Response of linseed (Linum usitatissimum L.) to fertilizer application and weeds control in South- Eastern Highlands of Ethiopia

The effect of N and P fertilizers and weeds control on yield and yield components of linseed (Linum usitatissimum L.) were studied in South-Eastern highlands of Ethiopia at four locations during 2009/2010 and 2010/2011 main cropping seasons. Split plot design with three replications was used. The main plot was allocated for four weeding frequencies and sub-plot was allocated for eight fertilizer rates. Results indicated that tiller numbers, pod numbers and final seed yield of linseed were significantly influenced by the effects of N and P fertilizers and weeds control treatments. Results showed that W4F5 treatment produced 58% seed yield advantage over the control in combined years over locations. Similarly, W4F6 produced seed yield advantage of 57% over the control in combined years over locations. Moreover, this study revealed that W4F5 treatment resulted in 38 and 43% increment in number of pods/plant and seed yield/plant, respectively compared to the control. Thus, the present results showed that treatments W4F5 to W4F6 were superior agronomic practices for linseed production in South-Eastern highlands of Ethiopia. Likewise, twice hand weeding alone brought 53% seed yield increment as compared to unweeded check. Besides, twice hand weeding resulted in 45 and 38% increment in number of pods/plant and seed yield/plant, respectively as compared unweeded check. Results have shown that dominant broadleaved and grass weeds vary across locations. The results of economic analysis also indicated that the highest net benefits were obtained from twice hand weeding and application of 23/23 kg/ha N/P2O5 to 23/34.5 kg/ha N/P2O5.

Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License proteins (up to 38%) (Altai, 2010). Linseed oil has been used as a drying agent for paints, varnishes, linoleum,lacquer, and printing ink. Medicinal uses of linseed include promotes heart health, lowers cholesterol, protects against strokes, lowers blood pressure, used for constipation and helps guard against breast cancer and other cancers (Budwig, 1994;Connor, 2000).
Ethiopia is the fivth largest producer of linseed in the world next to Canada, China, USA and India (Adugna, 2007). In 2008/2009, Ethiopia allocated 181 thousand hectares of land for linseed and produced 0.16 million tons (CSA, 2009). Likewise, Arsi and West Arsi Zones alone allocated about 74 thousand hectares of land and produced 72 thousand tons of linseed. In other words, 57% of the areas allocated for linseed production in Oromiya Region and 41% of the areas allocated for linseed production in the country as a whole had come from Arsi and West Arsi Zones. Besides, 61% of total linseed production in Oromiya Region and 46% of linseed production in Ethiopia was obtained from these zones (CSA, 2009).
Despite numerous uses of linseed, large areas allocation, and many years production, tradition linseed productivity is very low in Ethiopia (0.86 t/ha) (CSA, 2009). Linseed production in Ethiopia is characterized by low input, low yield and poor product quality mainly due to attitude and poor management practices such as lack of proper weed management system, poor seed and field hygiene, poor seed bed preparation, inadequate plant nutrition, inappropriate seeding rate, improper threshing ground and improper cleaning. On the other hand, using improved varieties along with good agronomic practices gave as high as 2.2 t/ha on research fields and some model farmers managed to produce as high as 2.0 t/ha when supported with improved seed of linseed, intensive training and close supervision (KARC, 2012).
Weeds are plants that are competitive, persistent, and pernicious (Ross and Lembi, 1985). In general, weeds cause loss of crop yield, loss of crop quality, stumble export, limit the choices of crop rotation sequences and cultural practices, harbor other crop pests, interfere with crop harvesting, necessitate extra cleaning and processing procedure, and lead to increased transportation cost. Crops vary widely in their ability to compete with weeds. In general, the competitive ability of a crop is related to its ability to access resources including light, water and nutrients. Generally speaking, crops with vigorous growth that reduce the quality and quantity of light beneath the crop canopy are the most competitive (Buhler, 2002). Specific characteristics that tend to influence a crop's competitive ability include: rapid germination and emergence, rapid biomass accumulation and ground cover, leaf characteristics (leaf area index), flag leaf length and angle, canopy structure (ability to intercept light), tillering capacity, and height. In fact, linseed cannot compete effectively with weeds, particularly up to two months after sowing; therefore, early removal of weeds is important before flowering and a yield reduction of up to 56% can be incurred depending on the infestation level (Rezene, 1992). Similarly, weeds caused 53% yield reduction in linseed in USA (Bridges, 1992).
Hence, weed control measure is a major and unavoidable operation for linseed production. Hand weeding is still by far the most widely practiced cultural weed control technique in field crop production throughout the country mainly due to the prohibitive costs of herbicides and fear of toxic residue coupled with lack of knowledge and clothings for their use at subsistence farmers' level.
Mean while, plants need certain nutrients to grow and prosper. On the other hand, primary macronutrients, namely N, P, and K can virtually be found in every brand of fertilizer on the market. In fact, many natural soils are deficinet in certain nutrients that must be supplied through fertilizer, either organic or inorganic.
In Ethiopia, linseed is being produced under rainfed, low input and poor management. Concerning fertilizer utilization for linseed production, 89% of the farmers apply neither organic (manure, compost, etc.) nor inorganic fertilizer (DAP, Urea, etc.) (Abebe et al., 2011). Only 7% of farmers apply 11 to 20 kg/ha DAP. On the other hand, national fertilizer recommendation for linseed production is 23/23 kg/ha N and P 2 O 5 (50 kg/ha DAP and 30 kg/ha Urea). Similarly, majority of farmers neither hand weed nor spray herbicides to control weeds on linseed fields. Only limited number of farmers carry out late and selective hand weeding for broad leaved weeds leaving grass weeds to compete with the crop. Even some farmers allow their sheep in side linseed fields assuming that they could selectively graze on grass weeds.
Therefore, the objectives of this study were: to investigate the effects of weeding frequencies and fertilizer rates on linseed seed yield and yield components.

