Effects of growth stage and growing degree day accumulations on triticale forages: 1. Dry matter yield, nutritive value, and in vitro dry matter disappearance

Abstract

The use of triticale (X Triticosecale Wittmack) in dairy-cropping systems has expanded greatly in recent years, partly to improve land stewardship by providing winter ground cover. Our objective was to establish relationships relating indices of nutritive value with growth stage or accumulated growing degree days >5°C for triticale forages grown in central Wisconsin. Replicated 3.7-m × 9.1-m plots were established following removal of corn for silage (fall 2015) and soybeans (fall 2016) and then harvested at various growth stages the following spring. Plants were assigned a numerical growth stage based on a linear staging system suitable for use as an independent regression variable. Response variables [e.g., dry matter (DM) yield, indices of nutritive value, and parameters from in vitro DM disappearance kinetics] were regressed on growth stage and growing degree days using linear, quadratic, cubic, or quartic models. For spring 2016, the mean DM yield at the boot stage (3,804 kg of DM/ha) was only 30% of that observed at the soft dough stage of growth (12,642 kg of DM/ha). Although yields were reduced during spring 2017, primarily due to spring flooding, the relationship between respective yields at these growth stages was similar (1,453 vs. 5,399 kg of DM/ha). Regressions of DM yield (kg/ha) on growth stage for 2016 were explained by a cubic model (Y = 0.0663x - 9.44x + 595x - 9,810) compared with a simple linear response for 2017 (Y = 103x - 3,024); in both cases, coefficients of determination were very high (R ≥ 0.934). Many nutritional and in vitro DM disappearance characteristics were affected by the juxtaposition and balance of 2 generally competing factors: (1) increased concentrations of structural plant fiber coupled with concurrent lignification as plants matured and (2) the accumulation of highly digestible carbohydrate during seed head development. A comparison of respective energy yields between the boot and soft dough stages of growth for 2016 (2,488 vs. 8,141 kg of total digestible nutrients/ha) and 2017 (1,033 vs. 3,520 kg of total digestible nutrients/ha) suggests that yields of energy are greater at soft dough stage and are mostly driven by DM yield. An informed harvest management decision for lactating cows may still favor a boot-stage harvest because of superior nutritional characteristics, a need to plant double-cropped corn expeditiously, or both. Harvest timing of triticale forages for other livestock classes would appear to be more flexible, but prioritizing a subsequent double crop may reduce the effects on DM yield to a secondary consideration.

Effects of growth stage and growing degree day accumulations on triticale forages: 2. In vitro disappearance of neutral detergent fiber

“…2016 Harvest. All specifics regarding establishment of triticale, soil fertility, fertilization, weather, and sampling procedures are described in detail in a companion report (Coblentz et al, 2018), and only a brief summary of salient points relevant to the experimental design is repeated here. Twenty-five 3.7-m × 9.1-m plots were established in 5 field blocks (5 plots/block) on September 30, 2015.…”

“…On October 22, 2016, 'Tri-Cal' triticale (Byron Seeds LLC, Rockville, IN) was no-till seeded into soybean stubble, creating 5 field blocks consisting of 6 plots/block (n = 30 plots). Although it was our intention to align growth stages at harvest across years, this was not possible due to the unseasonably wet conditions observed from April through June of 2017, when cumulative rainfall totaled 470 mm (Coblentz et al, 2018). As such, one complete field block (6 plots) was lost to flooding, and some harvests had to be delayed because of muddy field conditions.…”

“…A 10.5-percentage unit decline occurred between the anthesis and soft dough stages of growth, which was directly related to the dilution of asNDFom by the physiological process of grain fill. All other indices of nutritive value are described and discussed in detail in a companion report (Coblentz et al, 2018).…”

“…Using this management approach, triticale silage has been successfully substituted for corn silage in diets of lactating cows at a rate of 10% of dietary DM (Harper et al, 2017). However, harvests at the late milk to early dough stages of growth also have occurred commonly for cereal grain forages (McDonald et al, 1991;McCartney and Vaage, 1994;Kennelly and Weinberg, 2003), and this delayed harvest approach provides a considerable yield advantage (>300%) over harvest at the boot stage of growth for triticale (Coblentz et al 2018). Substantial yield differentials between harvests at the boot and soft dough stages of growth also have been reported for other cereal grain forages (Acosta et al, 1991;Edmisten et al, 1998).…”

“…Initially, these concepts focused some attention on differences between forage types (Raffrenato and Van Amburgh, 2010); however, within-species effects of accumulated growing degree days (GDD) >5°C or plant growth stage at harvest have not been investigated. In a companion report, we described the effects of growth stage or GDD on various indices of nutritive value (Coblentz et al, 2018). Based on the increased use of triticale forages in the north-central United States, our objectives were to use 2P and 3P nonlinear models to characterize in vitro disappearance of asNDFom (NDFD) and then describe the relationship between estimated parameters from those models with plant growth stage or GDD for triticale forages harvested during 2016 and 2017 in Marshfield, Wisconsin.…”