A collaboration between

Acknowledgments

Acknowledgments

Funding provided by:

Guidelines and Webpage Design:

Daniel Geisseler, Ph.D.; UCCE Specialist in Nutrient Management; Department of Land, Air and Water Resources, University of California, Davis

Reviewers:

Bruce A. Linquist, Ph.D.; Project Scientist; Department of Plant Sciences, University of California, Davis

Randall Mutters, Ph.D.; Farm Advisor; University of California Cooperative Extension Butte County

William R. Horwath, Ph.D.; Professor of Soil Biogeochemistry and James G. Boswell Endowed Chair in Soil Science; Department of Land, Air and Water Resources, University of California, Davis

Support:

Asif Maan, Ph.D.; Branch Chief Feed, Fertilizer, and Livestock Drugs Regulatory Services, California Department of Food and Agriculture

Amrith Gunasekara, Ph.D.; Science Advisor to the Secretary; California Department of Food and Agriculture

Erika Lewis; Fertilizer Reserach and Education Program, California Department of Food and Agriculture

Last Update: September, 2015

Additional Information:

Rice Nitrogen Uptake and Partitioning

What about drill seeded rice?

Drill Seeded Rice

The application rates for N, P and K are the same as for water seeded rice; however, pre-plant fertilizer is generally not required. All of the N, P, and K should be applied just before permanent flood, 3-5 weeks after planting in the form of granular fertilizer.

As with water seeded rice, midseason applications are only done if necessary and should be based on a leaf color chart or chlorophyll meter readings. Applications should not be made after panicle initiation, which occurs approximately 55-60 days after planting. Contact your local farm advisor for more information.

California Fertilization Guidelines

Water Seeded Rice

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Preplant

Sowing

Tillering

Panicle
Initiation

Heading

Maturation

The decision of whether or not to top dress can be made based on sampling leaves for N concentration or using a leaf color chart or SPAD meter to estimate leaf N concentration. If the leaf N concentration is below the critical concentration yield reductions are likely. This can often be corrected using a top-dress N application.

Leaf Sampling

Leaf Nitrogen Content

Leaf Color Chart

Chlorophyll Meter

Preplant N

The optimal fertilization program depends on water management. With continuous flooding, N is generally applied pre-plant ^[N23]. When fields are drained early in the season for prolonged periods, a split application may be considered (See below).

Pre-Plant vs. Split Applications

Split applications with part of the N applied pre-flooding and the rest as a topdressing generally do not result in increased yields compared to a single pre-flooding application ^{[N1,

N15, N22]}.

Pre-plant N applications to rice, typically applied as aqua ammonia, do not increase the risk of nitrate leaching and high N use efficiencies can be achieved ^{[N9, N11]}. When the field is flooded soon after the application of the fertilizer, ammonium is not oxidized to nitrate. Ammonium, being a positively charged ion, does not leach as easily as nitrate. In addition, rice is grown in fields with high clay content or an impermeable layer, that considerably reduce downward movement of water and dissolved nutrients. In fact, Liang and coworkers ^[N6] found low nitrate concentrations below the rooting zone, suggesting that leaching of nitrate is not of concern. Furthermore, applying all N pre-plant is simple and requires less labor than other programs.

However, high pre-plant application rates result in high ammonium concentrations early in the season when plant uptake is still small, which may result in increased risk of lodging, disease and weed pressure. The possibilities for in-season adjustments are also more limited when rice N fertilizer needs are different than expected ^[N23].

When the field is drained early in the season (first 40 days), the N applications are best split and part of the N topdressed ^[N23]. Short drain periods for establishment (i.e. Leather's method) or weed control are normally not considered prolonged. In general, a prolonged period can be considered as longer than a week with water off the field. An example of a prolonged period is when fields are drained and allowed to dry to the point where the soil can support a vehicle. During a prolonged drain period, a considerable proportion of the ammonium still present from the pre-plant or starter application may be nitrified to nitrate. The nitrate not taken up by the rice plants until the field is flooded again is likely lost due to denitrification. In a survey of 22 fields, Linquist and coworkers ^[N11] found that on average 1.8 lbs/acre of nitrate-N were produced during each day a field was drained. A 10- to 11-day drain period, 1-2 weeks after planting, resulted in the accumulation of up to 30 lbs/acre nitrate-N in the top 6 inches of the soil profile ^[N11]. N uptake data suggested that about 60% of the nitrate was lost when the field was flooded again. Therefore, extended drain periods should be avoided, particularly in the first 40 days when fertilizer N is still in the soil.

Application Rate

A total N application rate of 150 lbs/acre is considered average ^[N21]. Maximum yields of up to 12,000 lbs/acre were obtained with application rates ranging from 140 to 190 lbs/acre ^{[N8, N9, N10]}. Due to site-specific factors, such as N mineralization potential of the soil, and yield expectations, the required fertilizer N may vary by location. Specialty varieties may also have lower N requirements due to lower yield potential and a higher risk of lodging. Contact your local farm advisor for more information.

Rice straw incorporation can increase the amount of N supplied by the mineralization of soil organic matter over the years, so that the N fertilization recommendation may be reduced by 10-20 lbs/acre when straw incorporation and winter flooding are consistently practiced after harvest ^{[N5, N7]}.

Due to variation, a good approach to an application rate for a particular field is to establish strips with different application rates down the length of the field using aqua rig. The rates applied in the strips should be 25 lbs/acre lower and higher than the rate typically applied to the field. The strips can then be harvested individually using a combine with a yield monitor and based on the differences in yield between the strips one can determine if the standard rate needs to be adjusted up or down. The strips should be located in representative parts of the field and this should be done over several years to get the most accurate rate possible.

Mode of Application

Fertilizer Type

Time of Application

Starter N

Topdress N

It is generally not recommended planning a for a mid-season topdress N application as research has shown it is most efficient to apply all the N at preplant. However, midseason applications are beneficial when the field is drained for a prolonged period during the early season (see Pre-plant N) or when a midseason leaf analysis indicates that N supply is insufficient.

Application Rate

Mode of Application

Fertilizer Type

Time of Application

Phosphorus (P₂O₅)

Soil Test