Effect of Fertility Source and Irrigation Levels On Forage Sorghum Production and Quality.

As the Ogallala Aquifer continues to decline, there is an increased need to improve forage production under limited water or dryland conditions with minimal inputs. Increasing quality and yield of forage sorghum, [FS; Sorghum bicolor (L.)] has become important in semi-arid regions due to its drought tolerant characteristics. This study was developed to test the effect of four fertility treatments: manure applied at recommended nitrogen (N) rates (MN), manure applied at recommended phosphorus (P) rates supplemented with inorganic N (MP), synthetic fertilizers applied at recommended N rate (SR), and an unfertilized control (C) at three irrigation levels: full (305 mm), deficit (152 mm), and dryland (0 mm). Due to low rainfall in 2011, supplemental irrigation was applied to all treatments including 100 mm immediately after planting and 25 mm three times throughout the study. Harvest plant populations for dryland treatments were 1.4 times greater than full irrigation treatments while dryland and full irrigation were similar to the deficit treatment. Plants under full irrigation averaged one tiller plant^-1 more than either the deficit or dryland treatments. Dry matter was not affected by fertility source, but was 2.5 and 3.5 times greater in the full irrigation treatment compared to the deficit and dryland, respectively. Forage crude protein was 1.8% higher in the SR than C treatments while both were similar to either manure fertility treatment. The results of this study emphasized the impact of irrigation on forage productivity and quality; however, fertility source had mixed effects in the first year.