IMPACT OF INORGANIC FERTILIZATION ON SORGHUM FORAGE QUALITY AND GROWTH PERFORMANCE OF BARKI LAMBS

The present study was conducted at Maryout Research Station, Desert Research Center. It was applied in two experiments (Agronomy and fodder evaluation experiment and animal growth experiment) to determine the response of sorghum quality and consequently the animal performance to the application of combined N and P fertilizer in newly reclaimed soil. The first experiment was for evaluating sorghum fodder (Sorghum bicolor L.) that sorted with nine treatment combinations (from T1 up to T9) comprising of three nitrogen (N) and phosphorus (P) fertilizers levels (N_80.4, N_100.5 and N_120.6 kg/feddan vs. P_20.2, P_30.2 and P_40.3 kg/feddan) in factorial randomized block design with three replications. The results of the agronomy experiment with considering the ISDMD, NEg and the cost of treatments, showed that two treatments (N₁₂₀P₃₀ and N₁₀₀P₄₀) could be nominated to the second experiment which was their evaluation as feeds for the growing Barki lambs as compared to control treatment (N₈₀P₂₀). So, two treatments and control were sorting again in the next summer season to evaluate their nutritive values by using 15 growing Barki lambs (5 lambs/ treatment) in a completely randomized block design. Lambs were on average 22.83 ± 0.29 kg as the initial body weight and aged 5 months. All animals fed concentrate feed mixture to cover 70% of their growth requirements (Kearl, 1982). However, the experimental fodders were offered ad lib. So the experimental animal groups were allowed for three rations for 85d as follows; R1: CFM + sorghum forage of T1 (N₈₀P₂₀) ad lib., (served as a control), R2: CFM + sorghum forage of T6 (N₁₂₀P₃₀) ad lib, and R3: CFM + sorghum forage of T8 (N₁₀₀P₄₀) ad lib. The results indicated that; Average daily gain differed significantly (P= 0.016) being values 158, 185 and 192g for lambs fed R1, R2 and R3, respectively. Animals in R2 and R3 consumed a higher (P=0.042) amount of sorghum compared with the control one. There is a significant effect (P< 0.05) of sorghum treatments on feed conversion ratio (FCR), where sheep fed R1 or R2 had better FCR as g DM/ g gain or g TDN/ g gain than those fed control sorghum ration. However, R1 revealed better FCR as g DCP/g gain as compared with the other groups. The digestibilities of DM, CP and CF were higher (P<0.05) for R2 and R3 compared to the control one. However, digestibilities of EE and NFE were not affected (P>0.05) by the experimental rations. Both R2 and R3 were the better (P<0.05) for both TDN and DCP values as compared with the control ration. Higher (P<0.05) N balance was observed with R2 than control. All lambs retained relatively similar (P>0.05) amounts of calcium. However, higher P content in sorghum of R2 and R3 revealed significantly higher P intake (P<0.05) and also P retained (P<0.05). The revealed insensible water loss (IWL) of the three groups was significantly different being values 144, 172 and 176 g/kg^0.82 for R1, R2 and R3, respectively. The rumen pH value of animal group fed control ration (R1) was significantly (P≤0.001) higher than other groups at all the sampling time. Animals who received R2 ration showed the highest NH₃-N values at 3h (P<0.01) and 6h (P<0.05) post-feeding as compared to the other groups; however R3 group showed the highest (P<0.05) value at zero hour post-feeding as compared to the groups. At 6h post-feeding, animals fed R2 showed the highest (P<0.05) TVFA value (22.14meq/dl) as compared to the other groups (19.68 and 21.45 meq/dl for R1 and R3, respectively).
It could be concluded that both of the sorghum treatments; N₁₂₀P₃₀ and N₁₀₀P₄₀ kg/fed; are in the same nutritive values and similar growth rate for Barki lambs but because of higher P drain away to the land below in case of N₁₀₀P₄₀ ration so it is recommended for N₁₂₀P₃₀ to be a better fertilizer rate for the fodder consumed by the Barki lambs and also for its potential to reduce the environmental pollution with the high level of P compared to the other treatment.