Chemical desiccation is often desirable to hasten maturity so seed can be harvested earlier than normal. Soybeans {Glycine max (L.) Merr.} were sprayed with paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion) at 0.6 and 1.1 kg/ha, glyphosphate {N‐(phosphonomethyl) glycine} at 1.7 and 3.4 kg/ha, and ametryn }2‐(ethylamino)‐4‐isopropyl amino‐6‐methythio‐s‐triazine} at 1.1 and 2.2 kg/ha 4, 3, and 2 weeks before the estimated harvest date to desiccate the soybeans and accelerate harvest. The objective was to determine the effect of pre‐harvest chemical desiccation on seed yield and quality. In field experiments, on a fine, montmorillonitic mesic Aquic Arguidoll, Flanagan series soil, harvest was accelerated, but all chemicals significantly reduced yields when they were applied 3 and 4 weeks before harvest. Yields were not significantly reduced by applications 2 weeks before harvest. Paraquat was the most effective desiccant for accelerating soybean harvest. Paraquat also reduced yield and seed weight the most while glyphosate had the least effect. Growth chamber studies indicate that ametryn and paraquat did not affect seed germination or seedling vigor, but all glyphosate applications significantly reduced germination and soybean seedling vigor. Chemical desiccation of soybeans prior to physiological maturity will significantly lower soybean yields. Glyphosate is not recommended as a desiccant.
Consenation tillage is being increasingly recommended as a means of reducing both cost of tillage and soil erosion. A study was conducted for two years with the objective of evaluating the performance of a determinate soybean (Glycine max (L.) Merr.) cultivar, Sprite, planted in narrow rows on a Nicollet (Aquic Hapludolls)-Webster (Typic Haplaquolls) complex, with different tillage systems and different levels of N, P, K fertilization for higher yield. Variables studied included: (i) three tillage systems (disk, chisel plow, and moldboard plow tillage) and (ii) three levels of N, P, and K fertilization (Pat 0, 74 and 111 kg/ha; Kat 0, 186, and 279 kg/ha; and Nat 0, 135, and 270 kg/ha). Plant population was unaffected by the treatments. Phosphorus and K applications increased soil and leaf P and K contents over time and with application levels. Tillage had no significant effect on grain yield. Lodging was significantly increased by P application. Lodging, plant height, and grain yield were significantly increased by K application. Nitrogen application increased lodging and plant height, but not yield. It was concluded that soybean can be successfully grown with reduced tillage in central Iowa without a yield reduction or change in fertility requirement. Soybean responded to K application when the soil test levels were medium to high.
The effect of corn (Zea mays L.) leaf orientation on grain yield and production practices has been the subject of conflicting reports over the past few years. Plant population is reported to be the cause of the discrepancies. The objectives of the present study were to determine the effect of plant population and leaf orientation on corn plant efficiencies and their interaction. Two contrasting leaf angles were compared by the use of near‐isogenic versions of the single‐cross hybrid (Hy2 ✕ C103) consisting of the liguleless (lg2) and its normal counterpart. Light penetration, light reflection, total dry matter production, and grain yields were measured to determine the effect of the leaf orientation, leaf area, and plant densities on corn production. Leaf angles of the two versions differed by 20°. Nine percent more light was intercepted by the horizontally oriented leaf type (HL). Plant populations (from 39,305 to 88,958 plants/ha) had no effect on leaf angle. High populations resulted in mutual shading which reduced the yield per plant. The mean leaf area per leaf of the HL was 17% larger than the vertically oriented leaf type (VL). Plants grown at 69,189 plants/ha had smaller leaves than those at the 49,421 population. Defoliation above the ear removed less leaf area than any of the other treatments and produced the smallest grain yield. All defoliation treatments reduced grain yield. Reflectors did not increase yield. Leaf orientation had little effect on corn production in rows spaced 76 cm apart.
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