African Journal of
Agricultural Research

  • Abbreviation: Afr. J. Agric. Res.
  • Language: English
  • ISSN: 1991-637X
  • DOI: 10.5897/AJAR
  • Start Year: 2006
  • Published Articles: 6169

Full Length Research Paper

Maize-lupine intercrop response to applied nitrogen and phosphorus in North-Western Ethiopia

Alemayehu Assefa
  • Alemayehu Assefa
  • Crop Research Directorate, Amhara Region Agricultural Research Institute, P. O. Box 8, Bahir Dar, Ethiopia.
  • Google Scholar
Charles S Wortmann
  • Charles S Wortmann
  • Agronomy and horticulture, University of Nebraska-Lincoln, P. O. Box 830915, Lincoln, NE 68583-0915, USA.
  • Google Scholar
Yigzaw Dessalegn
  • Yigzaw Dessalegn
  • LIVE Project, International Livestock Research Institute, P. O. Box 5689, Addis Ababa, Ethiopia.
  • Google Scholar
Kinde Tesfaye
  • Kinde Tesfaye
  • Crop Modeling and GIS for Agricultural Systems, International Maize and Wheat Improvement Center, P. O. Box 5689, Addis Ababa, Ethiopia.
  • Google Scholar
Tamado Tana
  • Tamado Tana
  • School of Plant Science, Haramaya University, P. O. Box 138, Dire Dawa, Ethiopia.
  • Google Scholar
Nigussie Dechassa
  • Nigussie Dechassa
  • School of Plant Science, Haramaya University, P. O. Box 138, Dire Dawa, Ethiopia.
  • Google Scholar


  •  Received: 24 March 2016
  •  Accepted: 06 June 2016
  •  Published: 07 February 2019

 ABSTRACT

Maize (Zea mays) is a major staple crop in North-Western Ethiopia. Narrow leaf lupine (Lupinus angustifolius) grain is a commercial concentrates for livestock feed. Maize-lupine intercropping is a sustainable and emerging crop production approach for the resource poor smallholder farmers of North-Western Ethiopia; however, there is no recommended fertilizer rate for the intercrop. Therefore, field experiment was undertaken to determine maize-lupine intercrop yield response to applied N and P; to determine N use efficiency of maize; and to establish the basis for determining the most economical N and P rates with varying costs and commodity prices for the intercrop. The experiment was conducted at South Achefer and Mecha areas of North-Western Ethiopia in 2013 crop season. Four levels of each N (0, 64, 128 and 192 kg N ha-1) and P (0, 20, 40 and 60 kg P ha-1) were arranged in factorial combination. Sole crop maize and lupine were included as check treatments. The treatments were laid out in a randomized complete block design with three replications. The results indicated that maize growth parameters and yield components, maize grain yield, and total maize-lupine intercrop yield increased significantly with applied N, P, and N x P interactions. The highest total intercrop yields were obtained on 162/45 kg N/P ha-1 at South Achefer and 205/61 kg N/P ha-1 at Mecha with yield advantage of 4.14 and 7.05 t ha-1 over unfertilized, respectively.  The economic optimum rates for maize-narrow leaf lupine intercrop were 130/39 kg N/P ha-1 at South Achefer and 177/53 kg N/P ha-1 at Mecha with cost price ratio of N cost kg-1/maize grain price kg-1 equal to 6 and P cost kg-1/maize grain price kg-1 equal to 11. The economic optimum rates decreased as cost price ratio increased, therefore, seasonal price information is vital to adjust the economic optimum rates. Maize N use efficiency declined as N rates increased in the maize-lupine intercrop.          

Key words:  Intercropping, lupine, maize, optimum rate, yield response.

 

Abbreviation: AEN,  agronomic  efficiency  of  applied Nitrogen; AONR, agronomic optimum Nitrogen Rate, AOPR, agronomic optimum phosphorus rate; CPR, cost price ratio; EONR, economic optimum nitrogen rate; EOPR, economic optimum phosphorus rate; EYM, equivalent Yield of Maize; LAI, leaf area index; PEN, physiological efficiency of applied nitrogen; PFPN, partial factor productivity of applied Nitrogen; REN, recovery efficiency of applied Nitrogen; TKW, thousand kernel weight.  

