Foliar N-Spray May Improve the Quality of Stockpiled Limpograss

December 2001
Dr. Martin B. Adjei - Range Cattle Research & Education Center

Adequate quantity and quality of cool-season forage are limiting factors to cow-calf production in south-central Florida. Limpograss is a forage with potential high dry matter production and total digestible nutrients (TDN) during the cool, short-day season. However, crude protein (CP) in stockpiled limpograss is often below 7% and this is below the maintenance requirement for cattle. Hence, cattle grazing stockpiled limpograss are usually supplemented with either liquid or dry protein feed at additional cost.

In 1964, Al Kretschmer, described a technique to increase the nitrogen (N) concentration in deferred warm season grass forage. He applied late N fertilization (LNF) to forage in November to early December, 2-3 weeks before the forage was utilized by cattle . Later, in 1996, Al Kretschmer and George Snyder improved upon their system where an initial N fertilizer (INF) was applied in September to increase dry matter yield of stockpiled limpograss followed by a late N fertilization in December to boost CP concentration in the fall-deferred Bigalta limpograss.

But up to this point, the influence of liquid foliar N spray on stockpiled limpograss has not been studied before. So, on November 19, 1999, John Arthington and I applied both granular and sprayable ammonium sulfate to a fall-deferred, mature Floralta limpograss stand at the Range Cattle Research and Education Center, Ona. Liquid N has a tendency to burn the top of forage grasses so we applied only 30 lb N/A in either form. We also had a control that received no N. Each treatment was replicated 3 times. Sections of the treated stockpiled forage were harvested to 6-inch stubble on 30, 60, 90 and 120 days after fertilization. Harvested forage samples were cut up into a "basal" (bottom 9") and a "top" (all above 9") sections, dried, ground and analyzed for CP and IVOMD. The 1999-2000 winter season was warm and standing forage increased from 3 to 4 ton/A across all treatments until frost occurred in mid January. The top canopy forage was 60% and basal canopy was 40% of total standing forage biomass.

The initial (19 Nov.) CP concentration in top canopy forage was 7% and in the basal canopy forage was about 5%. The CP concentration in top canopy forage was 7, 10, and 12% on 30 days, and 6, 8, and 11% on 60 days for the control, granular and liquid ammonium sulfate treatments, respectively. The mid-Jan freeze of 1999 brought down the top canopy CP on all treatments to <6% on 90 days after fertilization. However, due to a more rapid regrowth after the frost, the top canopy forage CP on 120 days after fertilization was 9% for the liquid N treatment compared with 6% for the control and granular N treatments. Basal canopy CP ranged from 4to 8% and also tended to be highest for the liquid N treatment. Forage TDN was always high and ranged from 50-62% regardless of our late N fertilization treatment.

In 2000-2001 winter season, John and I tried a wider range of liquid N fertilizer including urea as foliar spray but run into bad luck when an early freeze occurred on 24 Nov., just 3 days after application. This was followed by 8 additional frosts in December and January and we had no plant response to our treatments. This year the weather looks warm and we have applied the treatments again in late November We hope to share this year's results with you soon.

Meanwhile, it appears that foliar N absorption at low rates of late N fertilization (20-30 N lb/A), 4-8 weeks before forage utilization, may help improve the CP concentration in fall-deferred Floralta limpograss. (MBA).

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