Leaching soils: who is to blame?

For three years now, 39-year- old Rose Musa has been growing her 20 by 25 m maize plot oddly. She does not cultivate, instead, she covers the ground on which she grows maize with maize stalks from the previous harvest, with this she harvests 12 bags- four times what one can get on the same plot, using the ridging way.

Among others, Musa is also practising mixed cropping, meaning; she plants more than one crop in her maize field.

“I am a happy woman, I can harvest enough for both home use and for sale and that’s how I have managed to buy a car,” says the mother of three.

Musa is responding to what many will attribute to conservation agriculture (CA). Agriculture experts argue that conservation agriculture systems are based upon minimal soil disturbance, crop residue retention, crop rotation or intercrop association as they are increasingly seen to recycle nutrients, increase yield and reduce production costs.

By laying maize stalk, for instance, the growing crops will benefit from soil moisture, meaning in the event that rain stops midway, the crops could still carry on growing, up to a period of four weeks. In addition, the maize stalk upon decomposing, will act as manure meaning no fertilisers will be required.

The 2013 Human Development Index shows that Malawi’s area is 11.8 million hectares, of which Lake Malawi occupies one-fifth of the total. Out of 9.4 million hectares of land, approximately 5.3 million ha, or 56 percent, is cultivable.

In addition 80 percent of the population lives in rural areas where subsistence farming is practised. For centuries, cultivation in Malawi has involved as many as 160 000 hoe strokes per hectare, a practice which is slowly being discouraged.

In the past, agriculture has looked at soil tillage as a main process in the introduction of new crops to an area. It was believed that tilling the soil would increase fertility within the soil through mineralisation that takes place in the soil.

Today tillage is seen as a way as destroying organic matter that can be provided within the soil cover. Also tilling of soil can cause severe erosion and crusting which will lead to a decrease in soil fertility.

Lilongwe University of Agriculture and Natural Resources (Luanar) soil scientist Patson Nalivata says plants or crops require a total of 16 essential nutrients to grow. These nutrients are divided into call macro nutrients namely Nitrogen (N), Phosphorus (P) and Potassium (K) as well as micro nutrients namely Iron (Fe), Manganese (Mn) and Zinc (Z) which can easily be found in the soil.

Interestingly, he says, these nutrients availability and acquisition depends on soil type.

“The form in which the nutrients are in the soil, the concentration of the nutrient in the soil in relation to other nutrients, relationship and interaction of different nutrients, environmental conditions, like moisture contents, presence on absence of acidic conditions (pH), plant rooting characteristics and its interaction with other biological agents,” he says.

“Therefore, when you see a crop or plant at any stage, in its physiological nature, it is comprised of all the 16 nutrients, that it picked up in the soil in different formats. What it means is that any time you take any produce out of that land [whether residues or grain or fruit etc] to home or market, you have exported or removed these important nutrients from that parcel of land. If you have removed more nutrients out of that land than what is available for the next crop, you need to replenish from somewhere. The easiest and quickest means is through chemical fertilisers,” he says.

Agriculture in Malawi has relied on the use of natural fertilisers, which have been replenishing the poor soils. Due to poor groundcover, most of the important nutrients in the soil get washed away and this has been the reason most soils have become degraded, hence the need for artificial fertilisers.

The biggest issue facing the use of chemical fertilisers is groundwater contamination. If one continuously apply chemical fertilisers without any basis (soil analysis). The soil can become degraded over time.

“Continued use of fertiliser will accelerate some other soil process than would have been normally, thereby, affecting the biology, chemical and even physical characteristics of your soil e.g. increased availability of nitrogen under tropical conditions will promote accelerated organic matter decomposition lowering the soil organic matter contents.

“Certain fertilisers are acidifying and may need proper management to reduce such effects. One can only deal with such problems if they have proper soil testing regime over time,” he says.

In addition, Nalivata says the burning of the residues after every growing season is a poor farming method that is degrading the soils.

According to him, by burning residues it means that all the nutrients which were captured by the plants and kept in the residues are lost.

When you fly over Malawi during dry season, you will notice a lot of burning especially in the Central and Northern regions. This inputs a lot of sulphur, a macronutrient, in the sky resulting in acid rains where concentration is high.

“Another common practice is over cultivating of soils which renders the soil too porous such that lots of nutrients are lost through leaching. Then there is reduced ground cover during rainy season. This has resulted in increased incidences of soil erosion which has deposited lots of nutrients to lower shire and Indian Ocean,” he adds.

Nalivata who has sampled most of the soils in Malawi believes smallholder farmers poorly manage the soils making the soil deficiency. He says that even the way fertiliser is applied in the fields is wrong and must be discouraged.

“With respect to soil fertility management, you will agree that our farmers across the country use 23:21:0+4S fertiliser for basal dressing (first application) and Urea or CAN for top dressing (second application) for maize production. You will notice that all farmers across Malawi regardless of soil type apply same quantities.

This is not right. Furthermore, you have also noticed that there are also some farmers who grow maize year in and year out without applying fertiliser or manure. They don’t get any economical yield but have the biomass which every year they export from the field taking out essential nutrients. Some of the farmers do not practice good soil management practices which expose their soil to huge losses of nutrients. Agronomically, you will notice that some farmers do not follow proper agronomic practices like ridge spacing, plant population, let alone cropping systems which can help to optimise the soil nutrients,” he says.

Malawi Lake Basin Programme Natural Resources management officer Brandina Nkhoma says as a result of poor soils, most farmers are not benefiting from their hard earned work. She says that soils are so poor that smallholder farmers get as low as two bags of maize on a huge piece of land.

“I have worked with farmers for a very long time and the problems are the same, poor harvests which translates to hunger and scramble for maize. In addition to the erratic rainfall, maize is not doing well and that’s where we are bringing in conservation agriculture. Much as it has its weaknesses, we have realized that, it’s better. At least that is what our farmers do, and we can have testimonies of farmers reaping more than what they have bargained for,” she says.