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Fluid Journal : Fall 2012
Table 3: Average yields and estimates of macronutrients removed with melon fruits, onions and grapefruits grown on calcareous soils in south Texas. Yield Yield N P K Ca Mg S tons/A lbs/A Melons 2009 15.2a 79.7b 15.2a 98.8b 32.2b 5.1b 2011 19.8a 92.3a 18.2a 121.4a 43.5a 7.9a Onions 2009 10.2b 44.2b 15.3b 55.0b 26.9b 3.7a 2011 13.8a 61.3a 19.4a 74.6a 31.9a 4.9a 27.2a Grapefruit 2011 12.2a 28.9 8.1 66.1 15.6 5 2.5 crops (melons, onions, and grapefruit). This is probably the result of nutrient remobilization from leaves as developing fruits and bulbs become stronger sinks for nutrients and assimilates. Tissues sampled in 2011 also had slightly lower nutrient concentrations than those sampled in 2009 (Table 2). At the time of grapefruit harvest, leaf mineral nutrient concentrations were significantly lower than recommended levels (Table 2). Yields. Average melon fruit yields in 2011 ranged from 15 to 20 t.acre-1 and were slightly higher compared to 2009. Fruit soluble solids ranged from 9.6 to 11.9 percent and were highly correlated with fruit K concentrations. This is consistent with previous greenhouse and field observations on melons. Sweet onion bulb yields showed significant variability across years and even within each growing season. Onion bulb yields in 2009 ranged from 7 to 13 tons/A, and from 10 to 16 tons/A in 2011. Grapefruit yields ranged from 290 to 321 boxes/A (average 311 boxes/A, or 12 ton/A fresh fruit). Removal rates. Estimates of nutrient removal amounts for melons and onions were significantly higher in 2011 than estimates for 2009 (Table 3). The 2011 removal estimates were also slightly higher than the averages reported for muskmelons in other regions under ideal growing conditions. These differences may be due to poor weather conditions (freeze events) during the growing season in 2009 and the generally low yields that year. Favorable weather conditions during the 2011 growing season and the associated higher fruit yields likely contributed to the higher removal rates. Average nutrient removal estimates for grapefruit in 2011 were 28.9, 8.1, and 66.1 lbs/A of marketable fresh fruit for N, P, and K, respectively. Macronutrients. Even though preplant soil macronutrient (especially K, Ca, and Mg) reserves were high in both years, a clear decline in tissue macronutrient contents during later stages of crop development was observed, indicating that nutrient supply was insufficient to maintain adequate tissue mineral concentrations (Table 2). This is plausible if competition for assimilates between roots and maturing fruits limits root activity and water/nutrient uptake. In this region, application of supplemental macronutrients (K, Ca, Mg) is generally not recommended due to the typically high soil test levels. Looking ahead High yields, high crop removal rates, and the declining trends in soil reserve levels over time highlight the need for a reassessment of fertilizer management practices, especially those aimed at achieving superior fruit quality. Continued sampling over multiple years, plus locations with varying weather conditions, soil types, and yield scenarios will be needed to establish realistic nutrient removal values that can be used to develop improved fertilizer management guidelines. CHELATE 10XL combines the benefits of 2 powerful chelating agents, EDTA and Citric Acid, creating the perfect balance to deliver maximum nutrition to the plant. learn more at: www.nulex.com Visit your Nulex Distributor or contact a sales representative at 800-831-4815 Dr. Jifon is Associate Professor of Crop Physiology at Texas A&M AgriLife Research Center in Weslaco, Texas.
Late Spring 2012