EFFECT OF RICE STRAW AND APPLICATIONS OF POTASSIUM SILICATE, POTASSIUM HUMATE AND SEAWEED EXTRACT ON GROWTH AND SOME MACRONUTRIENTS OF SWEET PEPPER PLANTS UNDER IRRIGATION DEFICIT

growing seasons of 2013-2014 and 2014-2015, in a private farm at El-Salheya El-Gedida City, Ismailia Governorate, Egypt, to investigate the effect of rice straw (RS) as alternative to sandy soil (SS) and drenching applications of potassium humate (K2-HA) at 2 g/l, potassium silicate (K2SiO3) at 5 g/l, and seaweed extract (SWE) at 0.5 g/l on improving growth of sweet pepper (capsicum annuum L.) plants under deficit irrigation every 2 (I2), 3 (I3) and 4 (I4) days in addition to daily irrigation (I1) as control. Plant samples were taken at 90 days after transplanting to record leaf area, shoot fresh and dry weights, in addition to, determination of leaf relative water content (LRWC), concentrations of  N, P, K and Ca. Mean values of drenching applications showed significant increase in the growth parameters ;shoot fresh and dry weights, leaf area, LRWC, as well as, concentrations of  N, P and Ca in the two seasons comparing to untreated control and the best results were due to K2-HA followed by SWE then K2SiO3. The highest concentration of  K was obtained by K2SiO3 followed by K2-HA then SWE. Plants were grown on RS showed significant increase in LRWC comparing to plants were grown on SS. Plants were applied with I2+ K2-HA+ SS showed the highest significant value of shoot fresh weight, shoot dry weight, leaf area, N, P and Ca concentrations followed by I2+SWE+SScomparing to control plants applied with I1+ SS without drenching applications. Plants were grown on RS showed significant increase in growth parameters comparing with control plants but less than those were grown on SS. The best results were achieved by I3 + K2-HA+ RS, I3 + SWE+ RS, I4 + K2-HA+ RS. Plants were grown on rice strawunderI3 irrigation and applied with K2-HA or SWE showed significant increase in N, P and Ca concentrations, while, under I4  irrigation an increase in N and P concentrations was obtained by K2-HA.The highest concentrations of k were observed with plants grown on SS under the highest level of irrigation deficit I4 by K2SiO3.It could be concluded from the present study that rice straw could alleviate the negative effect of low water supply and applications of K2-HA and SWE are recommended for enhancing sweet pepper growth and nutrient elements uptake under water deficit conditions.