Wheat management in warm environments : Effect of organic and inorganic fertilizers, irrigation frequency, and mulching
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Wheat (Triticum aestivum L.) yields are reduced by heat stress in many countries worldwide. The main objective of this study was to determine whether modifications to currently recommended crop management practices could improve wheat yield at hot-environment sites in three countries. Field trials were conducted between 1991 and 1993 in Sudan and Bangladesh by their respective national agricultural research systems (NARS) and in Mexico by the International Maize and Wheat Improvement Center (CIMMYT). Crop establishment and other plant characteristics were measured to help understand the basis of improved performance and to identify potential diagnostic traits. Management factors included (i) irrigation, (ii) inorganic fertilizer (NPK), (iii) organic fertilizer in the form of farmyard manure (FYM), (iv) straw mulch, (v) genotype, and (vi) sowing date. Control treatments represented recommended practices and gave yields of 3.6 t ha(-1), averaged across all environments. Considering main effects, FYM (10 t ha(-1)) gave the highest yield response (14%) and approximately equivalent levels of NPK gave the lowest (5.5%), suggesting that organic fertilizer provided growth factors in addition to nutrient content. Mulch and extra irrigation increased yield in Sudan and Mexico, which are hot environments with low relative humidity, but not in hot, humid Bangladesh. In Mexico, extra inputs were more beneficial under hotter, spring-sown conditions than for winter sowings, with responses of 17 and 8% to extra NPK, 17 and 14% to FYM, and 11 and 6% to mulch, respectively. Comparison of heat-tolerant (Glennson 81) and heat-sensitive (Pavon 76) genotypes showed that the heat-tolerant genotype was generally more responsive to additional inputs. Improved performance in response to inputs was generally associated with better stand establishment, and with significant increases in plant height, grain per unit area, and aboveground biomass; in Mexico, there was also an association with higher canopy temperature depression and light interception. The possibilities of realizing the benefits of applied organic matter and mulch treatments through residue retention and reduced tillage are briefly discussed.
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