Saturday, April 13, 2024
Home Farming Tips How Does Soil Lose Fertility?

How Does Soil Lose Fertility?

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“The causes of degradation cut across so many factors in Uganda. These include poor tillage and poor choice of crops, over grazing in case of the cattle corridor, bush burning and non-application of fertility enhancers,” Dr Robert Muzira, a soil scientist from Mbarara Zonal Agricultural Research Institute says. 

Soil is made up of different nutrients as seen above – organic matter which is always on top of the soil is washed away through soil erosion, bush burning leading to loss of nutrients like nitrogen, sulphur as these escape. This leaves the soil bare; when these are missing from the soil, the fertility of the soil is lost.

-Soil erosion – loss of top fertile soil, occurs when it rains heavily.

-Bush burning causes loss of nitrogen and potassium.

-Over tillage/over ploughing – loss of soil structure due compaction, which affects absorption.

-Over grazing leaves the soils bare, hence affected by direct sunshine, which leads to loss of moisture.  

-Not replacing removed nutrients leading to negative nutrient balance of around: -21, -8 and -43 for NPK.

-Mono-cropping deprives soils of possible nutrient enhancing crops like legumes. This is why intercropping is important.

-Use of undergradable materials – polythene, because they prevent water from seeping into the soils.

-Cemented elements near the farmland, for example graves. Cement affects the nutrients in the soils.

Such soils cannot allow root penetration, but also the larger spaces that take in air, will be blocked and nutrients including oxygen will not find their way in the soil to get to the roots.

Continuous tillage/ploughing affects the larger spaces for air which tend to disappear especially where there is clay, affecting fertility.  

Weeding by removing all the weeds and placing them onto the boundary exposes the soil to direct heat and rains. This again takes away fertility in the top soils. Best thing to do is to weed, but let the cut grass remain and rot on top of the soils  

How are farmers contributing to loss of soil fertility?

“Unfortunately most farmers do not replace lost nutrients after harvesting their crops. When we harvest crops, we have to replenish the lost nutrients through application of fertilizers, which has not been embraced most Ugandans,” says Prof. Kitungulu Zaake, a soil scientist.

Zaake says for comparison purposes an average farmer in South Africa uses 51kg of NPK per year and one in Kenya uses 23kg per year.

In Malawi, Mozambique and Tanzania the figure stands at 16, 4 and 6 respectively, while in Uganda we use an average of 1.5kg per year!

Zaake says that this means that Uganda is in negative nutrient balance which is against 2005 AU resolution in which member countries were tasked to use at least 50kgs of nitrogen per year to date.

If farmers do not replace the nutrients in the soil after harvest, production must go down. It is just like having a shop which you take out but are reluctant to restock.  

How to deal with the above issues

For famers to understand what nutrients are lacking from their soils, they should go for experts from the National Agricultural Research Organisation (NARO) centres, including consulting extension workers near them for information on how best they can understand their soils.

Unfortunately, there are only two big centres with such services that is National Agriculture Research Laboratories (Kawanda) and Makerere University (Kabanyoro). This is why a mobile testing kit comes in handy.

“I am sure there are farmers who need to test their soils, but access to the right equipment stops them,” Lwakuba said. 

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