 INTRODUCTION

In Ethiopia, maize ranks second next to tef (Eragrostis tef L) in area coverage and first in quantity of grain produced (CSA, 2015). Mean maize yield, however, is very low (3.43 t ha-1) (CSA, 2015) as compared to  a  global  mean of 5.0 t ha-1 (CIMMYT and IITA, 2011). It is a priority staple food crop in many parts of the country. Narrow leaf lupine is of a recent introduction to Ethiopia and is commercial  concentrate  feeds  for   livestock   in   North-Western Ethiopia (Likawent et al., 2012). The grain is an alternative to dry bean (Phaseolus vulgaris) and soya bean (Glycine max) for human consumption, and several modern cultivars have been developed for use as human food (Shahidul et al., 2011).

Maize-legume intercropping systems offer several advantages to small-scale maize farmers such as improved soil fertility, healthier diets, increased productivity, and reduced risk of total crop failure (CCRP, 2009). Seran and Brintha (2010) reported legume intercropping with maize as a way to grow a staple crop while benefiting from the additional crop. Higher productivity of the system as a whole in maize-common bean intercrop compared with maize sole crop has been reported for other parts of Ethiopia (Wortmann et al., 1996; Tamado and Eshetu, 2000).

Nitrogen (N) and phosphorus (P) are important constraints to maize production in Ethiopia (Kebede et al., 1993). Tilahun et al. (2007) recommended application of 128 kg N and 40 kg P ha-1 to maximize net returns to fertilizer use with sole crop maize in Dera area of North-Western Ethiopia. However, information is scarce on fertility response of maize-legume intercrop in North-Western Ethiopia. Narrow leaf lupine, hereafter referred to as lupine, is a relatively new crop with grain and forage potential in the region and more information is needed on intercropping it with maize. Optimum nutrient application rates and efficiency for maize-lupine intercrop is required to increase crop yields and profitability while minimizing environmental pollution. Therefore, this study was conducted to: 1) determine maize-lupine intercrop yield response to applied N and P; 2) determine N use efficiency of maize; and 3) establish the basis for determining the most economical N and P rates with varying costs and commodity prices for the intercrop.

 


 MATERIALS AND METHODS

The experiment was conducted on Nitosols at Mecha (11.39° latitude and 37.11° longitude, 1982 meters above sea level) and South Achefer (11.34° latitude and 36.94° longitude, 2021 m above sea level) of North-Western Ethiopia in the 2013 crop growing season (June to October).

The soil analysis result at soil depth of 0 to 40 cm indicated that the sites had clay texture with low values of pH and available P (Table 1). According to Halm (1978), the available P was low (0-15 mg kg-1, Bray) and according to the ratings by Tekalign (1991) the soils for both sites are strongly acid (4.5 to 5.2), organic carbon was moderate (15 to 30 g kg-1), and total N content was high (1.2 to 2.5 g kg-1) at both sites.

 

 

Treatments consisted of N (0, 64, 128 and 192 kg N ha-1) and P (0, 20, 40 and 60 kg P ha-1) arranged in factorial arrangement. Sole crop maize at spacing of 75 cm x 30 cm with recommended fertilizer rate of 128/40 N/P kg ha-1 and sole crop lupine at spacing of 40 cm x  10 cm  with  no  fertilizer  application  were  included  as check treatments. The treatments were laid out in randomized complete block design with three replications. The fertilizer urea (46% N), DAP (18% N and 20% P) and triple super phosphate (TSP) (20% P) were used as sources of N and P.  The fertilizers were applied as band application in the maize furrow. All P was applied at planting while one-third of the N was applied at planting and the remaining N was side-dress applied, and covered, at the 8- to 10-leaf stage of maize. The crop varieties used for the experiment were BH-540 for maize and Sanabor for narrow leaf lupine. Both crops were planted in June at the same date in an additive series with 100% of maize plant population, and with lupine planted at 40% of sole crop stands. Maize was planted in paired rows spaced at 50 and 112.5 cm within and between paired rows, respectively. Paired rows of lupine were planted between the paired maize rows with 37.5 cm apart from adjacent maize row and within paired rows lupine (Figure 1). Intra row spacing was 30 and 10 cm for maize and lupine, respectively. Maize leaf area index (LAI) was recorded at silking stage (Dwyer and Stewart, 1986). Plant height, above ground dry biomass yield, ears plant-1, kernels ear-1 were determined in middle 4 rows of 1.8m length which was the net plot for determination of grain yield of both crops.

