By Dr. Kim Schneider, Assistant Professor in Forage and Service crops, University of Guelph, and Puja Lamichhane (MSc student)

Soil fertility is a critical component of achieving desired crop yield outcomes; however, less attention is typically given to forage fertility than other annual cash crops. Perhaps that is because perennial plants don’t require a high amount of nutrients in a short time period like annual crops do.  There are anecdotal reports of producers applying 100 lbs/acre of a 19-19-19 (N-P-K) fertilizer annually to their forages and it is unclear whether this is a beneficial practice. In addition, despite the introduction of new forage plant varieties, including grasses such as Festulolium species (a cross between a ryegrass and a fescue), forage fertility recommendations in Ontario have not been updated since the 1980’s.

About the Project

This trial evaluates the impact of fertility management on the yield and quality of 19 different forage mixtures available on the Ontario market. These treatments ranged from pure grasses to pure legumes and included common hay and pasture grass-legume mixes available on the market. The three fertility treatments to be tested include: 1) zero fertility control, 2) a one-time application/yr of 100 lbs/acre of 19-19 -19 (N-P-K) fertilizer, or 3) fertilize as needed according to OMAFRA guidelines based on soil testing. The 100 lbs/acre of 19-19-19 (NPK) was a light application of nutrients and less than the OMFRA recommended rates.  An economic analysis also provides information on profitable mixtures or species for producers in Ontario.  The project spanned three years (field seasons were 2020, 2021, and 2022) and was conducted at the Ontario Crops Research Centre in Elora.

Fertility Results

At this site, where soils were low in extractable potassium (63 ppm) and moderate for soil test phosphorus (11 ppm) at the start of the trial, the fertilize as needed treatment had a large impact on forage yield. Figure 1 shows the total forage yields over three year of production for both grasses and grass-legume mixtures and across fertility treatments.  The impact of fertility on yield became greater as time went on.  Overall, the fertilize as needed treatment had the highest yields and the 100 lbs/acre of 19-19-19 (NPK) was not significantly different from adding no fertilizer at all.  

In order to better understand the limiting factor (phosphorus or potassium) for the legume-grass mixtures (which did not receive nitrogen in the fertilize as needed treatment because it is not recommended when legume content is greater than ~30%), we analyzed plant tissues for P and K content.  Our analysis revealed that P was not limiting, even in the zero fertility control treatment, but potassium was lower than the critical tissue K concentration (~1.7%) in the control and the 100 lbs per acre of 19-19-19 fertilizer treatments. By the third year of production, the soil tests for P and K were both considered low (~7 and 60 ppm respectively), but potassium appeared to be the limiting factor for plant growth.

Forage Species / Mixtures

For forages that contained only grasses, a few trends were observed. In the first year of production (2020), grass monocultures yielded higher than grass mixtures. The Festulolium grasses had the highest yields, closely followed by Italian ryegrass, while in 2021 and 2022, grass mixtures (especially those including orchardgrass) outperformed grass monocultures. Italian ryegrass also became increasingly weedy over the three years (going from 10% in year 1 to 25% in year 3), likely owing to the fact that it is not a perennial species.  In general, mixtures with legumes and grasses out-yielded those containing only grasses.  The red clover based mixture outperformed alfalfa-based mixtures in the first year of production, but this trend didn’t last into the second and third years, where alfalfa-based mixtures had greater yields than those with red clover. Thus if wanting more forage in the short-term (ie. first year following establishment), red clover may be a good option, but if site conditions allow for alfalfa growth (good drainage, neutral pH), alfalfa will likely outperform red clover over a longer time period.  When alfalfa was planted as a monoculture, it produced yields that were similar to alfalfa-grass mixtures, however, it had a greater proportion of weeds (>30%) than grass-legume mixtures (<10%) by the third year of the study. We tested several different alfalfa varieties in this study, but found all were performing quite similar to each other in terms of yield.

Forage Quality

Forage quality was tested in the first year of the trial; it was found that the fertility treatment did not affect forage quality, but that the mixture’s species was the driving effect. In general, mixtures and monocultures with timothy and meadow fescue had greater Relative Forage Quality (RFQ) indices and protein concentrations, which is to be expected with these grasses. Unsurprisingly, legume mixtures with alfalfa, red clover, white clover, and grasses also produced good RFQ values and protein concentrations.

Economic Findings

Generally, all mixtures across all fertility treatments had a net positive profit, however, significant differences were found across treatments.  Grass-legume mixtures and the alfalfa monoculture had the highest profit over three years, compared to grasses.  For these treatments, it was more profitable when fertilizer was applied according to OMAFRA recommendations for P and K.  Interestingly, it was not more profitable to fertilize according to recommendations for forages that only had grasses in them (it was not less profitable either, but similar).  This is due to the higher nitrogen fertilizer cost for the fertilize as needed treatment, which increased production costs and offset the benefits of higher yields.  Grass mixtures tended to be more profitable than grass monocultures when looked at over three production years.

Conclusions and Significance

To produce higher yields at Elora, which had low soil test K concentrations at the start, the best fertility management regime to maximize yields was to soil test and fertilize according to OMAFRA recommendations. Over three years, applying 100 lbs. acre^-1 of 19-19-19 (NPK) fertilizer (a common producer practice) did not lead to increased yields relative to the zero fertility control. Hence, it does not appear worth the effort to apply fertilizer if you don’t know what you need.  Grass-legume mixtures provided consistently higher yields than solely grass-based mixtures and do not require nitrogen applications, making them more economical.  Alfalfa-grass mixtures produced the highest yields over three years when fertilized according to recommendations and were the most profitable across the forages tested. Low soil extractable potassium concentrations impacted forage yield; this underscores the importance of potassium in forage fertility programs.  The transferability of our study to other sites will vary depending on starting soil fertility levels. Thus, it is recommended that soil fertility testing of forage fields should be done regularly to determine your site specific characteristics.

Table 1: Forage identification key for species and species mixtures used in the three-year field experiment at the Elora Research Station, University of Guelph (Elora, ON).

Ontario Forage Council would like to thank Dr. Kim Schneider and Puja Lamichhane for providing this article.