Experimental treatments, design and data
The experiment was conducted during the 2009/2010 and 2010/2011 main cropping seasons. The experimental fields were ploughed once and disced twice prior to planting using mold-board and disc ploughs, respectively. Split plot design with three replications was used. The main plot was allocated for four weeding frequencies (W1=no weeding,W2= once weeding at 30 to 35 days after sowing, W3=once weeding at 55 to 60 days after sowing, W4=twice weeding at W2 and W3) and sub-plot was allocated for eight fertilizer rates (F1=No fertilizer, F2=11.5/11.5 kg/ha N and P2O5, F3=11.5/23 kg/ha N and P2O5, F4=23/11.5 kg/ha N and P2O5, F5=23/23 kg/ha N and P2O5, F6=23/34.5 kg/ha N and P2O5, F7=34.5/23 kg/ha N and P2O5, F8=34.5/34.5 kg/ha N and P2O5). Diammonium phosphate (DAP) and urea were used as a source of N and P2O5 based on calculation. Linseed variety 'Tolle' was used and sown at a seed rate of 25 kg/ha. Each treatment was planted in a plot consisting of six rows of 5 m long with spacing of 20 cm between rows. The distance between replications was 2 m. Disease or insect control chemicals were not applied during the growth of linseed. On the other hand, all other recommended cultural practices were properly followed in order to sucessfully grow the crop. Sowing was done from second week of June to first week of July each season. As a crop rotation, linsed followed either wheat or barley in both years. Data was collected both on plot and 10 plant basis on 11 parameters including stand percentage, date of 50% flowering and 90% maturity, plant height, lodging%, 1000-seed weight and seed yield. After threshing seeds were cleaned, weighed and adjusted to 7% moisture content. Total seed yield recorded on plot basis was converted to kg/ha for statistical analysis.
The data collected were subjected to analysis using MSTATC and SAS softwares (SAS, 2004). Moreover, partial budget analysis was performed in order to evaluate the economic feasibity of the treatments (CIMMYT, 1988).

Partial budget analysis
Variable cost of fertilizer and weeding was used for partial budget analysis. Price fluctuations during the production season were considered. Marginal Rate of Return (MRR), which refers to net income obtained by incurring a unit cost of input, was calculated by dividing the net increase in yield of linseed due to the application of each input to the total cost of each input applied at each rate. This enables us to identify the optimum rate of fertilizer and weeding frequency for linseed production.

Weed Flora
Different weed species belonging to genera and plant familes were identified, including broadleaved and grassy weeds (Table 3). Convolvulus arvensis L. was quite dominant broad leaved weed species at Kulumsa comprising 65% of weeds density. However, Corrigiola capensis was the dominant broad leaved weed followed by Taraxacum spp. and Daucus carrota at Bekoji. On the other hand, at Kofele major broad leaved species were Galinsoga parviflora, Plantago lanceolata L., and Polygonum spp. Considering grass weed species Setaria faberii, Phalaris paradoxa and Eragrostis spp. were the dominant species at Kulumsa, Bekoji and Kofele, respectively (Table 3). Hence, listed weed species were among the most important linseed yield limiting species in these areas that need to be controlled by employing integrated weed management options.
Linseed is weak especially at seedling stage and a poor competitor to weeds as compared to other oil crops. The critical period of weed competition in linseed varies from three to eight weeks or from early estabilishment to early flowering stage. Getinet and Nigussie (1997) reported that linseed should receive an early (3 to 4 weeks after sowing) weeding to be followed by a one mid season one. Weeding linseed during or after flowering is not a gain but a loss of time, energy and money mainly due to high comptetion between the weed and the crop for space, nutrition, moisture and light.