 

 

Components of N use efficiencies of maize were calculated as described by Cassman et al. (2002).

Where, PFPN = Partial factor productivity of applied N (kg grain per kg N applied); YN = crop yield (0% moisture) with applied N (kg ha-1); FN = amount of N applied (kg ha-1); AEN =Agronomic efficiency of applied N (kg grain increase per kg N applied); Y0 = crop yield (0% moisture) in a control treatment with no fertilizer (kg ha-1); REN = Crop recovery efficiency of applied N (kg increase in N uptake kg-1 N applied); UN = total grain N uptake at maturity (kg ha-1) in a plot that received N; U0 = total grain N uptake at maturity (kg ha-1) in a plot that received no N; and PEN = Physiological efficiency of applied N (kg grain increase kg-1 increase in N uptake from fertilizer). A 500-g grain sample was taken to measure maize grain protein using Infratec 1241 Grain Analyser (Foss, Hilleroed, Denmark) and N concentration in the dry grain was calculated as protein content divided by 6.25.

Total intercrop yield (measured as equivalent yield of maize, EYM) was calculated as  (Verma and Modgal, 1983), where YML = intercrop maize grain yield ha-1; YLM = intercrop lupine grain yield; PM = price of maize grain kg-1; PL = price of lupine grain kg-1. Grain moisture content was measured using a grain moisture tester (Dickey-John Multigrain) and final grain yield was adjusted to the moisture contents of 12.5% for maize and 10% for lupine.

Data were analyzed using the GLM procedure of the SAS 9.4 version (SAS Institute, 2013). Maize grain and total intercrop yield response to N, P, and N x P interaction were tested using single degree of freedom orthogonal contrasts to determine whether the response was linear or not. Mean separation for significant responses were compared using SAS LSMEANS test (probability of difference, PDIFF) at P < 0.05. Prediction of the optimal level of N and P for maximum and economic yield of the total intercrop was done using polynomial response equation (Dillon and Andreson, 1991). Economic return from the intercrop was performed at three scenarios of fertilizer cost to grain price ratios (CPR) for each N and  P including ratios of 6, 9 and 13 for N cost kg-1 to maize grain price kg-1; and 11, 18 and 25 for P cost kg-1 to maize grain price kg-1. Cost of N, Birr 26.5 kg-1 (derived from cost of urea, Birr 12.2 kg-1); cost of P, Birr 51 kg-1 (derived from cost of DAP, Birr 15 kg-1) of the year 2013; and mean price  of  the  maize  grain  (Birr 4.5 kg-1)  and lupine grain (Birr 3.0  kg-1) from December to February of the year 2013/2014 were used as base for determination of current cost price ratio of 6 for N cost kg-1 to maize grain price kg-1 and 11 for P cost kg-1 to maize grain price kg-1. The other CPR were determined based on the existing trend in  increasing  cost  of production  and it was assumed that cost of N increased to 42 and 58, cost of P to 82 and 112 while maize and lupine grain price kept constant.

 

 

 


 RESULTS AND DISCUSSION

The intercrop system was 60% more productive at south Achefer and 100% more productive at Mecha relative to sole crop production as measured from land equivalent ratio (Table 2). Yield advantages of 27% at South Achefer and 61% at Mecha were obtained from intercropped maize relative to sole-cropped maize at 128/40 kg N/P ha-1 applied. Increased maize yield when intercropped with lupine relative to sole-cropped maize might be due to a positive effect of lupine to maize crop. Palmason et al. (1992) reported significant N transfer from narrow-leaf lupine to intercropped ryegrass (Lolium multiflorum).

