Cropping Practices and Effects on Soil Nutrient Adequacy Levels and Cassava Yield of Smallholder Farmers in Northern Zambia

Cassava is a staple food and a major source of income for many smallholder farmers. However, its yields are less than 6 t ha-1 compared to a potential yield of 20-25 t ha-1 in Zambia. Understanding cropping practices and constraints in cassava production systems is imperative for sustainable intensification. Therefore, a survey of 40 households each with three fields of cassava at 12, 24, and 36 months after planting (MAP) was conducted. Analyzed soil data, leaf area index (LAI), intercepted photosynthetically active radiation, and management practices from 120 fields were collected and subjected to descriptive statistics. To explain yield differences within the same cassava growth stage group, the data were grouped into low- and high-yield categories using the median, before applying a nonparametric test for one independent sample. Stepwise regressions were performed on each growth stage and the whole dataset to determine factors affecting tuber yield. Cassava intercropping and monocropping systems were the main cropping systems for the 12 and 24-36 MAP, respectively. Cassava yields declined by 209 and 633 kg ha-1 at 12 and 36 MAP due to soil nutrient depletion for each year of cultivation until field abandonment at 8-9 years. Fresh cassava yields ranged from 3.51-8.51, 13.52-25.84, and 16.92-30.98 t ha-1 at 12, 24, and 36 MAP, respectively. For every one unit increment in exchangeable K (cmol (+)/kg soil), cassava yield increased by 435, 268, and 406 kg ha-1 at 12, 24, and 36 MAP, respectively. One unit increment of magnesium (cmol (+)/kg soil) gave the highest yield increase of 525 kg ha-1 at 24 MAP. The low levels of soil organic carbon explained the deficient nitrogen in cassava fields, which limits the LAI growth and consequently reduced intercepted radiation and low yields. The effect of exchangeable K on growth was limited by the moderate availability of Mg and low N, thus the need for balanced fertilizer regimes. © 2021 Peter Kaluba et al

Physiological and Morphological Responses of Cassava Genotypes to Fertilization Regimes in Chromi-Haplic Acrisols Soils

The objective of this study was to evaluate the performances of three cassava genotypes on yield, physiology and morphological traits under different fertilization regimes. A field experiment was conducted in a split-plot design for two consecutive seasons in the Mansa district of the Luapula Province of Northern Zambia in the highly weathered Chromi-haplic Acrisol soils. Four fertilization regimes, control-M3, lime-M1, NPK fertilizer-M4 and NPK fertilizer + lime-M2 were the main plots, while three varieties (Mweru-V1, Bangweulu-V2 and Katobamputa (local)-V3) were subplots. Periodic measurements of leaf area index, light interception, yield and yield components from 75 days after planting (DAP) up to 410 DAP and daily weather measurements of data were recorded. Fertilization significantly increased the radiation use efficiency (RUE) and light extinction coefficient (K) in two seasons compared to the control. Significant fertilization regimes and varietal effects were observed for seasonal LAI, stem yield, root yield, biomass, harvest index (HI), tuber number, root diameter, plant height and SPAD (chlorophyll index). A significant year’s effects on root yield, yield components and physiological performances were observed while significant fertilization × variety interaction was observed on seasonal LAI, tuber number, root diameter, plant height and SPAD. Significant fertilization × year interaction effects were observed on root yield, yield components and physiological performances. Variety × year interaction was significant for seasonal LAI, stem yield, harvest index and plant height and no three-way interactions were observed on all the traits. NPK fertilizer + lime and NPK fertilizer treatments may be adopted to increase the response of cassava varietal yield, physiology and morphological traits in low soil nutrient conditions under high rain-fed conditions

Efficiency of water and nitrogen use by wheat and legumes in Zambia

Maximum wheat (Triticum aestivum L.) yields in Zambia were obtained with weekly irrigation at 85% of class A pan evaporation during the whole irrigation interval and split application of urea N of which the initial portion of the fertilizer was either broadcast and incorporated or broadcast after the crop had established itself. This corresponded with maximum utilization of fertilizer N. The proportion of N derived from fertilizer was independent of fertilizer placement at various water regimes and N utilization was primarily a function of water availability.Two nonnodulating soybean (Glycine max L.) cultivars, Clark RJ1 and N77, or in their absence Pearl millet (Panicum glaucum L.) were judged to be appropriate reference crops for estimating N$sb2$ fixation by soybeans using $sp{15}{ rm N}$ isotope dilution techniques. A local soybean cultivar, Magoye, was rated highest among three cultivars tested for its ability to support N$sb2$ fixation by Bradyrhizobium japonicum and contributed biologically fixed N$sb2$ to a subsequent wheat crop

