Sorghum (Sorghum bicolor (L.) Moench) is the fifth most important cereal grain crop in the world. It is thought to have been originated in north-eastern Africa around Ethiopia, Sudan and East Africa (Dogget, 1988; Acquaah, 2007). Sorghum is unique in its ability to produce under a wide array of harsh environmental conditions. Thus, it is undoubtedly the crop of poor people providing cheap sources for food and feed specially in the sub-Saharan Africa, and India.

 

Initially, sorghum grain is used primarily for food; however, its use as a feed exceeds its use as  food  since

the mid of 1960s, especially in developed countries  (Dendy, 1995). In view of the pressing demand for fodder coupled with the fact that grain sorghum is the stable diet for millions of poor people, it is imperative to reconsider the present mono-commodity breeding strategy of sorghum. Kelly et al. (1991) questioned the strategy of strictly adopting grain-yield criteria in evaluating sorghum genotypes arguing that fodder’s contribution to the total value of sorghum production has increased considerably. Residues of sorghum are becoming important feed sources for   livestock   raised  by  resource-poor  smallholders  in southern Asia and sub-Saharan Africa (Mohanraj et al., 2011). However, attributes relating to crop residue improvement has been largely ignored, with emphasis being placed on grain yield. Thus, dwarf high-yielding grain cultivars with fewer residue has been released in the early days of cereal improvement programs (Reddy and Sanjana., 2003). The same situation exists in Sudan, where breeding objectives were set to develop short statured combinable grain cultivars. Since recognition of crop residues as a viable source of feed, emphasis has been shifted to dual-purpose cultivars for grain and forage. Stover traits can be easily incorporated into existing breeding programs to generate superior dual-purpose (grain/fodder) sorghum varieties suited to smallholder farmers.

 

Sudan is endowed with a wealth of genetic variability in sorghum (Yasin, 1978) enabling selection for most economic traits. Local efforts to exploit such variability to develop dual sorghum types have been very limited and mostly directed towards developing improved grain types. Simultaneous improvement of sorghum for both fodder and grain attributes will result in developing dual cultivars that maximize grain and fodder yields and reducing costs of productions by saving time, labor and inputs under the constraints imposed by the environment and the prevailing production systems. Hence, the end result will be increasing the incomes of poor-resource farmers and sustaining their food security. Therefore, a breeding program has been launched to develop dual purpose fodder/grain sorghum genotypes and we are able to identify some of the elite genotypes. Further investigations are, however, needed to explore different factors required to increase the benefits gained from developing dual purpose varieties.

 

The objectives of this work were to investigate the performance of dual purpose (grain/fodder) sorghum genotypes under different harvest options required to maximize the benefits gained from combining grain and fodder attributes in one cultivar.

The experimental site

 

The study was conducted in Shambat (lat.15° 39 N; Long.32° 31  E) in the Research Farm of the Collage of Agricultural Studies, Sudan University of Science and Technology during the summer season of 2012 and the winter season of 2012/2013. The soil is heavy clay, non-saline, non-sodic with pH 7.8. The summer season has short rainy period extending from July to September with scant and fluctuating precipitation. The min-max temp during summer averaged 26 to 39°C. The winter is dry with 16 to 35°C average min-max temperature.

 

Treatments and experimental design

 

 

Six sorghum genotypes (Table 1) selected for their high performance dual purpose ability were used in the study. The selection criteria and the steps followed to develop these genotypes are presented in the companion paper. The genotypes were tested against the check Abnaffain, a traditional dual grain/forage cultivar.  The performance of the 7 genotypes was assessed under two harvest options viz:

 

1. Option 1 (HOP1): The crop was cut at heading time to evaluate forage production and the ratoon (regenerated crop) was evaluated for grain production

2. Option 2 (HOP2): The crop was left to grow up to grain maturity to evaluate both grain and stover yield

 

The treatments were replicated 4 times in split- split plot design with the harvest options assigned to the main plot and genotypes to the sub plot.

 

The experiment

 

The study was conducted during the summer and winter seasons. Sowing dates were effected on 13 July 2012 and 15 October 2012, respectively. The plot consists of 4 ridges 6 m long spaced at 0.75 m. Sowing method, planting density and management practices were similar to those mentioned in the accompanying paper.

 

The data taken included: Forage yield (t/ha), grain yield in kg/ha (estimated from 3 replicates), stover yield, days to boot (taken in ratoon crop), days to heading, plant height (cm) and stem diameter (cm).

 

Statistical analysis

 

The data sets of each harvest option in each season was subjected to single ANOVA before performing the combined analysis which was carried out for characters that showed homogeneous error variance (Snedecor and Cochran, 1967). Analysis of variance of split plot in RCB design was performed as per Cochran and Cox (1957). The statistical packages GenStat (2011) was used to run the analysis.

 

 

In each harvest option, highly significant differences were detected among genotypes for all traits studied in both seasons. The same is true for traits analyzed under combined analysis across seasons. Differences between harvest options and genotypes for grain yield were highly significant (Table 2). The interaction of genotypes with harvest options for gain yield was highly significant indicating that the genotypes performed differently in each harvest option with regard to grain yield. This may imply the need for evaluating dual sorghum cultivars across different harvest options.

