Mechanization of harvesting operations in Sweet Sorghum

It was observed that the harvesting operation contributes 30 % of the cultivation cost of the sweet sorghum apart from high drudgery involved in the harvesting operations.  Especially women who were majorly involved in this operation suffer a lot under the scorchingheat.  Since there were no small to medium scale harvesters available in the market, experiments were conducted with the modified self propelled reapers which were normally used for paddy and other fodder crops. These modifications were carried out at CRIDA, Hyderabad, India based on the initial feedback from the farmers after testing the equipment in the field.

i) Modification of tractor front mounted reaper as sweet sorghum harvester:

A tractor front mounted reaper which can be attached to the tractor is modified to suit the harvesting operation of sweet sorghum crop (Fig. 1). The said reaper was a multi-crop harvester and is suitable to harvest soybean, paddy, wheat and other crops.  It consists of cutting bar and guiding wheels to convey the crop to the near to the cutting blade.The cut crop stalks were conveyed to a side to form a windrow with the belt of the reaper.

Since the sweet sorghum crop height was more than 240 cm, the reaper was not found suitable for harvesting. As the  stalk thickness was more than the normal sorghum, the present cutting blades were not enough to cut the them.Modificationswere carried out by increasing the height of the reaper to support the sweet sorghum stalk and conveying the same to the top of the harvester. One more set of guiding wheels were fixed to the conveyer as shown in the figure 5   to pick up the stem and bring it near to the vibratory cutting blade.

Field testing of the modified tractor drawn front mounted reaper revealed that it required some more modifications to cut and carry the stalks properly.  Hence it was decided to work with small scale harvester for effective cutting and conveying the sweet sorghum stalk.    

ii) Modification of self propelled harvesters: Three models of advanced and commercially available self propelled reappers (harvesters) were modified to harvest sweet sorghum crop. The height of the front frame was increased up to 120 cm and an additional chain for conveying the stalks were arranged (Fig. 2).

The models which are modified and tested are:

•  6.5 h.p. petrol engine driven P.D.K.V,  Akola model
•  5 h.p. diesel engine driven Kisankraft reaper
•  5.h.p. diesel engine driven Greaves reaper

Field test revealed that these reapers were not suitable for harvest the sweet sorghum crop which grows taller than 2.4m height. As the stem girth was also more than the conventional sorghum, it was found hard to cut the stem with the scissor type cutting mechanism.

Results from Mechanized harvesting experiments

            All the three models of harvesters were evaluated in field trials and the physical and experimental observations are given below

• Success rate of self propelled harvester in the sweet sorghum crop  was found only 70 %
• It was difficult to operate in loamy and sandy soils as the traction power is very poor
• Perfect stem cutting was not achieved in the trials of conventionally sown fields as numbers of plants per hill are observed to be more than one in many places.
• Precision machine control provisions are not available in the three models as it was difficulty in operating in loamy soils.
• Some promising results were achieved with the newly designed self propelled harvester; however, some more modifications are needed to commercialize the same for sweet sorghum harvesting operation.

iii) Development of single row self propelled harvester: As the sweet sorghum wastaller (around 320-350 cm)  than the normal sorghum with girth ranging from 16-30mm, it was found very difficult to use the commercial self-propelled reapers which were available in the market.  Apart from the problems of cutting, conveying the stalk to the side was found very difficult because of its size and weight. To solve this problem, a new machine was conceptualized and developed at CRIDA workshop. It is mainly powered by 6.5 h.p. petrol engine which reduced the normal vibrations. A 3 tier conveying system with chain mechanism was developed by anchoring with mild steel mesh panels on two sides. A horizontal 3- blade cutting disc was used to cut the stems as the machine moved forward (Fig. 3). The rpm of the blade was adjusted to 850. The conveying speed was adjusted to synchronize with walking speed (3-3.5 km/hour).  Iinitial trials showed promising results and the design is under final refinement before commercializing it. It wasalso planned to develop a tractor drawn harvester to make it suitable for 2- 3 rows.