Phosphorus Fertilization of Annual Ryegrass and Comparison of Soil Phosphorus Extractants

ABSTRACT

It is unclear how much phosphorus (P) fertilizer is needed to maximize annual ryegrass (Lolium multiflorum Lam.cv. ‘TAM90’) forage yield and nutritive value in lower-rainfall climates. It is equally unclear which soil-P extractant is most effective when making P fertilization decisions. A 3-yr field study addressed these issues using small replicated plots during the winter months in north-central Texas. The addition of P increased yields every year of the trial, but optimum levels depended on rainfall distribution: 19 kg P ha^{− 1} yr^{− 1} was optimum two years, while 28 kg P ha^{− 1} yr^{− 1} increased yields 51% the year with good mid-season moisture. The addition of P fertilizer did not increase forage crude protein or affect fiber concentrations but did increase P yields. Percent relative yield of ryegrass was correlated with Mehlich III soil test P, soil pH, and P application rate. Conversely, the acidified NH₄OAc-EDTA soil P extractant failed to relate to percent relative yield.

Keywords:

• phosphorus
• ryegrass
• Mehlich III
• ammonium acetate

Notes

*Fisher's Protected LSD test at P = 0.05.

°NS, non-significant, P > 0.05.

*Fisher's Protected LSD test at P = 0.05.

°NS, non-significant, P > 0.05.

*Initial soil test over the area: pH = 5.1, 6 g N kg^{− 1}, 6 mg P kg^{− 1}(NH₄OAc-EDTA).

°Fisher's Protected LSD test at P = 0.05.

^‡NS, non-significant, P > 0.05.