Nitrogen Fertigation Frequency for
Drip Irrigated Broccoli
•
•
•
•
Dr. Jim Walworth
Dr. Tom Thompson
Mr. Scott White
Mr. Greg Sower
Objectives
• Determine effects of nitrogen rate and
frequency on
– yield
– quality
– nitrogen use efficiency
of subsurface drip-irrigated broccoli
Experimental Methods
• Field experiments at Maricopa Agricultural
Center during 1998-2000 growing seasons
• Drip tubing buried 8” deep in raised beds
• ‘Marathon’ broccoli direct-seeded, thinned
to 40,000 plants/acre
• Irrigated to maintain water tension at
8 to 10 cbars
• Nitrogen applied through irrigation system
Nitrogen Treatments
• Nitrogen application rates
– 1998-1999: 176 or 268 lbs N/a
– 1999-2000: 223 or 312 lbs N/a
– 2000-2002: 223 or 312 lbs N/a
• Fertigation frequency
– Daily
– Weekly
– Bi-weekly
– Monthly
200
Fertigation
Interval (days)
Cumulative N Applied (lb/ac)
150
1
7
14
28
100
50
0
0
20
40
60
80
100
120
300
Fertigation
Interval (days)
250
200
1
7
14
28
150
100
50
0
0
20
40
60
80
100
Days After Planting
120
Data Collection
• Broccoli heads hand harvested
ƒ Trimmed to ‘US Fancy’
ƒ Graded for diameter, weight, discoloration,
hollow stem
• Fertilizer N use efficiency
ƒ (N uptake in treated plots – N uptake from
unfertilized control plots)
7
6
1998-99
Marketable Yield (tons/ac)
5
1
7
14
28
4
3
2
N
Freq
N*Freq
1
0
12
10
178
268
1999-2000
8
1
7
14
28
6
4
N
Freq
N*Freq
2
0
12
10
223
NS
NS
NS
312
2000-01
8
1
7
14
28
6
4
N
Freq
N*Freq
2
0
**
NS
NS
223
312
N Rate (lb/ac)
**
NS
NS
5
1998-99
4
1
7
14
28
3
2
N
Freq
N*Freq
Head Diameter (in.)
1
0
5
178
NS
NS
NS
268
1999-2000
4
1
7
14
28
3
2
N
Freq
N*Freq
1
0
5
4
223
312
2000-01
1
7
14
28
3
2
N
Freq
N*Freq
1
0
NS
NS
NS
223
312
N Rate (lb/ac)
**
**
NS
Fertilizer N Use Efficiency (%)
100
1999-2000
80
1
7
14
28
60
40
20
0
N
**
Freq
**
N*Freq NS
223
100
312
2000-01
80
1
7
14
28
60
40
N
*
Freq
NS
N*Freq NS
20
0
223
N Rate (lb/ac)
312
Conclusions
• When N was applied daily, weekly, bi-weekly, or
monthly to subsurface drip-irrigated broccoli
– Broccoli yield and quality were affected by N rate, but
there were almost no significant effects from
fertigation frequency
– High-frequency fertigation is not an important
management variable sandy loam or finer textured
soils
• More work is needed on coarser soils and on
summer crops