EFFECT OF ORGANIC AND INORGANIC FERTILIZER REGIMES ON GRAIN SORGHUM GROWTH AND YIELD

Productivity of sorghum has been below potential in arid and semi-arid lands (ASALs) of Kenya, mainly due to poor agronomic practices, especially nutrient deficiency. Although sorghum crop is fairly drought tolerant, resistant to water logging and yields are reasonably better on infertile soils compared to other crops, increasing its nutrition would significantly increase the yields as well as the nutrient loads to the grains and the crop residues used for livestock feed. The objective of this study was to determine the farmers‟ existing sorghum production practices and the effect of using organic and inorganic fertilizers on the growth and yield of grain sorghum.

A survey involving 90 farmers from sorghum producing areas in Makueni County was conducted in February 2017. The survey focused on; farmer‟s sorghum production objectives, the size of land used for sorghum production, source of information on sorghum production, challenges and constraints in sorghum production, source of sorghum seeds used by farmers, varieties of sorghum produced and preferred, intercropping in sorghum production, cropping system and fertilizer use in sorghum production, sorghum yield, sorghum use and conservation as animal feed in Makueni County. The data was analyzed in a Statistical Package for the Social Sciences (SPSS) program version 20.The survey results showed that most farmers (70%) used uncertified seeds from own saved sources, and the commonly grown variety was Seredo (47.2%) due to resistance to birds‟ damage. Most (31.7%) of farmers recorded very low yield of sorghum grain of between 0.151 to 0.25 t/ha which is below the potential yields of 10.5t/ha. Most farmers (66.6%) used farmyard manure in sorghum production while 30.9 % of the farmers did not use any fertilizer. All farmers indicated that their greatest challenge in sorghum production was inadequate rainfall. Bird damage to sorghum crop was a chronic problem to most (71.6%) farmers. Most (56.8%) of the farmers conserved sorghum residue for feed as hay.

A field experiment was conducted in a randomized complete block design with split plot arrangement, to evaluate the effects of two fertilizer sources (Organic and inorganic) on productivity of three sorghum varieties (Gadam, Kari Mtama 1and Macia) as main crop and ratoon crop under supplemental irrigation. The fertilizer treatments levels were: 5tFYM/ha, 15tFYM/ha, 25kgN/ha NPK + 25kgN/ha Urea, 50kgN/ha NPK + 50kgN/ha Urea, 5tFYM/ha

+25kgN/ha NPK+ 25kg Urea, 15tFYM/ha + 50kgN/ha NPK + 50kgN/ha Urea. The crop growth parameters measured were; number of productive tillers per plant, panicle length, time to 50% flowering, 1000-grain weight, plant stand at harvest, number of panicles, number of grains per panicle, threshing percentage, stover yield and grain yield. The data obtained was subjected to analysis of variance using GENSTAT© statistical package.

The field experiment showed number of productive tillers increased with increase in fertilizer level used in both the main crop and the ratoon crop. Gadam variety had the highest number of productive tillers per plant compared to Kari Mtama 1 and Macia, in the ratoon crop with 2.19, 1.81 and 0.667 tillers, respectively. The panicle length and days to 50% flowering was affected by the levels of fertilization in both main and ratoon crop. Macia had the highest panicle length (28.5 cm main crop; 26.76 cm ratoon crop) compared to the other varieties (Gadam 22.8cm main crop; 20.01cm ratoon crop and Kari Mtama124.73cm main crop; 22.7cm ratoon crop). Gadam took fewer days (50days) to 50% flowering in the main crop and 36 days in the ratoon crop. The highest number of panicles was observed in Gadam followed by Kari Mtama 1 and Macia with