Effect of fertilizer rates and weeding frequency on yield and yield components of linseed
The combined analysis of variance over locations and years revealed that significant (P≤0.05) main effects occured for all traits evaluated including day to flowering, days to maturity, powdery mildew, pasmo and wilt diseases, plant height, number of tillers/plant, number of pods/plant, seed yield/plant, stand percentage and seed yield/plot for weeding frequencies. Likewise, weeds control practiced and fertilizer rates interacted significantly (P≤0.05) for all traits. The results are inconsistent with Getachew et al. (2006). Interaction of weeding freqency and fertilizer rate was significant (P≤0.05) for seed yield (kg/ha) for individual years but non significant (P≤0.05) for combined locations over years (Table 4). In general, the 2009/2010 cropping season was bad year in tems of crops productivity compared to 2010/2011 cropping season mainly due to heavy and prolonged rainfall that in turn resulted in poor seed bed preparation, poor weed control, low photosynthesis efficiency, flowers abortion and low seed set. Yet, interaction of weeding frequencies and fertilizer rates effect showed consistent results over years. The present results showed that W4F5 treatment produced consistently the highest yield for individual years as well as for combined years over locations (Table 4). In other words, W4F5 treatment produced 333, 554 and 444 kg/ha seed yield advantage over the control (W1F1) in 2009/2010, 2010/2011 and in combined years over locations. That is, W4F5 treatment produced 51, 64 and 58% seed yield advantage over the control in the first, the second and in combined years over locations, respectively. Moreover, the present results revealed that W3F5 treatment produced 43, 29 and 35% seed yield advantage over the control in the first year, the second year and in combined years over locations, respectively. Similarly, W2F5 produced 34, 28 and 31% seed yield advantage over the control in the first, the second and in combined years over locations, respectively (Table 4). Furthermore, W4F6 produced seed yield advantage of 45, 67 and 57% over the control in the first year, the second year and in combined years over locations, respectively.
However, W1F5 treatment produced 13 and 6% seed yield penality over the control in the second and combined years, respectively. Similar trends were observed when W4F6 treatment was used. This showed that adding fetilizer without weeds control practices resulted in double losses, once in terms of seed yield reduction and the other was in terms of cost of ferilizer or loss of money to purchase fertilizer. This result also showed that weeds became more competent and vigorous, if ferilizer was added without weeding the crop and would result in more yield loss. Based on results of combined locations over years, interaction of weeding frequencies and fertilizer rates showed significant differences (P≤0.05) for yield components like plant height, number of tillers/plant and number of pods/plant (Table 5). However, significant difference was not observed for seed yield/plant. This  showed that treatments W4F5 to W4F6 were superior agronomic practices for linseed production in South-Eastern highlands of Ethipia.

Effect of weeding frequencies
Results showed that twice hand weeding siginificantly (P≤0.05) increased yield components like number of tillers/plant, number of pods/plant, seed yield/plant and final seed yield as compared to unweeded check. When we compare 2009/2010 and 2010/2011 cropping seasons, the 2010/2011 was by far better in terms of productivity than the 2009/2010 due to bad weather condition of the 2009/2010 cropping season which was mainly menifested by heavy and prolonged rainfall that inturn affected land preparation, enhanced flowers defoliation, reduced efficiency of photosenthesis and created suitable condition for dieases severity and incidence. Eventually, the 2009/2010 cropping season is being remembered by bread wheat yellow rust disease epidemic whereby highly popular varieties like 'Kubsa' and 'Galama' were badly affected from highland to midland and from their seedling stage throughout gain filling period throughout the country and linseed was not special.
Combined results of the two cropping seasons have shown that twice hand weeding resulted in 45 and 38% increment in number of pods/plant and seed yield/plant as compared to unweeded check (Table 6). Besides, twice hand weeding brought 13% increase in number of tillers/plant in comparison to the control. In line with the present findings, El Naim et al. (2010) reported that weeds significantly reduced the vegetative growth attributes measured. Similarly, number of pods/plant, seed yield and 1000-seed weight were significantly (P≤0.05) infulenced by time and weeding frequencies (Meseret et al., 2008).
Likewise, twice hand weeding produced 396 kg/ha seed yield advatage over the control. In other words, 53% seed yield increment of linseed was acheived by employing W4 treatment as compared to unweeded check. Supporting evidences were reported in different crops by El Naim et al. (2010) and Tolera and Daba (2004). Similar to the present results weeding twice had the highest number of pods/plant, 100-seed weight, seed yield/plant and final seed yield (El Naim et al., 2010). On the other hand, twice hand weeding negatively affected plant height. In other words, twice hand weeding decreased plant height by 8% as compared to unweeded check. This might be due to the fact that the crop used its energy for tillering, branching and pods setting rather than for height increment, which finally have more positive effect on the final product, seed yield. This result did not agree with reports of Alemayehu et al. (2008) andEl Naim et al. (2010), as they found that increasing weeding times significantly increased plant height.

