**6. Abiotic stresses and cell wall composition**

In addition to limiting pollination, heat stress can limit kernel development after ovule fecundation [14, 15]. Kernel development is divided by a lag phase with little kernel growth and a linear growing phase with major accumulation of dry matter. The lag phase, which starts immediately after pollination and lasts 10 to 12 days after pollination, is critical for kernel development [15]. The endosperm is the structure of the corn kernel that contains starch granules. Cell division of the endosperm cells during the lag phase determines the capacity of

**Figure 5.** Daily maximum temperatures (line) and rainfalls (columns) during the crop cycle at two regions during 2011 and 2012 in the state of Virginia. The shaded region represents the critical stage for kernel development. The thick horizontal line represents the threshold temperature for heat stress (>35 °C). Prolonged heat stress after silking occurred only in the Southern Piedmont region during 2012 (C), but not in other site-years (A, B, and D). Data from Ferreira et

High temperatures immediately after silking limit starch accumulation within the kernels and increase the rate of kernel abortion as well. Cheikh and Jones [15] cultured corn kernels in vitro at different temperatures and observed that heat-stressed kernels (i.e., kernels cultured at 35 °C) accumulated 18–75 % less DM than non-stressed kernels (i.e., kernels cultured at 25 °C). Reduced dry matter accumulation can be related to reductions in starch synthesis within the endosperm when kernels are subjected to temperatures greater than 35 °C [14]. In addition to reduced kernel growth, Cheikh and Jones [15] reported 23–97 % kernel abortion when

In their retrospective study, Ferreira et al. [4] observed that in 2011, maximum temperatures were below 35 °C throughout the whole critical period of kernel development for the Southern Piedmont region, whereas in the Shenandoah Valley region, maximum temperatures were above 35 °C for only a few days during the critical period of kernel development (**Figure 5B**).

the endosperm to accumulate starch within the grain [15].

46 Advances in Silage Production and Utilization

al. [4].

subjected to heat stress.

The effects of abiotic stresses on cell wall composition are less clear than their effects on kernel development. In general terms, and from a nutritional perspective, drought stress would likely increase fiber digestibility (**Table 3**, data Argentina), whereas heat stress would decrease fiber digestibility [16]. These statements are somehow conflicting in the sense that drought stress and heat stress likely occur simultaneously.


**Table 3.** Nutritional composition and digestibility of corn silages in Buenos Aires (Argentina) during normal (2008) and drought (2009) years.

Drought stress during early vegetative stages can result in shorter internode lengths as a consequence of limited cell growth or elongation (**Figure 6**). As internodes contain highly lignified tissues (e.g., lignified vascular bundles), the concentration of lignin within the cell wall could be reduced when considering the whole corn plant. In addition to changes in whole plant structure (i.e., internode elongation), lignification might decrease at the tissue level when corn plants are subjected to drought stress [17, 18]. Vincent et al. [17] reported that lignin accumulation in the apical zone of corn leaves was reduced in response to drought stress. Alvarez et al. [18] reported higher concentrations of lignin precursors (i.e., p-coumaric and

might increase porosity of the silage. Under these scenarios, the use of inoculants to enhance

Environmental Factors Affecting Corn Quality for Silage Production

http://dx.doi.org/10.5772/64381

49

Abiotic stresses such as drought and heat stress can substantially affect corn silage yield and quality, although the mechanisms by which they act are different. Depending on the moment at which occurs, drought stress can have varying impacts. If drought stress occurs only at vegetative stages, dry matter yields can be compromised but not necessarily its nutritional composition. Alternatively, if drought stress occurs during reproductive stages (i.e., silking), both dry matter yield and nutritional composition can be affected. Heat stress, defined as temperatures above 35 °C, during the initial stages of kernel development can have a major negative impact in both corn silage yields and nutritional composition. Management practices, such as hybrid selection and planting date, should be considered to avoid silking and early

The authors thank Ms. Christy L. Teets for her assistance in revising this manuscript. The authors also acknowledge the partial support of this project by USDA-NIFA Hatch Project VA-160025 and USDA-NIFA Multistate Project VA-136291 (NC-2042, Management Systems to

kernel development during season of very high environmental temperatures.

Improve the Economic and Environmental Sustainability of Dairy Enterprises).

Department of Dairy Science, Virginia Tech, Blacksburg, VA, United States

[1] USDA, Cattle. 2014, Washington, DC: National Agricultural Statistics Service.

[2] USDA, Crop Production 2013. 2014, Washington, DC: National Agricultural Statistics

and Alston N. Brown

\*Address all correspondence to: gonf@vt.edu

fermentation is highly advised.

**8. Conclusions**

**Acknowledgements**

**Author details**

Gonzalo Ferreira\*

**References**

Service.

**Figure 6.** Drought-stressed corn crop passed tassel emergence, showing reduced elongation of internodes.

caffeic acids) in xylem sap of drought-stressed corn compared to well-watered corn, suggesting reductions in lignin concentration under drought stress.
