=Paper=
{{Paper
|id=Vol-1498/HAICTA_2015_paper72
|storemode=property
|title=Multi-species Cover Crop Biomass Evaluation Using a Hand-held Normalized Difference Vegetation Index (NDVI) Sensor and Photosynthetically Active Radiation (PAR) Sensor
|pdfUrl=https://ceur-ws.org/Vol-1498/HAICTA_2015_paper72.pdf
|volume=Vol-1498
|dblpUrl=https://dblp.org/rec/conf/haicta/VasilikiotisGZN15
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==Multi-species Cover Crop Biomass Evaluation Using a Hand-held Normalized Difference Vegetation Index (NDVI) Sensor and Photosynthetically Active Radiation (PAR) Sensor==
https://ceur-ws.org/Vol-1498/HAICTA_2015_paper72.pdf
Multi-species Cover Crop Biomass Evaluation Using a
Hand-held Normalized Difference Vegetation Index
(NDVI) Sensor and Photosynthetically Active Radiation
(PAR) Sensor
Christos Vasilikiotis1, Athanasios Gertsis2, Konstantinos Zoukidis2 and Ali
Nasrallah3
1
Department of Environmental Systems Management, Precision Agriculture Laboratory,
Perrotis College, American Farm School, Thessaloniki, Greece, e-mail: cvasil@afs.edu.gr
2
Department of Environmental Systems Management, Precision Agriculture Laboratory,
Perrotis College, American Farm School, Thessaloniki, Greece
3
Mediterranean Agronomic Institute of Chania (MAICh), Alsyllio Agrokepio, 1 Makedonias
str. PO Box 85, Chania 73100, Crete, Greece
Abstract. Cover crops are essential in agricultural management and especially
in organic farming for protecting the soil from erosion, competing with weeds,
preventing evaporative losses and improving soil quality and fertility. The
choice of cover crop species is crucial in achieving the highest level of weed
suppression and soil fertility enhancement. Cover crop systems with rye or
mixtures of legumes and grasses were set up in a randomized complete block
design in Northern Greece. A hand held sensor was used to measure
Normalized Difference Vegetation Index (NDVI) of the cover crop plots with
parallel measurements of light interception with a PAR sensor, and destructive
biomass determination. Weed biomass was also determined for each cover
crop mixture. Multi-species cover crops produced higher total biomass than
single-species cover crop systems. All cover crop systems evaluated were able
to suppress weeds. Remote sensing results showed that NDVI could be used to
estimate the total biomass of single cover crops but not cover crop mixtures.
Keywords: cover crops, biomass, weed suppression, NDVI (Normalized
Difference Vegetation Index), light interception, PAR, organic agriculture.
1 Introduction
A key issue in organic agriculture is weed suppression to prevent competition with
cultivated crops. The use of chemical herbicides is not allowed in organic agriculture,
creating a great need to enlist cultural or mechanical methods to control weeds.
Mechanical methods include plowing and frequent use of hoeing, disking, harrowing
or cultivating (Liebman and Davis, 2009). Mechanical disturbance of the soil
increases the risk of soil erosion and exposes lower soil layers to increased oxidation
resulting in loss of CO2 (Rodale Institute, 2012). Cultural weed control methods
include intercropping, crop rotations and the use of cover crops (Liebman and Davis,
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2009). Cover crops are crops planted with the sole purpose of protecting the soil,
competing with weeds and improving soil quality and fertility (Clark (ed.), 2007).
Cover crops provide a wide range of benefits. They help reduce soil erosion, improve
soil quality, control weeds, assist with biological control and enhance soil fertility
(Dabney et al., 2001; Worsham, 1991). Single species or multi-species cover crop
mixtures can be used depending on the agroecological zone and the type of farming
system used (Wortman et al., 2012). The choice of cover crop species is crucial for
the achieving the highest level of weed suppression and soil fertility enhancement.