Comparative effects of partial conservation farming practices on plant development and yield

Sustainable farming systems are being introduced to ensure optimum agricultural productivity despite climate change and environmental degradation. One such sustainable agricultural technology is conservation farming (CF). The uptake of this technology has remained low at about 5% years after its introduction. CF has five interrelated practices but for a variety of reasons, farmers are unable or unwilling to adopt all recommended practices. This study studied the agronomic effects of incomplete or partial conservation practice whereby not all the five practices are used, mimicking actual practices adopted by farmers. A split- plot design experiment involving partial or incomplete CF mainly use of basins, ripping were compared to conventional farming of normal ploughing (as main plots) and three crops - cowpea, millet and sorghum (split plot) was conducted. The objective was to determine the agronomic effects and efficacy of partial adoption of CF compared to conventional farming system. Data were collected on vegetative and reproductive parameters including, plant height, germination percentage, canopy density, number of leaves, number of branches/tillers/stems, SPAD (Soil Plant Analysis Development) readings a proxy for leaf chlorophyll content. Plants grown in basins had higher plant development (plant height, total biomass) and higher yields compared to those on conventional methods. This effect could be explained by better soil physical and chemical conditions in the basins as indicated by higher SPAD readings. Int. J. Agril. Res. Innov. Tech. 12(1): 115-119, June 202

Genotypic Variation in Seedling Tolerance to Aluminum Toxicity in Historical Maize Inbred Lines of Zambia

Maize (Zea mays L) is the most important food grain in sub-Saharan Africa and is mostly grown by small-scale farmers under rainfed conditions. Aluminum toxicity caused by low pH is one of the abiotic factors limiting maize production among smallholder farmers. Therefore, breeding maize hybrids that are tolerant to aluminum toxicity will sustain and increase maize production in these areas. Hence this study was undertaken to assess the genotypic variation for aluminum toxicity in maize inbred lines. Fourteen maize inbred lines of historical importance that are used in maize hybrid breeding in Zambia were studied for seedling root variation under different aluminum concentrations using hydroponic conditions. The aluminum tolerance membership index based on three traits (actual root length, relative root length and root length response) classified genotypes L3233 and L1214 as highly tolerant, L5527 and ZM421 as tolerant, and L12, L3234, and ZM521 as intermediate. The high PCV, GCV, and heritability observed for the root traits indicate that opportunities for selection and breeding for aluminum tolerance among Zambian inbred lines exist. Furthermore, the study indicated that a higher genetic gain would be expected from net root growth followed by shoot length response as selection traits, thus supporting the use of root traits for aluminum tolerance screening

Comparative effects of partial conservation farming practices on plant development and yield

Sustainable farming systems are being introduced to ensure optimum agricultural productivity despite climate change and environmental degradation. One such sustainable agricultural technology is conservation farming (CF). The uptake of this technology has remained low at about 5% years after its introduction. CF has five interrelated practices but for a variety of reasons, farmers are unable or unwilling to adopt all recommended practices. This study studied the agronomic effects of incomplete or partial conservation practice whereby not all the five practices are used, mimicking actual practices adopted by farmers. A split- plot design experiment involving partial or incomplete CF mainly use of basins, ripping were compared to conventional farming of normal ploughing (as main plots) and three crops - cowpea, millet and sorghum (split plot) was conducted. The objective was to determine the agronomic effects and efficacy of partial adoption of CF compared to conventional farming system. Data were collected on vegetative and reproductive parameters including, plant height, germination percentage, canopy density, number of leaves, number of branches/tillers/stems, SPAD (Soil Plant Analysis Development) readings a proxy for leaf chlorophyll content. Plants grown in basins had higher plant development (plant height, total biomass) and higher yields compared to those on conventional methods. This effect could be explained by better soil physical and chemical conditions in the basins as indicated by higher SPAD readings

Optimizing Soil Moisture and Nitrogen Use Efficiency of Some Maize (Zea mays) Varieties under Conservation Farming System

