Evaluation of NPSZnB fertilizer levels on yield and yield component of maize (Zea mays L.) at Laelay Adiyabo and Medebay Zana districts, Western Tigray, Ethiopia

The use of right amount of fertilizer based on crop requirement has a significant importance for sustainable crop production. Study was undertaken to investigate the effects of NPSZnB blended fertilizer for maize yield production at Laelay Adiyabo and Medebay Zana districts. Seven treatments were used for the field experiment. Treatments were without fertilizer, blanket recommended NP (64 kg N ha -1 +69 kg P2O5 ha -1 ) and five treatments of blended fertilizer rates (150, 200, 250, 300, and 350 kg NPSZnB ha -1 ). Treatments were laid out in RCBD design with three replications. The results revealed that among fertilizers rates significantly (P ≤ 0.05) affected almost all the maize traits tested except tasseling, silking and maturity in Laelay Adiyabo district. However, in Medebay Zana district except tasseling, silking and maturity, plant height and thousand seeds weight, the rest parameters of above ground biomass yield, stover yield grain yield and harvest index were found significantly (P<0.05) affected by the fertilizer treatments. Highest stover yields (11.12 and 11.76 t ha -1 ) were obtained from application of 150 and 250 kg NPSZnB ha -1 for Laelay Adiyabo and Medebay Zana districts, respectively. At both districts of Laelay Adiyabo and Medebay Zana areas the highest grain yields (3.20 and 2.97 t ha -


INTRODUCTION
In Ethiopia agriculture, maize is one of the pillar cereal crops ranking first in total production and productivity, and second to tef in area coverage (FAOSTAT, 2017). In spite of the large area coverage under maize, the national (Ethiopia) and regional (Tigray) average grain yields were reached about 3.6 t ha -1 FAOSTAT (2017) and 2.48 t ha -1 CSA (2015), respectively and these yields were certainly below the world's average yield which was about 5.6 t ha -1 (FAOSTAT, 2017). Maize crop production in Tigray is particularly practicing in north western zone at the districts of Medebay Zana, Tahtay Koraro and Laelay Adiyabo (CSA, 2015).
However, the yield obtained by the farmers in the study areas is low mainly due to poor essential soil nutrient (ATA, 2014). Declining soil fertility, shallow soil depth, high run-off and low infiltration capacity of the soil are the major constraint for sustainable agricultural production in Tigray. Soil erosion and limited use of external nutrient inputs severely exhausted plant nutrients from the soil and declined soil fertility because of high nutrient losses, and are the major factors limiting crop production in rainfed and irrigated farms of the different agro-ecological zones of Tigray (Virgo and Munro, 1978;Mitiku, 1996). Nutrient mining due to sub optimal fertilizer use coupled with unblended fertilizer use favored the emergence of multi nutrient deficiency in Ethiopian soils (Astatke et al., 2004;Wassie et al., 2010;Wassie and Shiferaw, 2011) and resulted in stagnant crop production.
To overcome this problem of nutrient deficiency balanced fertilizers containing N, P, S, B, Fe and Zn have been recommended for site specific nutrient deficiencies and thereby increase crop production and productivity, water and labor productivity. The major recently recommended blended fertilizers for Tigray region by MOA and ATA are NPS, NPSB, NPSZn, NPSZnB, NPSFeZn and NPSFeZnB (ATA, 2014).
Although the type of required blended fertilizers are identified for the region, optimum rates of the major recommended blended fertilizer types for different crops, agro ecologies and soil types is not yet determined for the region. Besides, it is quite essential to verify the soil fertility map for major crops grown in different agro ecologies and on different soil types to increase and to improve quality of major crops grown in Tigray region. Therefore, the main objective of the study was to evaluate the effects of NPSZNB fertilizer rates on yield, yield component of maize at Laelay Adiyabo and Medebay Zana districts.

