Lecture 11 2010

Lecture 11 2010 - Negative Interference Competition...

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Unformatted text preview: Negative Interference Competition Alelopathy Parasitism Competition • Plants compete for growth resources when their supply is below the collective demand • Resources are the consumable space Light Nutrients Water CO2, oxygen • Plants compete for space capture Competition for soil resources a. Nutrients • N is often the most competed for Soluble, mass flow across a distance P and K less mobile • Fertilization vs. weed control? Appleby et al. 1976 Competition for soil resources b. Water • Rooting depth Plasticity Average rooting depth (cm) Broad generalization for soil resources: plants should compete first for water then for N lastly for P and K Competition for Light • Probably the most relevant in most situations • Shading is a major factor limiting growth • Plasticity provides adaptation to shade • Light capture: leaf area and height The Timing of Competition a. Time of emergence b. Duration Emergence with the crop when to start weeding 110 Rice grain yields (%) 100 90 80 70 60 50 40 30 20 10 0 0 15 30 45 60 75 90 105 120 135 150 Days weedy after seeding rice (DAS) Delayed emergence Rend. grão (%) 100 90 80 70 60 50 40 30 20 10 0 when to stop Strongly related to competition for light Pt 0 PT IP IF Y = 94.2 / (1 + e (-T - 1.4) / 5.8) 2 approx. r = 0.73 15 30 45 60 75 90 105 120 135 150 Dias após a semeadura Days weed-free after seeding 75 Critical Period of Competition Grain yield 100 % control Days after seeding Critical period of competition Even so, why do people often spray or control weeds late? • They sprayed late the first time, weeds were too big and continued growing • The weeds have developed resistance to the herbicide and continued growing • The crop was stressed or there was not a uniform crop stand to ensure full canopy closure • If weeds are still present late in the season, they need to be eliminated to prevent seed shattering ARROZ PADDY (Tons/ha) PADDY RICE 7 6 5 4 3 2 1 SIN MALEZAS WEEDS REMOVED 0 0 20 40 60 80 100 120 140 160 DAYS AFTER LA EMERGENCIA DIAS DESPUES DE EMERGENCE The Effect of Planting Arrangement equidistant 30,000 plants/ha 60-cm rows The Effect of Density Yield loss (%) ET Number of weeds/unit area apply control when infestation reaches this level Economic threshold Value losses = cost of control Yield loss (%) Economic threshold Value losses = cost of control ET Ocupancy (density, weed biomass, leaf area, etc.) apply control when infestation reaches this level Plants not controlled still produce seeds: soil seed-bank buildup Field-level infestations are heterogeneous Compare tactics based on economic merit • Competition can be managed to reduce the critical weed-free period • Early resource capture: Crop management for early canopy and root growth • Basis for certain Cultural Weed control tactics Crop row spacing Crop cultivars Crop density Smother crops Crop rotation ...
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