Boost Rice Yield by 8% with 20% Less Fertilizer: Variable-Rate Fertilization with DJI Multispectral Drone

 

When it comes to rice in Japan, the super-premium Koshihikari rice is considered the best representation of authentic Japanese food culture. However, Koshihikari rice is a low-yield rice variety which easily suffers from lodging and diseases. As an affordable alternative to Koshihikari rice, Hoshijirushi rice has higher resistance to diseases as well as higher yield. 

 

One of the important producing areas of Hoshijirushi rice is Kaizu Town of Kaizu City in Gifu Prefecture, which is located in the central part of Japan. With the majority of rice producers within the area being agricultural corporations, the annual revenue of local agricultural produce is estimated to be 5.2 billion yen (37.9 million USD), of which rice accounted for a quarter.

 

 

As the fertilizer is usually sprayed evenly on a large scale, rice producers often encounter the following pain points:

 

1. Over-fertilization occasionally happens when fertilizer is spread evenly on the entire field, which might cause nitrogen burns on seedlings, crop lodging in later stage, decrease in rice quality, and waste of fertilizer.
2. If conducting variable-rate fertilization with prescription maps generated from satellite imagery, the quality of operation will be highly dependent on quality of satellite imageries, which is unpredictable due to weather conduction, revisit frequency, and low resolution.
3. During the mature period of crops, top-dressing with traditional agricultural machinery like tractors could cause severe damages to the plants when moving in the fields.
4. Traditional agricultural machineries might be trapped by the muddy soil during or after the rain.

 

To solve the aforementioned pain points, DJI Agriculture Japan teamed up with Yanmar and a local rice producer to conduct variable-rate fertilization from July to November of 2022, which proved that variable rate fertilization conducted by agricultural drones can reduce 2533 yen/hectare (18.5 USD/hectare) of fertilizer cost and increase 777kg of yield per hectare. With the average price for rice in Japan being 559 yen/kg (4.1 USD/kg), the total savings and earnings per hectare exceed 436,000 yen/hectare (3202 USD/hectare).

 

The successful fertilization consists of the following procedures: land survey with DJI Phantom 4 Multispectral drone, image processing and reconstruction with DJI Terra and variable-rate precision spraying with T30 agricultural drone. The next sections will introduce the operation and parameter settings from an all-around scope.

 

 

The Pain-point killer: DJI multispectral drone & T30

 

By preparing two fields with similar size, DJI agriculture team partnered with Yanmar to conduct fertilization operation on fields provided by local rice producers. To validate the effectiveness of land surveying conducted by DJI multispectral drone and variable-rate fertilization with the agricultural drone, fertilizer amount and yield of two experimental fields after the operation were to be compared.

 

In terms of how the drones work in the specifically, the first step was to conduct a land survey with the DJI P4M drone. After uploading the land survey data to DJI Terra, a prescription map was generated. Based on the prescription map, Yanmar operated the DJI T30 drone to conduct fertilization operations. We will walk through the entire experiment in the next section.

 

Multispectral Land surveying and onsite Image Reconstruction with DJI Terra

 

 

Experiment Procedure Overview

 

DJI Agriculture Japan set up two experimental fields. The size of the variable-rate fertilization field was 3.11 hectares while the size of the fixed-rate fertilization field was 3.43 hectares. Both fields were spread with MIX20, a compound fertilizer with 20% of nitrogen contained. The top-dressing process was conducted with an agricultural drone at an operation height of 2 meters at the speed of 18-22 km/h, with a width of furrows for sowing of 7 meters.

 

Step 1: Land Survey with DJI multispectral drone and Image Reconstruction with DJI Terra

 

The first step was to collect multispectral images with a DJI P4M drone. Then, upload the image to DJI Terra for image reconstruction, prescription generation, and flight mission planning for agriculture drone.

