Availability of Phosphorus after Long‐term Whole and Separated Slurry Application to Perennial Grass prior to Corn Silage

Abstract

Removing solids from whole dairy slurry (WS) can reduce P loading on fields. This study investigated the effects of 11 yr of applications of WS, separated liquid fraction (LF), commercial fertilizer, WS plus fertilizer, and a control on total and extractable (Kelowna) soil P in perennial grass ( Schreb.) and two subsequent silage corn ( L.) crops. Plots received 200 kg N ha with or without 40 kg P ha. Shoot biomass, P uptake, arbuscular mycorrhizal fungi root colonization, and soil microbial P were determined for corn at six leaves. Whole-crop and grain yield, P uptake, dry matter, and grain content were determined at maturity. The LF treatment received 30% less manure P than WS, had lower extractable soil P at 0 to 15 and 15 to 30 cm, and had lower total P at 0 to 15 cm. Historical treatments had no effect on soil microbial P or arbuscular mycorrhizal fungi colonization. At six leaves, corn shoot biomass, P concentration, and P uptake were related to historical P rates in Year 2, but the relationship was not apparent in Year 1. Starter P fertilizer increased shoot yield and P uptake for all treatments in both years. At maturity, most yield parameters for WS and LF were similar in Year 1, but in Year 2, there was a significant response to starter P fertilizer and a positive relationship between historical P rate and corn performance. This study shows that long-term LF treatments reduced the risk of P pollution with relatively little effect on the P response of subsequent corn crops.

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

“…Starter P fertilizer rates for silage corn are 5 to 15 kg P ha −1 in Ontario and Quebec (Preston, 2019) and 5 to 13 kg P ha −1 in the US (Jokela, 1992). In cool and moist coastal BC, almost all silage corn is side-banded at approximately 30-40 kg P ha −1 , and most of the corn receives manure (Zhang et al, 2018). The critical starter P rates obtained in our study are below local recommendations (British Columbia Ministry of Agriculture [BCMA], 2010).…”

“…Silage corn (8500 ha) and forage grass (13,670 ha) rotation is the main cropping system providing feed for dairy cows in BC. Phosphorus fertilization recommendations for the silage corn phase of the rotation averaged 90 kg P ha −1 , including 50 kg P ha −1 as dairy manure and 40 kg P ha −1 as starter fertilizer P for a crop that exports on average 35 kg P ha −1 (Bittman et al, 2006;Zhang et al, 2018). The annual P surplus for forage grass and silage corn rotation systems is 3030 Mg (50 kg P ha −1 ) (Bittman et al, 2017), which contributes to buildup of legacy soil P. A better match of P applications to silage corn needs is necessary to maintain or drawdown legacy soil P.…”

Year-Round N2O Emissions From Long-Term Applications of Whole and Separated Liquid Dairy Slurry on a Perennial Grass Sward and Strategies for Mitigation

“…Treatment emission factors (EF) were determined for each year using values for annual N 2 O-N emissions from treated plots minus emissions from the CTRL plot in that replicate and divided by the total-N applied, then multiplying by 100. Emissions were calculated relative to values of crop yield and crop N uptake, which were partially reported in Bittman et al (2011) and Zhang et al (2018). Measurements taken of soil temperature, soil moisture, bulk density, water-filled pore space and soil mineral N will be reported in a future manuscript.…”

“…The P-rich sludge fraction may be precision-injected at planting to both replace commercial starter fertilizer and to provide adequate season-long P for a corn crop (Bittman et al, 2012). The separated liquid fraction has higher N use efficiency than whole slurry and can be applied at agronomic rates with reduced excess P (Bittman et al, 2011;Neufeld et al, 2017;Zhang et al, 2018). The liquid fraction is less viscous than the whole slurry hence infiltrates more rapidly into the soil, thereby reducing opportunity for ammonia loss (Sommer et al, 2006), although results are sometimes inconsistent (Bhandral et al, 2009).…”

“…The objectives of this 5 year field study, conducted on long term grass-slurry manure plots (described by Bittman et al, 2011;Neufeld et al, 2017;Zhang et al, 2018), were to (1) quantify N 2 O emissions after multiple slurry applications on grass over the growing season, (2) quantify emission spikes due to wet/dry and freeze/thaw events, (3) compare emissions from applications of whole slurry (WS), separated liquid fraction (SLF), and mineral fertilizer (FERT) at comparable rates of mineral and total N, 4) identify methods that may mitigate N 2 O emissions from intensively fertilized grassland.…”