156.9 panicles in main crop; 136.5 panicles in the ratoon crop, 102 panicles in main crop; 96 panicles in the ratoon crop, 85.3 panicles in main crop; 80.4 panicles in the ratoon crop, respectively. Different fertilization levels had no significant (p≤0.05) effect on 1000-grain weight for the three varieties in both main and ratoon crop seasons. However, there was significant differences in 1000-grain weight amongst the varieties with Kari Mtama 1 having the highest 1000-grain weight of 36.05g in main crop; 34.19g in ratoon crop, followed by Gadam with 31.43g in main crop; 30.9g in ratoon crop and lastly Macia with 29.43g in main crop; 26.67g in ratoon crop. There was significant difference in the stover and grain yield in t/ha among the sorghum varieties. Gadam had the highest grain yield of 5.54t/ha in main crop; 4.5t/ha in ratoon crop, Kari Mtama 1 recorded 4.81t/ha in main crop; 3.96t/ha ratoon crop and Macia recorded the least grain yield of 4.79t/ha in main crop; 3.96t/ha in ratoon crop. Macia had the highest stover yield of 16.47t/ha in main crop; 17.7t/ha in ratoon crop, while Gadam had the least stover yield of 12.6t/ha in main crop and 13.15t/ha in ratoon crop.

The findings show there is need to provide technical information and guidance to farmers on sorghum varieties to grow, agronomic practices for soil fertility management and proper use and conservation of sorghum residue as animal feeds in Makueni County. Use of both organic and inorganic fertilizer can highly influence yield and the yield attributes of grain sorghum. Gadam variety proved to be better than Kari Mtama 1 and Macia across all fertilizer levels and the highest yields were obtained where fertilizer and manure application was done at the rate of15t/ha FYM+100kgN/ha. Macia does well as a dual purpose because it has a high residual yield than Gadam and Kari Mtama 1 across all the fertilizer levels.

Key words: Dual purpose, Gadam, ratoon crop, stover yield, uncertified seeds

 

 

 

 

 

Generating a sustainable food and feed supply that to match the increasing demand is, by far, the most formidable challenge facing sub-Saharan Africa (SSA) agriculture (Hounkonnouet al., 2012; Jayne and Shahidur, 2013). Enormous increases in human and livestock populations are projected to occur in the decades to come, coupled with massive increase in levels of urbanization. The anticipated population growth is also projected to generate heightened competition for land and increased scarcity of cropland (Strassburg et al, 2014; Mueller and Binder, 2015) and especially in the rangelands. This may in turn induce agricultural intensification, in particular, integrated crop/livestock production (Baudron et al, 2014; Kindu et al. 2014; Castellanos-Navarrete et al, 2015). This is already happening in Kenyan arid rangelands. Thus, crop residue is becoming the dominant feed resources for livestock in these Eco zones as more rangeland is converted into cropland.

Sorghum bicolor L. Moench commonly known as sorghum is a grass species cultivated for its grain, which is used for human food and feed for animals, and for ethanol production (Rhodeset al, 2015). The United States is the world's largest producer of grain sorghum followed by India, Nigeria, and Mexico, while the leading exporters are the United States, Australia and Argentina (Rao et al, 2014). Sorghum provides human dietary calories from direct cereal consumption or from livestock products from animals fed with sorghum grains and their byproducts (Taylor, 2003). It is likely that sorghum will continue to account for the bulk of the future human food supply because it produces higher yields of human edible grains, easily grown even under low rainfall areas, easy to store and transport and requires less fuel and labor for processing and cooking than other food crops.

Sorghum is an under-utilized crop and one of the most important cereals in semi-arid tropics (Muui et al, 2013; Jacob et al, 2013). In Kenya, sorghum is grown in the often drought prone marginal agricultural areas of Eastern, Nyanza and coast provinces (Muui et al, 2013). Most people in these regions regard sorghum as a poor man's crop and some still prefer to grow maize even in areas where it does not do well and as a result, there is increasing food insecurity (Gregory et al, 2005). A wide range of naturally occurring biotic and abiotic constraints including poor soils, water scarcity, crop pests, diseases, weeds and unsuitable temperatures are well known to reduce the productivity of sorghum leading to low efficiencies of input use, suppressed crop output and reduced food security (Strange and Scott, 2005). Nitrogen losses through gaseous plant emissions, soil denitrification, surface runoff, volatilization and leaching are increasing with time, especially in nutrient poor soils. This results to a minimal amount of nitrogen available for cereal crops such as sorghum, which cannot do nitrogen fixation leading to low yields (William et al, 1999). Other constraints in sorghum production include; water logging, water runoff and soil erosion, which represent major yield constraints (Murty et al,2007). Low temperatures, low soil P and N, Fe toxicity, acid soils, and wind damage (blown sand) also hinder crop yields, while downy mildew, insect pests, and weeds such as Striga also cause severe losses (Clay, 2013).

