Fertilizer placement to improve crop nutrient acquisition and yield: A review and meta-analysis

In agricultural soils, plant-available nitrogen (N) and phosphorous (P) may be inadequate for crop production although total N and P concentrations are high. Therefore, N and/or P fertilizer is commonly applied to field soil by broadcast, even though broadcast does not ensure that a considerable proportion of applied fertilizer is available at the right time and place for optimal root uptake. Fertilizer placement in soil, which refers to precise application of specific fertilizer formulations close to seeds or plant roots to ensure high nutrient availability, may be a more effective alternative to broadcast application. The objectives of this paper are: (1) to summarize current techniques for fertilizer placement in soil and to identify fertilizers that are suitable for subsurface placement; and (2) to quantify the relative effects of fertilizer placement to fertilizer broadcast on crop nutrient acquisition and yield. To achieve these aims, we reviewed scientific literature on the dynamics of nutrient movement from soil into roots and studies on fertilizer placement under field conditions. Additionally, we performed three meta-analyses according to the method of baseline contrasts on the relative effects of fertilizer placement (Treatment) to fertilizer broadcast (Control) on yield, nutrient concentration and content in above-ground plant parts. In all, we used 1022 datasets from 40 field studies published from 1982 to 2015 (85% of studies from 2000). Results showed that overall, fertilizer placement led to 3.7% higher yield, 3.7% higher nutrient concentration and 11.9% higher nutrient content in above-ground parts than fertilizer broadcast. For CO(NH2)(2) and soluble phosphate (PO43-), NH4+ and PO43-, CO(NH2)(2), NH4+, and PO43-, fertilizer placement led to 27.3%, 14.7%, 11.6%, 3.8% and 0.0% increase in yield in comparison to broadcast respectively. Increase in relative yield and relative nutrient uptake from subsurface placed CO(NH2)(2), CO(NH2)(2) and PO43-, NH4+, NH4+ and PO43- or ICE tend to increase with increasing placement depth to more than 10 cm. Results show that deep subsurface placed NH4+ (+/- PO43-) or CO(NH2)(2) (+/- PO43-), K+, solid or liquid manure is more,effective to improve deep rooting, nutrient uptake and yield than broadcast. Thus, deep subsurface fertilizer placement could be one more tool to mitigate negative consequences of increasingly frequent high temperatures and drought that threaten food production globally. (C) 2016 Elsevier B.V. All rights reserved.