Use of remote sensing to determine mid-season nitrogen

needs in rice systems

Bruce Linquist and Telha Rehman

CALASA conference

Fresno, CA

February 4 and 5, 2020

California Rice Systems

• 200,000 ha (500,000 ac)• Mostly in the Sacramento Valley

• Yields: among the highest in the world• 9.5 to 10 t/ha (8500-9,000 lb/ac)

• Heavy clay soils• unsuitable for other crops

• Water-seeded system

GlennButte

Yolo

Colusa

Sacramento

Sutter

Yuba

Placer

Nitrogen management

• Total: 170 - 200 kg N/ha (150 - 180 lb N/ac)

• N sources• Aqua-ammonia (NH3)

• Preplant

• Starter N-P-K blend• Preplant to 30 DAS

• Ammonium sulfate/urea• 30-35 kg N/ha

• Top dress 45-55 DAS (during panicle initiation – PI)

Nitrogen management recommendation

• Recommendation• Apply your total N needs for average season using aqua NH3 and Starter.

• Aqua-NH3

• Injected 3-4 inches below soil surface/ field kept flooded

• efficient (50-60% Nitrogen Uptake Efficiency)

• Apply as much of the total N rate as aqua as possible

• Starter (N-P-K blend): Lowest amount of N possible but apply P, K and other nutrient needs

• At panicle initiation (PI) access the crop for N needs and apply if necessary

• Why PI?

Why is PI a good time to access N status?

• All of the early season fertilizer N has been taken up by the crop

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Preplant N Rate (kg/ha)

Davis-16

RES-16

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Williams-17

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Biggs-18

Marysville-18

Nicolaus-18

LaHue et al., 2016PI

Why is PI a good time to access N status? (cont)

• Small window of opportunity remains to apply N to maximum benefit.

Linquist and Sengxua, 2003

Accessing the crop at PI

directindustry.com calricenews.org geoagri.com micasense.com

SPAD meter Leaf Color Chart GreenSeeker (NDVI) Drone equipped with sensors

Increasing speed and area accessed

Accessing the crop at PI

directindustry.com calricenews.org geoagri.com micasense.com

SPAD meter Leaf Color Chart GreenSeeker (NDVI) Drone equipped with sensors

Increasing speed and area accessed

• Current technologies being used• Takes a lot of time and only covers a small area of the field.

• Problem: Most growers still guessing

• Objective: develop robust tools to rapidly access crop N status mid-season

• Normalized Difference Vegetation Index (NDVI)

• Normalized Difference Red Edge (NDRE)

NDVI vs NDRE

• When only N is limiting

• NDVI good estimate of N uptake • Biomass X N concentration

Rehman et al., 2019

What does NDVI measure in rice at PI?

What do NDVI/NDRE images tell us?

• By themselves • General indicator of plant stand

• Scouting required to determine problem• Low N

• Weeds

• Thin stand

• Pest/disease damage

• Narrowing it down to a nitrogen deficiency• Response Index

What is a response index?

Objective

• Develop methodology using NDVI or NDRE to determine if rice requires a top-dress of N at panicle initiation.• Use Response Index in relation to yield response to a top-dress N application

Methodology

• 14 site-years (12 on-farm)• 3 in 2016• 3 in 2017• 4 in 2018• 4 in 2019

• Treatments• Preplant N rates

• -ranged from 0 to excessive (210-235 kg N/ha)

• Top-dress at PI• 0 and 34 kg N/ha

• NDVI (NDRE in 2018, 19) taken at PI before top-dress• Drone-MicaSense camera (NDVI and NDRE)• GreenSeeker (NDVI only)

• Harvested all plots for yield

Sensitivity of NDVI & NDRE to N uptake at PI

R² = 0.60

R² = 0.63

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PI Total Nitrogen Uptake (lbs/acre)

NDVI - Drone vs. GreenSeeker

GreenSeeker NDVI

Drone NDVI

R² = 0.63

R² = 0.73

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PI Total Nitrogen Uptake (lbs/acre)

