Determination of Plant Density on Groundnut (Arachis hypogaea L.) Intercropped with Sorghum (Sorghum bicolor L. Moench) at Fadis and Erer of Eastern Hararghe

In eastern part of Ethiopia groundnut is very commonly intercropped with sorghum. Even though intercropping of sorghum with groundnut is practiced in the eastern part of Ethiopia the population density at what ratio should not be known. Therefore determining the population ratio is found to be crucial to draw management options. The study was conducted at two locations at Fadis (on station) and Babile (substation). Sorghum variety (Teshale) and groundnut (Fetene) were used as planting materials. All agronomic data were collected and analyzed by using GenStat software. Significant different were obtained among the treatments. The research result showed that, there were significance difference for both sorghum and ground nut yield per hectare in the years (2014 and 2015) among treatments. The result over time(in 2014 and 2015) at Fadis and Erer showed that the highest sorghum and groundnut yield per hectare were obtained/harvested from the intra row spacing of 25cmx20cm and 30cmx20cm intercropping sorghum with ground nut system with (1.27 and 1.31) respectively. The highest LER (1.31) and highest GMV (10218.00 ETBr/ha) were obtained from the intercropping of 30cmx20cm (Sorghum & groundnut). Clearly showed that, with intercropping of sorghum and Groundnut, it is possible to produce additional yield of sorghum without significant reduction in groundnut yield. As a result of this, the intra spacing of the main crop (sorghum) 25cm and 30cm and for the subsidiary crop (groundnut) 20cm was recommended for further production in the study areas of eastern Harerghe zone and similar agro-ecologies


INTRODUCTION
. In intercropping it is worthy to find out the optimum plant density to draw maximum benefit from the intercropping system. (Billore et al, 1992). In research conducted on sorghum/groundnut with different plant densities of groundnut revealed that planting 100% sorghum and 50% groundnut resulted in highest total yield than the lowest and highest densities of 100% sorghum, 25% groundnut and 100% sorghum, 75% groundnut respectively showing that plant density is crucial in crop production (Billore et al, 1992). In Africa and, India groundnut is very commonly intercropped with sorghum. Some reports have emphasized that significant yield reductions of groundnuts have been obtained when they have been intercropped with sorghum.
Even though intercropping of sorghum with groundnut is practiced in the eastern part of Ethiopia the population density at what ratio should not be known. Therefore determining the population ratio is found to be crucial to draw management options. Hence the present study was conducted to evaluate and promote appropriate plant densities of groundnut intercropping with sorghum at Fadis and Babile(Erer) which is located at eastern part of Ethiopia.

Intercropping
Intercropping was an age old practice of growing simultaneously two or more crops on the same piece of land. Intercropping is mainly practiced to cover the risk of failure of one of the crops due to vagaries of weather or pest and disease incidence. Intercropping may also lead to increased production per unit area per unit time without affecting the yield of main crop to a greater extent. When legumes are used as intercrops, they provide the beneficial effect on soil fertility by fixing atmospheric nitrogen.
In intercropping system yields, of component crops are not simply added. This is because yield of different crops cannot simply be added together or compared directly with each other, special methods have to be used (Reddy, 1990). There are many different methods for assessing output yield advantages from intercrops yields. Among the methods, the first was comparing component yields with their sole crop yield for every crop in the mixture and add the ratios together.
Another possibility method is to compare the land area needed to obtain similar component yields in sole and intercrops (Reddy, 1990).
The aim of legume-cereal intercropping in the cropping systems is to optimize the use of spatial, temporal and physical resources both above and below ground, by maximizing positive interactions and minimizing negative ones among the components (Ndakidemi, 2006).
It is well known that weeds are among the major crop production constraints. The growing of companion crops in close proximity to one another in intercropping provides greater plant density than sole crops and this should result in greater competition against weeds (Moody and Shetty, 1981). Proper weed control is crucial in enhancing crop productivity in a given unit of area (Aleman, 2000). Liebman and Dick (1993) stated that weed suppression is greater with intercropping than in a single crop.

