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Irrigated Annual Ryegrass Responses to Nitrogen and Phosphorus on Calcareous Soil

^a Texas Agric. Exp. Stn., 1619 Garner Field Rd., Uvalde, TX 78801
^b Texas Agric. Exp. Stn., P.O. Box 200, Overton, TX 75684
^c Dep. of Soil and Crop Science, Texas A&M Univ., College Station, TX 77843

View larger version (29K): [in a new window]   Fig. 1. Treatment means for DM yield, Year 1. Model equation: t ha–1 = 2.836 + (NA x 1.142 x 10–2) + (PA x 3.907 x 10–2) + (NA x PA x 1.435 x 10–4) – (NA x NA x 1.585 x 10–5) – (PA x PA x 6.399 x 10–4), (n = 83, R2 = 0.92, s = 0.419).

View larger version (29K): [in a new window]   Fig. 2. Treatment means for DM yield, Year 2. Model equation: t ha–1 = 1.071 + (NA x 1.959 x 10–2) + (PA x.129) + (NA x PA x 1.746 x 10–4) – (NA x NA x 3.079 x 10–5) – (PA x PA x 1.690 x 10–3), (n = 83, R2 = 0.93, s = 0.764).

View larger version (29K): [in a new window]   Fig. 3. Treatment means for DM yield, Year 3. Model equation: t ha–1 = 0.964 + (NA x 1.330 x 10–2) + (PA x 0.1448) + (NA x PA x 1.555 x 10–4) – (NA x NA x 2.348 x 10–5) – (PA x PA x 1.874 x 10–3), (n = 83, R2 = 0.89, s = 0.846).

View larger version (26K): [in a new window]   Fig. 4. Treatment means for P uptake, Year 1. Model equation: kg ha–1 = 7.034 + (NA x 0.02918) + (PA x 0.1529) + (NA x PA x 3.671 x 10–4) – (NA x NA x 4.18 x 10–5) – (PA x PA x 2.097 x 10–3), (n = 20, R2 = 0.98, s = 0.69).

View larger version (27K): [in a new window]   Fig. 5. Treatment means for P uptake, Year 2. Model equation: kg ha–1 = 2.809 + (NA x 0.05415) + (PA x 0.4300) + (NA x PA x 6.046 x 10–4) – (NA x NA x 8.661 x 10–5) – (PA x PA x 5.315 x 10–3), (n = 21, R2 = 0.97, s = 2.05).

View larger version (26K): [in a new window]   Fig. 6. Treatment means for P uptake, Year 3. Model equation: kg ha–1 = 2.998 + (NA x 0.02890) + (PA x 0.3777) + (NA x PA x 3.863 x 10–4) – (NA x NA x 5.246 x 10–5) – (PA x PA x 4.280 x 10–3), (n = 21, R2 = 0.93, s = 2.10).

View larger version (16K): [in a new window]   Fig. 7. Pattern of forage P concentration by harvest for Years 1, 2, and 3.

View larger version (26K): [in a new window]   Fig. 8. Treatment means for N uptake, Year 1. Model equation: kg ha–1 = 40.16 + (NA x 0.5673) + (PA x 1.314) + (NA x PA x 4.332 x 10–3) – (NA x NA x 6.625 x 10–4) – (PA x PA x 2.236 x 10–2), (n = 20, R2 = 0.99, s = 7.70).

View larger version (26K): [in a new window]   Fig. 9. Treatment means for N uptake, Year 2. Model equation: kg ha–1 = 5.62 + (NA x 0.7608) + (PA x 4.234) + (NA x PA x 7.386 x 10–3) – (NA x NA x 10.86 x 10–4) – (PA x PA x 6.043 x 10–2), (n = 21, R2 = 0.97, s = 21.37).

View larger version (24K): [in a new window]   Fig. 10. Treatment means for N uptake, Year 3. Model equation: kg ha–1 = –4.78 + (NA x 0.5999) + (PA x 4.067) + (NA x PA x 6.418 x 10–3) – (NA x NA x 9.23 x 10–4) – (PA x PA x 5.812 x 10–2), (n = 21, R2 = 0.96, s = 20.62).