Drone NDVI vs. NDRE

Drone NDVI

Drone NDRE

Sensitivity of NDVI & NDRE to N uptake at PI

R² = 0.60

R² = 0.63

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PI Total Nitrogen Uptake (lbs/acre)

NDVI - Drone vs. GreenSeeker

GreenSeeker NDVI

Drone NDVI

R² = 0.63

R² = 0.73

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PI Total Nitrogen Uptake (lbs/acre)

Drone NDVI vs. NDRE

Drone NDVI

Drone NDRE

Developing the response index

• Non-limited area:• Highest preplant N rate

at site• Confirmed excessive

• Test area:• All other preplant N

rates

R² = 0.97

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Yield response vs NDRE (drone)(2018-2019)

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Drone NDRE Response Index

Yield response vs GreenSeeker Response Index(2016-2019)

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GreenSeeker NDVI Response Index

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GreenSeeker NDVI Response Index

Likelihood of a yield response

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GreenSeeker NDVI Response Index

Likelihood of a Positive Yield Response (%)

WHY?

Soil N supply

• N uptake: PI to maturity• not related to fertilizer N rate

• Highly variable

• Not related to total soil C

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l N U

pta

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(kg

N/h

a/d

ay)

Preplant N Rate (kg/ha)

Davis-16

RES-16

Nicolaus-17

Williams-17

Arbuckle-18

Biggs-18

Marysville-18

Nicolaus-18

R² = 0.2586

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Total Phenols (mg/ 100mg OC)

Post-PI N uptake related to phenols in soil carbon

R² = 0.2586

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Total Phenols (mg/ 100mg OC)

Post-PI N uptake related to phenols in soil carbon• In rice systems, phenolic compounds

covalently bind nitrogen into recalcitrant forms (Olk et al., 2006).

• Anaerobic decomposition of crop residues may be the key • promotes the accumulation of

phenolic lignin residues

• hence the covalent binding of soil N.

Future research

• Is phenol accumulation the key?

• If so, what affects phenol accumulation and how can we mitigate?• Soil type?

• Extended periods of anaerobic conditions seem to favor (Olk et al., 2009)

• Winter fallow management• Straw and flooding

• Understanding these dynamics may help fine tune mid-season N recommendations

In Summary

• GreenSeekers and drones are useful tools• provides a more accurate assessment of crop nitrogen needs.

• However,• Positive yield responses still observed when RI < 1.10.

• Still room for improvement

• Understanding the role of straw and winter flood management on phenol accumulation and binding N may help refine our recommendations

Thank you

Nitrogen Response Trials

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Drone NDRE Response Index

Likelihood of a Positive Yield Response

Nitrogen Response Trials

Four sites: Arbuckle,

Marysville, Davis, and RES

Main Plot Treatment:

Six N rates ranging from 0-210 lbs

N/acre

Sub Plot Treatment:

Top dress N rates of 0 or 30 lbs/acre

applied at PI

Experiments were arranged

according to a split plot

randomized complete block design (RCBD)

Olk et al., 2006

• This review summarizes independent reports of yield decreases in several agricultural systems that are associated with repeated cropping under wet or submerged soil conditions. Crop and soil data from most of these agroecosystems have led researchers toattribute yield decreases to a reduction in crop uptake of N mineralized from soil organic matter (SOM). These trends are most evident in several long-term field experiments on continuous lowland rice systems in the Philippines, but similar trends are evident in a continuous rice rotation in Arkansas, USA and with no-till cropping systems in North American regions with cool, wet climatic conditions in Spring. Soil analyses from some of these systems have found an accumulation of phenolic lignin compounds in SOM. Phenolic compounds covalently bind nitrogenous compounds into recalcitrant forms in laboratory conditions and occurrence of this chemical immobilization under field conditions would be consistent with field observations of reduced soil N supply. However, technological shortcomings have precluded its demonstration for naturally formed SOM. Through recent advances in nuclear magnetic resonance spectroscopy, agronomically significant quantities of lignin-bound N were found in a triple-cropped rice soil in the Philippines. A major research challenge is to demonstrate in the anaerobic agroecosystems that these lignin residues bindsufficient quantities of soil N to cause the observed yield decreases. A key objective will be to elucidate the cycling dynamics of lignin-bound N relative to the seasonal pattern of crop N demand. Anaerobic decomposition of crop residues may be the key feature of anaerobic cropping systems that promotes the accumulation of phenolic lignin residues and hence the covalent binding of soil N. Potential mitigation options include improved timing of applied N fertilizer, which has already been shown to reverseyield decreases in tropical rice, and aerobic decomposition of crop residues, which can be accomplished through field drainage or timing of tillage operations. Future research will evaluate whether aerobic decomposition promotes the formation of phenol-depleted SOM and greater in-season N mineralization, even when the soil is otherwise maintained under flooded conditions during the growing season.

