Jan03

IRRI Agronomy Challenge 2: Fertilizer basics

Author // Dr. Achim Dobermann Categories // Achim Dobermann's blog

 18 January

Now 29 days after transplanting, the plants are safe from harm by snails and relatively weed-free. There is the odd ugly patch. The weather has not been good in the last 10 days — rainy, cloudy, and relatively cool — and the plants show it. They have commenced tillering, but are not yet thriving. There is really no cure for unfavorable weather, but a timely topdressing will allow the plants to take full advantage of any future improvement.

We applied 100 kg/ha of urea, which equates to 46 kg N/ha, onto dryish soil and irrigated within hours after this. I would give myself a 7 out of 10 for the uniformity of my topdressing. The dry soil does make it easier to see the density of granules on the ground and to adjust the application rate a little as you go.

Fertilizer top-dressing with Leigh Vial.

Fertilizer top-dressing with Leigh Vial.

At this time, I do regret the mechanical transplanter’s 30-cm spacing between rows. Around 20, or at most 25 cm, would have been better. Currently, the 30-cm spacing looks to be a wide expanse, ready to be occupied by things other than rice, especially where we have the odd vacant site (or ‘hill’ to the purists), vacant from an imperfect transplanting process. Mother Nature hates an empty space so we will definitely need a second herbicide application.

Please help us pray for sunny weather, or can you only pray for rain?

28 December

I came back about a week after planting to apply the first dose of fertilizer. We went through the basics of that in our post last year. We found that using Nutrient Manager made this all very easy because answering the series of simple questions about our field and the previous and planned management practices took only about 5 minutes. Most importantly, it resulted in an “actionable” recommendation we could easily implement. So, what’s going to be different this time? Actually not that much.

In terms of information technology, we have an exciting new version of Nutrient Manager for Rice available in the Philippines (version 2.2.) which has been re-programmed in HTML 5 language. The main advantage of that is that the software has become device-independent, i.e., it runs in the “cloud” on any hardware, including desktops, laptops, tablets or any of the available smartphones. Soon it will also receive further extensions in functions towards making other critical crop management decisions.

In terms of agronomy, we have to consider that this time we have planted an inbred and a hybrid variety. That has three major implications for nutrient management:

(i) the hybrid should have a higher yield potential and thus also higher attainable yield than an inbred cultivar; hence it will need some more nutrients too,

(ii) previous research has shown that to fully exploit the higher yield potential a hybrid is more likely to benefit from a small late N application at heading stage than an inbred, and

(iii) the growth duration is different and hybrids may also have more early vigor than inbred, affecting the timing of fertilizer applications. The hybrid we have chosen, Mestiso 26 (IR82372H), is expected to mature about 1 week earlier than the inbred NSIC Rc302 (IR05A272).

So, I ran the Nutrient Manager separately for each of the two cultivars, assuming a target yield of about 7 t/ha for the inbred (about 70-80% of yield potential for an average dry season climate at Los Banos) and 7.5 t/ha for the hybrid. Here are the two concrete recommendations:

Inbred  
Early 0-14 days after transplanting: 30 kg N/ha, 29 kg P2O5/ha, 26 kg K2O/ha
Active tillering  26-30 days after transplanting: 45 kg N/ha
Panicle initiation  40-44 days after sowing: 45 kg N/ha
Hybrid  
Early 0-10 days after transplanting: 40 kg N/ha, 32 kg P2O5/ha, 38 kg K2O/ha
Active tillering 21-25 days after transplanting: 38 kg N/ha
Panicle initiation 33-37 days after sowing: 38 kg N/ha
Heading 60-64 days after sowing: 20 kg N/ha
Nutrient manager for Rice mobile

Nutrient Manager for Rice, Philippines.


In practical terms the differences in timing of applications are quite small, so we’ll aim to do it all on the same days for both varieties (the late date range of the hybrid, which is close to the early date range of the inbred). In terms of product choices we’ll keep things simple an go with 14-14-14 compound fertilizer for the basal (Early) application, which translates into about 4 bags/ha for the inbred and 4 ½ bags/ha for the hybrid. It took me about half an hour to complete this first broadcast application, although I had to do an extra pass on the hybrid to apply a little more fertilizer that had been left over.

I realize more and more that spreading fertilizer by hand on the soil surface is not going to help us much with increasing fertilizer efficiency in the future. At this early stage the seedlings are barely growing and cannot take up nutrients quickly. Moreover, the machine we used planted at 30 cm row spacing, leaving a lot of empty surface space on which the fertilizer granules fell. I wish we had the possibility to place it close to the rows of young plants, into the soil, but we don’t have such a machine yet. Adding fertilizer boxes to the mechanical planter would also add more weight to it, complicating the planting operation. I’m dreaming that someday we’ll have a small- or medium-size crop care machine that can do more precise applications of fertilizers and pesticides in row-planted rice crops, perhaps even with precision guidance….

Achim Dobermann prepares to apply fertilizer

Achim gets ready to apply fertilizer.

Back to reality, our idea was to apply a small amount of irrigation water to “wash” the fertilizer into the soil. That’s what we did on the morning after fertilizer application, with an undesired consequence: it helped the Golden Apple snails to become mobile and move into the field. If you have young seedlings, that’s a major worry during the first two weeks after transplanting. The only way to control it is to not have standing water at that stage in the field. So, a day later Leigh went out to drain off the very shallow water layer we had created. We’re hoping that it didn’t cause us much loss of nutrients. It’s a fine balance between doing good or evil in crop management.

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About the Author

Dr. Achim Dobermann

Dr. Achim Dobermann

Achim is a soil scientist and agronomist with 25 years experience working in Asia, North America and Europe. He is recognized internationally as an authority on science and technology for food security and sustainable management of the world's major cereal cropping systems. He has authored or co-authored over 250 scientific papers and two books on nutrients in rice and has received numerous awards from various academic, government and industry organizations. He is a Fellow of the American Society of Agronomy and a Fellow of the Soil Science Society of America.

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