 

 

Growth and yield components of maize such as LAI, plant height, biomass yield, ear plant-1, kernel ear-1, and TKW were significantly affected by N and P application at both sites. Interaction effect of N and P significantly affected plant height at South Achefer, and LAI, plant height, biomass yield and number of kernels ear-1 at Mecha. Maize LAI and plant height increased as N and P rates increased (Tables 3 and 4). The highest LAI and plant height were recorded on the application of 192/60 N/P kg ha-1 at both sites (Table 4). Increases in maize plant height and LAI in response to N and P was reported by Onasanya et al. (2009). The effect of N fertilization in enhancing LAI is well documented in maize because of higher photo assimilates that result in more dry matter accumulation (Uhart and Andrade, 1995).

 

 

Biomass yield, TKW, number of kernels ear-1 and ears plant-1 were also increased in response to N and P applied (Table 5). The increase in biomass yield and TKW with N applications was consistent with the findings of Kaleem et al. (2012) who reported significant increase in biomass yield and TKW with increasing N rates as high as 210 kg N ha-1. The response of TKW to N and P rate is due to the fact that N and P deficiency decrease biomass production and partitioning, especially in reproductive organs, resulting in small kernel size (Uhart and Andrade, 1995). The increase in kernels ear-1 with N application was also consistent with those of Ali and Raouf (2012) who reported highest maize kernels ear-1 at the highest N rate of 225 kg N ha-1. The highest biomass yield (17.07 t ha-1) at Mecha was obtained at the highest fertilizer rates of 192/60 N/P kg ha-1 (Table 5).

 

 

Maize grain yield and the total intercrop yield, which was measured as equivalent yield of maize, were significantly affected by N and P application at both sites. Maize grain yield and equivalent yield of maize were significantly affected by N x P interaction at Mecha but not at South Achefer. Yield response functions were polynomial for the applied N and P rates at both sites with greater response at Mecha (Figure 2) though basal soil fertility status of the  two sites was at the same  range  as indicated in Table 1. Therefore, the greater responses at Mecha compared to South Achefer suggests the need to repeat the study over seasons and sites to verify the results. Yields increased with nutrient rate to certain level. Averaged over P, total intercrop yield ranged from 3.68 to 6.07 t ha-1 at 0 and 162 kg N ha-1, respectively at South Achefer (Figure 2a), and from 1.64 to 6.22 t ha-1 at 0 and 165 kg N ha-1, respectively at Mecha (Figure 2b). Yield increased by 65 and 279% at South Achefer and Mecha, respectively, due to N application. Similarly, averaged over N, yield ranged from 4.10 to 5.83 t ha-1 at South Achefer (Figure 2c) and from 2.68 to 5.60 t ha-1 at Mecha (Figure 2d) at 0 and 45 kg P ha-1, respectively. Yield increased by 42 and 109% at South Achefer and Mecha, respectively, due to P application.

 

 

The total intercrop yield (equivalent yield of maize) response functions for N and P applications were:

The increased maize yield in both sites with N and P application has commonly occurred with maize (Ardell and Michael, 2014; Sun et al., 2014). The polynomial response for the highest N and P rates may suggest levels below the highest rates plus the residual nutrients in the soil is sufficient to sustain normal vegetative growth of maize.  Depression in grain yield at higher levels of N and P might be also due to nutrient imbalances. Komljenovic et al. (2010) reported significant reduction of zinc status in the maize leaf at higher level of P application. Depression in grain yield of maize at higher N supply was reported (Sun et al., 2014).

The N x P interaction was very important to maize-lupine intercrop yield. Dramatically, yield increased at the lower rates of each nutrient in the presence of the other one (Figure 2) demonstrated the two nutrients are equally important and yield limiting for maize at these sites. Yield responses to N without P application (Figure 2a, b) and to P without N application (Figure 2c, d) were low. This result is in agreement with those of Alzubaidi et al. (1990) who reported significant grain yield response of maize for the interaction effect of N and P compared to application of N and P alone. Masaka (2006) further indicated that this was partly attributed to better plant growth by which N-fertilized plants have larger root systems for the capture of  other nutrients. However, the N x P interaction is likely to be much less important in cases where N is much more limiting than P deficiency (Dobermann et al., 2011; Kaizzi et al., 2012).

