Row-injected cattle slurry can replace mineral P starter fertiliser and reduce P surpluses without compromising final yields of silage maize

Abstract

Accumulation of phosphorus (P) in soil can be a problem on intensive livestock farms with maize cropping, when mineral P starter fertilisers are applied in combination with evenly injected liquid manure before sowing. We examined the possibilities of replacing mineral P starter fertiliser with placement of cattle slurry close to the maize row before sowing in a two-year field study. The study was carried out on a sandy loam (pH of 6.1 and Olsen-P content of 44 mg P kg−1) and a coarse sandy soil (pH of 5.9 and Olsen-P content of 34 mg P kg−1) in Denmark. Slurry was row-injected at 10 cm depth in a broad-band with a 26-cm wide goosefoot tine or in a narrow-band. These two row-injection methods were combined with a nitrification inhibitor and/or slurry acidification. Treatments with evenly injected slurry at random lateral positions relative to the maize row (non-placed slurry) with increasing amounts of mineral starter P (0, 10 and 30 kg P ha−1, respectively) were included as reference treatments. Slurry placement in narrow or broad bands combined with slurry acidification or a nitrification inhibitor resulted in leaf P concentrations at the five-leaf stage that were significantly higher than the reference treatment with non-placed slurry and no mineral starter P. However, increased leaf P concentrations at the early growth stage did not always turn into higher yields at harvest. The highest dry matter yields (up to +1.9 Mg dry matter yield ha−1 compared to the reference treatment with non-placed slurry and no mineral starter P) were obtained when slurry was applied in a broad band below the maize row, but on the sandy loam only in combination with a nitrification inhibitor or slurry acidification. The P uptake at harvest did not differ among treatments (averaged 37 and 28 kg P ha-1 on the sandy loam and coarse sandy soil, respectively), and consequently the P surplus could be markedly reduced by omitting the use of mineral starter P fertiliser. We conclude that placement of cattle slurry in broad bands below the row can substitute the use of mineral P starter fertiliser and thus reduce farm P surpluses in silage maize cropping.