Morphological characters, dry matter production, and feed quality of three maize (Zea mays L.) varieties as influenced by milk and dough harvest stages

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Introduction

Maize (Zea may L.) is the most versatile and important crop and can be grown worldwide in varied agro-climatic environments. In Ethiopia, second to teff (Eragrostis tef), the crop covered over 2.5 million hectares of land but stands in the first position in grain production, with around 10.6 million tons produced (CSA, 2020/21). Although it has remarkable productive potential, the average national yield of maize in the country is 3.38 tons ha-1 showing an increasing trend, but still far below as compared to the world average of 5.5 tons ha-1 (Mosisa, 2011; Cochrane and Bekele, 2018). The crop is grown commonly in crop-livestock mixed farming systems and, there is a great deal of interdependence between the production of crops and livestock (Tegegne, et al., 2013; Ertiro, et al., 2013). For instance; the crop residues provide a source of feed dominantly during the dry season; on the other hand, Livestock contributes organic manure for crop production as a source of cash for the purchase inputs (Tolera and Said, 1992; Thornton, 2010; Dejene et al., 2022). Maize can be directly used for human consumption (food), and (feed) the stovers as animal fodder has great potential to support higher animal performance in crop-livestock production (FAOSTAT, 2008; Saiyad and Kumar, 2018). It contributes a significant amount of fodder either green or as dry stover for livestock feeding more importantly in the major maize growing areas (Geleti, et al., 2011; Gebre and Mohammed, 2015).

Knowing the factors that affect forage quality is very important for producing suitable quality feed by following up on the management practices for a given situation. Several factors for instance; biotic (pest and disease) or abiotic stress (drought, salinity, and nutrition), genotypes, stage of crop harvest, and environmental effects during growth have great contributions to the influence biomass quantity and quality (Somegowda, et al., 2021). The maize genotypes and/or improved varieties have a substantial contribution to the influence of both biomass yield and quality of stovers. Many studies investigated that the quantity and quality attributes (crude protein (CP), neutral detergent fiber (NDF), Acid detergent fiber (ADF), dry matter digestibility (DMD), and in-vitro organic matter digestibility (IVOMD) were affected by genotypic or varietal differences (Tolera, et al., 1999; Geleti, et al., 2011; Ertiro, et al., 2013; Anandan, et al., 2013).

In addition, agronomic practices, and stage of crop harvest, provide good stover yield and quality feed contribution. The maize stovers are used as animal feed either in green or dry stover form. when the green cobs are harvested for human consumption, thereby the green stovers containing the stalk, leaves, husks, and tassels are utilized as animal feed due to their high carbohydrate content, good biomass yield, highly palatable, and useful for feeding all kinds of livestock (Zom, et al., 2012; Tuturoong, et al., 2020). If the maize stover is harvested at the proper harvesting stage, it is the best-suited crop for silage and exhibits high dry matter yield, good intake characteristics and digestibility potentials, and high starch contents that enhance fermentation and storage in the silo (Kennington, et al., 2005; Wang, et al., 2020). Thus, the stover contains 10.5% Crude protein, 91.9% dry matter, and 59.5 to 88.7% dry matter and organic matter digestibility (Tuturoong, Malalantang, and Moningkey 2020). On the other hand, the dry stovers, when harvested at grain maturity, are characterized by a high concentration of fiber and low concentration of nitrogen, with low voluntary intake and poor animal performance (Tolera and Sundstol, 1999; Ertiro, et al., 2013).

Furthermore, maize has different growing stages; the milk stage is one of the reproductive growth processes that begins about three weeks after flowering, when the corn kernels begin grain filling, in which it turned to yellow with a milky fluid on the inside. At this stage it is suitable for consumption, and for forage. The dough stage occurs about 26 days after the silking and the milky inner fluid of the kernels will have accumulated 50% of their dry weight or the maize can be used as an edible product (Jia, et al., 2020). Detecting the variations exhibited in stover quantity and quality due to varietal differences and stage of harvest is crucial to optimize the use of the feeding value of the stovers. Thus, the purposes of this study were to evaluate the morphological characteristics, biomass production, and nutritional quality of three selected maize varieties harvested at milk and dough stages under rainfed conditions in Holetta, the central highland of Ethiopia.

Materials and Methods

Experimental site, soil characteristics and weather condition

The experiment was carried out in the research field of Holetta Agricultural Research under rainfed conditions in the years 2019-2020. Geographically, the center is located at 9°3' N latitude and 38°30' E longitude with an altitude of 2400 meters above sea levels. The farming system of the study area is characterized by a mixed crop-livestock production system.

