Based on field experiments conducted during 1998 to 2006 in a semi-arid vertisol at Arjia on maize and blackgram crop an attempt was made to assess the effect of rainfall received during June to September and the soil moisture at the times of sowing and harvest on the biological yield. The study was conducted in 3 blocks of maize, blackgram and maize + blackgram by superimposing 9 fertilizer treatments. The soil moisture at sowing and harvest and biological yield attained by treatments differed significantly based on ANOVA in different years. The treatment–wise regression models of yield through rainfall of June to September and soil moisture at sowing and harvest had a predictability of 0.62 to 0.98 in maize block, 0.73 to 0.98 in blackgram block and 0.54 to 0.98 in maize + blackgram block.