 

Main and ratoon crop option (HOP1)

 

When harvesting the main crop for forage and grain from ratoon crop, Abjaro seemed to give the best forage yield and ratoon grain yield especially during winter season (Table 3). Its GMY and DMY averaged 47.9 and 10.9 t/ha, respectively. The Abu Sabein selection S.25Abu70 ranked second with respective yields of 43.8 t/ha and 8.29 t/ha. The winter ratoon grain yield of Abjaro was strikingly high (1504 kg/ha) exceeding that of S.03Abu70 (the 2^nd best genotype) by > than twice and that of Abnaffain by > 3 folds. The Abu Sabein genotypes (S.03Abu70 in winter and S.25Abu70 in summer) ranked second to Abjaro in grain yield. In spite of that the choice of farmers may go for Abu Sabein since it was remarkably earlier than Abjaro especially in the summer season. This is especially true for S.25Abu70 in summer season which was 58 day earlier in heading time (Table 4) while keeping comparable ratoon grain yield to Abjaro (Table 3). The benefits gained from increased forage yield of Abjaro over that of Abu Sabein may not justify affording additional costs and implications imposed by delaying harvest for about nearly 2 months. On the other hand the Abu Sabein genotype S.25Abu70 may represent a good replacement for Abnaffain when used for producing forage and grain from main and ratoon crop, respectively.

 

Abjaro was significantly the latest among the material tested taking 65.5 and 115 days to heading in winter and summer seasons, respectively. Abnaffain was the earliest in winter season with 43.5 days to heading (Table 4). All genotypes    headed   earlier   in  winter    than   summer.

 

 

 

However, Abjaro and E-35-1 showed contrasting difference in heading time between the two seasons with respective ranges amounting to 50 and 37 days. Hence both cultivars could be regarded as photoperiod sensitive. Sorghum is a short day plant requiring short photoperiods to flower, with some variability among varieties (Clerget et al., 2004). Late tropical land races (like Abjaro) are known to be highly photoperiod-sensitive (Clerget et al., 2007). On the other hand, Abu Sabein genotypes could be considered as neutral or slightly photoperiod sensitive with seasonal difference in heading time of 4 to 6 days. These results may explain the farmers’ practice of growing Abu Sabein during most of the year (Feb to Nov) while restricting Abjaro cultivation to winter sowings. Earliness is highly favored under limited   moisture  conditions.  It  could  be  noted  that  by growing Abu Sabein in summer instead of Abjaro, the farmers can spare 55 day (Table 4), enough to allow them maximizing the benefits gained from harvesting both grain and fodder. Since, in summer, the ratoon grain yield of Abu Sabein (S.25Abu70) is comparable to that of Abjaro (Table 3), growing of this cultivar in summer is suggested for harvesting fodder from the main crop and grain from the ratoon. In contrast, in the winter season Abjaro could be regarded as the right choice for a dual fodder/grain production since it gave ratoon grain yield of more than twice of that of the best Abu Sabein genotype (Table 3) while only being 13 day later in heading time (Table 4). The above suggestions will not be affected by the difference in ratoon days to boot as it almost followed the same trend of days to heading in the main crop (Table 5). This is in agreement with the finding of Gerik et al. (1990) that suggests similar phenology of planted and ratoon crops.

 

Ratooning is a cultural practice to stimulate regrowth of the basal or lower epigeal buds after removal of the photo-synthetically active material. A successful grain sorghum ratoon crop depends upon the production and development of healthy, grain-bearing tillers from these buds in the stubble of the preceding crop (Wilson, 2011). In the present study, tiller development has not been evaluated; however, the large stem diameter (Table 4) might be one of the reasons behind the high ratoon grain yield of Abjaro. Thicker stems contribute to increased content of soluble carbohydrates in the stubble which has been considered essential to the ratooned plant’s survival and re-growth in the absence of roots and leaves (Enserink, 1995; Oizumi, 1977).

 

Main crop option (HOP2)

 

 

 

When harvesting grain and stover from the main crop, Abjaro also kept the top rank in both attributes in winter and summer seasons with respective grain yields amounting to 4139 and 3086 t/ha, whereas the respective stover yields were 58.6 and 39.8 t/ha (Table 6). However, Abjaro yields were not significantly different from that of Abu Sabin genotypes except for stover in the summer season. Considering the lateness of Abjaro (Table 7), farmers may favor growing Abu Sabin for grain/stover production in both seasons unless the stover value of the summer season is high enough to justify growing Abjaro, or if quality aspects of the stover were considered. In the Sudan, sorghum stover has the greater contribution in maintaining the national herd  (Mohammed  and  Zakaria, 2014). High stover yielding cultivars are becoming increasingly valued over high grain but lower stover yielding ones. Similar trends were reported in the developing countries (Traxler and Byerlee, 1993) where farmers consistently select sorghum types that would compromise the desired fodder and grain attributes. Increased stover, however, must be digestible to contribute to improvement of livestock productivity (Kristjanson and Zerbini, 1999). In this study, the quality of stover was not investigated, however, in the companion paper the data presented for leaf to stem ration showed that Abjaro was leafier than Abu Sabein genotypes. Increased leaf to stem ratio indicates better digestibility and nutritional value of sorghum fodder (Mohammed and Zakaria, 2014). Improving stover digestibility is feasible without sacrificing grain yields as considerable variations in the quality value of sorghum stover exist (Blümmel and Reddy, 2006).

The study revealed that performance of dual sorghum cultivars differ across harvest options and seasons. To maximize grain and fodder yields from dual sorghum cultivars, different genotypes were suggested for different harvest options in different seasons. When harvesting the main crop for forage and grain from ratoon crop, the best choice is to grow the cultivar Abjaro during winter and S.25Abu70 during summer. When harvesting grain and stover from the main crop, Abjaro also kept the top rank in both attributes in winter and summer seasons however, considering the lateness of Abjaro, farmers may favor growing Abu Sabein unless the stover value of the summer season is high enough to justify growing Abjaro, or if quality aspects of the stover were considered. Future results should focus on developing dual sorghum cultivars with high quality stover with special emphasis on improved digestibility.

The authors have not declared any conflict of interests.