conducted to identify patterns of yield response to late-N fertilization (post tenth-leaf, V10) across site-years studies. The goals of this study were to: 1) quantify the effect of late-season N fertilization on maize yield; and 2) identify an indicator for decision support of late-N fertilization. Published and unpublished sources from 1983 until 2018 were included in the meta-analysis (14 studies; n = 625 treatment means). Early-season (E_N, ≈ 100% of fertilizer applied prior to the sixth-leaf, V6) and late-season (L_N, < 50% N applied before V10) N fertilization were compared to determine the effect of application timing on yield, N uptake, and N recovery efficiency (REN, N uptake increase per unit of N applied).

Across studies, the timing of application of N was not associated with a quantifiable change in maize yield. Due to significant heterogeneity across experiments (I² = 48%), there is an opportunity to explore plausible effects of the practice when N is limiting (LN improved yield) on yield and effective use of N. Increased post-silking N uptake (>28% of N uptake at maturity occurring after silking) was positively related with yield increases for LN (+577 kg ha⁻¹), and the contrast in REN between L_N and E_N was 0.04 kg kg⁻¹. Environments prone to a greater N uptake during reproductive stages are proposed to be more suitable for late N applications. Prediction algorithms to inform tactical N management that can both increase productivity and sustainability could be developed provided adequate links between late-season N uptake and growing-season indicators could be established.