Soil fertility
It is possible to maintain soil fertility under continuous cultivation through intercropping legume with cereals. In order to maintain soil fertility under continuous cultivation in SSA, the soil N content need to be increased. To have high N level the traditional farming system should be modified in a way that satisfies the economic need of the farmer and also improving the soil N requirements. Reports on the results of intercropping for soil fertility management revealed that the contribution of legumes root to the soil N level ranges from 5 to 15kg/ha (Nnadi and Haque, 1986).
Soils obtain nitrogen from different sources but much is derived from N-fixed by legumes, which has greater potential and cheapest sources as well. Biologically fixed N is transformed into leguminous protein and this may be consumed directly by animals to meet their protein requirements and excess return to soil through manure, hence, legumes are crucial to maintaining the N-balance in nature (Gutteridge and Shelton, 1994). Legumes are universally known for their ability to fix chemically inactive atmospheric nitrogen to satisfy their nitrogen requirements.
They achieve this through symbiotic relationship with N-fixing Rhizobium bacteria, which is found in nodules of their roots (Nnadi and Haque, 1986).

Agronomic importance of intercropping
Planting pattern influences both yield of sorghum as well as that of groundnut. In research conducted on millet/stylo intercropping, average millet grain yield from the alternate triple row millet/Stylosanthes hamata treatment decreased by 78% as compared with sole plots millet yield.
Millet stover yields were 10-53% less from intercrops than sole crops. When millet was grown with S. hamata in alternate triple rows, total biomass yield decreased by 40 to 49% (Kuoame et al., 1993).

Yield stability
Intercropping is not the only mechanism to increase the yield of component crops. Apart ecological and socio-economic aspects, the main advantage of intercropping is yield stability, which is reliable food and feed production over the years. In reality, intercropping systems give more stable yields than sole cropping system. This is one of the main reasons why farmers still prefer mixed cropping (Altieri, 1998). There were many reasons behind the stability of yield in

Assessing intercropping yield advantage
There are different intercropping situations that satisfied different requirements of yield advantages. Willey (1979) identified three distinct situations to assess the yield advantage more precisely and to plan intercropping research with relevant rationale. In the first place, intercropping must give full yield of the main crop and some yield of the associated crop. More specifically, main crop gives full yield and in addition there is associated crop that gives extra yield reducing the principal crop yield. This situation is applicable where the promising requirement is for a full yield of some staple food crops.
The second situation is the higher sole crop yield is lower than the intercrop yield. In this intercropping requirement, the combined yield of the component crops must be exceed the yield of either of the sole crops, particularly the yield of the intercrop that gives higher in monoculture.
It is based on the assumption that gives unit yield of each crop component crops is simply for maximum yield regardless of the crop from which it comes. The third situation is combined intercrop yield must exceed a combined sole crop yield. This criterion is based on the assumption that producers usually needs to grow more than one crop; which is aimed at satisfying food requirements, spreading labor peaks and to guard against risks.
In research conducted to identify chemical composition and best cropping system of groundnut and sorghum under mixed and monocrop, it was found out that the sorghum fodder yields were lower in the monocrop and even less in the mixed crops. Among crops in association there were competitions between them. The degree of competition between mixed crops is determined by plant populations and intercropping patterns. Intercrops may be sown in alternate hills within rows, alternate rows, paired rows or strips of more than two rows (Shehu et al., 1999). In general, when plants are in closer contacts due to type of intercropping patterns used, the competition among plants will be higher. The opportunities for sharing resource are greatest when two crops are planted in alternate hills within rows or are broadcasted rather than sown in rows, and the closed proximity of the crops can also lead to more direct competition between intercrops (Ibrahim et al., 1993).
Intercropping also has an agronomic advantages of rising, ambient temperature that limits the chance of frost damage, and increase protection of the ground against sunlight and impact of high-intensity raindrops, so that erosion is impeded (Humphreys, 1994). Intercropping also has a role in increasing the quality of grains of the main crops. In experiment conducted at Debre Zeit, Ethiopia, higher nitrogen content in maize grain when intercropped with vetch was obtained (Nnadi and Haque, 1986).

Description of Experimental Site
The   Table 2).