Area description
The field experiments were conducted at Laelay Adyabo and Medebay Zana districts (figure 1) , North western Zone of Tigray regional state located at 1783 and 2093 m above sea level, respectively for two consecutive main cropping seasons under rain fed conditions during 2017 and 2018. The soils of LaelayAdyabo and Medebay Zana districts were characterized with Cambisols and vertisols, respectively. Laelay Adyabo district received annual rainfall of 563.5 and 975.7 mm while Medebay Zana district received annual rainfall of 1013 and 1208 mm during growing years of 2017 and 2018, respectively ( Figure 2a) Figure 2b).

Experimental design and treatment
The experiments were laid out in randomized complete block design (RCBD) with three replications in two administrative places (kebeles) in Laelay Adyabo district with two farmers each and in Medebay Zana district it was done on one kebele in two farmers. The experiments were consisting total of seven treatments including recommended blanket NP fertilizer with an amount of 64 kg N ha -1 and 69 kg P 2 O 5 ha -1 . Urea was used as source of N and TSP was used as source P 2 O 5 for the treatment of blanket recommendation. The blended fertilizer rates were consisted of six levels of NPSZnB (0,150,200,250,300 and 350 kg ha -1 ) and were adjusted with N to N of the recommended NP since the N content of blended fertilizer of NPSZnB is smaller as compared to P 2 O 5 which the N content of 100 kg NPSZnB is about 17 kg. This revealed that all treatments except control received 64 kg N ha -1 . A full dose of blended fertilizer was applied at planting time close to seed drilling line, while N fertilizer was applied half of the total at four leaf stage and the rest at knee height period for the N adjusted and the blanket recommended treatments. The plot size was 3.75 m × 4 m (15 m 2 ) and the net harvested plot size area was 9.375 m 2 . The spacing between replications, plots, rows and plants were 1.5, 0.5, 0.75 and 0.4 m, respectively. For both study districts improved melkasa6Q variety with the recommended seed rate of 30 kg ha -1 was used and sown using drilling method at depth of 10 cm. All recommended cultural practices (plowing, digging and weeding, pesticides) for the test crop was done as per the recommendation of the area.

Soil sampling and analysis
A Disturbed composite soil sample of the study sites were collected from 0-20 cm depth before planting for physical and chemical soil characterization at laboratory of Shire Soil Research Center. Soil texture was determined using the Bouyoucos hydrometer method (Bouyoucos, 1962). The pH of the soil was measured in the supernatant suspension of a 1:2.5 soil to water ratio using a pH meter (Rhoades, 1982). And electrical conductivity (EC) 1:2.5 soil to water suspension was measured according to the method described by (Jackson 1967). Organic carbon (%) was determined by method as described by (Walkely and Black 1934). Available P (ppm) was analyzed by employing the Olsen method using ascorbic acid as the reducing agent (Olsen et al., 1954). Total nitrogen was measured using Kjedahl method as described by (Bremner and Mulvaney 1982). CEC in cmol (+) kg -1 soil was determined by ammonium acetate method.

Data collection and analysis
Data collected for the experiment were days to 50% taseling, days to 50% silking, days to 90% maturity, plant height (cm), biomass yield (kg ha -1 ), stover yield (kg ha -1 ), thousand seeds weight (g), grain yield (kg ha -1 ) and harvest index(%). Data were collected for the experiment on yield and yield component related parameters on plot basis and converted to ha -1 . The collected data were subjected to statistical analysis of variance (ANOVA) using SAS version of 9.0 (SAS, 2002). Significant difference between and among treatment means were assessed using the least significant difference (LSD) at 0.05 level of probability (Gomez and Gomez, 1984). To evaluate the feasibility of  different treatments partial budget analysis technique of CIMMYT (1988) was applied to stover and grain yield. The partial budget analysis was performed based on the field price of the crop with prices of 0.35 and 0.014 $ kg -1 for grain and stover of maize, respectively. Based on the CIMMYT manuscript it is expected that experimental yields are often higher than the yields that farmers could expect using the same treatments. Hence, in economic calculations, the grain yield has been adjusted 10% lower than the actual yield obtained from the experimental plots to make the representative yield at the farmers' fields, (CIMMT, 1988). It also included all the variable costs such as application costs and prices of each fertilizer that vary for each treatment.  Where, pH-power of hydrogen, ECe-paste extracts electrical conductivity, OC-organic carbon, TN-total nitrogen, Ava.P-available phosphorus, CEC-cation exchange capacity, Tex-texture, L-loam, SCL-sandy clay loam, C-clayey, CL-clay loam, SL-sandy loam, SY -denoting sampling sites of respective years in respective districts.

