Utilization of liquid hog manure to fertilize grasslands in southeast Manitoba: impact of application timing and forage harvest strategy on nutrient utilization and accumulation

Abstract

Liquid hog manure (LHM) is used to improve productivity of grasslands in western Canada. However, application of manure to meet crop N requirements can result in excessive accumulation of P, especially in grazing systems. A three-year study was carried out to assess the impact of timing of liquid hog manure application and harvest strategy on nutrient utilization and accumulation by grasslands in southeast Manitoba. Liquid hog manure was applied annually at a full rate of 142 ± 20 kg available N ha−1 in spring (Single application) or as two half rate applications of 70 ± 6 kg available N ha−1, one in fall and one in spring (Split application). Two harvest strategies, haying and grazing, were employed to export nutrients from grasslands. Spring-applied manure averaged 8.9% dry matter, 5.7 g total N L−1, 1.5 g total P L−1, and 2.1 g total K L−1 and fall-applied manure from the same source averaged 3.9% dry matter, 4.4 g total N L−1, 0.7 g total P L−1, and 2.2 g total K L−1. Manure application based on grass N requirements resulted in at least two times more P and K applied than recommended for Manitoba grasslands. Nutrient (N, P, and K) export from grasslands was five times higher when grass forage was harvested as hay than through grazing. Average nutrient utilization when forage was harvested as hay was 153 kg N ha−1, 18 kg P ha−1, and 123 kg K ha−1 and was higher in the years with increased precipitation. Grazing was not effective in removing nutrients from grasslands as indicated by lower N, P, and K utilization efficiency (% applied nutrient) in grazed (30% for N, 7% for P, and 18% for K) relative to hayed (75% for N 32% for P, and 103% for K) paddocks. Nutrient accumulation was impacted by a combination of harvest strategy and timing of manure application. Both single and split applications increased soil extractable nutrients, but soil extractable nutrients were higher in grazed relative to hayed paddocks following single manure application. After 3 years of manure application, the amount of Olsen-P (62 kg ha−1) exceeded that required for optimal forage growth. However, soil levels did not exceed the soil Olsen-P regulatory threshold (60 mg kg−1) that restricts manure P applications in Manitoba. An analysis of P balance, for this particular soil, indicated that a surplus of 18.9 kg manure P ha−1 (in excess of forage P exported as hay or weight gain) increased the soil Olsen-P concentration by 1 mg kg−1. Nutrient utilization and accumulation will be impacted by timing of manure application and harvest strategy employed as well as amount of precipitation received during the growing season.