The physical and chemical properties of soil in the area are mainly red nitosol soil type and texturally clay dominated over sand and silt with moderately acidic pH (4.9). The soil had low organic carbon content (1.8%), available total nitrogen (0.18%), and available phosphorus 5.6 ppm, 5.03 mg kg^-1 potassium, 29.5 mg kg^-1 calcium, 13.7 mg kg^-1 magnesium and 0.16 mg kg^-1 Sodium.

The long-term (thirty years) average annual rainfall of the area is 1055 mm. The area has a bimodal rainfall distribution with 70% falling from June to September, and the remaining 30% occurring from March to May. The temperature ranged from 6.1°C to 22.2°C.

The area also had an average relative humidity of 60.6%. During the experimental periods, the area received a mean annual rainfall of 112.0 and 105.5 mm in 2019 and 2020 years, respectively (Table 1). The mean monthly temperature ranged from 13.2 to 17.8°C with an average of 15.8°C in the first year, and 12.5 to 17.1°C with an average of 15.3°C in the second year.

Table 1. Monthly total rainfall (mm) and mean monthly temperature (°C) at Holetta, during 2019 and 2020 cropping years.

Experimental treatments, design, and management

Three highland maize varieties including Jibat, Kuleni, and Kolba were selected and evaluated in their response to the milk and dough harvesting stage. The experiment was performed with two sets of trials (set one; harvested at the milk stage, and set two; harvested at the dough stage). Each set of experiment was laid out in randomized complete block design (RCBD) with four replications and each set consisting of a total of twelve plots. Planting was made on a gross plot size of 15 m² (3 m x 5 m) with a recommended space of 0.75 m between rows, followed by 0.25 m between plants. The space between plots and blocks was 1m and 1.5 m, respectively.

Before sowing the experimental land was plowed. Planting was done in good soil moisture contents in a fine seedbed, two seeds per hole were dropped and then covered by light soil. Diammonium phosphate (DAP) fertilizer at the rate of 200 kg ha^-1 as a basal application at sowing time. To maintain the optimal plant population, thinning of unwanted plants was done 15 days after planting. Urea was applied at the rate of 120 kg ha^-1 in split applications twice during the growing season and the remaining top-dressed at the knee-high stage. Weeding and earthing-up using hoe were done two times manually.

Data collection and sampling

Data on morphological characters collected in this study were plant height at harvest, leaf length, cob length, number of leaves per plant, number of cobs per plant, and forage dry matter yield. Plant height (PH) is the measurement taken from the base of the plant just above the ground level to the tip of the uppermost of extended leaf and measured from 6 randomly taken sample plants in the central rows, and the mean values of each plot were calculated and recorded for data analysis. Leaf length (LL), is the length taken from the flag leaf and measured from the point of the leaf ligule to the tip of the leaf blade of 6 sample plants. Cob length (CL) is the length measured from 6 randomly taken cobs when reached at the dough stage. The number of cobs per plant (NCPP) number of cobs arising from the stem of 6 randomly taken sample plants in central rows was counted and the average of these cobs was calculated and recorded for data analysis. Dry matter yields (DMY) of the maize varieties were determined from two separate sets of experiments in different harvesting stages when the kernel was at milk and dough stages. The total fresh biomass yield was recorded from each plot in the field and a sub-sample of 500 g was taken from each plot to the laboratory to determine dry matter yield. The dry matter content was determined by oven drying at 65oC for 72 hours.

Chemical analysis and in-vitro dry matter digestibility

Chemical analysis and in-vitro dry matterdigestibility of the three maize varieties harvested at milk and dough stages were determined at Holetta Agricultural Research animal nutrition laboratory. The oven-dried samples were ground to pass through a 1 mm sieve size for laboratory analysis. Before scanning, the samples were dried at 60°C overnight in an oven at a constant weight and then 3 g of each sample was scanned by, the Near Infra-Red Spectroscopy (NIRS). Dried samples were subjected to analysis of dry matter (DM), ash, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and lignin using a calibrated NIRS (Foss 5000 apparatus and Win ISI II software) and reported on DM basis. The oven-dried samples were ground to pass through 1 mm sieve in a Wiley mill and stored in polyethylene bags pending the chemical analysis. In-vitro dry matter digestibility (IVDMD) was determined using two-stage in-vitro digestibility technique of (Tilley and Terry, 1963).

Statistical analysis

Data were subjected to analysis of variance of the SAS general linear model statistical software (SAS, 2011). The means were compared using the least significant difference (LSD) at 5% level of significance. The general linear model used for the analysis of the data was;

Y_ijk=μ+V_i+Y_j+B_k+(VY)_ij+e_ijk;

Where Y_ijk=Response variables; μ=the overall mean; V_i=effect due to variety (i=1-3); Y_j=effect due to year (j=2019 and 2020); B_k=effect due to block k; (VY)_ij=effect due to interaction between i^th variety and j^th year; e_ijk=the random error.

