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10 AGRONOMY NEWS | |||||||||||||||||||
| Dry Bean Response To Zinc Foliar application on irrigated dry beans in southwestern Colorado increased yield in one out of two years. Dry bean is an important crop in Colorado. It ranks fifth in acreage and total value in Colorado and fourth in the U.S. in production. In southwestern Colorado, dry bean is produced mostly under dryland conditions but much higher yields can be achieved with supplemental irrigation. Most agricultural soils in southwestern Colorado have relatively high pH (7.0 to 8.0) and are low in organic matter and available P. High pH and low organic matter are among the factors that favor the development of Zn deficiency. Zinc deficiency causes chlorosis in bean plants and can delay maturity and reduce seed yield. Khan and Soltanpour (Khan, A., and P.N. Soltanpour. 1978. Factors associated with Zn chlorosis in dryland beans. Agron. J. 70: 1022-1026) attributed chlorosis in dryland dry bean in southwestern Colorado to high soil P/Zn ratio and a high incidence of root rot disease. The chlorotic bean plants were situated lower on the slope than the green plants, which led the authors to speculate that the higher soil moisture in lower areas may have increased P availability. Soil Zn level was about the same, 0.5 ppm in the areas with green or chlorotic bean plants. Spraying the chlorotic plants with a 1% Zn solution removed chlorosis and increased bean yield by 18 to 92%, but not up to the yield level of the healthy plants. The difference in yield between the green plants and those sprayed with Zn was attributed to the higher incidence of root rot in the chlorotic plants. Root rot resistant pinto bean varieties have been released since 1981 and are now widely grown in southwestern Colorado. A field experiment was initiated in 1999 to determine the effect of Zn application rate and method on irrigated pinto bean yield in southwestern Colorado. `Bill Z' pinto bean was planted in early June at approximately 22 seeds m-2 in 1999 and 2000 at the Southwestern Colorado Research Center at Yellow Jacket, CO. A second variety, `Poncho' was included in the 2000 experiment. The soil type was Wetherill silty clay loam. Zinc sulfate was broadcast shortly before planting beans in both years at 5 and 10 lbs Zn/acre and incorporated into the soil with a field cultivator. Foliar spray of a 7% zinc sulfate solution was made at the same rates with a 3-m boom sprayer four to five weeks after planting. Bean seed yield was much higher in 2000 (2936 lbs/acre) than in 1999 (2120 lbs/acre), probably due to better irrigation water management in 2000. No symptoms of zinc deficiency were visible before or after the foliar spray in any of the treatments in 1999 or 2000. However, a foliar application of 5 lbs Zn/acre resulted in significantly higher Bill Z seed yield in 1999 compared to the control (over 500 lbs/acre more). The broadcast treatments had no yield effect in 1999. Zinc application rate or method did not affect Bill Z or Poncho seed yield in 2000. Future studies will include shallower soil sampling and a close look at soil spatial variability since chlorosis often occurs in patches in bean fields in southwestern Colorado. Table 1. Soil test results
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