Agronomic Characteristics of Red Napier Grass ( Pennisetum purpureum cv. Red) under Different Level of Nitrogen Fertilization and Harvest Ages

. This experiment aimed to find out the morphological characteristics and biomass DM production of Red Napier grass ( Pennisetum purpureum cv. Red) under different levels of nitrogen fertilization and harvest ages. The grass stem cuttings were planted on polybags. A Completely Randomized Factorial Design (CRFD) was employed comprising 2 treatment factors. The first factor was harvest age of K1: 50 days of age K2: 60 days of age and K3: 70 days of age and the second factor was level of N fertilization comprised P1: no fertilization, P2: 100 kg N /ha/year, P3: 200 kg N/ha/year, P4: 300 kg N/ha/year. The treatments were applied after the grasses were trimmed at 90 days after planting. The variables measured include plant height, number of tillers, leaves-to-stem ratio, and biomass production. Data collected were subjected to analysis of variance and least significant difference test. It was found that interaction of treatments significantly (P<0.01) affects plant height and biomass DM production. Treatments of age of harvest and level of N fertilization, respectively significantly (P<0.01) affect either number of tillers or leaves-to-stem ratio. It was concluded that K3 and P3 gave the highest value for all variables measured.


Introduction
Napier grass (Pennisetum purpureum) is one of the forages from the grass family that is widely cultivated and used by farmers in Indonesia to feed their livestock.There are two groups of Napier grass cultivars i.e. the tall cultivars (>130 cm height) such as Common Napier, Pennisetum purpureum cv.Red, Taiwan Napier, Indian Napier, Uganda Napier, and King Grass while the short type cultivars (<90 cm height) include Dwarf Napier, Dwarf "Mott" and Australian Dwarf [1].The Pennisetum purpureum cv.Red, called Red Napier, has recently been introduced in Indonesia via some e-commerce platforms selling grass stem cuttings.Field observation, however, indicated that the cultivation of the grass by farmers is still negligible.This may be due to relatively limited information on the common management practices such as fertilization and harvest on agronomic characteristics of the grass that can be informed to the farmers.
It is commonly known that the type and level of fertilizer application influence plant growth and quality.Improve quantity and quality of grass production can be achieved through fertilization of nitrogen as a vital macronutrient required by plants for optimal growth and production [2].Farmers commonly use urea as nitrogen fertilizer.It is a single-component fertilizer with a nitrogen (N) content of around 46% [3].In the experiment by Daryatmo, et al. (2019), it was shown that the application of different doses of urea fertilization affects the production of Dry Matter (DM) and the application of 200 kg N/ha gave the highest plant height and biomass production [4].
Apart from fertilization, harvest age is known to affect the quantity and quality of forage production.Extending harvest age leads to higher biomass production but reduced quality of forages.Such dynamics on production are also influenced by the changes in agronomic characteristics of the forage including plant height, number of tillers, and leaves-to-stem ratio [5].
Considering the above, this experiment was conducted to find out the effect of nitrogen fertilization and harvest age on the agronomic characteristics and biomass production of Red Napier grass.

Location
The experiment was executed from March to August 2023 at the greenhouse of the Livestock Forage Plant Laboratory at the Field Laboratory of the Faculty of Animal Husbandry, Brawijaya University located at Sumbersekar Village, Dau District, Malang Regency, East Java.Dry Matter (DM) content analysis was conducted at the Animal Nutrition Laboratory, Faculty of Animal Sciences, Brawijaya University.Soil analysis was done at Soil Physics Laboratory, Faculty of Agriculture, Brawijaya University.The soil contains low Nitrogen (N) of 0.14 %, a medium C/N ratio of 11, and very high available Phosphorus (P) of 84.60 mg.kg-1.

Research Variables
The variables measured were plant height, number of tillers, leaves-to-stem ratio (in DM), and aerial biomass DM production.

