Abstract
In sub-Saharan Africa, crops are often grown under low nitrogen (N) and low phosphorus (P) conditions, which may impact on the nutritional components of the grains. The aim of this study was to investigate the effect of low N and low P and a combination of the two on iron (Fe), zinc (Zn) and phytic acid content in two commercial South African spring wheat cultivars (PAN3497 and SST806). Phenotypic traits were also investigated. Although cultivar effects were not significant, treatment effects were highly significant for the phenotypic and nutritional traits. Low P stress increased Fe and Zn levels, whereas low N stress had the opposite effect. In addition, low P stress inhibited phytic acid accumulation the most, suggesting that under this treatment, Fe and Zn were more available because of less interaction with phytic acid. Compared to the low N treatment, the low P treatment led to lower reductions in the number of tillers, plant height, stem thickness, number of seeds, weight of seeds and dry weight for both cultivars. While low P had positive effects on the nutritional value of wheat, the combination of low N and P treatment had a negative impact on most of the measured characteristics. Low N conditions had more negative effects on all measured characteristics than low P conditions and was very detrimental to wheat nutritional value and yield.Significance:
 
 Results from this study emphasise the impact of fertilisation and the impact of insufficient nitrogen and phosphorus fertiliser on wheat productivity.
 Low nitrogen and phosphorus fertilisation impact grain microelement content and bioavailability which impact nutritional value.
Highlights
Nitrogen deficiency is one of the major crop production constraints in the world.[1]
Wide variation in Fe and Zn concentrations has been recorded in wheat grain.[25,26,27]
The range of Zn concentration was reported to be between 20.4 mg/kg and 30.5 mg/kg in wheat grains.[29]
Summary
Nitrogen deficiency is one of the major crop production constraints in the world.[1]. P fertiliser application is required to address soil P deficiencies. Both N and P are essential macronutrients required for vegetative and reproductive plant growth.[7,8,9] Small-scale farmers in sub-Saharan Africa often do not have access to fertiliser, due mainly to the cost, leading to poor N and P status of soils.[10] Artificial fertilisers mainly contain N, P and potassium (K) while microelements are present in natural organic fertilisers such as compost.[11] Some industrial by-products and waste materials can be used as micro-fertilisers in case of iron (Fe) deficiency.[12]
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