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CORN

Long-Term Cropping Effects on Maize

Crop Evapotranspiration and Grain Yield

^a Cátedra de Cerealicultura, Universidad de Buenos Aires, Av. San Martín 4453 (1417), Buenos Aires, Argentina
^b Cátedra de Ecología Vegetal, Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453 (1417), Buenos Aires, Argentina

jcarcova{at}agro.uba.ar

Long-term cropping in the Rolling Pampa of Argentina may reduce available soil water for maize (Zea mays L.) production. Grain yield, however, has not decreased possibly because of genetic improvement. Our objectives were to: (i) evaluate root and shoot growth and its relation to crop evapotranspiration (ET_a), (ii) analyze interactions among hybrids and length of the cropping period on grain yield and its components, and (iii) establish functional relations between grain yield components and their determinant processes. Three hybrids with contrasting production stability coefficients and representing different eras of maize breeding were grown at three farms in 1994 to 1996 in fields with short (S) and long (L) cropping periods on silty clay loam soils (fine, illitic, thermic Typic Argiudolls). Silking took place 5 to 6 d later in L than in S and a significant (P < 0.05) reduction (21–36%) of ET_a was observed in L vs. S around this stage. Lower root abundance (reduction of 60%) and canopy size (reduction of 6–13%) in L have probably contributed to less ET_a. In addition, the ontogenic delay exposed crops grown in L to more stressful meteorological conditions around silking. Kernel number (KN), closely related to grain yield (r² > 0.65), was significantly associated with daily ET_a around silking. The modern hybrid established a greater KN mm^-1 d of ET_a (853 kernels m^-2 mm^-1 d) compared with the older ones (386 kernels m^-2 mm^-1 d). This characteristic may mask the deleterious effects of long-term cropping on maize grain yield.

Abbreviations: ASW, available soil water • C_O, organic carbon • ET_a, actual crop evapotranspiration • ET_o, reference evapotranspiration • fIPAR, fraction of incident PAR intercepted by the canopy • KN, kernel number • KW, kernel weight • L, field with a long cropping period • N_T, total nitrogen • PAR, photosynthetically active radiation • PWG k^-1, plant weight gain per kernel • S, field with a short cropping period • S_S, index of relative soil aggregate stability • SWC, soil water content

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