Effect of N and P fertilizer rates
Significant difference (P≤0.05) was observed on yield components like plant height, number of tillers/plant and number of pods/plant due to application of different rates of N and P fertilizer for combined years over locations (Table 7). On the other hand, significant diferences were not observed for seed yield/plant for individual as well as combined years. These results agreed with Khajani et al. (2012). They found that increased N and P fertilizer rates significantly increased pods and branches number. In general, the present results showed that responses of linseed to fertilizer rates was very low compared to its responses to weeding frequencies. These results were in good agreement with the reports of Getinet and Nigussie (1997). In other words, as fertilizer rates vary from F1 to F8, the observed difference was low on yield as well as yield components. Yet, the highest rate gave the highest plant height, the highest number of tillers/plant and number of pods/plant. Similar to the present findings, plant height exhibited positive response to applications of high rates of N fertilizer (Genene et al., 2006). The authors also reported that only stand count and 1000seed weight increased with increased P rates, while most of the other agronomic parameters showed incosistent F1=No fertilizer, F2=11.5/11.5 kg/ha N and P2O5, F3=11.5/23 kg/ha N and P2O5, F4=23/11.5 kg/ha N and P2O5, F5=23/23 kg/ha N and P2O5, F6=23/34.5 kg/ha N and P2O5, F7=34.5/23 kg/ha N and P2O5, F8=34.5/34.5 kg/ha N and P2O5; NS=non significant at 0.05 probability level. Price of DAP per 100 kg=1400 birr; price of Urea per 100 kg=1300 birr; price of linseed grain per 100 kg=1800 birr; price of labor=50 birr/day; labor of hand weeding=16 days/ha=800 birr; labor of twice hand weeding=1600 birr; and labor to apply fertilizer for a ha=100 birr.
trends. Moreover, Genene et al. (2006) reported the absence of discernible effects of applications of N and P fertilizers on the number of pods/plant, which did not agree with the present investigation. According to these authors, both the main and interaction effects of N and P rates were inconsistent on several yield components. Yet, 11.5 and 34.5 kg N/P 2 O 5 per ha was determined as optimum fertilizer application for linseed production under Bale conditions (Genene et al., 2006) (Table 8). Data of combined locations and years showed 4 and 9% increment in plant height and number of tillers/plant as fertilizer rate was increased from F1 to F5 and F8, respectively. Simlarly, number of pods/plant and seed yield/plant were increased by 10 and 15% as fertilizer rates increased from F1 to F5 and F8, respectively. However, only 2 and 5% seed yield advantage was obtained when F5 and F6 treatments were used as compared to the control (Table 7).

Partial and marginal budget analysis of treatments
For a treatment to be considered as a worthwhile option to farmers, the marginal rate of return (MRR) needs to be at least between 50 and 100% (CIMMYT, 1988). However, for the present study, 100% MRR was considered as a reasonable minimum acceptable rate since farmers in the study areas usually neither practice weeding nor apply fertilizer for linseed production (Abebe et al., 2011). The partial budget analysis in the present study indicated that high MRR (210 to 222%) was obtained by applying 23/34.5 kg/ha N/P 2 O 5 (F6) with twice hand weeding (W4) and 23/23 kg/ha N/P 2 O 5 (F5) with twice hand weeding, respectively (Tables 9 and 11). Price of DAP per 100 kg=1400 birr; price of Urea per 100 kg=1300 birr; price of linseed grain per 100 kg=1800 birr; price of labor=50 birr/day; labor of hand weeding=16 days/ha=800 birr; labor of twice hand weeding=1600 birr; and labor to apply fertilizer for a ha=100 birr. Price of DAP per 100 kg=1400 birr; price of Urea per 100 kg=1300 birr; price of linseed grain per 100 kg=1800 birr; price of labor=50 birr/day; labor of hand weeding=16 days/ha=800 birr; labor of twice hand weeding=1600 birr; and labor to apply fertilizer for a ha=100 birr.
This means that the income obtained by applying F5/F6 with W4 for linseed was more than 2.22/2.10 times a uint total NP fertilizer and twice weeding cost. This analysis was done by considering only grain yield of linseed. If we add the value of the chaff, the straw, meal, pests cycle break, the return will obviously become more than the already estimated income. This is in line with the findings of Kedir et al. (2005), where by seeding rate of 25 to 30 kg/ha combined with twice hand weeding gave optimum seed yield and recommended for linseed production under Bale conditions.