Olk et al., 2009

• Soil C stocks in the Grand Prairie region of eastern Arkansas have declined under the prevalent 2-yr rotation of rice (Orzya sativa L.)-soybean [Glycine max (L.) Merr.]. Continuous rice cropping could promote soil C sequestration, but in previous work continuous rice averaged 19% less grain yield than rice following soybean, apparently due to N deficiency. To further study N cycling, microplots were imbedded during the rice phase of a crop rotation field study in 2002 and 2004. Urea labeled with (15)N was applied preflood, when all N fertilizer is conventionally applied. Crop biomass was often smaller with continuous rice than with rice following soybean (sampled both years) and rice following corn (Zea mays L.) (sampled only in 2004), although the difference varied by growth stage. Crop uptake of native (14)N, presumably mineralized from soil organic matter, was inhibited with continuous rice in both years. This trend was clearest at harvest (P = 0.02), when continuous rice averaged 40 kg (14)N ha(-1) less uptake than rice in the two rotations. Fertilizer (15)N averaged only 30% of total crop N and its uptake differed among cropping treatments only in 2002. At harvest, soil C with continuous rice cropping was enriched by 42% with syringyl phenols and by 83% with cinnamic phenols compared with the rotations. These enrichments appear unrelated to estimated input rates of lignin-derived phenols. Results support the hypothesis that continuous rice cropping promotes the binding of soil N by lignin-derived phenols, thereby inhibiting N mineralization and late-season crop growth. Similar observations were reported for tropical rice production, suggesting that the responsible soil processes might be common in continuous rice cropping.

Olk et al., 2009

• Soil phenols have been implicated as inhibitors of soil N cycling within many agroecosystems, including irrigated lowland rice (Oryza sativa L.). To quantify the effects of crop management on temporal patterns of phenol accumulation in lowland rice soils, we measured phenol concentrations in two humic fractions at two crop growth stages in each growing season during a 4-yr field study at the International Rice Research Institute (Philippines). Samples were collected from two double-crop rotations (continuous rice and rice-maize [Zea mays L.]) with two N fertilizer rates (0 and nonlimiting), and with either aerobic or anaerobic decomposition of incorporated crop residues. Phenols were determined by tetramethylammonium hydroxide thermochemolysis. Compared with the other field treatments, anaerobic decomposition of crop residues with continuous rice and nonlimiting rates of N fertilizer promoted a gradual increase in the relative enrichment of phenols in the mobile humic acid fraction during the 4 yr. The level of enrichment varied among phenol compounds, developing the fastest and becoming most pronounced with the smaller molecules of molecular weight 168 or less. Anaerobic decomposition had less effect on phenol enrichment for continuous rice cropping without N fertilizer. No phenol enrichment was found with anaerobic decomposition of rice residues in the rice-maize rotation. Our results are consistent with previous findings of inhibited mineralization of humic N with anaerobic decomposition, continuous rice, and nonlimiting rates of N fertilizer. Rotation of maize with rice or other techniques to ensure aerobic decomposition of crop residues may help mitigate or prevent phenol accumulation.