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SeedCo explains the impact of yield limiting factors on maize

SC 647 maize at Triple S Ranch.

by Adrian Chibanga

In our previous article, we focused on the yield advantages of SeedCo’s SC 647, even when it is grown in limiting environments.

We reported on a 2019-2020 season yield that averaged 11,5 tonnes per hectare, harvested from a 50 hectares field by a farmer in Copperbelt Province. From this farmer’s experience, we highlighted two major yield advantages he gained by choosing SC 647.

These were:

•3,5 tonnes extra yields over and above his fertilisation target, in soil with a pH of 5,5. His input programme targeted 8 tonnes, so the 3,5 tonnes excess that made his extra profits was a bonus, credited to variety choice and good management practices.

•The excellent grain quality in a season that delivered 1 550 mm of rain, with half of that pouring down during the crop’s reproductive, maturity and dry-down phases. You will agree that 800 mm more rain is a cause for worry for a crop that is early to medium maturity and is at grain fill stage. But the SC 647 received it with joy.

This article highlights the two environmental factors that would impact/limit the yields and quality of your grain maize.

Table 1: pH Scale and mineral nutrient availability.

These are:

i.Soil pH and

ii.Precipitation/rainfall quantities and distribution over a season.

Soil pH is simply an indication of the acidity or alkalinity of a soil environment. It is measured in pH units, hence its definition being the negative logarithm of the hydrogen ion concentration in a soil or water sample. The scale of measure runs from 0 to 14, with 7 as the neutral, and 0 to 6,9 being the acid scale, and 7 to 14 being the alkaline scale. The pH of a soil has an impact (positive or negative) on the fertility of the soil, and consequently, on its ability to maximise yield potential of a crop.

Many studies, including one summarised in table 1 above, have illustrated how soil pH impacts on plant available nutrients. Table 2 illustrates soil acidity (pH Level) and its impact on the uptake of mineral nutrients by plants, with a special focus on N, P and K.

The two tables above can be used to work out the quantity of fertiliser lost when a crop is produced in a soil environment with a pH scale below 6.

Table 2: N, P, K availability/uptake in a pH scale of 4,5 to 6,8.

Soil acidification is caused by one or a combination of these three major factors:

•Natural acidification: The dissolving of atmospheric carbon dioxide in rainwater to form a carbonic acid. The carbonic acid reacts with soil and its parent material, and depending on the intensity of the reaction, the soil and parent material are stripped of bases and silica. This leaves hydroxides of aluminium and iron, and mostly at levels that are toxic to plant roots.

•Acid deposition: The combination of nitrogen and sulphur gases released from industry, with rainwater to form nitric and sulphuric acids. These acids become a source of hydrogen ions that drive the process of acidification of soils in regions like the Copperbelt and Northern Provinces of Zambia where we receive high rainfall and have a lot of industrial activity.

•Fertilisation: Ammonium-containing fertilisers such as urea, anhydrous ammonia, and ammonium salts that are applied to mostly cereal crops contribute to soil acidity. Good agronomy practices such as crop rotation and corrective liming are recommended to keep the acid scale at acceptable levels.

This acidic condition was prevalent in the soil environment where the SC 647 was planted at Triple S Ranch in Mufulira last season (2019/2020). The pH was at 5,5, and the farmer’s NPK fertilisation was targeted for a yield of 8 tonnes per hectare. Ordinarily, a variety that is not tolerant to soil acid should have been giving the farmer yields ranging between 6 and 7 tonnes per hectare, but the SC 647 proved to be both acid tolerant and very efficient at utilising soil reserve nutrients, and provided the farmer with a 3,5 to 5 tonne yield advantage.

Figure 1: Rainfall/maize yield relationship (Southern Province Zambia).

Rainfall/precipitation amounts and distribution

Plants are generally described as being composed of 75% water and 25% dry matter. Therefore, the role that water plays in crop production between seeding and harvesting is critical and can be the reason for higher or lower yields. Most maize crops can grow on quantities between 350 and 800 mm of rainfall, depending on the maturity group, rainfall distribution and soil structure. The critical stages of water requirement by the maize plant are crop establishment, flowering, and grain fill.

Drought imposed moisture stress during these phases have resulted in significant yield reductions before. Figure 1 above shows a relationship between yield and rainfall records obtained in the Southern Province over a period of 15 years. SeedCo has worked hard to release maize varieties such as SC 303 that will maximise yields with rainfall as low as 300 mm over a period of three months. The case of above normal rainfall could cause a limit on yield and grain quality of maize, but the SC 647 has proven to be the seed solution not only for our customers at Triple S, who recently gained 2 to 5 tonnes per hectare more in a 1 550 mm season. The variety has pleased a whole lot of customers beyond our borders, including in the high rainfall areas of the DRC.

If you are looking for a rewarding crop of maize, SeedCo will make your farm a home of bumper harvests by helping you to make the right seed choice. Contact SeedCo at seedco@seedco.co.zm or +26(0)96-795-8009 for advice.

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