Soil analysis
Soil analysis of the experimental sites indicated that many soils were sup-optimal for the production of linseed since the pH, available N and available P were below optimum range, thereby affecting the response of seed yield to applied P (Getachew and Sommer, 2000;KARC, 2013). Soil anaysis results revealed that available soil P was low for Kofele, Bekoji and Kulumsa, but medium for Asasa according to KARC (2013). Besides, available soil N was medium for Asasa and Kulumsa, but fair for Bekoji and high for Kofele (Tables 1 and 2). Thus, soil analysis results showed that soils of Kofele and Bekoji require high DAP but low urea. On the other hand, soils of Asasa and Kulumsa require high Urea but low DAP. In addition, Kofele and Bekoji soils were strongly acidic, but that of Kulumsa and Asasa were moderately acidic. In several cases, soils with pH lower than 5.5 are not suitable for linseed production unless they are reclamed with lime (Getinet and Nigussie, 1997;Adugna, 2007). In such soils, the proportion of P fertilizer that could immediately be available to the crop becomes inadequate and residues of the fertilizer may be released very slowly Price of DAP per 100 kg=1400 birr; price of Urea per 100 kg=1300 birr; price of linseed grain per 100 kg=1800 birr; price of labor=50 birr/day; labor of hand weeding=16 days/ha=800 birr; labor of twice hand weeding=1600 birr; and labor to apply fertilizer for a ha=100 birr. (Sikora et al., 1991). Varieties may differ in their ability to grow in soils of low P status, Getinet and Nigussie (1997) reported that linseed grows best in soils with pH 5.5 to 6.6 and marginally grown in soils with pH 4.9 to 5.5 and in soils with pH 6.6 to 7.6.

CONCLUSION AND RECOMMENDATIONS
In Ethiopia, cultivation and usage of linseed is an old practice. Besides, the crop is being used for many purposes; including as a source of food, feed, cash, medicine, raw-material for industries and export commodity. Despite its multipurpose usage and large areas allocation for its production, its productivity, quality and marketing is still low, largely due to sup-optimal management practices of which absence of weeds control and absence of fertilizer application are the major ones. Linseed is currently marginalized and being produced under rainfed, minimum care and low input. These situations should be diverted in order to improve income, livelihood and health of farmers, minimize shortage of cooking oil, supply emering agro-industries and markets, and benefit the country at large. The results of the present study showed that twice hand weeding produced 53% seed yield advantage over unweeded check. Likewise, twice hand weeding resulted in 13, 45 and 38% increment in number of tillers/plant, number of pods/plant and seed yield/plant, respectively as compared to unweeded check. On the other hand, the present results showed that response of linseed to fertilizer application was low as compared to its response to weeding frequencies. In fact, W4F5 and W4F6 treatments produced more than 50% seed yield advantage over the control. Moreover, these treatments resulted in more than 35% increment in yield components like number of pods/plant and seed yield/plant as compared to the control. Furthermore, the partial budget analysis in the present study indicated that high marginal rate of return (210 to 222%) was obtained by applying 23/34.5 kg/ha N/P 2 O 5 (F6) with twice hand weeding (W4) and 23/23 kg/ha N/P 2 O 5 (F5) with twice hand weeding, respectively. In other words, application of 75 kg/ha DAP and 21 kg/ha urea along with twice hand weeding, and application of 50 kg/ha DAP and 30 kg/ha urea together with twice hand weeding gave optimum seed yield and yield components of linseed and hence farmers have to follow these agronomic recommendations for linseed production in South-Eastern highlands of Ethiopia. Further investigation has to be carried out on farmers fields in order to further confirm the present results.