Sugar bean success with drip irrigation

Venturing into sugar bean production, Fourie decided to implement Netafim’s seasonal drip irrigation solutions on some of the hectares available. A total of 5 hectares of sugar beans were irrigated by drip, and the rest by pivot. The goal was not only to achieve efficiency in these fields but also to test the impact these products can have and the efficiency that can be brought to sugar bean production. You see, as an irrigation designer but also a farmer, Fourie has the privilege of gaining first-hand knowledge and experience in his own fields and imparting insight about the benefits of these products and how to implement them optimally when servicing TTI clients.

Here’s everything you need to know about the drip-irrigated sugar bean production setup:

Before discussing anything else, let’s answer everyone’s biggest question: How do the yield and water-use of the drip irrigation and pivot plots compare?

Here’s what you need to know:

Note: Through the course of the season, they realised that the N to K ratio on the drip fields were skewing. Corrective action was taken resulting in the high use of K per hectare on the drip plots. Read more about fertigation lessons learned under the ‘Fertigation Approach’ heading.

Yield Quality

Beyond the benefits of drip irrigation illustrated in the table above and mentioned in the discussions below, Fourie also flags benefits of better yield quality and lower crop disease risk. “One of the concerns regarding the implementation of more precise irrigation is the cost of the tools required, and whether the farmer will be able to harvest the necessary return on investment. Yield quality is one of the many factors that will contribute to level of income from the field. There was a definite difference in the quality of sugar beans yielded from the drip-irrigated plots compared to the pivot plots this season. This meant that we got a higher price per tonne for those bags, further contributing to the economic success of the drip-irrigated fields.

Another benefit, says Fourie, concerns input costs and environmental impact. “Due to the fact that the water was not applied overhead, and the leaves therefore not wetted, the fungal disease pressure was much lower on the drip plots, and we were able to adjust the chemical spraying programme downwards for those plots.”

The sugar beans yielded from the drip-irrigated plots were of a very high quality.

Product Selection

“Over the years, I‘ve had many discussions with Netafim about drip irrigation on cash crops. When I got the opportunity to plant some fields myself, my thoughts around applying the benefits of drip irrigation to maize, sugar beans and similar crops took root again. I spoke to the team at Netafim and together we decided on the suitable products and how they can be applied,” says Fourie.

He wanted to use, and test, the entire seasonal drip irrigation product offer. “We can have long discussions about the benefits of drip irrigation, the different approaches that can be tested and more, but all of this is irrelevant without access to suitable products that can efficiently take on the task at hand and are economically feasible.”

According to Fourie the greatest advantage of quality seasonal driplines, such as Streamline™ X, is that these products make drip irrigation a reality for short-term crop production. “If we were to use long-term or permanent drip solutions, we won’t be able to justify the costs, even with astonishing yields. In addition, long-term products are not practically suited to the way these crops are farmed.”

“In this context I also see massive benefit in starting every season with fresh drip. Although there are possibilities of using it for multiple seasons, extreme precision in irrigation remains my main goal, and I therefore find more value in starting every season with a blank slate and knowing that I can achieve the level of precision I want to. The relatively lower input costs of these solutions make this economically feasible. It just makes sense, but only because these driplines were developed to be used in this way and manufactured with high quality standards.”

About his experience using FlexNet™ flexible pipes as submain and mainlines, Fourie says that it truly is a great product. “As it is a somewhat new product, the industry still needs to make progress in its optimal application and other aspects, but its potential in saving time and labour costs is massive. It is simply so easy to work with. We were not even geared with all the right equipment yet, but it was so easy to roll out, retrieve, connect, and move. I believe this product can do a lot for farmers in terms of ease-of-use, storage capacity and labour requirements.’

Francois Fourie showing off the yield at harvest time.  

Irrigation Approach

“It is crucial to have the right tools to plan and carry out a precise irrigation scheduling approach. This includes flow meters, valves, irrigation controllers, probes, tensiometers as well as suitable software for scheduling calculations and interpreting readings from the field. It is about watering and feeding the plant at a rate as close as possible to the rate at which the plant uses water and nutrients, and you need the necessary tools to make this a reality.”

Fourie says that there has been a lot of progress in the way we schedule irrigation as we continue to understand crop requirements better and better. “But I still don’t think we fully appreciate the potential of plants yet. Do we really grasp what we can achieve as we bring water and nutrient delivery closer and closer to water and nutrient use? It is about not irrigating past the root zone and keeping soil moisture levels as close as possible to field capacity. If we can water and feed the plant in small but precise and regular amounts, giving the plant what it needs when it needs it, there is still a lot of potential to be unlocked. You can only truly achieve this level of precision through drip irrigation.”

It is with this mindset that irrigation scheduling was done for the drip-irrigated sugar bean fields. “Our understanding of crop requirements and good drip irrigation management even impacted the way we managed irrigation scheduling for the pivot-irrigated fields,” he adds.

“The water-use in the drip-irrigated fields was even lower in comparison to water-use under the pivots early in the season, but as the plants developed and more vegetative growth occurred, water-use in the drip-irrigated fields increased driven by increased biomass. We still saw relatively low water use, but the massive difference between water-use at the start of and later in the season illustrates the importance of irrigating according to crop needs. As the plant grew more leaves, flowers, and later pods to look after, it needed more water.

