To study the effect of farmyard manure rates (0, 10 and 20m³ fed^-1), silicate bacteria (without and with inoculation) and potassium fertilizer levels (0, 50 and 100 K kg fed^-1) on status of soil-N and K nutrients at different growth stages of potato plants cultivated in alluvial soil, a field experiment was laid out at private farm (Kafr EL-Arab, Talkha, Dakahlia Governorate, Egypt during winter 2005/2006 season. The obtained results could be summarized as follows: Obtained results show that increasing rates of farmyard manure from 0 up 10 to 20 m³ fed^-1, K fertilizer levels from 0 up 50 to 100 kg fed ^-1 and inoculation of silicate bacteria (Bacillus circulans) markedly increased tuber yield (ton fed^-1) of potato plants at 70, 90 and 110 days after planting during (DAP) 2005/2006 season. Data clear that application of farmyard manure (FYM) had a positive effect on soil-N forms contents i. e. NO^-₃, NH⁺₄ and total available N (TAN) at 70, 90 and 110 DAP, respectively. Also, data reveal that the contents of soil-NO^-₃, NH⁺₄ and total available N (mg kg soil^-1) slightly affected due to inoculation of silicate bacteria as compared to the control, respectively. Moreover, application of K fertilizer had a slight effect on contents of soil-NO^-₃ and total available N (mg kg soil^-1). Meanwhile, there is a descent trend on soil-NH⁺₄ content due to increasing levels of potassium fertilizer at 70, 90 and 110 DAP during 2005/2006 season. Statistical analysis reveal that, the addition of farmyard manure0 up 10 to 20 m³ fed^-1, silicate bacteria (Bacillus circulans) and K-fertilizer from 0 up to 50 and 100 K kg fed^-1 caused vigorously enhancing in available soil-K content (mg kg soil^-1) at different growth stages of potato crop at 70, 90 and 110 DAP. Multiple linear regression from the following equation revealed that N-forms and available soil-K had a pronounced effect on predicting the tuber yield (ton fed^-1) of potato plants (r² = 88.5%). The expected equation to predict the tuber yield was:- Tuber yield (ton fed^-1) = 3.73 + 0.131soil-NO^-₃ - 0.165 soil-NH⁺₄ + 0.284 soil-TAN + 0.641 available soil-K.