Abstract
<title>Abstract</title> <p>Rising temperatures and heat waves can be very detrimental to crop yields in agriculture. In order to adjust to climate changes increased use of fertilizers and pesticides are often applied as observed also in Vietnamese agriculture. There are some temperature threshold values which will make agrochemicals decline in efficiency if exceeding the respective critical temperature levels. The present study analyses extreme heat effects of fertilizer and pesticides usage in Vietnam where extreme heat is quantified by the number of days with temperature exceeding thirty-five degrees Celsius, and the number of tropical nights. A modified Cobb-Douglas production function with climate variables is estimated in a FMOLS framework and allowing for interaction terms between heat and agrochemicals. The results show a declining efficiency of both fertilizers and pesticides with increasing heat during the last decades, and for fertilizers there may have been periods with negative marginal outcome from the increased use of fertilizer nutrients.</p>