High Tunnel Production of lettuce using paper mulch, bare ground and earth boxes

Crop Romaine Lettuce
Date Transplanted 2/14/00
Treatments Paper mulch, Bare ground, Earth Box (covered with black plastic mulch)
Plot Design One row of earth boxes;
Paper mulch and Bare ground treatments: Double rows; 8 inches between plants in row and 12 inches between double rows
Fertigation 20lbs/A of 20-20-20 on 2/21/00 and 3/3/00
Irrigation Hand Watering


Summary:
During the first few weeks, temperatures were 4-50F higher under paper mulch compared to bare ground. Temperatures were slightly higher (1-20F) in the earth box compared to the paper mulch treatments. Plants growing in the earth boxes grew significantly faster than plants in either bare ground or paper mulch treatments.

Plants in paper and bare ground treatments were watered significantly more times than those in the earth boxes. It was noted that lettuce plants grown on the outer row (edge row) were slightly larger than plants harvested from the two inner rows. This could be attributed to additional moisture from snow that was packed on the tunnel sides. Uneven hand watering throughout the growing season could also have contributed to the differences in the plant size.
Forty-five days after transplanting, sample leaves were harvested from each of the treatments and oven dried at 85C for 48 hours. Samples were then sent in for a tissue analysis. A standard ICP (Inductively coupled plasmas) analysis run as well as a nitrogen test was run. The results are shown in Table 1.


Table 1. Tissue Analysis:

 

P

K

Ca

Mg

Mn

Fe

Cu

B

Al

Zn

Na

Treatment

%

%

%

%

ug/g

ug/g

ug/g

ug/g

ug/g

ug/g

Ug/g

Bare

0.27

4.30

1.20

0.39

101

148

8

18

131

29

460

Paper

0.23

4.91

1.24

0.39

94

146

8

17

127

24

336

Earth Box

0.94

6.69

0.77

0.54

108

115

7

59

32

86

>2500


There were significant differences between the earth box, bare and paper treatments. Percent of P, K, & Mg and ug/g of B, Zn, and Na were significantly higher in the earth box treatments compared to the other two treatments. Al, Fe, and Ca levels were lower in the earth box treatments. No significant differences were noted between the bare and paper treatments. The very high levels of Na could be attributed to the coconut fiber media used in the earth boxes. Coconut fiber when analysed seems to have high levels of Na. The plant system may have very well picked up this from the media.

Harvest:
Lettuce plants growing in earth boxes matured faster than from the other two treatments. Lettuce 'heads' from the earth boxes was harvested on April 17th. . Harvests from the paper and bare ground treatments were made on May 12th 2000.
Ten 'heads' per treatment were harvested and weighed (Table 2). 'Heads' from the earth boxes were slightly heavier than those from the other two treatments, however differences were not significant among the treatments.

Taste test results seemed to suggest that lettuce grown in the earth boxes was sweeter than that from paper mulch and bare ground treatments.

Table 2: Lettuce weight (lbs)

Treatment: Earth Box Paper Mulch Bare Ground
(lbs/plant)      
  0.70 0.60 0.46
  0.69 0.59 0.55
  0.67 0.68 0.44
  0.70 0.48 0.50
  0.81 0.81 0.48
  0.59 0.55 0.49
  0.71 0.66 0.52
  0.70 0.70 0.48
  0.73 0.79 0.36
  0.67 0.69 0.44