From response of N, P, and the N x P, polynomial response function for the intercrop yields were generated for each of the site.

Agronomic optimum N rate (AONR) and P rate (AOPR) at South Achefer were calculated from the following equations which were generated from Equation 1.

Similarly, AONR and AOPR at Mecha were calculated from the following two simultaneous equations which were generated from Equation 2.

The agronomic optimum rates for total intercrop yield were 162/45 kg N/P ha-1 at South Achefer and 205/61 kg N/P ha-1 at Mecha. Yield ranged from 2.56 at 0/0 N/P to 6.70 t ha-1 at 162/45 kg N/P ha-1 at South Achefer (Figure 3a), and from 1.01 at 0/0 N/P to 8.06 t ha-1 at 205/61 kg N/P ha-1 at Mecha (Figure 3b). Yield increased by 4.14 and 7.05 t ha-1 at South Achefer and Mecha, respectively relative to the unfertilized.

 

 

The cost price ratio affects the economic optimum N rate (EONR) and P rate (EOPR). The economic optimum rates decreased as cost price ratio increased. EONR and EOPR at South Achefer were calculated from equations which were generated from Equation 1 at cost price ratio of N cost kg-1 / maize grain price kg-1 equals to 6, and P cost kg-1 / maize grain price kg-1 equals to 11.

Similarly, EONR and EOPR at Mecha were calculated from simultaneous equations which were generated from Equation 2.

The economic optimum rates were 130/39, 110/35 and 91/31 kg N/P ha-1 at South Achefer and 177/53, 160/48 and 143/43 kg N/P ha-1 at Mecha at cost price ratios N cost kg-1/maize grain price kg-1 and P cost kg-1/maize grain price kg-1 of 6 and 11, 9 and 18, 13 and 25, respectively (Figure 4).

 

 

Accordingly, the maximum economic net return that can be estimated from maize-lupine intercrop on the above economic optimum rates are 24123, 21110 and 18512 Birr ha-1 at South Achefer, and  28338, 24121 and 20314 Birr ha-1 at Mecha, respectively. Net return decreased by 23 and 28% at South Achefer and Mecha, respectively, as cost price ratio of N/maize grain and P/maize grain increased from 6 and 11 to 13 and 25. Fertilizer costs and grain prices can fluctuate across years, therefore, profitability of fertilizer use is highly variable. Variations in the profitability of fertilizer use due to variable cost price ratios require that farmers adjust the EONR and EOPR based on current information.

Components of N use efficiencies declined as N rates increased. The decline was significant for most efficiencies except PEN at South Achefer, and REN and AEN at Mecha (Table 6). At South Achefer, the decline was from 53 to 22, 22 to 12, and 0.32 to 0.19 kg kg-1 for PFPN, AEN, and REN, respectively, as N rates increased from 64 to 192 kg ha-1 whereas at Mecha, the decline was from 47 to 24 and from 97 to 69 kg kg-1 for PFPN and PEN, respectively as N rates increased from 64 to 192 kg ha-1. These declines in N use efficiency might be due to more loss of N in the higher N rate than lower N rate. Decreases in N use efficiencies of maize as N rates increased was due to substantial N losses to the environment and low N use efficiency (Kaizzi et al., 2012 and Wortmann et al., 2011). Ardell and Michael (2014) reported significant decrease in PFP and AE as N rate increased.  Sun  et  al. (2014) and Xueli et al. (2014) also reported low N use efficiency at higher N application with increased residual soil nitrate and increased risk of N leaching.

 

 

 

 

 

 

 

 

 


 CONCLUSIONS

Maize-lupine intercrop responded to N and P application in North-Western Ethiopia with yield increase of 4.14 t ha-1 at South Achefer and 7.05 t ha-1 at Mecha over unfertilized. Economic optimum rates decreased from 130/39 to 91/31 N/P kg ha-1 at South Achefer and from 177/53 to 143/43 kg N/P ha-1 at Mecha as cost price ratios of N cost kg-1/maize grain price kg-1 increased from 6 to 13 and P cost kg-1/maize grain price kg-1 increased from 11 to 25. Therefore, seasonal price information is vital to adjust the economic optimum rates. Nitrogen use efficiencies of maize decreased as high as 58% in maize-lupine intercropping when N applied increased from 64 to 192 kg N ha-1. Further studies need to be conducted over seasons and locations to verify the results.

