Soil Fertility Research
Soil Fertility Research
Critical levels of Zinc in Intensive Agriculture
Deficiencies of zinc occur in many parts of the world on a wide range of soil types but semi-arid areas with calcareous soils, tropical regions with highly weathered soils and sandy-textured soils in several different climatic zones tend to be the most seriously affected. An experiment was set up in 1995 to evaluate maize response to zinc application in intensively managed commercial enterprise in order to establish the critical soil test zinc level and optimum zinc rate of application. The objective of the study was to determine the critical level of zinc and the optimum rate of application in intensive agriculture farming system in Zambia. The results showed that 5 kg ha-1 of zinc sulphate ZnSO4.7H2O significantly increased maize grain yield over the control treatment. The optimum rate of zinc was established as 10 kg ha-1 applied as ZnSO4.7H2O while the critical rate was established at 5 kg ha-1. The critical soil test level of zinc was determined to be 2 mg kg-1 soil. It was recommended that in intensively managed commercial farming system where soil pH could be above neutral (7.0), 5 kg ha-1 of zinc sulphate ZnSO4.7H2O is enough to increase zinc requirements for maize. However, if soil test zinc level is below the critical level 10 kg ha-1 of ZnSO4.7H2O should be applied.
Dambo Utilization in Some Districts of Zambia
The productivity of dambos and their water availability make dambos ideal supplement to upland field cultivation during drought periods among the rural dwellers. The study was carried out in 2006 to evaluate current dambo utilization in some districts of Zambia. The objective was to evaluate dambo utilization in Mambwe, Kazungula and Sesheke districts. The study employed two methods namely use of a questionnaire to obtain secondary information from respondents on dambo utilization and soil analysis to obtain primary data on nutrient condition. The data collected were used to recommend best practices in conserving dambo resources to sustain and secure livelihoods of the rural dwellers. The results showed that Mambwe district is dominated by valley dambos that are utilized for vegetable, bananas and green maize production for consumption and sale. The calendar for wetland cropping is between April and September. The nutrient levels are relatively very high and as such no external inputs are currently necessary for crop production. Kazungula is dominated by river dambos and are mostly used for vegetable cultivation and as a source of water for domestic and livestock. Basic cations are comparatively high but require inputs of nitrogen and phosphorus that are below critical levels. Cattle manure is mostly used to boost soil fertility. The calendar for wetland cropping is between August and October and is relatively short because of extremely low temperatures in June and July. Sesheke is dominated by valley dambos that are utilized mainly for maize production, cattle grazing and as a source of water for domestic and livestock. The nutrient levels are extremely very low to support crop production without external input. Mostly cattle manure is used for maize production. The cropping calendar is the same as for Kazungula. In all districts the cultivated portion is less than a Lima and a hand hoe is used for tillage. The dambos in Mambwe are the most utilized and the most fertile followed by those in Kazungula and Sesheke. Current methods of cultivation and soil improvements are highly recommended because they quite conservative. However, reforestation of the dambo margin in Sesheke is highly recommended in order to improve hydrological conditions.
Management of Acid Soils for Soybean Production
Soil acidity is the most limiting constraint to crop production in highly leached soils of the high rain fall areas of Zambia. These soils are not suitable for growing most arable soils including soybeans (glycine max L) without controlling the levels of acidity. The most effective technique of reducing soil acidity is by lime application. However, the agricultural lime on the market contains higher calcium (Ca) than magnesium (Mg). Use of liming material that contains relatively high Mg and other essential nutrient like zinc could have some advantages over the commercial lime currently at the market. Nampundwe mine tailing (NMT) contain relatively high concentration of Mg and zinc and is readily available at Nampundwe mine for use. An experiment was set in 1995/97 seasons at Misamfu Regional Research Station to evaluate the effectiveness of NMT. The objective of the study was to evaluate the effectiveness of the NMT in managing soil acidity for soybeans production in comparison with commercial agricultural lime (AgLi). The results showed that in the first season (1995/96) AgLi significantly increased soil pH from 4.3 to 4.8 and exchangeable calcium (Ca) of the study soil from 0.12 to 0.50 cmolckg-1 more than NMT. Additionally, agricultural lime significantly reduced exchangeable aluminium from 0.82 to 0.40 cmolckg-1 less than NMT. The residual effect of both NMT and AgLi significantly increased soil pH to 4.8 and 5.0 respectively, in the second season (1996/97). The residual effect of NMT significantly increased exchangeable Mg from 0.10 to 0.30 cmolckg-1. Both NMT and AgLi did not significantly increase soybean grain yield in 1995/96 season. The residual effect in the third season was not studied because of financial limitations. However, it was concluded that to exploit fully the potential of NMT in managing acidity effectively for soybeans production, a study of residual effect for a long period is needed.
