Combined Starter Phosphorus and Manure Applications on Silage Corn Yield and Phosphorus Uptake in Southern BC

Abstract

Phosphorus (P) management using mineral and manure P in excess of plant needs contributes to legacy soil P in coastal British Columbia, Canada. The objectives of this study were (a) to assess the effects of starter P at early growth stages and their carryover through corn maturity, and (b) to determine how corn yields relate to soil P saturation indicators. Eleven 1-year experiments were conducted on sites with contrasting legacy soil P in 2018 (three sites) and 2019 (eight sites). Six combinations of starter and manure P rates (T1: 0P starter + 0P manure ; T2: 0P starter + 35P manure ; T3: 5P starter + 30P manure ; T4: 10P starter + 25P manure ; T5: 15P starter + 20P manure ; T6: 20P starter + 15P manure) were assigned to a RCBD with four replicates. In 2018, corn dry matter weight (DMY) at the 6-leaf stage was affected by starter P in all sites, and the response curve was described by a linear-plus-plateau model with critical starter P of 5.0 and 7.5 kg ha −1. In 2019, corn DMY at early growth stages was not affected by starter P. Corn DMY at harvest varied between 15.2 Mg ha −1 in sites with low initial soil P and 27.2 Mg ha −1 in sites with excess P. Four sites exhibited a trend of high DMY with treatment comprising low starter P and high side-dressed manure P additions. The degree of P saturation (DPS, 14.0 to 38.0%) and P saturation index (PSI, 3.0 to 14.0%) were related to corn DMY by quadratic functions (R 2 = 0.76-0.94). From these results, we can conclude that the effect of starter P on young corn plants varies with year, but does not carryover through harvest. Moreover, current starter P (30-40 kg ha −1) recommended for corn can be reduced by up to 75% (5.0-7.5 kg ha −1) without affecting yield, thus reducing annual P inputs and farmers' production costs. Finally, PSI as a proxy of DPS is a possible agro-environmental indicator that, coupled with reduced starter P fertilizer, can further contribute to reducing the risk of P transfer from agricultural soils in coastal British Columbia.

Phosphorus saturation index and water-extractable phosphorus in high-legacy phosphorus soils in southern British Columbia, Canada

“…The soils in the area belong to the order Brunisolic, Gleysolic, Luvisolic, Podzolic, and Regosolic (Soil Classification Working Group 1998). The minimum and maximum general soil properties across all sites were soil pH: 4.9-6.0, total carbon (C): 0.94%-11.35%, total N: 0.07%-0.82%, and 32 mg•kg −1 (Messiga et al 2020). Phosphorus fertilization in the silage corn fields included applications of 35 kg P•ha −1 as starter and manure P (Messiga et al 2020).…”

“…The minimum and maximum general soil properties across all sites were soil pH: 4.9-6.0, total carbon (C): 0.94%-11.35%, total N: 0.07%-0.82%, and 32 mg•kg −1 (Messiga et al 2020). Phosphorus fertilization in the silage corn fields included applications of 35 kg P•ha −1 as starter and manure P (Messiga et al 2020). Phosphorus fertilization recommendations in BC blueberry production guides are based on leaf analysis and are well beyond crop removal (BC berries production guide 2018b).…”

“…The PSI alone can overestimate the risk of P loss to the environment, but coupled with soil pH or Pw, it provides an assessment of the environmental risk of the soil. In silage corn sites, application of manure and supplement of starter fertilizer blends as the main source of N has little effects on the acidity of the soil (Zhang et al 2018;Messiga et al 2020). Lower soil pH, in the blueberry sites compared with the silage corn sites is due to the use of ammonium sulfate and other acidifying N fertilizers by local farmers as source of N to inhibit the nitrification process because blueberry plants preferentially absorb ammonium over nitrate (Messiga et al 2018).…”

“…For soils with PSI above critical values, annual P inputs should be less than outputs, and reliance for plant P nutrition should be placed on legacy soil P. For silage corn, one strategy will consist of limiting the use of starter fertilizer P; another strategy is to find ways to adequately address dairy manure application, which is the biggest constraint because of high animal stocking densities in south coastal BC . We recently demonstrated that P fertilizer recommendations for silage corn can be refined by decreasing starter P rates to "5.0 to 7.5" kg P•ha −1 without decreasing dry matter yield at harvest (Messiga et al 2020). For blueberry production systems, there is a need for scientific evidence on optimum P fertilizer rates to refine actual fertilizer P recommendations.…”

“…High soil P levels resulting from this P surplus may contribute to water quality impairments, which can last for decades if sound strategies to reduce soil P are not implemented (Carpenter 2008). Utilizing legacy soil P can also have significant agronomic (McDowell et al 2020;Messiga et al 2020) and economic benefits (Zhang et al 2020).…”