Sweet Sorghum

Introduction
Sweet sorghum is an annual C4 plant having high concentration of sugars in stalks and can be used as a biofuel crop (Rooney et al., 2007). It can be grown successfully in semi-arid regions and known as the sugarcane of the desert.
This plant can produce 45-65 t/ha stalk yield and 3-7 t/ha sugar yield in short duration with less water requirement like rain fed crops (Rao et al., 2013). Improvement in stalk yield and sugar accumulation is the major concern of sweet sorghum production.
Differences in nutrient can change yield in sweet sorghum. Magnesium is one of the most important minerals in the structure of chlorophyll for harvesting of solar energy and synthesis of nucleic acids (Wiedenhoeft, 2006). Its roles are more related

In grain filling period, sugar reserves in stalks depleted and transport to developing seeds. In India, de-heading of sweet sorghum at anthesis increase main stalk diameter 20%, juice yield 30% and sugar yield 10%, but 5% less Brix, sucrose concentration and juice purity (Rajendran et al., 2000). Erickson et al (2011) evaluated that de-heading of sweet sorghum stalks increased Brix value and sugar yield in different locations and there are no difference between boot stage and flowering for top removal. In sugarcane, several chemical compounds like glyphosate (Martin et al., 1981), fluazifop, sulfometuron and trinexapac-ethyl (Resende et al., 2000) applied as ripeners and suppress flowering (Solomon et al., 1997; McDonald et al., 2001). Ethephon (2-chloroethylphosphonic acid) among ripeners as plant growth regulator indicated good potential to control flowering (Li and Solomon, 2003). Studies showed that application of ethephon not only suppress flowering but also increase sugar yield in sugarcane (Moore and Osgood, 1989; Humm, 2001). However, there is no report of the ethephon application on sweet sorghum as a flower inhibitor in Iran.
Even though, sweet sorghum is seen as a potential cash crop in arid and semi-arid regions of Middle East, but more information on management practices on sugar yield, nutrient requirement and biomass production of this crop

There were four rows in each plot, which the row width and length was 0.6 and 6 m, respectively. At third leaf stage, plants were thinned for the appropriate final stand of 160000plants ha-1.
The applied factors consist of sweet sorghum varieties (KFS2 and KFS3), top removal treatments (control, mechanical removal and chemical removal with ethephon) and magnesium sulfate rates (0, 4 and 8 mM). Sweet sorghum varieties are new hybrids released in Iran. Magnesium sulfate levels sprayed at the rapid plants growth stage that was approximately 60 days after planting and repeated in 10 days later. Plots with zero rates, spraying with distilled water.
In mechanical top removal plots, the top of plants cut with garden shears just above the leaf below the flag leaf. This treatment was done at boot stage (head enclosed in the swollen flag leaf sheath). After top removal, the heads discarded and were not included in further analyses. For Chemical treatment, ethephon with 500 mg.l-1 concentration was sprayed 50 days after planting. No top removal and chemical treatment occurred until harvest for control