Effect of Hi-Qualime on Maize and soybeans Grain Yields
Hi-Qualime contains 19% calcium and 10% magnesium and is mined in Mkushi district. Hi-Qualime was evaluated using maize and soybeans as test crops between 2003/07 seasons. The objective was to determine its effectiveness and optimum rate of application. Two application methods were used in both Mkushi and Serenje districts. The results showed that Hi-Qualime was effective in increasing soil pH in both districts by both methods of application. The residual effect of lime on soil pH was only effective upto the second season (2003/04) only. In the third season soil pH declined and the decline was confirmed in the fourth season (2006/07). The lime applied by both methods did not significantly increase maize grain yield in 2003/04 season in both districts. In Mkushi the residual effect of lime by spot application significantly increased soybean grain yield in 2004/05 season, but broadcasting application did not significantly increase soybean grain yield in the same season. Residual effect by spot application of lime in Serenje did not significantly increase both maize and soybeans grain yields. However, residual effect of lime by broadcasting application increased both maize and soybeans grain yield at Mkushi in the third and fourth seasons (2005/06 and 2006/07). The optimum liming rate for both Serenje and Mkushi districts was estimated to be 1000 kg/ha. It was recommended that Hi-Qualime should be applied at 1000 kg/ha in both districts and same amount re-applied every third season to maintain the soil pH in the desirable range (pH 5.5-6.5).
Effect of Organic Inputs on Soil Phosphorus Sorption and Chemical Properties of Some acid Soils of Zambia.
P deficiency is the major constraint that limits crop production in acid soils due to low native phosphorus (P) and high P fixation by Iron and aluminium oxides. Use of high quality organic inputs such as Tithonia diversfolia prunings, a common shrub in Zambia has been found to reduce P sorption in acid soils and increase P availability in the soil solution for plant uptake. The objective of this work was to evaluate the effect of different sources of organic inputs on P sorption and chemical properties of acid soils in Zambia. The results showed that Tithonia and soybeans residues were the most effective in reducing P sorption and increasing P availability of acid soils under study than maize residues. However, Tithonia was found superior to soybeans residues in reducing P sorption and increasing P availability in the soil solution. Additionally, both Tithonia prunings and soybean residues increased exchangeable calcium and magnesium in all acid soils. It was recommended that the potential that Tithonia prunings and soybean residues have in reducing P sorption and increasing P availability in acid soils should further be tested in field trials.
Assessment of Heavy Metals in Potentially Polluted Soils of Zambia
Potentially polluted sites could be a source of heavy metals that if their levels are not checked and controlled could lead to the pollution of human and livestock food chain. An assessment of the extent and accumulation of heavy metals in potentially polluted sites was carried in 2001 on four stationary and four mobile source sites. The objective was to assess the extent and accumulation of lead, cadmium, copper and zinc in potentially polluted sites in Zambia. The assessment confirmed that the soil adjacent to Kabwe disused mine is polluted with lead, zinc and copper. The soil at the mine was estimated to have 85 times more lead (Pb), 82 times more zinc Zn) and 5.5 times more copper (Cu) than the earth’s crust concentration. The concentration of these metals on the western side was found to be reducing with distance from the mine. When the concentrations of Pb, Zn and Cu were compared to the Dutch and South African guidelines they were found to be well above their limits indicating that pollution of the soil had occurred. Along the mobile phase pollution of Pb, Zn and Cu occurred along Kapiri and Kabwe-Chibombo highways. The pollution reduces with distance from the highway. The source of Pb pollution was linked to automobiles particularly those that use gasoline. It was recommended that education campaign should be undertaken to sensitize the general public in mainly Kabwe on risks of metal pollution to encourage behavioral changes mitigating risks of Pb pollution. Reduction of Pb in gasoline or slowly phasing out of leaded gasoline will help to reduce Pb concentration along the highway.
