Global production of agricultural products must continue to increase if shortages are to be avoided. While irrigated production is substantial since water available for both current and future production is limited, rainfed production will become increasingly important. In-season weather variability results in instability in rainfed production and in order to gain information on the mechanisms involved and their potential mitigation, it is important to monitor production over a range of possible environmental scenarios. We designed and implemented a rain matrix experimental approach for cotton based on a series of sequential plantings coupled with a rain-simulation protocol. The rain matrix in two years produced 56 growing environments with rain and thermal variability and 44 yield:environment comparisons. The yield:rain relationship was not strong (R2
= 0.35) Analysis of heat units over the matrix indicated (1) heat units varied with planting date and (2) heat units were sufficient to achieve maturity. Plantings reached maturity with <1250 heat units and reached maturity before a lethal freeze. The rain matrix design increased the number of yield:environment comparisons in a single year and though it is subject to undefined thermal interactions, may prove useful in understanding rainfed cotton production.
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