Underground Water Use and Peanut Production: Effects of Sowing Date and Initial Soil Water Availability.

Peanut (Arachis hypogaea L.) production in Argentina takes place in a region of (i) monsoon climate and average rainfall of 539 mm during crop cycle (November-March), (ii) variable levels of plant available soil water (PAW) at sowing, and (iii) water deficit during the period of pod set (R3-R6.5). The objective of the present research was to study the effect on aparent rooting depth velocity (ARDV, in cm day^-1) and on rate of water uptake (K, in mm mm^-1 day^-1) of (i) contrasting evaporative demands produce by sowing dates (early on 21-Oct and late on 2-Dec, in the main plots),  (ii) different levels of underground (60-200 cm soil depth) PAW (30% and 70%, in the subplots) from R₃ (start of pod growth) onwards, and (iii) two cultivars of contrasting cycle duration (short Asem and late Florman, in the sub-subplots). ARDV was affected only by PAW, and reached 2.34 cm day^-1 at 70% PAW. Reduced PAW promoted a delay in ARDV, which caused a reduction in (i) maximum rooting depth (250 cm for 70% PAW and 150 cm for 30% PAW), and (ii) soil depth for maximum water extraction (i.e., soil dessication to permanent wilting point). Values of K were maximum for all treatments up to 70 cm soil depth. Beyond this depth, K values were affected by treatments; maximum rates corresponded to 70% PAW at the late sowing date, for which maximum biomass production was obtained up to R3. The smallest K values were registered for cv. Florman growing with 30% underground PAW in the early sowing date. Differences in K between cultivars growing with 30% PAW may be related to differences in root density in response to assimilate production and soil strength.