Fig. 1. Treatment means for DM yield, Year 1. Model equation: t ha1 = 2.836 + (NA x 1.142 x 102) + (PA x 3.907 x 102) + (NA x PA x 1.435 x 104) (NA x NA x 1.585 x 105) (PA x PA x 6.399 x 104), (n = 83, R2 = 0.92, s = 0.419).