Physical properties of the soil
Soil particle size distribution: The soils sampled from sites of Laelay Adiyabo and Medebay Zana districts were dominated by clay loam textural class having an approximately average proportion of sand (39.13%), silt (33.13%) and clay contents (27.75%), and sand (36.75%), silt (32.5%) and clay contents (30.75%), respectively (Table 1). McDonald et al. (1994) stated that soils ranged from 30 to 35% of clay content described as textural class of clay loam. Geeves et al. (2007a) recognized that water infiltration capacity of clay loam texture as moderate. Hence, soil texture of both districts was found suitable for growing of maize crop.

Soil reaction (pH) and Soil electrical conductivity (ECe):
The average pH value of soils of the study sites were 5.48 and 6.1 for Laelay Adiyabo and Medebay Zana districts, respectively, with a higher pH in MedebayZana district (Table 1). According to Tekalign (1991) pH ranging from 5.3 to 5.9 rated as moderately acidic. Therefore, the average pH of sampled soil of Laelay Adiyabo sites was fall in the rating of moderately acidic.
Whereas the average soil pH Medebay Zana district sites was rating as slightly acid according (Tekalign 1991). Both pH results were suitable for availability of plant nutrients thus the pH were appropriate for growing of maize crop without any addition of amendments. The surface soil of the study areas exhibited an average ECe of 1.94 and 0.9 dS m -1 for Laelay Adiyabo and Medebay Zana districts, respectively. Average ECe of sites of Laelay Adiyabo district was found higher than the average ECe of sites of Medebay Zana district, this probably due to low rainfall and in return low leaching of cation in Laelay Adiyabo district. Soils having ECe less than 2 dS m -1 has negligible salt effect on plant growth (Richards, 1954). Therefore, the sites were having optimum ECe for cultivating of maize crop.

Soil organic carbon (OC) and total nitrogen contents:
Soil OC contents of the study sites were 1.39 and 0.75 %, respectively for Laelay Adiyabo and Medebay Zana districts (Table 1). Better soil OC was measured in Laelay Adiyabo district as contrasted to Medebay Zana district this may be due to farmers manuring practice of organic fertilizers in their field. However, both districts having low OC according to Tekalign (1991) rating scale of OC content of the soil between 0.5 -1.5 is low. The average value of total N contents of the soils of the study sites of Laelay Adiyabo and Medebay Zana were 0.13 and 0.05%, respectively (Table 1). This low N content in MedebayZana district could be attributed to the low organic carbon content of the soil. Tekalign (1991) rated that soil total N content between 0.05 to 0.12% is considered as medium so that the soil of Medebay Zana district was found in a medium total N content. However, the soil of Laelay Adiyabo districts found having high total soil N content according to Tekalign (1991) ratings of soil total N.

Available phosphorus
The average available P of soils of the study sites were measured with 17.12 and 8.58 ppm for the districts of Laelay Adiyabo and Medebay Zana, respectively (Table  1). When the two sites were compared higher available P was recorded from the district of LaelayAdiyabo. According Olsen et al. (1954) soils having available P from 5 to 10 ppm is considered medium, greater than 10 ppm regarded as high.  Metson (1961) and Landon (1991) soils having CEC greater than 40 cmol (+)/kg were considered as very high.

