Michel P. Sedogo

Developing Indicators for Soil and Fertilizer Nitrogen Use Efficiency for Maize Using On-Farm Experiments in Burkina Faso

Measurement of recovery of fertilizer N and soil mineral N by maize must be improved in the western semiarid tropics for maximizing crop yield and reducing environmental pollution. The relevant variables for characterizing this N use are the N uptake by the plant from the applied fertilizer (NdfF) and that from the soil (NdfS). The direct measurement of these two variables requires the use of 15 N labeled fertilizer, a difficult and expensive technique. It would therefore be useful to have sensitive indicators for these variables. This study was conducted to measure the variability in the N use from soils. The experiments were carried out with maize at 24 sites in a 3000 ha area of village land with Luvisols located in the central zone of Burkina Faso. Each site had two treatments with two replicates: 0 and 80 kg N ha −1 applied as urea labeled with 15 N. Statistical analysis of the results identified three groups of fields differing in soil fertility, each corresponding to a certain distance from the farmstead, and provided a relationship between the variables NdfF, NdfS, and easily measured indicators. The most pertinent indicators (r 2 >0.9) were: (a) for NdfS, the total N in plant without fertilizer (Nplt0) and the apparent crop recovery of N fertilizer (ACR %), and (b) for Nplt0, Nav (available N) as measured by the Waring Bremner test, exchangeable K, and (c) the clay content. The coefficients of determination improved when the regressions were calculated for each soil fertility group. These results have two important applications: (a) the possibility of estimating easily the part of N taken up by maize that comes, respectively, from the soil and the fertilizer; and (b) the identification of two factors limiting soil fertility, that is, the mineral N and exchangeable K + content of the soil before cropping.

Role of Local Agro-minerals in Mineral Fertilizer Recommandations for Crops: Examples of Some West Africa Phosphate Rocks

One of the major constraints to enhanced crop productivity in West Africa is low soil fertility and particularly soil deficiency in available phosphorus (P). When P is limiting, crop production is greatly compromised even though the other nutrients are available in large amounts. The use of soluble P fertilizers is hampered by the cost of the P fertilizers commercially available, too high for resource-poor farmers. Therefore, exploitation of the locally available phosphate rock (PR) deposits represents an alternative for soil P supply to ensure mineral plant nutrition. The effectiveness of a particular PR depends mainly on its chemical and mineralogical composition, and to some extent on environmental conditions, crop type and management practices. This communication highlights some results of the research works that have been carried out in the region to enhance the direct use of PR in agriculture and how theses PR can be integrated in fertilizer recommendations for crops. Direct application of phosphate rocks may be an economical alternative to the use of the more expensive imported water-soluble P fertilizers for certain crops and soils.

Effectiveness of combined application of Kodjari phosphate rock, water soluble phosphorus fertilizer and manure in a Ferric Lixisol in the centre west of Burkina Faso

ABSTRACT Increasing soil phosphorus and organic matter content for crop production while reducing the cost of production are required to facilitate the achievement of green revolution in Africa. Field and pot experiments were laid out during 2012 and 2013 to assess the effects of combined application of Kodjari phosphate rock (PR) and water soluble phosphorus on sorghum yields, P uptake and Lixisol characteristics in the centre west of Burkina Faso. Five P fertilizers treatments (zero P, 100% TSP (triple super phosphate), 100% PR, 50% PR + 50% TSP, 75% PR + 25% TSP) and two cow manure treatments (zero, 5 t ha−1) were tested. In field experiment, 50% PR + 50% TSP was as effective as 100% TSP in increasing sorghum yield above the control by 30% in 2012 and 50% in 2013 and P uptake by 30% in both years. Manure had an additive effect on phosphorus fertilizers in increasing sorghum yields and P uptake. In pot experiment, increases of Ca uptake, soil pH and microbial P were observed with the application of 50% PR + 50% TSP. Our results suggest that formulation of fertilizer combining phosphate rock and mineral P would improve sorghum yields and income of smallholders.

Biological Nitrogen Fixation by Local and Improved Genotypes of Cowpea in Burkina Faso (West Africa): Total Nitrogen Accumulated can be used for Quick Estimation

Biological nitrogen fixation (BNF) by legumes is an indicator of their potential contribution to recycling nitrogen in cropping systems. Many techniques exist for the quantitative measurement of legume BNF. The isotopic dilution (ID) methods are the most accurate but are too expensive, time-consuming and require technical expertise. There is a gap between the simple but less accurate Total Nitrogen Difference (TND) method and the Isotopic Dilution (ID) methods. By measuring the BNF of 11 cowpea (Vigna unguiculata) genotypes, this study aimed to develop a simple model as an improved tool for the quick estimation of BNF. Total N accumulated by traditional genotypes from Burkina Faso varied from 23 to 41 kg ha−1. Approximately 40 to 65% of this was nitrogen derived from the atmosphere (Ndfa) when the TND method was used (Ndfa-TND), while the ID method indicated that 29 to 37% of N accumulated was derived from the atmosphere (Ndfa-ID). The TND method overestimated the BNF of high N-yielding genotypes but underestimated the BNF of low N-yielding genotypes (N-accumulated below 31 kg N ha−1). The relationship between N-accumulated and Ndfa-ID was described by a polynomial regression: = 0.0127 - 0.5354 + 17.44, where and represent Ndfa-ID and N-accumulated, respectively (P<0.05, R2 =0.92). The model was validated and could be used for quick estimation of BNF directly from the N accumulated.

Cropping System Effects on Soil Monosaccharides in Western Burkina Faso

Labile pools of soil organic matter (SOM), including soil sugars, are important to the formation and stabilization of soil aggregates and to microbial activity and nutrient cycling. The effects of cropping systems at farm level in tropical areas on SOM labile pool dynamics have not been adequately studied and the results are sparse and inconsistent. The objective of this study was to determine the effects of soil management intensity on soil sugar monomers derived from plant debris or microbial activity in cotton ( Gossypium herbaceum )-based cropping systems of western Burkina Faso. Thirty-three (33) plots were sampled at 0-15 cm soil depth considering field-fallow successions and tillage intensity. Two pentose (arabinose, xylose) and four hexose (glucose, galactose, mannose, glucosamine) monomers accounted for 2 to 18% of soil organic carbon (SOC) content. Total sugar content was significantly less with tillage, especially for the hexose monomeric sugars glucose and mannose, the latter of microbial origin. Soil mannose was 63 and 80% less after 10 years of cultivation, without and with annual ploughing respectively, compared with fallow conditions. Soil monosaccharide content was rapidly restored with fallow and soon approached the equilibrium level observed under old fallow lands. Therefore, the soil monosaccharides, in particular galactose and mannose from microbial synthesis are early indicators of changes in SOC.