Research Procedure
Stem cuttings were individually planted in 0.491m2 surface area polybags containing soil.The stem cuttings and soil originated from the research location.The research followed a Factorial Randomized Design comprising 2 treatment factors.The first factor was harvest age of K1: 50 days of age K2: 60 days of age, and K3: 70 days of age, and the second factor was level of N fertilization comprised P1 no fertilization, P2: 100 kg N /ha/year, P3: 200 kg N/ha/year, P4: 300 kg N/ha/year.These treatments were applied after the grasses were trimmed at 90 days after planting.
Plant height was measured just before the grass was harvested.Leaves blades and stems (including leaf sheaths) were separated from the harvested plant biomass and composite samples of each were brought to the laboratory for DM analysis following the AOAC (2005) method.Leaf to stem ratio was measured as leaves DM production divided by stems DM production.Plant biomass production was measured by summing the leaves DM and stems DM.The number of tillers was physically counted after harvest.

Statistical Analysis
The collected data were subjected to Analysis of Variance (ANOVA) according to the following formula: Yijk = Observation of factor A in treatment i, factor B in treatment j, and replication k  = Overall mean i = Effect of factor A in treatment i j = Effect of factor B in treatment j ij = Interaction between factor A in treatment i and factor B in treatment j ijk = Error effect in factor A in treatment i, factor B in treatment j, and replication k If the ANOVA indicated a significant effect of the treatment then the Least Significant Difference (LSD) test was applied to find the best treatment.

Plant Height
The analysis of variance found that the interaction of treatments was very significant (P<0.01) in affecting the height of Red Napier grass.Data on plant height under the different treatments is presented in Table 1.
Table 1 shows that plant height increases by extending harvest age and the effect of different levels of N fertilizer becomes obvious at 60 days of age (K2).At harvest ages of 60 and 70 days, level N application at the rate of 200 and 300 kg/ha/y (P3 and P4) resulted in similar plant height and both are significantly higher as compared to the height of those received N application below 200 kg N/ha/y.Interaction between harvest age and N fertilizer application shows that the highest plant height is found at harvest age of 70 days (K3) and fertilization of N at 200 and 300 kg/ha/y (P3 and P4).On the basis of economic reasons, the application of P3 i.e. 200 kg N/ha/y (P3) is considered to be a better option than that of 300 kg n/ha/y (P4).
The increase of the grass height by increasing harvest age as above is attributed to the elongation of stem internodes which is influenced by the continuous division of apical stem meristem tissue that increases plant height and volume [1].In addition, supply of more the most essential nutrient for vegetative plant growth i.e.N in the form of urea, up to 200 kg n/ha/y intensifies cell division and elongation [6].

Number of Tillers
The analysis of variance found that either harvest age or levels of N fertilization were highly significant (P<0.01)affected the number of tillers of the Red Napier grass while the interaction of the treatments did not significantly (P>0.05)affect the number of tillers.Data on the number of tillers/clumps under the different treatments is presented in Tables 2 and 3.As shown in Table 2, longer harvest age and higher levels of N fertilizer respectively increase the number of tiller/clumps.The number of tillers is an indicator of the forager's ability to regrow and a sign of its potential biomass production [7].As the plant's age increases, it provides more time for the photosynthesis process.In this experiment, the highest number of tillers (20.13 ± 3.13) was at harvest age of 70 days (K3).This number of tillers was lower than Pennisetum purpureum cv.Roxo harvested at 182 days i.e. 27.1 per clump reported by Rueda, et al. (2018) [8].
Table 3 shows higher N fertilizer application up to 200 kg N/ha/y increase the number of tillers and higher N fertilization significantly (P<0.01)decrease the number of tillers/clumps which could be because availability of N and P in the soil became imbalanced.Application of N fertilizer may increase cytokinin hormones that help accelerate cell division in the formation of new shoots [9].In this experiment, the highest number of tillers is found at N fertilization level of 200 kg N/ha/y (P3) i.e. 28.22 ± 3.51 per clump which is higher as compared to the number of tillers of 300 kg/ha/y N fertilized Pennisetum purpureum cv.Mott reported by Mulyadi, et al. (2018) that harvested at 42 days [10].