Crop phenology
At both study locations tasseling, silking and maturity of maize crop was not significantly affected by fertilization of blended fertilizer doses (Table 3). It was known that blended fertilizers with different rates of N, P, S Zn and B might have encouraged early establishment, rapid growth and development of crop thus; shortening the days to tasseling silking and maturity but the current result were divergent in this respect. This may be due to effect of fertilizers on tasseling, silking and maturity of the single maize variety tested. The other probable reason could application of N fertilizer except on control treatment applied at the same rate to all treatment of levels of blended fertilizer and thus effect of N was insignificant. Dagne (2016) found that days to silking were significantly affected by the application of blended fertilizers. Meanwhile, Bakala (2018) found that 50% silking, tasseling and maturity to be significantly affected by the application of blended fertilizer rates.

Plant height
Plant height of maize crop was significantly (P=0.014) affected by the application of blended fertilizer in Laelay Adiyabo district but this was not the case in Medebay Zana district (Table 2). Here the shortest plant height (177.62 cm) was measured in the control treatment. However, there were no significant differences amongst the plots treated with blended fertilizers at (150,200,250,300 and 350 kg ha -1 ) and the blanket recommendation of NP fertilizers. This increment in plant height might be due to increase in cell elongation and more vegetative growth attributed to different nutrient contents of NPSZnB blended fertilizer. On the other hand, the least plant height in unfertilized plots might have been due to the low soil fertility level in the study area. Plant growth and development may be retarded if any of nutrient elements is less than its critical value in the soil or not adequately balanced with fertilization. Plant growth and development may be retarded significantly if any of the nutrient elements is less than its threshold value in the soil or not adequately balanced with other nutrient elements (Landon, 1991). Tamene et al. (2018) found that effect of N rates under blended fertilizer of PKSZnB with highly significantly effect on plant height as compared to negative control and standard control (92 N, 69 P 2 O 5 ) kg ha -1 when N levels increased from 0, 46, 92, 138, 176 and 222 kg ha -1 . This result is also in agreement with that of Dagne (2016), and Tekle and Wassie (2018) who found that application of blended fertilizers and blanket NP recommendation which significantly increased plant height as compared to the control. Likewise, Bakala (2018) found that blended fertilizers had significantly influenced plant height.

Biomass yield
Biomass yields were significantly higher in all plots treated with blended fertilizers compared to untreated checks in all study sites (   Where, means followed by the same letters are not significantly different (P≤0.05), BY-biomass yield, SY-stover yield, TSW-thousand seeds weight, NS-non-significance, CV-coefficient of variance.
because of continuous vegetative growth of maize crop until the rainfall withdrew. However, in Laelay Adiyabo district low amount of rainfall was rained during the growing seasons as a result the vegetative growing of maize crop was proportionally gone with the received low amount of rainfall. Even though, lowest biomass yields were recorded from the unfertilized plots in both study districts there was no consistent increase in yield amongst the different blended fertilizer levels. This could be due to N effect since N levels were adjusted to the same amounts of 64 kg N ha -1 in all except the control treatments. It is a known fact that plants require huge amounts of N nutrients compared to all other essential nutrients. Therefore, the low yields in unfertilized plots might have been due to reduced leaf area development resulting in smaller radiation interception which further translates to low efficiency in the conversion of solar radiation to maintain efficient photosynthesis. The current results are in agreement with that of Tamene et al. (2018) who obtained significantly highest biomass yield of maize crop at the rate of 46 kg N ha -1 under blended fertilizer of PKSZnB as compared to negative control, standard control (92 N, 69 P 2 O 5 ) kg ha -1 and 222 kg N ha -1 at N treatments under blended arranged from 0, 46, 92, 138,