Monitor, Action and Adjust

“I place a lot of weight on soil temperature in deciding when to start irrigation. One of the important lessons I remember from my studies, is that we underestimate how many reactions are triggered in a plant when soil temperature changes. We monitor soil temperature on every 100 mm down to 600 mm to determine when soil temperature starts rising. The turning point is early in the morning and as soon as the temperature starts climbing, we start irrigating. By doing this we know that the plant’s roots have access to the water required to drive the many reactions triggered by the temperature change.” Fourie says that these soil temperature changes start in the top 100 mm. “It is not heat rising from the bottom. Even though it is still dark, the top layer of soil gets warmer at a certain time early in the morning.” Another interesting fact regarding soil temperature, is that the average soil temperature was around 7 degrees lower under drip irrigation than under pivot irrigation.

Speaking about knowing how much to irrigate, Fourie says that careful management of the length of the irrigation pulses allowed them to prevent over irrigation beyond the root-zone. “As capacitance probes only give an indication of the presence of moisture at a certain depth, we also make use of tensiometers placed throughout the root zone to set the upper and lower moisture lines on the capacitance probes. By doing this, moisture lines are set according to plant available water, measured in a scientific way. The irrigation pulse length is determined by the time it takes for the irrigated water to reach the maximum root depth, which was managed at 35 cm on the sugar beans. If the probes graph showed that the water infiltrated past the 40 cm line after a 40-minute pulse, the irrigation pulse was cut to 35 minutes.”

It is about keeping the plant happy, he says. “If I monitor soil moisture closely, I can ensure that the plant is never under stress. There are some approaches that encourage using plant stress strategically, but I do not agree with that. It makes sense when there are specific goals, such as building sugar content through deficit irrigation when growing citrus and other tree crops. Beyond that I do not see any value in not keeping the plant as happy as possible so that it can achieve optimal production.”

The last note Fourie shares about scheduling drip irrigation on sugar beans, is about the water it requires during germination. “I am sure that I over-irrigated this season during germination as I was worried about whether the seeds will have enough water for germination under the drip irrigation. Looking back, the seeds did not need as much water for germination as I thought, and I will without a doubt irrigate less during this stage next season.”

Fertigation Approach

The initial purpose of having both drip and pivot plots, was to determine what the difference in water-use and the impact on yield will be, under different irrigation methods, but the same fertilizer programme. However, important fertigation lessons were also learned during this exercise.

“We started off with the same fertilizer program across the board. With one big difference, of course – the way it was applied. “We were able to apply fertilizer more efficiently on the drip irrigation plots. For example, the fertilizer program required us to apply ammonium nitrate through the pivot every week for the first three weeks. On the drip plot we could apply it little by little with the irrigation, eventually still applying the same amount per hectare.”

“Although there is a lot of industry knowledge on the fertilization of crops such as sugar beans, there is not a lot of experience in applying these elements optimally on this crop through drip irrigation. It’s a balancing act in which we have to find the balance between the necessary elements, get the timing of applications right and get to the know the crop even better.”

“I have done a lot of thinking about the timing of fertilizer applications and the method of application. Fertigation through drip irrigation gives us the capacity to apply fertilizer very precisely. Just as with the application of water, it is about applying fertilizer at a rate as close as possible to the rate at which it is used by the plant. If I feed the plants every time I irrigate, more potential is unlocked from the plant. This does not only hold the potential benefit of increased yield and quality, but also allows better soil health management and will benefit the longevity of the soil.”

Fourie confirms that there were times during the season when they did not get it right and had to adjust to minimise the negative impact on yield and quality. “The design of our pumphouse, that feeds both the pivot and drip irrigation systems, made it possible to adjust when necessary as we had the tools we needed.”

“Even with the fertilization mistakes we made and the in-season adjustments, the results are very pleasing and shows a lot of potential. We will definitely make a lot of adjustments to our approach, and I predict that we will require less fertilizer.”

Fourie smiles when he tells us about the massive leaves and intense root development they saw with the plants on the drip-irrigated plot. “At first we were worried that we would end up only growing a lot of leaves and that there will not be many pods, but when the leaves were opened there were massive amounts of pods as well. We still need to find the right balance, as it is about balancing vegetative growth and production. We don’t want the plant to spend too much energy on vegetative growth, rather than production, but we know that the plant needs to be big and strong enough to carry the high yield. Fact is that you will achieve standard yields with standard plants, but if you want to start chasing higher yields - plant size, fertilizer budgets, water-use and many other factors will have to rise to the same high level.

Adapting Expertise

According to Fourie the standard approach of calculating fertilizer requirements based on yield potential and water and soil nutrient levels remains very important. “I must however remember that we are working in a different context when fertigating through drip irrigation. Even greater focus should be placed on the different growth stages of the crop and decisions based on EC levels should be included. The biggest challenge remains to ensure that we do not run out of time for smaller precise applications, forcing us to apply fertilizer in large quantities at once.

The only possible challenge he sees in fertigating continuously through drip irrigation, will occur in seasons with extremely high rainfall. “We only had 11 mm of rain over the entirety of the production season and all the necessary nutrient enriched water could be applied. If that is not the case, the fertilizer dosing rate will have to be adjusted in order to apply the necessary fertilizer in time.”

The plants on the drip-irrigated plots boasted massive leaves and intense root development.  

Precision is Possible

According to Fourie, we still have a long way to go in making the necessary mind shift regarding the crops and circumstances that allow for this level of precision. We often think that only high-level crops can finance the investment required. “If we build a state-of-the-art pump house, you may think that a cash crop cannot carry that investment. I believe it can. If you do the math based on the higher yield potential and associated savings, the economic feasibility is clear. If we argue that we are working with an extensive crop and we should approach it with extensive management practices, I believe we will lose out on a lot of the value that efficient application of water and nutrients can bring to any crop. It is about unlocking the true potential of every plant, which I think is much higher than most of us think.”

For more information, email us at infoza@netafim.com, or connect with Francois at coisfourie@tt-i.co.za.