Multi-species cover crop mixtures containing both legume and grass cover crops
have been shown to have increased productivity and resilience compared to single
species cover crops (Wortman et al., 2012). This effect appears to depend on the type
of cover crop mixtures used and the farming system and in some cases, no enhanced
weed suppression or increased productivity of the subsequent crop was observed in
multi-species cover crop mixtures when compared to single cover crops (Smith et al.,
2014).
A cover crop trial was set up where individual species or multi-species cover
crops were compared for their ability to suppress weeds and enhance soil fertility.
The effect of each cover crop system on weed species was monitored and the
biomass and diversity of weed species in each cover crop system was measured. To
avoid the need to use destructive methods of biomass estimation, a hand held NDVI
sensor was used. Remote sensing with NDVI sensors shows high correlation with
biomass in grasses (Serrano et al., 2000).
Total crop biomass was measured by collecting crop samples and the relationship
between normalized difference vegetation index (NDVI) from a hand-held sensor
and the estimated crop biomass was evaluated. The objective of the study was to
assess the ability to monitor the development of cover crop mixtures and be able to
estimate final crop biomass through the use of non-destructive NDVI sensors. Partial
results are reported in this paper.
2 Materials & Methods
2.1 Experimental Design
The cover crop trial was set up at Zannas Farm owned by the American Farm
School, which is located in Chalkidona, Greece, with annual precipitation of 450
mm. The experimental design was a Complete Randomized Block Design (CRBD)
with four blocks and six treatments within each block. The size of each plot was 30 x
9 m.
Five cover crop systems were used; a) AVEX + Rye, b) TRITIMIX, c) Vetch +
Oats, d) Rye, e) Lollium, and f) a non-cultivated fallow as a control. The crop
composition of each multi-species mixture is listed in Table 1. The two crop mixtures
AVEX and TRITIMIX were provided by the seed company Fertiprado in Portugal.
The field was cultivated and planted in mid-January. The establishment of the cover
crops was originally planned for late October, but due to unusual wet weather in
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Northern Greece during the months of October to December we were not able to
prepare the fields and plant before January.
Table 1. Composition of cover crop mixtures
Cover crop Original cover crop species Added species
misture
AVEX + Rye Avena strigosa, Lollium multiflorum Vicia vilosa, 12.5% rye (Secale
Vicia Sativa, trifolium suaveolens, trifolium cereale)
squarrosum, trifolium bersim
TRITIMIX Triticum secale, Lollium multiflorum, Vicia vilosa,
Vicia sativa, Trifolium suaveolens, Trifolium
squarrosum, Trifolium bersim
Vetch + oats Vicia sativa (80%) 20% oats (Avena sativa)
The seeding rate used listed in Table 2. There was no fertilizer added to the plots.
Table 2. Seeding rate of cover crops
Cover crop mixture Kg/ ha, Kg/ha,
primary added crop
mixture
AVEX + Rye 61 9
TRITIMIX 70 β
Vetch + Oats 56 14
Rye 70 β
Lollium 70 β
2.2 NDVI and incident Photosynthetically Active Radiation (PAR) light
monitoring
NDVI monitoring was performed using an NDVI hand-held sensor. PAR light
above and below the cover crop canopy was measured with a canopy analysis system
(Delta-T Devices SunScan SS1) and the percent of PAR light intercepted (Li %) was
calculated using equation 1.
ππ΄π
! (1)
πΏπ Β % = 1 β β 100 Β .
ππ΄π
!
Where Li = PAR light intercepted, PARt = PAR transmitted through the canopy,
PARb = PAR beam incident upon the canopy.
2.3 Field biomass sampling
In early May, at the full flowering stage for most crops, three samples from each
plot were harvested using a 0.5m*0.5m square frame. The weeds were separated and
the samples were dried at 60Β°C to a constant dry weight.
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2.4 Statistical analysis
Statistical analysis was performed using JMP Pro v.11.0, SAS Institute Inc.