Stover yield
Stover yield was significantly (P<0.0001) and (P=0.0005) affected by the application of blended fertilizers in Laelay Adiyabo and Medebay Zana districts, respectively (Table  3). In Laelay Adiyabo district the higher yield (11118.2 kg ha -1 ) was obtained from fertilization of maize plots with 150 kg NPSZnB ha -1 , there was however, no significant difference amongst the different rates of 200, 250, 300 and 350 kg NPSZnB ha -1 . The lowest yields (6339.6 kg ha -1 ) were recorded from the negative and positive controls (standard checks). Meanwhile, in Medebay Zana the highest yields (11762.5 kg ha -1 ) were recorded from plots that had 250 kg ha -1 blended fertilizers. In this district there were no significant differences in stover yields among the other levels of blended fertilizer rates of 200, 250, 300 and 350 kg ha -1 and the recommended NP fertilizers. The lowest yields (8171.5 kg ha -1 ) were recorded in the control treatment. Comparably the two districts higher stover yield was recorded in Medebay Zana districts this perhaps due to improved vegetative growth coupled to the required higher amount of rainfall. Nevertheless, there was no consistent increase of stover yields in both districts from blended fertilizer applications and levels. This could be due to N effect since N in except control treatment in all treatments adjusted to the same amount of 64 kg N ha -1 . It is known that plants require huge amounts of N nutrient compared to all other essential nutrients. Therefore, low yield in unfertilized plots might have been due to reduced leaf area development resulting in reduced radiation interception and, consequently, low efficiency in the conversion of solar radiation. Related tendency observed with Bakala (2018) in maize crop who declared stover yield was significantly affected by blended fertilizer. These results were also in agreement with the findings of Tekle and Wassie (2018) who found that straw of tef (Eragrotis tef) was found to be highest in blended fertilizers compared to control treatments and recommended rate blanket NP applications.

Thousand seeds weight
In the study of Laelay Adiyabo and Medebay Zana districts thousand seeds weight of maize crop were found to be significantly affected by blended fertilizer rates compared to the negative control (Table 3). The five NPSZnB blended fertilizer rates of 150, 200, 250, 300 and 350 kg ha -1 did not show any significant variations amongst each other in thousand seeds weight of maize.
The standard check was also in par with the positive rates of the blended fertilizer rates. This result is in harmony with Dagne (2016) and Tekle and Wassie (2018) who found that application of blended fertilizers significantly increased thousand seeds weight as compared to the control.

Grain yield
The result of experiment indicated that grain yield of maize crop was highly significantly (<0.0001) affected by blended fertilizer rates in both districts (Table 4). In the district of Laelay Adiyabo plots treated with zero fertilizer had significantly lower yield (2058.4 kg ha -1 ) as compared with the five rates of NPSZnB blended fertilizer of 150, 200, 250, 300, 350 kg ha -1 and standard check. But, there was no significant variation amongst the four rates of 150, 200, 250 and 300 kg ha -1 NPSZnB blended fertilizer. Accordingly, the highest grain yield (3200 kg ha -1 ) was obtained from application of 300 kg NPSZnB ha -1 . In Medebay Zana district significance highest yield (2973 kg ha -1 ) was acquired from application of 300 kg NPSZnB ha -1 as weighed against to NPSZnB fertilizer levels (200 and 350 kg ha -1 ), recommended NP fertilizes and the control treatment. In both study districts the highest yield was obtained from the same treatment of blended fertilizer with an amount of 300 kg NPSZnBha -1 . But, in both districts there was no increase of grain yield consistently amongst the blended fertilizer levels. This is probably due to N effect which was equally adjusted to 64 kg N ha -1 in all treatments and was not sufficient enough since plants usually require huge amounts of N nutrients compared to all other essential nutrients. When both districts of Laelay Adiyabo and Medebay Zana compared each other the somewhat higher yield was exhibited in the district of Laelay Adiyabo this was may be due to improved soil result of available P and total N in this district. These results are in line with the findings of Benti (1993) who stated that, although adoption of new varieties especially maize hybrids is moving fast in Ethiopia, fertilizer management techniques need to supplement the existing potential of these varieties. This also tentatively showed that low soil fertility is amongst the greatest constraints to maize production in Ethiopia (Kelsa et al., 1992). The increase in grain yield could be attributed to beneficial effect of yield contributing characters and positive interaction of nutrients in the blended fertilizer. It was known that plants required huge amount of N nutrient as compared to all essential nutrients. The increase in grain yield could be attributed to beneficial effect of yield contributing characters and positive interaction of nutrients in the blended fertilizer. The association of grain yield with thousand seeds weight observed in this study agrees with the findings of Khatun et al. (1999) Dagne (2016) verified that application of blended fertilizer on maize crop as brought significantly highest grain yield as compared to negative control, standard control of NP and recommended NP + Cu +Zn.
In agreement with the current findings Tekle and Wassie (2018) found that grain yield of tef was found highest in blended fertilizers as compared to control treatment and recommended NP fertilizers. Additionally, Jafer (2018) found better grain yield from application of blended fertilizer compare to recommended NP fertilizer and unfertilized plot.

