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XPONENTIAL population growth and soaring fertilizer prices are among the main challenges threating food security worldwide. Probably, substituting chemical inputs (partially or completely) with organic and/or bio-alternatives are the keys to achieve sustainable development. Thus, a field experiment was conducted for two successive seasons in a randomized block design to achieve this goal, comprising the following treatments: 100% mineral P and K fertilizers (T 1 , control), 10 g potassium humate (KH) kg -1 (T 2 ), 10 g humic acid (HA) kg -1 (T 3 ) and 10 g kg -1 fulvic acid (FA) (T 4 ). For treatments from T 2 to T 4 , supplementary doses of chemical fertilizers were added to satisfy wheat needs for P and K. Also, a combined treatment of 50% biogas (added on nitrogen bases) plus supplementary PK doses in the form of (i) rock phosphate and feldspars + biofertilizers (Bacillus megatherium and Bacillus circulans) (T 5 ) or (ii) chemical P and K fertilizers were included (T 6 ). All plots were planted with wheat and received 20% of the recommended N requirements via N 2 -fixation with Bacillus polymyxa while the other 80% was accomplished as ammonium nitrate (after considering the added N in organic additives). Key findings indicate that application of biogas+ supplementary chemical PK fertilizers (T 6 ) recorded the highest increases in P and K available contents in soil. This in turn significantly raised their concentrations within different plant parts and boosted straw and grain yields during the two seasons of study. Application of 100% mineral PK (T 1 ) recorded significantly lower values in all abovementioned parameters versus T 6 . Nevertheless, these two treatments (T 1 and T 6 ) recorded comparable increases in 1000-grain weight, plant height, spike lengths and number of grains per spike. Application of KH, HA and FA as partial substitutes for chemical fertilizers (T 2 -T 4 ) lessened significantly nutrient bioavailability and their contents within wheat parts; as a result, plant growth and yield components declined significantly. The least values were recorded for the treatment that received biogas+ rock phosphate and feldspar + biofertilizers (T 5 ). Overall, straw and grain yields of wheat plants were correlated significantly with P and K contents in both shoots and grains. In conclusion, the combination between biogas and chemical fertilizers seemed to be the optimum selection to satisfy wheat needs for nutrients; hence increase wheat productivity under arid conditions.

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