3 Results & Discussion
All five cover crop systems evaluated were able to suppress weed growth in most
experimental plots. The cover crop with the highest biomass was TRITIMIX, which
was significantly higher than the single-species cover crops Lollium and Rye, with an
estimated biomass of 12,470 kg/ha (Table 3.). AVEX+Rye and Vetch+Oats had the
second largest biomass, but they were not significantly different from Lollium or Rye
(Table 3).
a
b
c
Fig. 1. The three photos illustrate the experimental plots with cover crops (a, b) and the non-
cultivated fallow plot (c).
Light interception by the cover crops ranged from 92.5% for Vetch+Oats to 38.3%
for Rye (Table 3). Even though Rye allowed more radiation to penetrate its canopy,
there were no weeds detected in the Rye plots, possibly due to the allelopathic
properties of Rye.
647
One possible explanation for the small differences detected is that the cover crops
were planted late. This prevented the legumes in the multi-species cover crops from
optimal development, while the grass species were better able to develop in the
colder temperatures of January. Legumes in the multi-species cover crops did not
perform as well as grass species and contributed less than their full potential in total
biomass (data not shown).
Table 3. Biomass, NDVI and % Li of cover crops before termination.
Weed
Biomass
Cover crop Biomass (kg/ha) (kg/ha) NDVI Intercepted PAR (Li %)
TRITIMIX 12,470 a ND* 0.63 b 64.9 a,b
AVEX + Rye 10,335 a,b ND* 0.69 a 74.9 a,b
Vetch+Oats 9,910 a,b ND* 0.71 a 92.5 a
Lollium 7,105 b,c ND* 0.69 a 60.6 a,b
Rye 5,950 b,c ND* 0.61 b 38.3 b,c
Fallow 2,630 c - 0.36 c 20.9 c
Levels not connected by the same letter are significantly different (LSD at the 5% level)
*ND = weeds not detected
Using a regression analysis of the relationship of NDVI with crop biomass found that
it was not statistically significant, when analyzing all field plots (Fig. 2).
15000
Biomass (kg/ha)
10000
5000
0
0.3 0.4 0.5 0.6 0.7 0.8
NDVI
Fig. 2. Regression analysis of biomass vs. NDVI of all cover crops.
When single cover crop systems were analyzed though, the relationship of NDVI
and crop biomass was statistically significant for the single cover crop species plots
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(Table 3.). A strong regression relationship was found for Lollium (R2=0.94) and for
Rye (R2=0.81). A similar relationship was found in the fallow plots, which were not
cultivated and only weeds were grown. The inability to obtain a good regression
relationship between NDVI and crop biomass can be attributed to the complex
canopy structure of densely planted cover crop mixtures, which contain grasses and
legumes. Grains, such as rye and oats grow taller, while some of the trifolium species
of legumes remain lower in the canopy. As leaf area index increases, the regression
relationship becomes weaker and NDVI cannot be used to predict biomass reliably
(Serrano et al., 2000).
Table 3. Results of the regression analysis of biomass vs. NDVI for individual cover crops.
Parameter R2
All field plots Biomass vs. NDVI 0.45*
Lollium biomass vs. NDVI 0.94*
Rye biomass vs. NDVI 0.81 ns
Tritimix biomass vs. NDVI 0.34 ns
Vetch-oats biomass vs. NDVI 0.42 ns
Avex+Rye biomass vs. NDVI 0.47 ns
Fallow biomass vs. NDVI 0.99*
* Significant at the 0.05 probability level.
4 Conclusions
All cover crop systems studied performed well in producing sufficient biomass
and suppressing weed development in the experimental plots. Multi-species cover
crops were more productive and demonstrated the potential to provide higher
biomass and very satisfactory weed suppression. In terms of using remote sensing to
monitor cover crop development, the complex canopy structure of a densely planted
multi-species cover crop, presents a greater challenge in using an NDVI sensor as a
monitoring device. Further studies will be required to determine a method of using
NDVI sensors in the ground and/or aerial measurements to estimate biomass in
multi-species cover crops. The handheld NDVI sensor along with the canopy
analysis system (PAR and Li) can be used successfully in estimating very efficiently
the biomass in single cover crops systems.
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