Results and Discussion

Variety, year, and their interactions

The analysis of variance (ANOVA) for variety, cropping year, and the interactions of three maize varieties are shown in (Table 2). The mean square of variance of variety revealed no significant (P>0.05) effect on the measured morphological traits both at milk and dough stages except for cob length (CL). Whereas CL is significantly (P<0.01) influenced by varietal differences at the milk stage. The combined analysis of variance over the year showed highly significant (P<0.001) for plant height (PH) and dry matter yield (DMY) both at the milk and dough harvesting stages. The maize varieties exhibited significant differences for PH and DMY across the year might the variation due to non-genetic factors such as, growing seasons, amount of rainfall distributions and temperature. However, CL and number of cops per plant (NCPP) were not significantly (P>0.05) affected by the year. The result indicates that the response of the maize varieties for cob length and cob number were stable over the cropping year. No significant interaction was found between variety and year for all measured traits both at the milk and dough stages. Conversely to the current study variety and year interaction had a significant effect on plant height and dry matter yield (Saiyad and Kumar, 2018).

Table 2. Mean squares of combining analysis of variety, cropping year, and their interactions of three maize varieties for morphological traits evaluated at milk and dough stages.

Year effect on morphological characteristics and dry matter yield

The effect of year on the plant height, cob length, number of cobs per plant, and dry matter yield of three highland maize varieties evaluated at milk and dough harvesting stages are indicated in (Table 3). The PH and DMY significantly (P<0.001) differed across the year. The results indicate that the highest plant was recorded in 2019 compared to 2020 at the milk stage and this was also consistent at the dough stage. The growing seasons, amount of rainfall distributions and temperature in 2019 might have positive impacts on the plant height of maize varieties at both stages. In 2020, at both harvesting stages, the highest DMY was achieved and increased by 22.6% and 36.3% at the milk and dough stages respectively, compared to the 2019 year. The higher DMY achieved in 2020 is probably due to variation in temperature and the amount of rainfall distributions might have positively or negatively influenced for the dry matter accumulation between years. In agreement with the present study, Szulc, et al., (2021) obtained a different dry matter yield results concerning variable in weather condition over the years.

Table 3. Combined means of cob length, number of cobs per plant, plant height, and dry matter yield maize varieties harvested at milk and dough stages during the 2019 and 2020 years.

Cob length and number of cobs per plant

The mean performance of cob length and the number of cobs per plant of the three maize varieties at the milk and dough stages are indicated in Table 4.

Table 4. The mean performances for cob length (CL) and number of cobs per plant (NCPP) of three maize varieties harvested at milk and dough stages during 2019 and 2020 years.

The CL recorded at the milk stage was not significantly different among the tested maize varieties in both years. On the contrary, the overall mean for CL significantly (P<0.05) varied among the maize varieties at the milk stage.

Accordingly, Kolba attained larger CL than Jibat and Kuleni maize varieties, whereas Jibat and Kuleni scored similar CL. No significant (P>0.05) variations were observed among the varieties for CL at the dough stage in the experimental years.

Similarly, significant (P<0.05) differences appeared among varieties for the number of cobs per plant (NCPP) in 2019 cropping year and the combined mean at milk stage, and this was also achieved in 2020 at the dough stage. consequently, Jibat and Kolba maize varieties had statistically higher NCPP than Kuleni in 2019 and the overall mean at the milk stage. Consistently, these varieties (Jibat and Kolba) attained higher NCPP than Kuleni in 2020 at the dough harvesting stage. This indicates that this trait (NCPP) was not influenced by both milk and dough stages.

Leaf length and number of leaves per plant

The tested maize varieties showed significant (P<0.01) differences for leaf length (LL) at the milk stage of harvesting, whereas they did not show significant differences for LL at the dough stage (Table 5). Jibat and Kolba maize varieties had statistically similar LL and were larger than Kolba variety. The leaf length we found in the present study was between previous records (57.1 and 93.2 cm) reported by Saiyad and Kumar (2018).

Table 5. Leaf length (LL) and Number of leaves per plant (NLPP) of the selected maize varieties at the milk and dough stages.

Leafy maize variety is an indication of good dry matter yield. Depending on the genotypes and climate maize can produce a total of 20-23 leaves. However, the first five to seven leaves drop off at early stage. The number of leaves per plant (NLPP) obtained both at the milk and dough harvesting stages were statistically insignificant (P>0.05) among the maize varieties. A study done by Tolera and Sundstøl (1999) demonstrate that the leafy maize variety to have good dry matter yield and show better digestibility and increase animal performance.

