Effect of row spacing and plant density on soil moisture, dry matter production, yield and water use efficiency in wheat in rainfed condition

This experiment was conducted for estimating the effect of row spacing and plant density on soil moisture change, wheat yield and water use efficiency in rainfed condition, using a three replicated randomized complete block design with factorial arrangement at Gorgan University of Agricultural Sciences and Natural Resources farm in Anbare-Ololum region in 2008-2009. The treatments that used were four plant density (125, 250, 375 and 500 plants per m^-2) and two row spacing (12.5 and 25 cm). Results showed that soil moisture in the flag leaf appearance stage in 25 cm row spacing was more than 12.5 cm row spacing (19.61 vs. 17.82%). Also, Soil moisture content in the middle of stem elongation stage, was 26.82, 25.66 and 25.11% in plant densities of 250, 375 and 500 per square meter, respectively, which all were more than corresponding value for 125 plants per square meter (23.32%). Row spacing of 25 cm and plant density increasing from 125 up to 375 plants per square meter, increased grain yield (9.5 and 46%), dry matter production (6.5 and 50%), water use efficiency in terms of  grain yield (0.07 and 3.7 kg ha^-1 mm^-1) and dry mater (2 and 17.5 kg ha^-1 mm^-1). Overall, wheat cultivation in this condition (rainfed cultivation, saline soil and seasonal growth rainfall about 250 mm), with 25 cm row spacing, from Mid-stem elongation stage using more densities via intensifying individuals and more plant height is more advisable than row spacing of 12.5 cm. In addition, the plant density of 375 was better than 125 plants per square meter, which is related to more surface coverage by higher density from stem elongation stage onward to pre-flowering. This can reduce radiation penetration and consequently soil surface evaporation and improve soil water content. More soil moisture storage at critical stages before flowering stage, increases dry matter production, grain yield and grain yield and dry matter production-base water use efficiency.