Ratio of Leaves and Stems
The analysis of variance found that either harvest age or levels of N fertilization was highly significant (P<0.01)affected leaves-to-stems ratio of the Red Napier grass while the interaction of the treatments did not significantly (P>0.05)affect the leaves-to-stems ratio.Data on leaves-to-stems ratio under different treatments is presented in Tables 4 and 5. Different superscripts on the same line indicate highly significant differences (p<0.01)Table 4 and 5 show that longer harvest age and higher levels of N fertilizer respectively decrease leaves-to-stems ratio.The highest leaves-stems ratio was found at the youngest age of the grass i.e. 1.62 ± 0.08 at K1 or at the lowest rate of N fertilization level i.e. 1.56 ± 0.28 at P1.The above trend indicated that longer harvest age and higher N fertilization, respectively lead to stem elongation, volume increase, and increase stem DM production.The lowest leaves-to-stems ratio in this experiment as shown in Table 4 and 5, however, is higher as compared to that of Pennisetum purpureum i.e. 0.65 at 45 days of age [11] or Pennisetum purpureum cv Mott i.e. 1.23 harvested at 30 days of age [12].Hence, the finding of this experiment indicates that the Red Napier grass is a leafy grass as also underlined by Onjai-uea, et al. (2023) [13].Leaves are preferred by livestock because they have higher palatability, digestibility, and nutritional value compared to stems [14].

Dry Matter Production
Based on the results of analysis of variance, interaction of treatments highly significant (P<0.01)affected the aerial biomass DM production of the Red Napier grass.Data on aerial biomass production of the grass under the different treatments is presented in Table 6.The effect of the level of N fertilization becomes obvious when the grass is harvested at 70 days.The interaction between harvest age and level of N fertilization indicates that the highest aerial biomass DM production is achieved at harvest age of 70 days (K3) and N fertilization level of 200 kg/ha/y.A higher DM production signifies that the photosynthesis process is more efficient, resulting in increased productivity and the development of tissue cells at a higher rate thus promoting better plant growth.The N fertilizer constitutes protein that promotes the division of meristem tissue and stimulates root growth and leaf development [15].The reduced aerial DM production at K3 under 300 kg N fertilization per ha per year (P4) as compared to that at P3 indicates that the application of a certain amount of N fertilizer i.e 200 kg N/ha/y (P3) at K3 can maximize the DM production of the grass biomass.This treatment (P3K3), apart from resulting in higher DM production, also gave the highest plant height.Although the leaves-to-stem ratio at P3K3 is lower than that at K1 or P1, it is still higher than 1 which can be considered leafy and able to provide good materials.

Conclusion
It can be concluded that the combined effect of harvest age at 70 days and N fertilization level of 200 kg N/ha/y (K3P3) produce highest DM biomass production and plant height.K3 and P3, respectively, also gave the highest number of tillers.Although it did not give the highest leaves-to-stems ratio, the value of this variable at K3 and P3 is still above 1.

Table 1 .
The average plant height of Red Napier Grass in different treatments.
dDifferent superscripts on the same line indicate highly significant differences (p<0.01)

Table 2 .
Number of tiller at different harvest ages.

Table 3 .
Number of tiller at different levels of nitrogen fertilization.

Table 4 .
The leaves-to-stems ratio at different harvest ages.

Table 6 .
The average plant height of Red Napier Grass in different treatments.Different superscripts on the same line indicate highly significant differences (p<0.01)Based on Table 6, the biomass DM production of the aerial part of the Red Napier grass increases with the increase of harvest age.It is highest at 70 days of harvest age.At this harvest age, aerial biomass DM is highest as compared to those harvested at a younger age at any level of N fertilization.