Nitrogen fertilizer use and climate interactions: Implications for maize yields in Kansas

CONTEXT: While climate change threatens maize growth and production, appropriate N fertilizer use (N) can help mitigate this threat and stabilize or improve maize yields. Accurate application of N fertilizer is of increasing interest as an adaptation measure for climate change by reducing greenhouse gas emissions and increasing economic returns. OBJECTIVE: The objectives of this study are to: 1) clarify how maize yields respond to N fertilizer use under changes in temperature and precipitation, and 2) explore the effects of various climate conditions on N fertilizer use efficiency. METHODS: We used a long-term and county-level maize N fertilizer use and climate dataset from 1981 to 2019 in Kansas to determine the impact of N fertilizer use on maize yield. We developed a panel data model with fixed effects, incorporating explanatory variables, including the interaction of growing-degree-days (GDD) with N fertilizer use (GDDit*Nit), it *N it ), extreme-degree-days (EDD) with N fertilizer use (EDDit*Nit), it *N it ), and precipitation (Precip) with N fertilizer use (Precipit*Nit), i t *Nit), along with a non-linear N-fertilizer use term. Then, the adaptive effects of N fertilizer use on climatic risks for maize were examined and the county-level results were aggregated into the nine crop reporting districts, as defined by the U.S. Department of Agriculture's National Agricultural Statistics Service. RESULTS AND CONCLUSIONS: Our results show that: 1) an increase in N fertilizer use magnified the negative effects of higher EDD on maize yield but enhanced the positive effects of higher GDD and precipitation on maize yield, impacts which were increasingly evident moving from western to eastern regions across Kansas; 2) hotter environments reduced maize yield by 7% in the west; conversely, warmer and wetter environmental conditions contributed to 2.4% yield gains in the southeast; changes in N fertilizer use impacted maize yield to a lesser extent than climate changes; and 3) under the averaged climate conditions, the optimal N fertilizer rate increased from northwestern (average 50 kg N ha-1 ) to eastern (average 158 kg N ha- 1 ) regions in Kansas. SIGNIFICANCE: Our results reveal the interaction between climate and N fertilization on maize yield and clarify how the efficiency of N fertilizer use is affected by various climatic conditions. Our findings highlight the quantifiable interactions between climate and N fertilizer use when evaluating dynamic N fertilizer applications and climate change adaptations.