 


 CONFLICT OF INTERESTS

The authors have not declared any conflict of interests.

 


 ACKNOWLEDGEMENT

Financial assistance for the field research and laboratory work was provided by SIMLESA (Sustainable intensification of maize-legume cropping systems for food security in eastern and southern Africa). A Borlaug LEAP Fellowship sponsored the travel to the University of Nebraska-Lincoln, USA for the data analysis and advisory support. The Amhara Agricultural Research Institute, specifically Adet Agricultural Research Center, facilitated the research work.

 



 REFERENCES

Ali RN, Raof SS (2012). Effects of rates and nitrogen application timing on yield, agronomic characteristics and nitrogen use efficiency in corn. International Journal of Agriculture and Crop Sciences 4:534-539.

 

Alzubaidi A, Aljanabi AS, Al-Rawi A (1990). Interaction between nitrogen and phosphorus fertilizers and soil salinity and its effect on growth and ionic composition of corn (Zea mays L.). Genetic Aspects of Plant Mineral Nutrition Developments in Plant and Soil Sciences 42:195-202
Crossref

 

Ardell DH, Michael EB (2014). Nitrogen Source and Rate Effects on Irrigated Corn Yields and Nitrogen Use Efficiency. Agronomy Journal 106:681-693.
Crossref

 

Cassman KG, Dobermann A, Walters DT (2002). Agroecosystems, Nitrogen Use Efficiency, and Nitrogen Management. Ambio 31(2):132-140.
Crossref

 

CCRP (Collaborative Crop Research Program McKnight Foundation) (2009). Towards increased agricultural productivity and food security in east Africa through capacity building in agroecological intensification. mcknight.ccrp.cornell.edu › CCRP projects

 

CIMMYT (International Maize and Wheat Improvement Center) and IITA (International Institute for Tropical Agriculture) (2011). MAIZE - Global Alliance for Improving Food Security and the Livelihoods of the Resource-poor in the Developing World. Proposal submitted by CIMMYT and IITA to the CGIAR Consortium Board, 4 March 2011, In collaboration with CIAT, ICRISAT, IFPRI, ILRI, IRRI, the World Agroforestry Centre.

 

Central Statistics Authority (CSA) (2015). Area, production and yield of crops for private peasant holdings for meher season 2014/2015 (2007 E.C), Addis Ababa, Ethiopia.

 

Dillon LJ, Andreson JR (1991). The Analysis of response in crop and livestock production. Third edition, Pergamon Press pp. 11-23.

 

Dobermann A, Wortmann CS, Ferguson RB, Hergert GW, Shapiro CA, Tarkalson DD, Walters D (2011). Nitrogen Response and Economics for Irrigated Corn in Nebraska. Agronomy Journal 103:67-75.
Crossref

 

Dwyer LM, Stewart DW (1986). Leaf area development in field-grown maize. Agronomy Journal 78:334-343.
Crossref

 

Halm AT (1978). Tentative soil fertility rating for available phosphorus. Ghana Journal Agricultural Science 11:11-15.

 

Kaizzi CK, John B, Onesmus S, Isaac A, Williams Z, Angella N, Patrick M, Peter E, Theodore H, Wortmann CS (2012). Maize response to Fertilizer and Nitrogen Use Efficiency in Uganda. Agronomy Journal 104:73-82.
Crossref

 

Kaleem MA, Majid MT, Andlib S, Mussawar I, Mohsin Z (2012). Yield and Nitrogen Use Efficiency of Rainfed Maize Response to Splitting and Nitrogen Rates in Kashmir, Pakistan. Agronomy Journal 104:448-457.
Crossref

 

Kebede M, Gezahagne B, Benti T, Mosisa W, Yigzaw D and Assefa A (1993). Maize Production Trends and research in Ethiopia. In: Benti T, Joel KR (eds.) Proceedings of the first National Maize Workshop of Ethiopia. 5-7 May 1992, Addis Addis Ababa, Ethiopia. IAR/CIMMYT, Addis Ababa.

