Any experienced peanut producer knows that water is the key to a successful growing season. But more precisely, the amount and timing of rainfall or irrigation are keys to success, says John Beasley, University of Georgia Extension peanut specialist.
“This was never more evident than in 2001,” says Beasley. “We had a good year throughout the Peanut Belt, and much of that was due to rainfall. We were fortunate to receive abundant rainfall in Georgia during the month of June and again following Labor Day. The timing of rainfall or irrigation is absolutely critical.”
When scheduling irrigation, he says, it's important that growers maintain a “water balance.”
“You're trying to balance the rainfall or irrigation your crop receives with evaporation from the soil and transpiration from the crop itself. You want to balance the amount of water coming in versus the amount of water going out,” says the agronomist.
Scheduling peanut irrigation efficiently requires that growers know their soil types, he continues.
“You also need to know your equipment limitations. Are you using a center pivot, cable-tow or hard-hose system? And, in a few isolated cases, growers might be using risers with sprinklers. It's important to know the capacity of these systems. It may take an entire week to for some pivots to make a circle and put out three fourths inch of water,” he says.
The water resource is another important consideration, says Beasley. “Is it underground or surface water? We've seen situations, especially in recent drought years, where growers have had limited underground water. The amount of water available becomes even more critical if you're irrigating with surface water. You need to know your water limitations so you can preserve water and use it for the most critical times,” he says.
Some crops need more water than others, says Beasley, and growers need to know the physiological growth stages of the crops they're managing.
“If you're growing peanuts and cotton, you need to know when each of the crops have their highest water requirement. Peanuts have a very low water requirement early in the season. But as you progress though the season, particularly at 85 to 105 days, the peak evapo-transpiration rate is about .03 inch per day.
“If your method of scheduling irrigation is to try and replace the water that's lost, peanuts will need about 2 inches of water per week during this peak period. In other words, any rainfall received should be supplemented with irrigation to equal 2 inches of water per week, especially in the latter growth stages.”
The peanut growth season is divided into four stages, explains Beasley. These include germination and emergence, early vegetation, fruiting and maturation.
“Germination and emergence covers planting through vegetative emergence. If you don't have moisture in the soil when you plant, you won't get adequate germination and emergence, and the plant won't establish a strong root system.”
The early vegetative stage, he says, covers from the time plants emerge until they start blooming. Susceptibility to drought is very low during this period, he adds.
“Peanut plants can survive with very little water during this stage, provided you have a good, uniform stand, a healthy, developing root system and no hardpan limiting root growth. During this stage, the deep root system of a peanut plant can utilize water deep in the soil profile to help maintain the plant vegetatively until it starts to bloom.”
The fruiting period covers from bloom to early pegging and through pod fill, says Beasley. Peanuts in this stage of growth are highly susceptible to drought.
“This is the critical stage at which you can get the highest yield reduction from a lack of water. You absolutely need to use your water during this time. But once you get to within one month of harvest, the water requirements begin to decrease. During this later period, you don't want the peanuts to be stressed. This creates conditions favorable for the development of aflatoxin.”
Growers should be aware of any water deficits or stress during each peanut growth period, says Beasley. Stress occurring during the first critical 30-day period could result in reduced flowering and pegging, he adds, eventually leading to a loss in yields.
“You must have water during that first fruiting stage. During early season drought stress, you'll see a delay in flowering. You should go ahead and water once the plant reaches the stage where it's trying to bloom and flower. You could see some reduced root growth during this early stage, and that could hurt you down the road. If growth is reduced early, and the plant goes into stress later in the season, the plant will wilt much quicker. Don't over-use water during the early vegetative stage, but don't let the plant become stressed.”
The greatest yield reduction in peanuts can occur from a lack of water during the 50- to 110-day growth period, says Beasley.