Ⅰ.INTRODUCTION
Due to frequent and heavy rainfall in the eastern mountain area of South Korea, silage has been a more common forage preservation practice. However, silage can’t be consumed and the quality can’t be checked before silage stable state. Therefore, instead of silage, the hay is used which is imported from other countries. This experiment aimed to help increase domestic hay production in South Korea. Haymaking is accomplished through rapid removal of moisture in forage to reach DM concentration above 800 g kg-1 which is DM level for long-term hay storage without further nutrient loss. Throughout the forage harvest, drying, and preservation process, forage loses DM and nutrients through chemical, physical, and biological reactions. Optimized hay production management is important to achieve consistent production of high quality hay.
Cutting height has been known for affecting regrowth of forage and also for affecting total biomass productivity. Dry matter and nutrition productions of forage were greater when harvested at a lower cutting height (Smith and Nelson ,1967; Kust and Smith, 1961). Lower cutting heights increased the forage yield, but also increased soil contamination in forage. Inclusion of pasture soil may result in poor quality or high ash containing hay. Quality of alfalfa (Medicago sativa L.) decreased when harvest was made at a lower cutting height. Relative Feed Value of alfalfa improved from 0.9 to 7 units per every increased inch of cutting height (Daniel et al., 2007). Leaves are higher in relative feed value (RFV) while stems typically contain higher levels of non-digestible nutrients. So, the nutritive value of stems is lower than leaves (Santis et al., 2004). It is proved by them that the nutritive value, IVDMD and CP declined with the reduction in leaf stem ratio (LSR) .Low cutting height also causes stand damage (Smith. 1972). The similar result was reported by Daniel et al. (2007).
This study aimed to investigate the effect of cutting height on the drying rate and hay quality of rye (Secale cereale L.) hay.
Ⅱ.MATERIAL AND METHODS
1.Hay preparation
These experiments were conducted in Pyeongchang Campus of Seoul National University in the Republic of Korea. During the experiment (5 May~9 May 2016), average temperature was 11 ℃, average amount of precipitation was 4.8mm, average wind speed was 4.7m/s, and the average humidity was 66.1%. Other details of meteorological data during the experimental period are shown in Table 2.
Two 10 m2 (5m x 2 m) plots were planted with rye at 150 kg/ha seeding rate on 25th of September in 2015 and harvested at heading stage on 5th of May in 2016 using a harvester (NOVACAT 301 & Alois poettinger) equipped with a hay conditioner (Table 1). Plots received 80 kg /ha N, 150 kg/ha P2O5, and 150 kg/ha K2O when planted. Over the winter all plots received the same dressing of N fertilizer, 70 kg/ha. Rye was harvested at 8cm or 15cm stubble height. Rye biomass was tedded at 09:00 and approximately 300g of grab sample was randomly collected three times (09:00, 13:00 and 17:00) a day to determine moisture content (MC) in the samples.
2.Hay Storage
All treated hay samples were stored in Nylon bags tightly and preserved in a dark-dried room in ambient temperature for two months (11 May~11 July, 2016). Temperature was recorded during the preservation progress for two months (11 May~11 July, 2016). Dial probe thermometers with 50mm size dial and 300mm size stainless were put into each Nylon bag of samples to check the variation of temperature, with the results recorded at 13:00 every day for two months. After two months’ preservation, the hay samples were evaluated in visual score (leafiness, odor, color, softness and mold) and dry matter loss. Visual score was estimated by the criterion written by Burns and Gary (1991). Dry matter loss was measured as difference of hay bale weight between baling and after preservation for two months.
3.Viable count of fungi
The spread-plate method was used for counting of fungi (Michael et al., 2012). Dilution was prepared by mixing 1g of hay sample with 9ml 0.85% NaCl. Then samples were pipetted onto the surface of a potato dextrose agar (PDA) plate and spread evenly over surface of agar using one-off plastic spreader. After 3 days of incubation at 29°C, the plates were checked for fungal growth.Table 2
4.Chemical analysis
Each sample of about 300g was collected and dried in a forced air drying oven at 65°C for 72 hours. Dried sample was ground using a Wiley mill to 1 mm particle size and stored in a plastic sample cup having an air-tight lid.
Crude protein (CP) was determined by the Dumas method (Nielson, 2010) using a nitrogen analyzer (EUROEA3000 elemental analyser ®, Eurovector). Acid detergent fiber (ADF) and neutral detergent fiber (NDF) were determined using ANKOM 2000 Automated Fiber Analyzer (Goering and Van Soest, 1970). The two-stage technique (Tilley and Terry, 1963) was used to measure in vitro dry matter disappearance (IVDMD). Relative feed value (RFV) was calculated by Holland et al (.1990). Total digestible nutrient (TDN) was calculated by known ADF (Holland et al., 1990): TDN = 88.9 - 0.79 x ADF %.
5.Statistical analyses
The effects of two different cutting height on CP, ADF, NDF, IVDMD, TDN, RFV and viable count of fungi were analyzed by PROC t-test (SAS, 2002). The level of probability for statistical difference was established at p<0.05.