Harvest index
At both study locations the application of blended fertilizers had significant effects on harvest index of maize crop. In the Laelay Adiyabo district the highest harvest (26.52%) index was realized from the application of 300 kg NPSZnB ha -1 as compared to blended fertilizer rates 150 and 350 kg NPSZnB ha -1 but, this was significantly similar with control treatment, standard check and NPSZnB fertilizer rates of 200 and 250 kg ha -1 . This result agrees with the findings of Tekle and Wassie (2018) who reported that harvest index of tef was found to be highest in blended fertilizer treatments. Meanwhile, in the Medebay Zana district harvest index was found to be significantly higher in plots that received blended fertilizers at rate of 150 kg NPSZnB ha -1 as contrasted to the control treatment and blended fertilizer levels of 200, 250 and 350 kg NPSZnB ha -1 but, it was significantly in par with 300 kg NPSZnB ha -1 and recommended NP fertilizers.

Partial budget analysis
As it were presented in Tables 5 and 6, the net farm benefit was calculated taking possible field variable costs and all benefits (stover and grain yields) for Laelay Adiyabo and Medebay Zana districts. The maximum farm net benefits were 1076.04 and 1073.76 $ ha -1 with the application of 150 and 300 kg NPSZnB ha -1 for Laelay Adiyabo and Medebay Zana districts, respectively. In both district the partial budget analysis revealed that application of 150 kg NPSZnB ha -1 was resulted in highest MRR% with values of 242 and 255 for Laelay Adiyabo and Medebay Zana districts, respectively. These values imply that with one $ cost it was attained 2.42 and 2.55 $ profit. Therefore, in both districts 150 kg NPSZnB ha -1 can be used for the production of maize.

CONCLUSIONS AND RECOMMENDATION
According to the combined mean analysis fertilizer rates and types at both districts revealed significance difference on above ground biomass, stover and grain yield. In Laelay Adiyabo district significantly maximum maize stover 11.12 t ha -1 was recorded with fertilization of 150 kg NPSZnB ha -1 , whereas in Medebay Zana district the maximum stover yield was found from application of 250 kg ha -1 with the stover yield of 14.55 t ha -1 , but in both districts the minimum stover yield was obtained from the control treatment. In both districts of Laelay Adiyabo and Medebay Zana maximum (3.2 and 2.97 t ha -1 ) and  minimum (2.1 and 1.5 t ha -1 ) grain yield was recorded with application of 300 kg NPSZnB ha -1 and control treatment, respectively. According to the partial budget analysis the highest marginal rate of return was attained from application of 150 kg NPSZnB ha -1 as the best rates recommended for maize production at areas of Laelay Adiyabo and Medebay Zana districts. Therefore, NPSZnB fertilizer at a rate of 150 kg ha -1 for improved maize production and can be used as a point of reference for additional study of NPSZnB fertilizer effect on maize (melkasa6Q) production.