Fertilizer Value of Nitrogen in Irrigation Water for Coastal Vegetable Production

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1 Fertilizer Value of Nitrogen in Irrigation Water for Coastal Vegetable Production Michael Cahn, Laura Murphy, Richard Smith, Tim Hartz UCCE Monterey and UCD Plant Sciences

2 SWRCB SBX2 1 Pump and fertilize was proposed as a partial solution for remediating nitrate contamination of ground water Harter and Lund 212

3 How much fertilizer credit should be taken for nitrogen in irrigation water? Is N in water fully equivalent to fertilizer N? Does a low concentration of nitrate in water have fertilizer value? Does over-applying water for leaching salts affect N recovery? Does the form of N in water (nitrate vs ammonium) affect crop recovery?

4 Irrigation Manifold for Simulating Water with Varying Concentrations of N Nitrogen salts: Calcium Nitrate, Sodium Nitrate, Ammonium Sulfate Salts proportioned to maintain sodium adsorption ratio (SAR) between 1.8 and 2.4

5 Water N treatments were applied by drip # Treatment Description Unfertilized control (approximately 2 PPM NO3-N in the irrigation water) Standard Fertilizer (15 lb N/Acre) 12 PPM NO3-N in irrigation water 22 PPM NO3-N in irrigation water 42 PPM NO3-N in irrigation water 42 PPM mineral N (12 PPM NO3-N and 3 PPM NH4-N in irrigation water)

6 Two irrigation rates were evaluated Applied Water Irrigation Treatment Crop ET Sprinkler Drip Total inches Standard Water Rate 11% High Water Rate 16%

7 How is nitrate in irrigation water converted to applied N? lbs of N/acre= applied water (inches) x NO 3 -N conc (ppm) x.23 Fertilizer N value Applied NO 3 -N concentration Irrigation Treatment Water 12 ppm 22 ppm 42 ppm inches lbs N/acre ---- Standard Water Rate High Water Rate

8 Nitrogen in water affected both plant size and N content of tissue 42 ppm N 2 ppm N

9 Biomass yield and Crop N recovery (summer lettuce 213) Biomass Yield Crop N uptake Biomass yield (lbsx1/acre) ppm 12 ppm Anticrustant 22 ppm 42 ppm Fertilizer Water N, Standard Water Rate Fertilizer N, Standard Water Rate Water N, High Water Rate Fertilizer N, High Water Rate Crop N uptake (lbs N/acre) Water N, Standard Water Rate Fertilizer N, Standard Water Rate Water N, High Water Rate Fertilizer N, High Water Rate Total Applied Nitrogen (lbs/acre) Total Applied Nitrogen (lbs/acre)

10 Crop uptake of N was similar for NH 4 and NO 3 -N sources in irrigation water (summer lettuce, 213) 12 NO 3 b b Crop N uptake (lbs N/acre) NO 3 + NH 4 a a Standard Water High Water Water N treatment (42 ppm N)

11 Broccoli: Deep rooted + high N demand (> 25 lbs N/acre)

12 Broccoli Crop N Recovery 25 Crop N uptake (lbs N/acre) Water N, Standard Water Rate Water N, High Water Rate Fertilizer N, Standard Water Rate Fertilizer N, High Water Rate Total Applied N (lbs N/acre)

13 215 Trials (summer lettuce and fall broccoli trials) Is the N in irrigation water equivalent to fertilizer N? Does a leaching fraction (High Water Rate) affect crop N recovery similarly from water and fertilizer?

14 Treatments for 215 Lettuce Trial trt # N Source Fertilizer Fertilizer Fertilizer Fertilizer Water Water Water N in water ppm NO3-N Fertilizer N lbs N/acre

15 Two irrigation rates were evaluated Irrigation Treatment Crop ET Applied Water % inches Standard Water Rate High Water Rate

16 Lettuce Biomass Yield 9 8 Biomass (lbs/acre) Fertilizer N, Standard Water Rate Fertilizer N, High Water Rate Water N, Standard Water Rate Water N, High Water Rate Applied N (lbs N/acre)

17 Lettuce N Uptake 12 Crop N uptake (lbs N/acre) Fertilizer N, Standard Water Rate Fertilizer N, High Water Rate Water N, Standard Water Rate Water N High Water Rate Applied N (lbs N/acre)

18 Conclusions N in irrigation water has the same nutrient value for lettuce and broccoli as fertilizer sources of N Low concentrations of nitrate-n (12 ppm) in irrigation water are taken up by lettuce and broccoli Fertilizer value of NH 4 and NO 3 sources of N are equivalent Applying extra water for leaching can reduce N recovery from irrigation water, but N recovery was generally better than from fertilizer