A few days of cool weather, with daytime temperatures in the low 70’s and nighttime mercury dipping into the 50’s, made for a nice change earlier in the week. Though we’ve avoided the really scorching weather this summer, the 90+ degree days we’ve had seem more than hot enough. When we moved cows to ungrazed pasture Monday the calves skittered around in the cool morning the way they did back in May. Which is somewhat remarkable, because these calves are stout. It’s been a good summer for growing calves.

It’s certainly been a remarkable year. We had a dry autumn last year and a harsh and mostly open winter, featuring cold and drying winds and little snow cover. Spring rains were a big question mark, right up until they arrived, and many ranchers wondered whether they’d be putting drought plans into action.

Last year we were actually a bit short on rainfall quantity. The long term average annual precipitation is about 16.8 inches, and in 2017 we totaled 16.3. Grass production proved adequate to sustain the cow herd and the grassland ecosystem, but biomass production was far from abundant. It’s been rather a different story this year, and at the end of July pastures remain lush and green.

The difference between this year and last is remarkable. Thus far we’ve had just over 17 inches of precip on the ranch, well ahead of the long term average. Quantity and timing of precipitation is the key to vegetative growth on the grasslands of the high plains, and the difference between this year’s lush pastures and last year’s brown and barely adequate forage production is a perfect illustration.

As with nearly all plants, photosynthesis drives grass production. Grass takes in nutrients from the ground and carbon dioxide from the air, and using sunshine as the energy source, chemically combines nutrients and carbon dioxide into carbohydrates – cellulose for structure, sugar for energy, and starch for storage.

Nutrients are always in the ground, CO2 is always in the atmosphere, and solar energy rains down whenever the sun is above the horizon. Therefore, the limiting factor for vegetative growth is water. A universal solvent, water carries nutrients and chemical building blocks throughout the plant as it grows. When little water is available, little vegetative growth can occur. When water is abundant, so is vegetative growth.

Our High Plains prairie grasses have evolved into cool season and warm season species, categorized by their growth response to air temperatures. Cool season grasses have maximum growth when air temperatures are 65-75 degrees; warm season when air temperatures hit 90-95 degrees. Most of the vegetative growth potential for cool and warm season grasses is largely limited to 30-day rapid growth windows beginning when air temperatures reach the required level.

Though both types of grasses will green up and slowly make new growth in response to rainfall outside their 30-day rapid growth window, actual vegetative production is very limited when compared to growth response during the rapid growth window. This is why rainfall timing is so critical. Dry conditions during the rapid growth window sharply limit vegetative growth, and precipitation falling after the rapid growth period will do little other than temporarily green a low yielding stand of grass. In fact, grass stands which remain dry much past the midpoint of their rapid growth window are generally sharply limited in production.

Across our shortgrass to mixed-grass prairies, cool season rapid growth windows run from early April through June. Each location is likely to be somewhat different, and elevation plays a large part in air temperature warm up, but the sequence of rapid growth windows is the same across the region. First come the sedges, or grass-like plants. Threadleaf and needleleaf sedge are good examples, and their rapid growth window begins in early April and ends 30 days later. Next come needlegrasses, most prolific in May, and finally wheatgrasses, with rapid growth in June. Later in the summer, from mid-July to mid-August, warm season grasses such as blue grama and buffalo grass take off.

May and June precipitation was abundant on the EJE and coincided with the shortgrass rapid growth window. In May we had 6.43 inches and in June 2.53. In July the rains slacked off a bit early but then returned to yield a monthly total of 2.5 inches, less than the 2.7 inch average, but adequate nonetheless. Soil moisture remained high enough for warm season grasses to grow well during the heat of summer, and this year’s blue grama and buffalograss production has been outstanding.

As you can see, precipitation timing is the key for the cattle producer. Timely and abundant rains in the March-May period will make for excellent grass production and portend good things. A dearth of spring rain will often make for a tough summer and constant worry about feeding the cow herd.

As we slowly trailed the herd toward their late-summer home Monday, I parked my pickup and got out and walked. The cool morning air was invigorating and the sunshine warm and delightful. The air was filled with the smell of lush pasture and the sound of birds, insects and cows. It’s hard to avoid enjoying such moments. As Grandpa used to say, “Enjoy the good years and endure the bad years.”