Strawberry Plasticulture - Mid-week advisory (3/13/02)
Vol. 3 No. 21 - Barclay Poling, Editor & Ext. Small Fruit Specialist, NC State

In this issue:
-1. Weather outlook (be sure row covers are OFF - daily highs much warmer now)
-2. Nutrition - low initial petiole nitrate levels at Clayton

-1. Weather outlook (Raleigh - AOL.com source)

Overall, there is no immediate prospect for frost/freeze. Row covers should be off. Warmer daily temperatures expected Thur-Fri could substantially elevate crop temperatures beneath row cover into 90s during the day (don't want this!). Relatively calm winds in the early part of the day Thursday may provide best opportunity for spraying over next several days. Precipitation returning by the weekend.

Important to make fungicide application for botrytis control at 10% bloom - we are going to be at this stage at Clayton by the weekend.

-2. Nutrition and tissue sampling
We have gotten back results from our tissue analysis from NCDA Agronomic Division (sample submitted March 5 - after row covers came off). In North Carolina, you can view your results at: http://agronomy.agr.state.nc.us/ . I noted that a Chandler plot where the canopy looked a bit washed out and had the appearance of needing nitrogen gave an initial reading of 480 ppm Nitrate N. However, plants in nearby rows that "looked healthier" also had low readings (approx. 500 ppm). We have also encountered low boron (B), and have made an injection this morning of 0.125 lb B/Acre. Since our calcium was also low, we injected calcium nitrate at 1 lb N/day/Acre (7 lb N/week/A). We are now taking a second tissue sample late this week, and hopefully, we'll have petiole nitrate values that are in the range of 3,000 ppm

Early in the season (right now for ENC, Sandhills, and lower piedmont) the Agronomic Division will normally recommend that you follow a program of applying 5.25 lb N/week or 0.75 lb N/day at the outset of the season, but because of larger plant size this year, an initial feeding at 1.0 lb N/day, or 7 lb N/week/A is sensible. Your second tissue sample report (after you've made an initial fertilizer injection) will tell you whether you need to make any adjustments in N feeding. For example, if your second report shows that petiole nitrates are below 3500 ppm, you will probably get a recommendation to go up on your N feeding rate. But, If the second report shows that your petiole nitrate nitrogen concentrations are above 3500 ppm, then you will continue feeding at the same level. It is rare that the Agronomic Division would recommend lowering your N feeding rate below 0.75 lb/day this early in the season. However, if in the third week of bloom you have a very high petiole nitrate, there will be a recommendation made to decrease your N feeding to 0.5 lb N/acre/day. The initial petiole nitrate levels before any drip fertilization (fertigation) in late February/early March are usually down around 1500 - 2000 ppm. That is normal and to be expected. After feeding they go up significantly (see chart above).

In most situations, there will be no reason to inject P or K through the drip system if proper amounts were applied in the fall. The main nutrient of concern would be N (and any other indicated by tissue testing to be low). From 30 to 60 lb N/acre need to be injected with the highest rate on deep sandy soils and the lower rate on heave textured soils. Medium-textured soils would need an intermediate amount (45 lb/acre). Historically, we have applied the 60 lb N/acre at Clayton in three applications with 3 weeks between applications. We apply the first one about the middle of March (now) when visible spring growth commences. The last application is usually about the last of April, shortly after harvest is in full swing. This approach has been quite successful and given yields and fruit quality equivalent to or superior to other approaches we have evaluated. However, making weekly applications are is fine for most growers (e.g. 7lb N/week/A = 1 lb N/day/A).

For the 30% Liquid N you only need to determine the total lbs of N you wish to deliver, and divide by 3.25 to get the number of gallons of this liquid fertilizer needed. For example, if the grower needs to inject 10 lbs of N, then divide 10 by 3.25 = 3.07 gallons needed. This product contains 3.25 lb of actual N per gallon.

The cheapest fertilizer N source to dissolve in water for injection is ammonium nitrate if tissue testing indicates all other nutrients are sufficient. Potassium nitrate is also very soluble if additional K is needed. Calcium nitrate is an excellent N source, but it is much less soluble in water. In any case, use a greenhouse grade of fertilizer that does not have a coating (usually clay) to protect it from absorbing water from the atmosphere. This coating can plug screens in the delivery line and can plug emitters in the drip tube if it bypasses the screens.

E. Barclay Poling, Small Fruit Specialist
Campus Box 7609
Kilgore Hall - Office 252
NC State University
Raleigh, North Carolina 27695-7609
919.515.1195
919.515.2505 (fax)
919.418.9687 (mobile)

Small Fruit web site:

http://intra.ces.ncsu.edu/depts/hort/berrydoc/

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