Although many producers view sorghum as a low maintenance crop, with its deep fibrous root system, sorghum responds well to nutrient applications especially in soils that are low in fertility. Nitrogen is the most often limiting in sorghum production, hence if managed efficiently, significant increase in the yields may be realized (Vanlauwe, 2014; Potgieter et al, 2016). This study therefore, focused on the use of both organic and inorganic fertilizers in sorghum production for increased yields and improved quality of grains for human food and residues for quality livestock feed.

Productivity of sorghum has been below potential in ASALs of Kenya, mainly due to poor agronomic practices, particularly nutrient deficiency (Chepkemoi et al, 2014; Janeth et al, 2014; Mwadalu, 2014). Nitrogen is the element most frequently lacking for optimum sorghum production (Barthélémy et al, 2014;Paiva et al, 2017). Although sorghum crop is fairly drought tolerant, resistant to water logging and yields are reasonably better on infertile soils compared to other crops (Rurinda et al, 2014), increasing its nutrition would significantly increase the yields as well as the nutrient loads to the grains and the crop residues used for livestock feed. Sadly, many sorghum farmers are traditionally known to be producing sorghum without the use of inorganic or organic fertilizers, which has contributed to very low yields (Kagwiria et al, 2019).This is due to the high costs of commercially produced fertilizers, and low adoption of organic fertilizer use. In areas where inorganic fertilizers are used, farmers poorly manage in terms of rates of application, time of application and method of application. This also has contributed to low sorghum yields even among large-scale producers. The current sorghum yields in small scale farming ranges from 0.5-1.5 tons/ha compared to the potential yield of 4tons/ha (Muui et al, 2013).

Sorghum, which is closely related to maize in utilization and is an alternative staple food crop in arid areas, with a competitive edge over maize due to drought resistance and better nutrient use efficiency, even under poor soils. As an indigenous Kenyan crop, sorghum could provide food security and become a suitable alternative in ASALs of Kenya. Despite its suitability in these areas, the area under sorghum production is still low and farmers attain low yields. Most farmers still opt to grow maize that is disadvantage by frequent crop failures (Muui et al, 2013). Many farmers also do not practice ratooning, which may be another agronomic practice to increase feed yield and reduce new crop establishment costs hence increased benefit to farmers.

Sorghum like any other crop requires good agronomic practices such as application of fertilizers at the right time and in right amounts to ensure vigorous plant growth and high yields. Absence of these nutrients such as nitrogen, magnesium, phosphorous, potassium, zinc, iron may lead to crop failure. It is likely that sorghum will continue to account for the bulk of the future human food supply because it produces greater yields of human edible food and this increases food security (Gruen and Loo, 2014). High sorghum yields will also reduce costs of sorghum imports from countries such as Uganda, Tanzania, United States and other European countries. (Kilambya et al, 2013). Nutrients such as nitrogen are subject to many losses for instance losses through gaseous plant emissions, soil denitrification, surface runoff, volatilization and leaching and hence should be efficiently managed to optimize on the yields (William et al, 1999). Use of organic fertilizers such as the farmyard manure may increase sorghum yield compared to the use of inorganic fertilizers alone. This is because organic manure contains other nutrients such as the micronutrients (iron, zinc, boron) which are absent in inorganic fertilizers and contribute to improved soil fertility and soil structure. Organic manures are also cheaper compared to the inorganic fertilizers and are readily available even to small-scale farmers. Use of both organic and inorganic fertilizers may greatly increase the yield of sorghum in the semiarid areas of Kenya.

 

To determine the existing farmers‟ production practices with respect to sorghum production and to evaluate the effects of different fertilizer regimes on the growth and yield of grain sorghum.