SOIL TESTING IS KEY REQUIREMENT IF YOU WANT BETTER YIELDS

A farmer (left) applies lime to the soils in his farm before planting Irish potatoes and the same farm (right) a few months later. Since lime reacts relatively slowly, it needs to be in place well before planting acid-sensitive crops to allow adequate time for the pH change to occur. PHOTO | JECINTA MWIRIGI | NMG 

By JECINTA MWIRIGI

Contrary to the expectation of many farmers, maximum yields are not achieved only after employment of good agricultural practices such as fertiliser application and use of certified seeds coupled with proper land preparation.

Soil also plays a key role. An investigation was carried out recently in one of the counties to find out the soil condition for farmers who intended to plant crops such as Irish potatoes, peas (green, snow), maize, beans and others.

Two aspects of the soils were examined, namely, soil fertility and the occurrence of bacterial wilt.

Soil fertility

On soil fertility, the status of macro elements such nitrogen, phosphorus and potassium (NPK), calcium and magnesium and micro elements like manganese, copper, zinc and iron were examined.

Other factors that were scrutinised include the unfavourable soil characteristics which contribute to plant nutrient uptake and physical characteristics such as pH and soil organic matter.

The results indicated that all (100 per cent) of the 60 soil samples had a pH of between 3.77 and 5.9, which was termed as extreme to moderately acidic for growing of the intended crops.

Further 30 per cent of the samples had inadequate soil organic matter content, while 81 per cent and 56 per cent had inadequate phosphorus and magnesium, respectively.

It was, therefore, recommended that the soil pH be maintained optimum for respective crops. This can be achieved through avoidance of acidifying fertilisers such as diammonium phosphate (DAP) and urea and at the same time apply fertilisers such as nitrogen, phosphorus and potassium (N: P: K) 17:17:17, 23:23:0, and 20:20:0.

The zero for potassium (K) was employed where there was no deficiency of the nutrient. In the extreme acidic cases especially where magnesium was also inadequate, broadcasting of dolomitic lime (magmax) on the affected farm was recommended.

The recommended application rates were between 200 and 400kg/ha depending on severity. Since lime reacts relatively slowly, it needs to be in place well before planting acid-sensitive crops to allow adequate time for the pH change to occur.

Generally, it takes three months for lime to react with the soil. Therefore, apply one month before planting and remember that lime requires water to react with the soil.

A November application can thus be preferred for a crop to be planted in March of the following year. Further, lime reacts faster when mixed well with the soil so ensure to apply prior to any tillage and oversee even spread on the whole plot including the edges.

Where organic matter was low, application of well decomposed manure mixed with the endorsed fertiliser was also recommended.

RECYCLING OF SEEDS DISCOURAGED

The recommended amount was between two and five tonnes/acre depending on level of depletion and the crop in question.

The change of the planting fertiliser did not affect topdressing fertilisers such as CAN and foliar feed for crops that need them.

It was also noted that Zinc and copper in the soil are getting depleted in most of the farms hence limiting crop yield. Of all the collected soil samples, 37 per cent had inadequate zinc and 26 per cent copper.

This is against a background whereby zinc has been found to increase yield of some crops such as maize by up to 40 per cent.

To correct copper and zinc deficiencies, about 5kg/acre of copper sulphate and zinc sulphate, respectively, was suggested for the exhausted substance.

It is recommended that application of fertilisers must be synchronised with moisture availability to optimise uptake. One potato farmers’ group that implemented the soil test results increased their production from 15 bags of 100kg per acre to 85 bags/acre.

Bacterial wilt
On bacterial wilt, more than half of the samples (52 per cent) were positive. This translates to huge crop loss especially the potatoes and some farmers with affected pieces of land have claimed to lose as much as 90 per cent of the produce through bacterial wilt.

To address the issue, crop rotation of Irish potatoes with maize, beans, sweet potatoes, kales, cabbages, and strawberry is recommended.

Planting crops of such as capsicum, eggplant, tomatoes, and tobacco together with potatoes was discouraged as they act as alternate host to the bacteria.

After cleaning the infected field, one is advised to always keep the field free from weeds as they act as alternate hosts. It is also sensible to uproot and destroy all the diseased plants as soon as they are detected.

In addition to that, disinfection of farm implements like working tools, gumboots and shoes is endorsed. A cleaning solution of dilution 500ml/1l of water can be used for the farm equipment while soil fumigants like metham sodium or basamid granular can be applied before planting.

Recycling of seeds is discouraged and farmers are encouraged to use certified seeds to reduce pests and disease incidence and improve on yields and quality.

SOURCE: NMG/SEEDSOFGOLD