Author(s):

Kalyani A, Sapkal SM, Bhoyar and PH Rathod

Abstract: The present experimentation entitled "Residual soil fertility and productivity of rainfed organic cotton in Vertisols” was conducted to study the effect of continuous use of organic manures on physical and chemical properties of soil after harvest of rainfed organic cotton at Cotton Research Unit (CRU) Central Research Station, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola in kharif 2017-18.There were eight treatments replicated three times in Randomized Block Design. The organic sources used were FYM, vermicompost, sunhemp and castor cake. The soil sample were collected from surface and subsurface layers for analyzing various physical and chemical properties of soils. The soils of experimental site were classified under order Vertisol. Initially (2010-11) soils were low, medium and high in available nitrogen, phosphorus and potassium, respectively. After 7^th cycle of fixed frame plot experimentation, continuous incorporation of FYM @ 10 t ha^-1 showed significant improvement in soil physical and chemical properties as well as overall residual nutritional status of soil. Significantly lowest pH at surface and subsurface soils 7.81 and 7.91 and EC 0.11 and 0.12 dSm^-1 were observed respectively. Same treatment 10 t ha^-1 FYM showed significant improvement of organic carbon content of soils at surface (6.04 g kg^-1) and subsurface (5.64 g kg^-1) layers. A regards of physical properties of surface and subsurface soils significant improvement in BD (1.23 and 1.27 Mg kg^-1), HC (1.29 and 1.24 cm hr^-1), AWC (17.3 and 9.71%) and MWD (1.84 and 1.64 mm) was recorded due to bulk application of organic matter through FYM @ 10 t ha^-1. Significantly, higher and statistically equal seed cotton yield harvested under the treatment FYM 10 t ha^-1 (19.28 q ha^-1) and concentrate organic manure 500 kg ha^-1 (19.16 q ha^-1) which led to higher PRI under both the treatments i.e.175.27 and 174.18 q ha^-1 per cent due to their continuous use of seven years. Thus, after 7^th cycle of the experimentation on organic cotton production, it can be concluded that, significant improvement of physical and chemical properties of Vertisols can be possible due to continuous use of organics as sources of nutrients to deshi cotton crop over the absolute control as well as initial status of soil. In general it was noticed that, surface soils showed more improvement as regards to all properties than the subsurface Vertisols. Furthermore, improvement of residual fertility status and was reflected on the productivity rating index of deshi cotton variety (AKA-8). However, as per the availability of bulky organic manure or concentrate organic manure either FYM @ 10 t ha^-1 or castor cake @ 500 kg ha^-1 can be used for obtaining optimum yield of deshi cotton in rainfed condition.

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