 

 

Step 2: Precision top-dressing with DJI T30 Agricultural Drone

 

Upon completion of image reconstruction and route planning, start the precision top-dressing operation with T30 agricultural drone for both pieces of fields after setting up the parameters below.

 

Variable-rate fertilization operation parameters (Field A):

 

Variable spray rate	Good growth rate: 75 kg/ha Average rate: 100 kg/ha Poor growth rate: 125 kg/ha As a result, the application rate will be in the range of [75, 125]kg/ha with an average of 100kg/ha
Flight speed	13.8 km/h
Spinner speed	700 rev/min
Flight altitude	2 m

 

 

Fixed-rate fertilization operation parameters (Field B):

 

Maximum spray rate	100.1 kg/ha
Flight speed	25.2 km/h
Spinner speed	700 rev/min
Flight altitude	2 m

 

 

As the initial prescription map shows, the rice grown in the variable-rate field (Field A) is in a poorer and more uneven condition compared to its fixed-rate counterpart (Field B).

 

                               

Left: variable-rate field (Field A)  Right: fixed-rate field (Field B)

 

However, the data collected on the harvest date shows that Field A produced 8% more rice than Field B, while Field A was applied with only 80% of the fertilizer amount used in Field B.

 

Parameters	Field A (Variable-rate fertilization)	Field B (Fixed-rate fertilization)
Actual Fertilizer Amount	302.8 L	371.9 L
Actual Fertilizer Cost	22296 JPY/ha	24829 JPY/ha
Yield	31591 KG →10157.88kg/ha	32176 KG →9380.76kg/ha
Harvest Date	2022.9.28	2022.9.29

 

Therefore, the variable-rate fertilization method proved to be effective, not only fixing the previously existing problems of Field A, but also significantly increased yield with less fertilizer, even exceeding that of Field B, which was in better condition in the beginning.

 

 

The Outcome: Save 2533 yen (18.5 USD) while increase 777kg of yield per hectare

 

Two weeks after the variable-rate top-dressing operation, it can be observed that colors in the field on the RGB light, NDVI and GNDVI images tend to distribute more evenly. The reason behind is that the P4M identified the growing difference in the field accurately, thus providing guidance for the T30 to conduct precision top-dressing to enhance the growing uniformity and yield of rice in the same paddy field.

 

                 

Before the operation

 

                        

Two weeks after the operation

 

From an economic perspective, the actual fertilizer amount used in variable-rate fertilization fields is less than the estimated amount, which improves the utilization rate of fertilizer and lowers the potential loss due to over fertilization. While saving 2533 yen/hectare (18.5 USD/hectare) of fertilizer cost, the yield increased by 777 kg/hectare.

 

 

Grow more with less by incorporating agricultural drones & precision agriculture

 

"Less is more" should not be considered merely an interpretation of minimalism in Japanese culture. As a matter of fact, the ideology now thrives in agriculture by bringing more actual outcomes with less input.  The application of technologies like agricultural drones makes it possible to grow more with less, which have been demonstrated by a growing number of successful case studies.

 

The application of DJI agricultural drones in top-dressing for paddy fields can lower the use of fertilizer and prevent loss caused by over fertilization. As population aging becomes a prevalent phenomenon in the country, agricultural drones can minimize physical strength required in daily operations, making agriculture an industry with higher inclusivity for the senior group. Meanwhile, agricultural drones can solve problems existing in traditional agricultural machinery operation, including crop damage during mature periods of crops and spatial limitations in rainy days.

 

DJI's agricultural corporate client which provided the experimental fields is also a loyal user of Yanmar, provider of unmanned helicopter crop protection services. After witnessing the outcome, the client not only added another 22.7-hectare paddy field for DJI Japan to conduct fertilization operation, but also expressed further interest in conducting more experiments with DJI and even incorporating DJI agricultural drones for future operations. The successful experiment was also reported on the Agriculture News, one of the major Japanese newspapers specializing in national agricultural updates.