Institut für Kulturpflanzenwissenschaften

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    Phosphorus- and water- deficiency induced morpho-physiological and yield changes in maize (Zea mays L.)
    (2024) Ning, Fangfang; Graeff-Hönninger, Simone
    Phosphorus (P) is a nonrenewable and finite resource for all living things. It plays a crucial role as an essential nutrient in crop production. However, plants have low efficiency in utilizing P due to its immobility and low bioavailability. P deficiency can cause irreversible effects, particularly during the early stages of maize growth. Drought further exacerbates nutrient uptake challenges, especially for P, by limiting its diffusion in the soil. Therefore, the dual stress of drought and P deficiency restricts plants' shoot and root growth. It is necessary to investigate the interaction between P deficiency and drought and better understand the response mechanisms, as the effect of P deficiency on plant growth precedes the plant's own drought regulatory mechanisms. In Paper I, the effects of placed diammonium phosphate (DAP) and rock phosphate (RP) on the growth and development of two maize cultivars (Stabil and Ricardinio) were investigated combined with soil liming. Maize cultivars differed in their P utilization characteristics under low-P field conditions. The results showed that RP resulted in a lower leaf area index and light interception than DAP. This led to a 33% lower silage yield and a 29% lower P content at harvest. The PUE of RP was found to be 18%, which is 37% lower than that of DAP. Furthermore, soil liming reduced shoot biomass and caused a 35% decrease in shoot P content at the six-leaf stage. Maize cultivar ‘Stabil’ showed higher yield and P uptake. This paper demonstrated that placed RP could not be used as a substitute for DAP in silage maize production regardless of the application of lime to the soil. Paper II explored the impact of different types of P fertilizer (DAP and RP) on the root systems of maize. The results showed that P deficiency in the early stages of growth hindered root growth. However, in later stages, the roots exhibited enhanced lateral root growth in response to P deficiency. Although the differences in organic acids and phytohormones across different zones of the maize root system were not significant due to the delayed sampling, it is still feasible and necessary to conduct further investigations on organic acids and phytohormones in various root locations. Paper III tested deep P fertilizer placement as a strategy to alleviate combined drought and P deficiency stress in maize. It was tested under greenhouse conditions involving three factors: P fertilizer amount (low-P: LP, and high-P: HP), fertilizer placement (mixed (M, 0-18 cm), lower (L, 10-18 cm), and upper (U, 0-9 cm)), and soil water content (DS, 45% of soil water holding capacity (WHC)) and well-watered: WW, 75% WHC) and well-watered: WW). LP decreased shoot P content and both root and shoot biomass compared to HP. Under DS, root biomass increased by 50% and 95% in 0-18 and 10-18 cm depth at the fourth-leaf stage compared to WW treatment. However, root biomass decreased by at least 41% in different depths at the tenth leaf stage. Plants under DS consistently exhibited lower shoot biomass and P uptake at both stages. Although L-DS did not improve shoot growth and P uptake until the tenth-leaf stage, more than 55% higher root biomass and increased root length could be found in 10-18 cm depth compared to M-DS and U-DS treatments. This could potentially enhance P exploration in a larger soil volume and enable water absorption from deeper soil layers. However, no advantage in P uptake was observed with LP and HP until the ten-leaf stage. In conclusion, this thesis highlights the importance of optimizing P utilization strategies in maize production systems facing the dual challenges of P deficiency and drought stress. While soil liming and cultivar selection can help, high-solubility P fertilizers like DAP remain irreplaceable by RP due to their superior ability to support root development. It also discussed the possibilities and mechanisms for mitigating P and water- deficiency by promoting root growth in deeper soil layers through applying P fertilizers. This study provides a comprehensive evaluation of the feasibility of various maize cultivation and management practices under combined P deficiency and drought conditions, offering valuable references and practical guidelines for sustainable maize production in resource-limited environments.