Plant height and Dry matter yield

The mean performance for plant height of three maize varieties harvested at milk and dough stages during 2019 and 2020 has shown in (Table 6). The result indicates that the maize varieties were not statistically (P>0.05) differed for plant height at the milk stage both in 2019 and 2020 years and also consistent with the combined mean. In 2019, plant height recorded at dough stages significantly varied among maize varieties. Whereas in 2020 and the combined mean of plant height showed a non-significant (P>0.05) difference among the maize varieties. Kulani and Jibat had significantly recorded the tallest plant height than Kolba in 2019. The present result in agreement with Faji, et al., (2021) found that Kuleni had the tallest plant height in Holetta at the green cob harvesting stage. The feed quality increases with height in maize stover.

Table 6. Mean performance for plant height (cm) and dry matter yield (DMY t ha^-1) of maize varieties harvested at milk and dough stages during 2019 and 2020 cropping seasons at Holetta.

There was an insignificant (P>0.05) difference among maize varieties for dry matter yield (DMY) both at milk and dough stages during 2019 and 2020 cropping seasons. Similarly, the overall means of the dry matter yield showed statistically insignificant difference among the evaluated maize varieties. The overall mean for DMY yield achieved at the milk stage ranged from 6.2 to 7.3 while at the dough stage it varied from 6.2 to 6.9 t ha^-1.The DMY obtained both at milk and dough stages of the tested maize varieties in the current study was found between 4.4-9.7 t ha^-1 reported by Ertiro, et al., (2013) conducted in 335 maize genotypes in different sites and years. The DMY of kuleni obtained in this study was lower than the values reported by Geleti, et al., (2011) for this variety 9.37 ± 0.36 t ha^-1 at Bako. This could be due to variation in soil type and climate conditions of the areas.

Nutritional composition

The nutritional compositions of three maize varieties at the milk and dough stage are shown in Table 7. The maize varieties showed significantly (P<0.05) differences in their chemical composition particularly for DM, NDF, ADF, and ADL at the milk stage, whereas a non-significant (P>0.05) difference was exhibited among the maize varieties both at milk and dough stages for ash, crude protein (CP) and in-vitro dry matter digestibility (IVDMD).

Table 7. Chemical composition of three maize varieties harvested at milk and dough stages

Kolba maize variety had significantly higher DM percentage than Jibat and kuleni at the milk stage. Conversely, at the dough stage, Jibat and Kuleni showed higher DM compared to Kolba. Kuleni had significantly lower neutral detergent fiber (NDF) content than jibat but statistically exhibited similar to Kolba. At the milk stage, Jibat had the lowest acid detergent fiber (ADF) and acid detergent lignin ADL as compared to Kuleni and Kolba.

The overall mean of CP and IVDMD of the tested maize varieties at the dough stage decreased by 1.3% and 3.5%, whereas NDF, ADF, and ADL increased by 0.3, 4.4, and 0.6% compared to milk stage. This might be due to differences in maturity stage (Neylon and Kung 2003). The mean value of maize varieties for CP obtained at the milk stage was higher than the previous records (Ertiro, et al., 2013; Tolera, et al., 1999). The mean value of NDF and ADF attained in this study both at milk and dough stages is lower than the finding of Geleti, et al., (2011).

The IVDM digestibility obtained in the current study higher than report made by (Tolera, et al., 1999). A study done by Saiyad and Kumar (2018) indicated that the quality of fodder stover is governed by genetic variability. Additionally, several factors including geographical location, soil fertilization, variety, environmental conditions, stage of plant maturity at harvesting, season, and postharvest storage method and duration nutritional can vary the composition of crop residues (Kennington, et al., 2005; Fekede, et al., 2015; Malik, et al., 2015).

Conclusion

Some traits (plant heigh and dry matter yield) of the tested maize varieties were significantly influenced by year in both harvesting stages. The maize varieties showed significant difference for CL and LL harvested at milk stages. Inconsistent variations were observed among the maize varieties for number of cobs per plant at milk and dough stages. However, no significant variation was observed among varieties for dry matter yield (DMY) at the milk and dough stages. Nutritionally, the existence of variations was exhibited in DM% both at milk and dough stages, while Jibat and Kuleni attained better nutritional quality in terms of fiber contents (ADF and ADL) at the milk stage. The study also highlighted no significant differences were observed among maize varieties in chemical compositions harvested at the dough stage. In conclusion, Stover’s of Jibat and Kuleni could be used as forage when harvested at milk, however, the three tested maize varieties are also used as animal feed at the dough stage after removing the green cobs for human consumption under the highland areas of Holetta and similar agro-ecologies. Furthermore, their feeding value on the animal performance should be validated.

Conflict of Interest

The authors declare no conflict of interest.

Acknowledegements

We are grateful to the Ethiopian Institute of Agricultural Research (EIAR) for the financial support to this work made possible. The authors are highly acknowledged the technical and field assistants of the forage and pasture research program of Holetta Agricultural Research Center for continuous data collection.

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