Ⅲ.RESULT AND DISCUSSION
Cutting rye at 15cm stubble height lost moisture faster than cutting at 8cm (Fig. 1). It is presumed because of less dense biomass and better air circulation at 15 cm stubble height. On the fourth day of field drying, both treatments achieved a moisture concentration below 200 g kg-1. Cutting height was related in the yield of forages. Curran and Posch (2000) reported about 12% decline in DM yield between cut heights that left 10.2 vs. 50 cm.
In a case of silage corn, increasing the cutting height improved nutritive value through reducing the concentration of NDF, ADF and ADL (Neylon and Kung, 2003). The result in this experiment showed that cutting in the rest part is 8cm and 15cm did not show significant difference in contents of ADF, NDF, IVDMD, TDN, and RFV (p>0.05). The hay tedder generally improves the drying conditions by spreading the hay swath over large area. In this study, the reason for no significant difference in achieving a moisture content below 20% was tedding practice once per day. Cutting at 15cm showed higher in CP content than cutting at 8cm (p<0.05) (Table 3). Studies reported CP loss during hay storage ranged from moderate (Davies and Warboy, 1978) to no change (Nelson, 1972). Rotz and Abrams (1988) reported insignificant or even a small increase of CP while greater degree of carbohydrate loss in high-moisture hay. The CP concentration in rye hay increased at15 cm cutting height when compared with that in fresh rye.
Cutting at 15cm stubble height loss more DM than cutting at 8cm (Fig. 2). This may also be due to more mature and greater fiber content in lower stem compared with the less mature top portion (Bolormaa. 2008). The two treatments did not show significant difference in contents of ADF, NDF, IVDMD, TDN, and RFV (p>0.05) (Table 3), even showed ineffective in the amount of total fungi during preservation. (p>0.05) (Table 5). Daniel et al. (2007) reported improved alfalfa quality from taller stubble height. The lowest sections of the alfalfa plant also contain higher concentration of fiber and fewer leaf proportion. A Nebraska study (Ogden and Kehr, 1968) where the top half of a full bloom alfalfa canopy was separated from the bottom half indicated that a larger percentage of the digestible nutrients and less fiber was found in the top half versus the bottom half of the plant.
Lima (2015) state that hay baled at over 20% moisture has a high probability of mold growth, which will decrease the quality of hay through degradation of protein and nonstructural carbohydrates, which can result in less palatable hay or a toxicity to livestock.
The digestibility of DM and nutrients usually decreases during storage (Davies and Warboy, 1978), but the digestibility of fiber changes is less effected (Nelson, 1968). This study indicated lower IVDMD and higher fiber content in post storage rye hay than pre-storage when harvested at 8 cm stubble height.
Visual scores of rye hays cut at 8 cm or at 15 cm indicated acceptable to good storage condition (83 and 85) (Table 4). Rye hays cut at 15 cm stubble height demonstrated better visual scores than those at 8 cm. It was proved that visual score also depends on harvest time. Visual score of the grass harvested at late boot was good (86), while at heading was good (80), and it was poor (63) when harvested at bloom stage (Seo et al., 2000).
All the temperature of treatments dropped down slightly at the first week of storage. The temperature then continually increased, maintaining a stable temperature around 24 °C after one-month preservation. Across the results, temperature of bales was affected by air temperature. When ambient temperature dropped on 3 June, all the temperature of treatments dropped down as well. And cutting in 8cm showed higher temperature than tedding in 15cm during preservation. The bale core temperature of cutting at 15cm remained below ambient temperature throughout the whole storage period while the temperature of cutting at 8cm was higher than ambient temperature from around at the 3nd week (23 May) of the storage period (Fig. 3). The reason is same as the result from Han and Kim. (1996) in that the amount of microorganisms increased with the increase of moisture content, causing more heat in hay bales during storage process. Rotz and Muck (1994) also demonstrated that in hay containing high moisture, microbial respiration causes heat accumulation in the core of hay bales during the first 3 to 5 weeks of storage. They also stated that heating during the first month of storage helps dry the hay. After the first month, hay would be relatively stable during the remaining storage period.
Baling hay with too much moisture can lead to spontaneous heating, mold development, DM loss, and nutrient loss (Barnes et al.,2007). The fungi counted at the two cutting heights did not differ (p>0.05). Moisture and temperature are major factors affecting populations of microbes in stored forage (Han and Kim. 1996.). Significant fungal growth in wet hay requires relative humidity to be at least 70% and temperature to be at or above 20℃ (Rees, 1982). The reason why the fungus was not high in this experiment is presumably because the temperature was above 20℃ but the moisture content of hay was low.Table 5
Ⅳ.CONCLUSION
Cutting in longer height (15cm) was faster on drying process due to better ventilation. Cutting in 15cm showed higher in CP content (p<0.05), but got more dry matter loss compared with cutting in 8cm (p<0.05). On another hand, cutting in 15cm and 8cm didn’t show significant difference in ADF, NDF, IVDMD, TDN and RFV, even showed ineffective in the amount of total fungi during preservation (p>0.05). Comprehensively considering yield, quality and drying rate, this research recommends cutting rye in a shorter height around 8cm.