Description of Experimental Materials
Sorghum variety (Teshale) and groundnut (Fetene) were used as planting materials. The seeds were collected from Melkassa Agricultural Research Center. The intra-row spacing for sorghum was 25cm, 30cm and 35cm and that of groundnut was 10cm, 15cm and 20cm. The row spacing was 60cm and 60cm for groundnut and sorghum, respectively. Groundnut and sorghum was planted solely at 60cm x 10cm and 60cm x 20cm for groundnut and sorghum respectively, to compare with the intercropping. Two rows of groundnut separated from each other by 60cm were planted between the sorghum rows, at 40cm away from sorghum rows.
The treatments were arranged as follows:

Panicle diameter
The analysis variance revealed that panicle diameter was not significantly affected due to main crop of sorghum population and subsidiary crop ground nut population. Also panicle diameter capacity was no significant due to main effect of sorghum population and groundnut population at Erer location. This might be similar variety are similar responsible for panicle diameter, even if the population of sorghum and intercropped groundnut increases or decreases

Panicle length
The analysis of variance revealed that panicle length was not significantly affected due to main effect of sorghum population and groundnut population.
Year by location showed that no significant difference due to panicle length. Cropping system in 2014 in Fadis showed that no significant effect on panicle length of sorghum; this might be due to environmental change from year to year. Similar trends was observed in Erer

Sorghum yield kg ha -1
The analysis of variance revealed that sorghum yield was significantly affected due to main effect of sorghum and groundnut population. And also significant difference was obtained in intercropping system. However highest sorghum grain yield was obtained in sole sorghum than intercropped sorghum. At both Fadis and Erer site sorghum grain yield significantly affected due to main effect of sorghum population and groundnut population.

Groundnut yields kg ha-1
The analysis of variance revealed that sorghum grain yield was significantly affected due to main effect of sorghum population density and groundnut population density. cropping system significantly influence groundnut population the highest groundnut population was recorded in sole groundnut while the lowest yield was obtained in intercropped groundnut .this might be due to competition effect of crops for nutrients , sun light and moisture. Similar result was obtained in 2014 at Erer Location (site).

Land Equivalent Ratio
Land equivalent ration was significantly affected due to main effect of sorghum population density and groundnut population density the highest LER was recorded due to cropping system the highest LER was recorded in intercropping system while the lowest was recorded in sole cropping system at all location. The research result showed that, there were significance difference for both sorghum and ground nut yield per hectare in the years (2014 and 2015) among treatments (table2). The sorghum sole yield in 2014 were (2974kgha -1sorghum and 2511kgha -1 groundnut ) and 2015(2501 kgha-1 sorghum and 1017kgha -1groundnut ), respectively. Even though the sole sorghum yield per hectare were relatively looks like high, the cumulative yield of intercropping yield were higher than the sole sorghum.
Highest yield ha-1 (2865kg ha-1 sorghum and 2729kg ha-1 groundnut ) and (2974 kg ha-1 sorghum and 2511kg ha-1 groundnut ) obtained at intra spacing of 30cm x20cm and 25cm x30cm, respectively under sorghum intercropping with ground nut and having more than one land equivalent ratio (1.31 and 1.27)(table2). This implies that intercropping of sorghum and ground nut at intra spacing of 30cm x20cm and 25cm x30cm of sorghum with groundnut was advisable for intercropping. This was because there was low competition beneath and above soil (low light, space, nutrient competition). And also the 1.31 and 1.27 land equivalent ratio showed that, we need additional 31% and 27% area of land to get same yield (2865kg ha-1 sorghum and 2729kg ha-

RECOMMENDATION AND CONCLUSION
The result over time(in 2014 and 2015) at Fadis and Erer showed that the highest sorghum and groundnut yield per hectare were obtained/harvested from the intra spacing of 25cmx20cm and 30cmx20cm intercropping sorghum with ground nut system with more than one land equivalent ratio. Therefore, the intra spacing of the main crop (sorghum) 25cm and 30cm and for the subsidiary crop (groundnut) 20cm was recommended for further production in the study areas of eastern Harerghe zone.