Tine tip width and placement depth by row-injection of cattle slurry influence initial leaf N and P concentrations and final yield of silage maize

Abstract

There is an urgent need to replace mineral phosphorus (P) fertilizers placed near the maize seed at sowing with other management strategies to ensure a more environmentally friendly silage maize production and to avoid depletion of the phosphate rock reserve. The main objective of this study was to test and investigate effects of different tine geometry (operation depth and tine width) and use of the nitrification inhibitor (NI) 3,4-Dimethylpyrazole phosphate (DMPP) on early growth and final yields of maize under field conditions with the purpose of replacing mineral starter P fertilizers with row-injected liquid dairy manure (slurry). A two-year field experiment was carried out on a sandy loam and a loamy sand with moderate soil P status according to the Olsen P soil test. Cattle slurry with a NI was row-injected before sowing using newly developed goosefoot tine tips of three widths (8, 17 or 26 cm) with a roller to control injection depth. For the widest tine (26 cm) slurry was placed at 7 or 10 cm depth directly under the maize seed, and for the other tines slurry was placed at 10 cm depth. One of the placement methods was tested with and without a NI. The placement methods were compared to traditional slurry injection with random lateral positions relative to the maize row (non-placed slurry) and increasing rates of mineral P starter fertilizer with and without NI. The study showed that slurry placement using goosefoot tines of 17 or 26 cm width injected at 10 cm depth combined with a NI resulted in similar final yields (up to 17 Mg DM yield ha−1) as when using mineral P as a starter fertilizer with non-placed slurry on the sandy loam. On the loamy sand, slurry placement increased early P concentration in maize, but final yield benefitted more from the mineral P fertilizer (+ 1.6 Mg DM yield ha−1 compared to the plots receiving non-placed slurry and no mineral P fertilizer). Addition of a NI to placed slurry increased early stage maize leaf P concentration on the sandy loam and early maize leaf N concentration on the loamy sand, but not with non-placed slurry. We conclude that maize yield benefitted from row-injection with medium or broad goosefoot tines placed at 10 cm depth combined with a NI, but only on the sandy loam soil in one of two trial years. The most optimal slurry distribution by placement varied with soil type and year.