Response of Natal grass (Melinis repens), an invasive species in Florida scrub vegetation, to supplemental additions of nitrogen and phosphorus

Natal grass invades Florida scrub vegetation, which harbors many state and federally listed species. Our study site has disturbed scrub vegetation occurring on highly leached, nutrient-poor, sandy soil. We tested natal grass response to addition of N, P, and both nutrients combined (NP) in pot cultures containing our study site soil.  Total amount of nutrients added in a solution over 4 applications was 12 μg/g of P and 20 μg/g of N to the P and N treatments, respectively.  The NP treatment received the combined amounts of N and P treatments. A complementary field study had two treatments: deionized water, NP, and control plants (no supplemental water or NP).  Nutrients were applied as a solution and 10 μg/g of N and 6 μg/g P were added in three applications (20 March, 21 April, and 19 May). Plant growth rates were monitored using an index based on stem numbers and size. Pot culture study plants were harvested after 60 days. In the pot culture study, addition of single nutrients alone did not significantly enhance plant growth rates or biomass production over that of the water control. However, NP treatment plants had significantly faster growth rates and higher biomass production than single nutrient treatments or control plants. Field study plants receiving N and P had significantly faster growth rates than plants receiving no supplemental nutrients or water. Nitrogen and phosphorus are limiting nutrients on our study site and availability of both nutrients must be increased to affect growth of Natal grass.