In western Canada most forage stands for grazing and hay production are usually established as grass-legume mixtures. Over time the productivity and livestock carrying capacity of these hay fields and pastures may decline, largely a result of reduced stand vigor, the invasion of unpalatable or less productive species, over-grazing, and poor soil fertility. Many farmers accept the gradual reduction in the proportion of legume forage in mixed forage stands, and reduced grass forage due to weeds, as a normal symptom of an aging stand. In the initial years of stand degradation, legume growth becomes variable and eventually grasses dominate the sward. In fact, the concentration of nutrients in ungrazed mature pasture grasses are commonly below optimum for efficient animal performance.
Various techniques have been used to improve unproductive stands, with fertilization using commercial fertilizer or livestock manure, often being an effective means of restoring forage productivity and quality. With the high cost and time associated with forage stand termination and re-establishment, farmers are anxious to identify all options for sustaining a forage stand. As a result, the use of fertilization of mature forage stands to both rejuvenate the stand and improve the forage quality can be important in managing established forage stands.
The nutrient requirements of top yielding forage crops are high as shown in the estimates of crop removal in Table 1. Given that the entire crop biomass is removed in the fodder, growing forages is one of the best means of drawing down the soils nutrient supply. It is estimated that only 25 percent of the improved pasture and hay is fertilized, and only 15 percent of alfalfa hay fields. Given the level of nutrient removal by forages, and these low levels of fertilizer addition, it is little wonder that farmers report that forage stands are only maintained for 3-5 years in high moisture regions of western Canada, and 6-9 years in the semiarid areas. A low forage yield is the most commonly cited reason for terminating a forage stand. Recent research carried out in Alberta and Saskatchewan indicates that there are some good opportunities to use fertilizer to rejuvenate established forage stands and avoid the cost of breaking.
Table 1. Nutrient removal by forage grass and alfalfa crops1.
|
Crop |
N |
P2O5 |
K2O |
S |
|
--- lbs/A --- |
||||
|
Alfalfa - 5 tons/A |
261-319 |
62-76 |
270-330 |
27-33 |
|
Grass hay - 3 tons/A |
92-113 |
27-33 |
117-143 |
11-14 |
1 From Nutrient Uptake and removal by field crops, Canadian Fertilizer Insititute (www.cfi.ca)
Hay land Fertilization Results
A series of nutrient response trials were established on forage stands in north-central Alberta. In one study evaluating hay yield responses, a two-year old alfalfa and timothy stand that tested 2 lb/A for phosphorus, 446 lb/A for potassium, 12 lb/Afor sulphur, and the soil N level being below the detectible limit. The fertilizer treatments included a complete blend of N (urea) at 90 lb N/A, phosphorus (triple super phosphate) at 67 lb P2O5/A, potassium (potassium chloride) at 78 lb K2O/A, and sulphur (ammonium sulfate) at 27 lb S/A, along with blends with each of the nutrients removed to determine which nutrient was most limiting to forage growth. Fertilizer was surface broadcast applied in the early spring and the forage harvested in July and September each year.
Results from this location indicate that while both N and P were limiting hay yield, P deficiency by far had the greatest impact (Figure 1). In fact, N accounted for approximately 23% of the forage yield response to fertilizer application, while P accounted for approximately 74%. High soil test K levels explained the lack of a response to K fertilizer application, and the application of S to the site in previous years would explain the absence of a S response. Given the low soil P levels at this locations, the impact of fertilizer P on forage yield was not surprising.
Based on the large yield response to N and P application, a fertilizer rate study was established at this location. The N rates applied were 0, 45 and 90 lb N/A, with a blanket application of 67 lb P2O5/A, 78 lb K2O/A, and 27 lb S/A. The P was applied at 0, 22 and 45 lb P2O5/A, with a blanket application of 90 lb N/A, 78 lb K2O/A, and 27 lb S/A. The mixed forage stand showed a response to the first increment of both N and P applied in this study (Figure 2). In the case of N, the majority of the response was recorded in the first cut in this two-cut harvesting system. However, with the P fertilizer addition improvements in dry matter yield were recorded in both the first and second cuts (data not shown). The absence of a response to the higher rate of P is supported by the yield and nutrient removal data in Table 1. The annual application of 22 lb P2O5/A is similar to the lower end of the removal rates in 3 tons/A hay yields.
Finally, an interesting observation was made in this 3-year fertilization project. There was an impact over years of fertilizer P application (Figure 3). The results indicate that annual addition of P fertilizer was improving both the vigour and regrowth of the forage stand, leading to improved yields as the study progressed. In fact, the best forage yield was harvested in 1999, which also was the driest year of this study, further illustrating the role of correcting nutrient deficiencies in sustaining forage productivity under a wide range of conditions. The response was immediate on the hay land site, reflecting that it was only in the early stages of stand deterioration. However, in the 30-year old pasture stand, it took two years of fertilizer P application before a forage yield and composition response was recorded on this severely deteriorated stand.
Summary
Low prices for annual crops have increased interest in improving forage production to support farm operations diversified into beef cattle. High yielding and high quality forages use large amounts of nutrients, both from the soil and applied as manure or fertilizer. Developing a soil testing and nutrient management plan for your forage stands, that includes early spring fertilizer application, will ensure sustained productivity of a quality product for an increased number of years.