Effect of Soil Chemical Amendments on Dry Matter Yield and Heavy Metal Uptake by Maize Plants Grown in a Polluted Soil
Dust fall out as a result of mining and smelting operation, deposits heavy metals on the soil that may give rise to the problem of soil pollution presenting an environmental hazard. An experiment was set up to investigate the effect of soil chemical amendments on the uptake of heavy metals in maize plants grown in a polluted soil. The objective of the study was to determine the effect of soil chemical amendments on maize dry matter yield and uptake of heavy metals by maize plants grown in a polluted soil. Chemical amendments significantly increased maize dry matter yield as compared to the dry matter yield of maize grown in a polluted soil. However, the increase in maize dry matter yield was not significant within chemical amendments. All chemical amendments did not significantly reduce the uptake of lead (Pb) in maize plants grown in a polluted soil. TSP reduced the uptake of zinc by maize plants more than CaCO3 amendment. Among the amendments only Ca(OH)2 was effective in reducing the uptake of cadmium (Cd) copper, (Cu) and zinc (Zn) by maize plants grown in a polluted soil. The results suggest that even though it was possible to increase maize dry matter yield by all chemical amendments, it was not possible to significantly reduce Pb and Cd uptake by maize plants grown in a polluted soil. Therefore, only Ca(OH)2 showed potential to reduce all heavy metals studied except Pb.
Soil Analysis Based Fertilizer Recommendations
Fertilizer application in Zambia primarily follows a blanket recommendation. Historical evident exists that continued fertilizer use without guided recommendation and lack of proper soil management resulted in declining soil productivity. A soil fertility survey was carried in 2001 in Eastern, Central and Southern Provinces of Zambia. The objective of the survey was to prepare fertilizer recommendations based on soil analysis for use by farmers in Eastern, Central and Southern Provinces of Zambia. A total of 651 composite soil samples were collected from small-scale farmers in Chipata, Chadidza, and Lundazi, Chongwe, Lusaka, and Chibombo, Mazabuka, Namwala and Kafue districts. The analysis showed that 51% of the total samples collected are strongly to very strongly acid. Most of these soil samples were from Chadidza, Lundazi, and Chongwe, Kafue, Mazabuka, Monze, Namwala, and Mumbwa districts. As a result 90% of the total soil samples from these districts have low to very low exchangeable magnesium and 49% very low exchangeable calcium. Available phosphorus for soils from Chongwe, Mazabuka, Gwembe, Kafue and Namwala, Lusaka and Mumbwa varies from low to very low. However, available phosphorus level in Lundazi, and Chadidza was found to be medium. While available phosphorus in Chipata district was found to be very high. Soil samples from Eastern, Southern and Central Provinces have medium to very high exchangeable potassium. More than 50% of the samples from Chongwe, Mazabuka, Kafue, Gwembe and Chibombo have low soil organic matter content, while 42% within the same district have medium soil organic matter content. Only 8% of the total samples mainly from Mumbwa and Mazabuka have high organic matter content. It was strongly recommended that lime be considered as one of the major inputs in the farming system of the surveyed provinces. It was further recommended that organic residues should not be burned but incorporated into the soil to improve soil organic matter. Green manures such as velvet beans and sunhemp were also recommended as a source of essential nutrients such as nitrogen. Inorganic fertilizer recommendations based on soil analysis were also given particularly for Central , Southern and some parts of Eastern Districts of Zambia.
Comparison of Phosphorus Impregnation and Bray 1 Soil Tests for Evaluating Plant Available Phosphorus
The relationship between soil test phosphorus and crop response has not been studied for maize in some major benchmark soils of Zambia. The suitable soil test procedure for estimating available phosphorus in various soil types needs to be identified. The objective of this study was to compare two soil test methods namely phosphorus impregnation (Pi) and Bray 1 for predicting P requirements of maize in different soil types. The phosphorus which was extracted from Makeni soil series by Pi soil test correlated highly significantly (r=0.966**) with maize dry matter yield while the correlation with Bray 1 P despite being high (R=0.908ns) was not significant. However, correlation of phosphorus uptake with phosphorus extracted by Bray 1 soil test was highly significant (r=0.991**) than correlation with phosphorus extracted by Pi soil test (r=0.958*). However, Bray-1 estimated more P than Pi soil test in all the study soils. Because Pi soil test estimated only soil solution phosphorus that correlated highly significant with maize dry matter yield could be a better method for predicting P requirements of maize.
Contacts:
Principal Investigator:Lackson Phiri
Email:soilsandwater@zari.gov.zm
