As a general rule of thumb farmers do an outstanding job of conserving water. We may have been guilty of applying too much in the past, or said another way, making an application once the crop was mature and from which only minimal benefit would take place. And it is true that tail water has been a problem with some furrow irrigation. In recent years though, many, many pivots have been put in which has drastically increased the efficiency of irrigation. Still one drawback to sprinkler irrigation is wet foliage and the longer the leaves stay wet, the more likely we are going to have a disease problem. So with sprinkler irrigation we increase the efficiency of our water application, but we increase the disease pressure on our crop.
To increase the efficiency of water applications we must realize that too much water is just as bad, if not more so, than not enough water. The only way plants can take up water is if oxygen is present in the root zone. Also, understand that the most effective roots are in the top 6-12 inches of the soil, as this is where the greatest oxygen levels are. So when we saturate the root zone, we essentially make water unavailable to the plant until oxygen re-enters the root zone.
Over the years we have shown that drip irrigation can greatly improve water use efficiency and in addition, the plant foliage stays dry. Still drip is not for every crop, but it can work for potential high value crops like melons, tomatoes and peppers and maybe a few specialty crops. Drip can be made even better with the addition of plastic mulch. In 1995 we were able to produce 645 cartons of cantaloupes per acre using four inches of water with a drip/plastic mulch system as opposed to 300 using furrow irrigation and 25 inches of water (table 1).
|Irrigation system||Amount of water used; inches||Yield; cartons/acre|
|Drip and plastic mulch||4.0||645|
Furthermore, sprinkler systems can be made more efficient through the use of plastic. Data collected in 2002 in La Pryor on watermelons showed that plastic could drastically improve the efficiency of the water application (table 2).
|Plastic covered beds||50,642|
Still even though drip and plastic can increase the efficiency of water applications and reduce the amount of water used, this is not always true. Case in point was a comparison of sorghum grown under three irrigation regimes in 2001.
|Irrigation system||Amount of water use; inches||Yield; lbs/acre||Gallons of water to produce a pound of sorghum|
The drip yield was the highest, but we applied more water with the drip than the pivot. We are not sure if the pivot yield would have approached the yield of the drip had the same amount of water been applied. Still in this study we produced one pound of sorghum for 31 gallons of water with the drip as opposed to 36 for the pivot and 40 for the furrow.
Lastly, it should be noted that the most efficient water use techniques, i.e. drip and plastic mulch, are best adapted for high value crops. By the same token, we should not attempt to “skimp” on water for high value crops. Be it spinach or melons, it is basically water we are selling. Hence, we cannot afford to permit undue stress and allow significant yield reduction to take place.
Publication updated April 2011