Ag Instructor Vic Martin: The Differences between Grasses and Broadleaves | Barton Community College

Ag Instructor Vic Martin: The Differences between Grasses and Broadleaves

Great Bend Tribune
Part I
Published May 20, 2018

First, more beneficial rainfall in spots this week to go along with last week.  Unfortunately parts of Western and South Central Kansas received damaging hail.  The Drought Monitor didn’t change a great deal (remember this is as of Tuesday morning).  However as this is being written, Thursday May 17, there are rain chances through early this week.  Wheat in the area is heading out and rain and moderate temperatures are key in maximizing the potential grain yield.  Today, let’s discuss the difference between grass crops (corn, wheat, grain sorghum) and broadleaves (alfalfa, soybeans, canola, sunflowers, cotton) and why these differences matter so much in the decisions producers make.  We will tackle these one at a time and why they matter.  First a little background on these two types of plants.  And for the Master gardeners out there, please understand this is a brief overview.

Both grasses and broadleaves are flowering plants (angiosperms) although the flowers of grasses are typically much less showy.  Grasses are part of the group termed monocotyledons which means they have one seed leaf (cotyledon)  This group includes the grass in your yard, the native prairie grasses, and our grain crops – corn, wheat, grain sorghum, oats, barley, triticale.  They can be winter annuals, summer annuals, perennials, and some species such as wheat, barley, and triticale are found as both winter and summer annuals.  Even though there is a great deal of diversity in this group based on appearance and life cycle, they are actually closely related.  Grasses are considered more advanced evolutionarily than broadleaves (dicots) and even other monocots.  One main reason is that unlike broadleaf species, grasses don’t have to rely on an outside source such as insects, bats, or birds for pollination.  While all grasses are monocots, not all monocots are grasses.  Non-grass monocots include lilies, onions, palm trees, tulips, orchids, and bananas.

Broadleaves are dicotyledons meaning they have two seed leaves at emergence.  When we mention flowering plants we most often think of brightly colored, showy flowers – dicots.  Common dicot crops include soybean, sunflower, canola, cotton, and alfalfa.  Dicots are an extremely diverse group ranging from deciduous trees and duckweed to the marigolds and petunias in your flower garden and the majority of vegetables in your local store.  They can also be winter or summer annuals, perennials, or something grasses can never be – biennials.  Biennials grow vegetatively the first year storing food in a large taproot to overwinter and regrow, flower, produce seed and die the second growing season.  You may have eaten a biennial recently as they include carrots, parsley, beets, turnips, parsnips and several others.  Certain garden flowers are biennials such as Sweet William and hollyhocks.  Onions are an example of a biennial monocot.

For the sake of brevity, you can tell a monocot from a dicot at emergence by noting whether it has one or two leaves at emergence.  And the simplest way with older plants, remembering that there are always an exception or two, to distinguish the two broad groups is that monocots have long, narrow leaves typically with a midrib to support the leaf in grassed and parallel veins in the leaf.  Broadleaves are just that, not long and narrow, with some type of net venation.  A perfect example is a maple leaf.

Next week will dig into the differences between grasses and broadleaves, why they are important as the differences are much greater than described here.

Part II
Published May 27, 2018

Last week’s column discussed the broad differences between grass crops such as corn and wheat compared to broadleaf crops such as soybeans and alfalfa.  Today, let’s get more specific about differences between the two and why these differences matter.

