The effects of super absorbent polymer application into soil and humic acid foliar application on some agrophysiological criteria and quantitative and qualitative yield of sugar beet (Beta vulgaris L.) under Mashhad conditions

Drought stress is the most limiting factor of agricultural production through the world. To evaluate the effect of super absorbent and humic acid to reduce drought stress in sugar beet production, a strip split plot arrangement based on randomized complete block design with three replications was conducted at Research Field of Faculty Agriculture, Ferdowsi University of Mashhad, Iran during growing season of 2010-2011. The main plot factor was application and no application of super absorbent polymer and the sub plot factor was foliar application and no application of humic acid. Two irrigation intervals (7 and 10 days) assigned to strip plots. The results showed that super absorbent application comparing to no super absorbent affected leaf area index (LAI), sugar gross yield (SGY) and SPAD readings significantly, as the highest amount for this traits were 3.4, 4.7 t ha-1 and 46.2, respectively. Humic acid foliar application resulted to the highest LAI (3.4) and SPAD reading (45.1) which significantly were different with other treatments. Irrigation interval of 7 days resulted to the highest LAI (3.8) and root yield (24.9 t ha-1). The highest SPAD reading (49.9) resulted from super absorbent and humic acid application with 7 days interval irrigation interaction. Dry matter yield (DM) and leaf number per plant showed a positive and significant correlation (p≤0.01) with tuber yield (TY), SGY and SPAD readings. The strongest correlation coefficients were obtained for DM and LAI, and between DM and SGY. This positive and significant correlation emphasis that any factor increasing LAI will increase DM and thereby, SGY. The positive and significant correlations were observed between DM and SPAD readings, and between SPAD readings and TY. SGY estimation model predicted that SGY was determined by some variables such as TY, SP and SPAD reading. In general, these results indicate super absorbent application could increase soil water holding capacity and consequently stabilize production under dry stress conditions. In addition, humic acid application could increase economic sugar beet production, moreover maintaining environmental health issues.