In Zambia, small holder farmers depend on producing maize (Zea mays), which is a major staple food for many Zambians. Maize productivity among the smallholder farmers is quite low, giving only 2.3 tons per hectare. The low yields are attributed to insufficient and erratic rain fall, low soil fertility, and poor farming practices. Therefore, the objective of this study was to evaluate the performance of maize genotypes for nitrogen use efficiency and soil moisture utilisation under conservation farming system. The trials were carried out at two sites with different soil types. Three maize varieties i.e. ZMS 606, GV 640 and GV 635 were evaluated in maize – cowpea rotation. Four cowpea varieties used for rotation with maize, i.e. Bubebe Lutembwe, BB 14-16-2-2 and LT 11-3-3-12. BB 14-16-2-2 and LT 11-3-3-12 are mutation-derived lines of Bubebe and Lutembwe cowpea parent varieties respectively. The experimental design used was split plot with three replications. The NUE was significantly (P< 0.05) higher in CF and accounted for 27 % and 15% more than conventional farming system which valued 17% and 3% at Chisamba and Batoka, respectively. while soil moisture content was higher at Batoka than Chisamba in CF system. ZMS 606 and GV 640 varieties were superior over GV 635 for NUE. Cowpea variety BB 14-16-2-2 significantly increased NUE of maize varieties. Therefore, smallholder farmers in Zambia can increase maize productivity in maize - cowpea rotation system due to the increased NUE. Recommendations are made for farmers to select improved nitrogen efficient maize varieties to optimize productivity of maize in conservation farming system

Evaluation of Cowpea (Vigna unguiculata L.walp) Genotypes for Biological Nitrogen Fixation in Maize-cowpea Crop Rotation

Nitrogen is a major plant nutrient which is most limiting in the soil due to soil losses of mineral nitrogen (N) form. To ensure availability of nitrogen in the soil, the study was conducted to screen four cowpea genotypes for Biological Nitrogen Fixation (BNF) and their contribution to maize yield in maize- cowpea rotation. The cowpea genotypes used were mutants LT11-3-3-12 (LT) and BB14-16-2-2 (BB) and their parental varieties Lutembwe (LTPRT) and Bubebe (BBPRT) respectively. Trials were established at two sites (Chisamba and Batoka) of different soil types. The Randomized Complete Block Design (RCBD) with three replications was used. Labelled 15N urea was applied at 20kgNha-1 on the four cowpea genotypes during 2015/16 growing season. Cowpea plant parts were dried and milled for 15N isotopic analysis. The data collected included Nitrogen content and atom % 15N excess in the fixing cowpea genotypes and non-nitrogen fixing pearl millet to determine total nitrogen derived from the atmosphere (TNdfa) and total nitrogen (TN) in plant parts which were further used to compute Biological Nitrogen Fixation (BNF). The results showed that BNF by cowpea genotypes at Chisamba was 63.9 kg ha-1 and was significantly (P<0.001) more than BNF of 6.6 kgha-1 at Batoka. The LT mutant fixed significantly (P<0.001) higher nitrogen of 86.1 kgha-1 and 16.5kg ha-1 at Chisamba and Batoka respectively than other genotypes. However, both BB and LT mutants significantly fixed more nitrogen than their parents and have demonstrated to increase maize grain yields up-to 12 tha-1 in the maize – cowpea rotation

Physiological and Morphological Responses of Cassava Genotypes to Fertilization Regimes in Chromi-Haplic Acrisols Soils

The objective of this study was to evaluate the performances of three cassava genotypes on yield, physiology and morphological traits under different fertilization regimes. A field experiment was conducted in a split-plot design for two consecutive seasons in the Mansa district of the Luapula Province of Northern Zambia in the highly weathered Chromi-haplic Acrisol soils. Four fertilization regimes, control-M3, lime-M1, NPK fertilizer-M4 and NPK fertilizer + lime-M2 were the main plots, while three varieties (Mweru-V1, Bangweulu-V2 and Katobamputa (local)-V3) were subplots. Periodic measurements of leaf area index, light interception, yield and yield components from 75 days after planting (DAP) up to 410 DAP and daily weather measurements of data were recorded. Fertilization significantly increased the radiation use efficiency (RUE) and light extinction coefficient (K) in two seasons compared to the control. Significant fertilization regimes and varietal effects were observed for seasonal LAI, stem yield, root yield, biomass, harvest index (HI), tuber number, root diameter, plant height and SPAD (chlorophyll index). A significant year’s effects on root yield, yield components and physiological performances were observed while significant fertilization × variety interaction was observed on seasonal LAI, tuber number, root diameter, plant height and SPAD. Significant fertilization × year interaction effects were observed on root yield, yield components and physiological performances. Variety × year interaction was significant for seasonal LAI, stem yield, harvest index and plant height and no three-way interactions were observed on all the traits. NPK fertilizer + lime and NPK fertilizer treatments may be adopted to increase the response of cassava varietal yield, physiology and morphological traits in low soil nutrient conditions under high rain-fed conditions