  • Germination – Grass seeds consist of the embryo, the plant, and a food source to establish the plant, the endosperm.  The seed stays where it is and sends up the cotyledon to the surface protected by a sheath, the coleoptile.  So only a long narrow point has to emerge from the soil.  The rest of the seed stays in the soil and in most cases can be found months after emergence.  In a crop like soybeans the two cotyledons, the seed leaves are the food source and the entire seed, except for sometimes the seed coat emerges above the soil.  This takes more “oomph” and energy as you have to pull the cotyledons up through the soil in an arch and break through the surface.
  • Growing points – The growing point in grasses stays below the soil surface for an extended period of time and is protected.  For broadleaves, the growing point is above the soil surface at emergence.  This matters for several reasons.  First for weeds, a contact herbicide like Paraquat will kill young broadleaf weeds as they kill the growing point.  But for seedling grass weeds, the growing point is protected and you need a systemic herbicide.  Second, this affects planting date and the danger of frost.  A frost on a seedling soybean plant can kill the growing point while the grass would only lose the above ground growth.  This dictates when you can safely plant.  Third, since the growth is above the growing point in grasses, it is much easier to graze grasses compared to alfalfa.  In alfalfa, when it is grazed or hayed, you are removing all the growing points and dormant growing points are activated.  In grasses, you keep the growing point and growth immediately resumes.  Think of your grass lawn and how rapidly is grows after mowing.
  • Root system – For a broadleaf crop like soybeans, the seed root (radicle) becomes the main root system as a tap root below the seed.  For a grass crop like corn the radicle sticks around for a while and roots termed seminal roots develop and support the developing plant early on.  However, the root system that develops into the main root system forms above, not below, the spot where the seed was planted from what are termed adventitious roots. This isn’t a taproot system but a fibrous root system and is much closer to the soil surface than the taproot system.  This is important for two reasons.  First, even with good soil moisture a producer has to be careful not to plant the seed to near the surface or the root system will be vulnerable to desiccation or if there are surface residues, it may even form on the soil surface.  For the broadleaf plant, the shallow planting has less impact as the root system forms below the seed.  Second, here on the Great Plains, grasses can better survive our rainfall patterns since most precipitation events are 0.20 inches or less and don’t penetrate deeply into the soil.  Grasses are better positioned to take advantage of this pattern.

Next week will wrap up this topic.  For now, enjoy the Memorial Day Weekend and reflect on those who gave their life for our liberty and safety.

Part III
Published June 3, 2018

Before returning to our discussion regarding grasses and broadleaves, a drought update. The Drought Monitor Report, updated as of Tuesday, May 29th, shows easing of drought conditions.  In the NW and SE corners of Kansas, the drought is gone and there is easing throughout much of the rest of the state.  The rains of the last several days should reflect further easing next week, however, the well above normal temperatures towards the end of this past week will somewhat erase some of the benefits.  At least much of the state now has the needed moisture to finish the wheat crop, benefit pastures and alfalfa greatly, and help the spring row crops establish strongly.  Now back to the topic at hand there are two more differences between grasses and broadleaf crops to mention.

  • Pollination – Broadleaves typically rely on help in achieving pollination such as insects, bats, and birds.  That normally isn’t a huge problem until the pollinators aren’t around.  If you pay the least bit of attention to agriculture news reports, it is virtually impossible to miss the declining European Honeybee populations being dealt with in the U.S. and other areas.  While there are many types of bees, producers of fruits, vegetables, and other crops such as alfalfa rely on these bee for pollination.  This is a weakness for these types of plants as having to rely on another organism to pollinate can lead to disaster if the organisms aren’t present.  Many plant items we rely on from broadleaves are in danger if the pollinators become scarce or disappear.  In California, the value of bee pollinated crops is in the hundreds of millions of dollars. While we didn’t go into differences here, grasses and broadleaves have markedly different flower structures.  Grasses lack petals and sepals since they don’t need petals as they don’t need to attract pollinators.  Instead grasses are self- or wind- pollinated.  This has the advantage of not needing to rely on another organism for seed production and is considered more evolutionarily advanced.
  • Vascular system – Both types of plants have a vascular system.  Xylem to transport water and nutrients from the roots throughout the plant and phloem to transport the products of photosynthesis throughout the plant for growth and reproduction.  Typically grasses such as corn and grain sorghum have vascular bundles scattered throughout the pith of the stem.  Broadleaves have their vascular bundles on the outer edge of the stem.  The easiest way to think of this is a deciduous tree such as an oak or maple.  Most know you can determine the age of the tree by counting the rings.  Each year is a ring with the youngest wood (xylem) on the outside.  Just beneath the bark are the actively growing vascular bundles.  This is why if you girdle a tree, cut into the trunk about an inch all the way around, you kill the tree as you have severed the vascular system.

There are many more differences between the two types of plants that matter but hopefully this provides a brief overview of basic differences and why they matter.

barton wordmark