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has been conducted on ameliorating the effects of heat stress through management practices.Wheat (Triticum aestivum L.) yields are reduced by heat stress in Optimal crop growth requires a nonlimiting supply many countries worldwide. The main objective of this study was to determine whether modifications to currently recommended crop of resources (water, nutrients, and radiation) and, as management practices could improve wheat yield at hot-environment temperatures rise, the demand for growth resources insites in three countries. Field trials were conducted between 1991 and creases due to higher rates of metabolism, development, 1993 in Sudan and Bangladesh by their respective national agricultural and evapotranspiration (Rawson, 1988). If growth reresearch systems (NARS) and in Mexico by the International Maize sources are limited under heat stress, then the size of and Wheat Improvement Center (CIMMYT). Crop establishment plant organs such as leaves, tillers, and spikes is reduced and other plant characteristics were measured to help understand the . The apparent sensitivity of metabolic basis of improved performance and to identify potential diagnostic processes to heat stress in the field environment (Reyntraits. Management factors included (i) irrigation, (ii) inorganic fertilolds et al., 1998), coupled with the reduced length of izer (NPK), (iii) organic fertilizer in the form of farmyard manure life cycle at high temperature (Midmore et al., 1984), (FYM), (iv) straw mulch, (v) genotype, and (vi) sowing date. Control treatments represented recommended practices and gave yields of 3.6 explains why grain yield is strongly associated with total t ha Ϫ1 , averaged across all environments. Considering main effects, plant biomass in hot environments (Reynolds et al., FYM (10 t ha Ϫ1 ) gave the highest yield response (14%) and approxi-1994a). These interactions make crop management facmately equivalent levels of NPK gave the lowest (5.5%), suggesting tors critical to sustaining wheat yields in warm envithat organic fertilizer provided growth factors in addition to nutrient ronments. content. Mulch and extra irrigation increased yield in Sudan and A few studies have shown benefits of specific manage-Mexico, which are hot environments with low relative humidity, but ment factors under stress. For example, the application not in hot, humid Bangladesh. In Mexico, extra inputs were more of farmyard manure (FYM) has been reported to imbeneficial under hotter, spring-sown conditions than for winter sowprove soil physical and chemical conditions and to help ings, with responses of 17 and 8% to extra NPK, 17 and 14% to FYM, conserve soil moisture (Sattar and Gaur, 1989; Gill and and 11 and 6% to mulch, respectively. Comparison of heat-tolerant (Glennson 81) and heat-sensitive (Pavon 76) genotypes showed that Meelu, 1982; Tran-Thuc-Son et al., 1995). One-time apthe heat-tolerant genotype was generally more responsive to addi-plication of FYM (10-15 t ha Ϫ1 ) increased wheat yields tional inputs. Improved performance in respo...

SUMMARYThe potential yield of wheat and the physiological basis of yield limitation in the lowland irrigated tropics was investigated in three cultivars planted at five sowing dates. Maximum grain yields were achieved by cultivars that flowered in January when the weather was coolest. The period from sowing to terminal spikelet initiation was similar for all varieties and all sowing treatments. The period from terminal spikelet initiation to ear emergence was increased when seed was sown in late November or early December rather than in October or early November. Manipulation of the sowing date in relation to the choice of cultivar had a considerable effect on grain yield.H. M. Ishag and O. A. A. Ageeb: Rendimiento del trigo en las zonas tropicales.

SUMMARYSowing date directly affected the grain yield of chick peas. Optimum sowing date was found to be between the end of October and the end of November, but different soil types showed some differences within this optimum.Grain yield was highly correlated with number of pods per plant and number of plants at harvest.Plant loss at the seedling stage was highly correlated with daily mean maximum air temperature, and was also significantly associated with sodium accumulation in shoots.