Effects of Different Soil Amendments on Soil pH and Heavy Metals Content in Maize (<i>Zea Mays</i> [l.

Abstract

Manure from livestock is an important source of nutrient for crop production in the small holder sector. It helps farmers reduce inputs of commercial fertiliser, thereby, increasing the profit margin of the farmer. Not much been done to determine the effects of kraal, goat, poultry and lime on soil pH in Swaziland and nothing has been done to assess if the levels of heavy metals each of these manure contributes to the soil in maize production are within the WHO’s safe standards for human consumption. The objectives of the study were to find out the effects of organic and inorganic soil amendments on soil pH and to find the content of heavy metals in maize tissues and grain on maize grown in soil amended with organic and inorganic soil ameliorants. A field experiment, in a randomised complete block design was conducted at Nhlangano Research Station in the 2014/2015 cropping season. Treatments were effective in increasing the soil pH. Goat manure treatment improved soil pH from 4.77 to pH 5.14 whilst the lime treatment improved the soil pH to pH 5.13 at full rate. Chicken manure treatment raised the pH to 4.86 at half rate whilst the goat manure treatment raised soil pH to 4.86 at half rate. The content of Zn was highest in the grain with the goat manure treatment at full rate (0.128 g/kg) and lowest in the chicken manure and lime treatments at half rate (0.025 and 0.021 g/kg). This was due to the high Zn content in the manure. The control treatment had 0.117 g/kg Fe in the grain while the cattle manure treatment at half rate had 0.101 g/kg Fe in the grain. Cadmium was highest in the lime treatment at full rate, goat manure at full rate and both chicken manure treatments (0.022 g/kg Cd). Copper was highest in the control treatment (0.009 g/kg) and lowest in the chicken manure treatment at half rate, goat and lime at full rate (0.003 g/kg). Goat and cattle manure was recommended for amelioration of acid soils.