 

Komljenovic I, Markovic M, Danijela K, Kovacevic V (2010). Response of maize to phosphorus fertilization on hydromorphic soil of Bosnian Posavina area. Poljoprivreda 16(2):9-13.

 

Likawent Y, Claudia K, Firew T, Kurt JP (2012). Sweet blue lupine (Lupinus angustifolius L.) seed as a substitute for concentrate mix supplement in the diets of yearling washera rams fed on natural pasture hay as basal diet in Ethiopia. Tropical Animal Health and Production 44:1255-1261.
Crossref

 

Masaka J (2006). The Effect of N Fertilizer Placement and Timing on the Aboveground Biometric Characteristics of Spring Wheat (Triticum aestivum L.) on Leached Chernozem. International Journal of Agricultural Research 1(1):68-75.
Crossref

 

Onasanya RO, Aiyelari OP, Onasanya A, Oikeh S, Nwilene FE, Oyelakin OO (2009). Growth and Yield Response of Maize (Zea mays L.) to Different Rates of Nitrogen and Phosphorus Fertilizers in Southern Nigeria. World Journal of Agricultural Sciences 5(4):400-407.

 

Palmason F, Danso SK, Hardarson A (1992). Nitrogen Accumulation in Sole and Mixed Stands of Sweet-Blue Lupine (Lupinus Angustifolius L.) Ryegrass and Oats. Plant and Soil 142:135-142.
Crossref

 

SAS (Statistical Analysis System) Institute (2013). SAS/AF® 9.4 Procedure Guide, Second Edition. Cary, NC, USA.

 

Seran TH, Brintha I (2010). Review on Maize Based Intercropping. Journal of Agronomy 9:135-145.
Crossref

 

Shahidul I, Wujun M, Junhong M, Bevan JB, Rudi A, Guijun Y (2011). Diversity of Seed Protein among the Australian Narrow-Leafed Lupine (Lupinus angustifolius L.) Cultivars. Crop and Pasture Science 62:765-775.
Crossref

 

Sun H, Zhang J, Jin L (2014). Problems and approaches of achieving high yield and high nitrogen use efficiency in maize production. Journal of Maize Sciences 1:143-148.

 

Tamado T, Eshetu M (2000). Evaluation of sorghum, maize and common bean cropping system in east Hararghe. Eastern Ethiopia. Ethiopian Journal of Agricultural Sciences 17(1/2):33-46.

 

Tekalign T (1991). Soil, plant, water, fertilizer, animal manure and compost analysis. Working Document No. 13. International Livestock Research Center for Africa, Addis Ababa.

 

Tilahun T, Minale L, Alemayehu A, Abreham M (2007). Maize fertilizer response at the major maize growing areas of northwest Ethiopia. In: Ermiase A, Akalu T, Alemayehu AG, Melaku W, Tadesse D, Tilahun T (eds.). Proceedings of the 1st Annual Regional Conference on Completed Crop Research Activities, 14- 17 August 2006. Amhara Regional Agricultural Research Institute. Bahir Dar, Ethiopia pp. 35-43.

 

Uhart SA, Andrade FH (1995) Nitrogen Deficiency in maize: I. Effects on Crop Growth, Development, Dry Matter Partitioning and Kernel Set. Crop Science 35:1376-1383.
Crossref

 

Verma SP, Modgal SC (1983). Production potential and economics of fertilizer application as resource constraints in maize-wheat crop sequence. Himachal Journal of Agricultural Research 9:89-92.

 

Wortmann CS, Schnier HF, Muriuki AW (1996). Estimation of the fertilizer response of maize and bean intercropping using sole crop response equations. African Crop Science Journal 4(1):51-55.

 

Wortmann CS, Tarkalson DD, Shapiro CA, Dobermann AR, Ferguson RB, Hergert GW, Walters D (2011). Nitrogen Use Efficiency of Irrigated Corn for Three Cropping Systems in Nebraska. Agronomy Journal 103(1):76-84.
Crossref

 




          */?>