Manganese (Mn) in excess of crop requirements is a serious problem when manganiferous soils become acid, waterlogged or amended with organic materials. We investigated the dynamics of manganese phytotoxicity and tested management options for growing crops in acid soils with excess Mn. We hypothesized that Mn phytotoxicity is governed by water use and expressed as continuous negative interaction between current plant/leaf growth rate (RGR PLant/Leaf) and future Mn accumulation rate (RAR Mn); and that under growth conditions where RGRPlant/Leaf exceeds RAR Mn, excess Mn can be managed by maximizing RGR Plant/Leaf and minimizing RAR Mn. The parameters RGR Plant/Leaf and RAR Mn were calculated using the conventional growth analysis techniques. The dynamics of Mn phytotoxicity was investigated by growing Mn-tolerant Lee and Mn-sensitive Forrest soybeans in the greenhouse using Wahiawa series, a manganiferous Oxisol in Hawaii. The soybeans were grown at soil pHs 4.78, 5.5, and 6.00 and five growth conditions (control, 80-90% field capacity, 40% shading, green manure and phosphorus at 150 mg kg-1). RAR Mn consistently exceeded RGR Leaf in most treatments. Over the range of soil pH and growth conditions, we found strong positive correlation between RGR Leaf and RAR Mn, this correlation mediated by a more fundamental correlation of both rate processes to plant water use. The dynamics of Mn phytotoxicity, referred to as the 'dual feedback effect' model described a continuous negative interaction between current RGR Leaf and future RAR Mn and between current RAR Mn and future RGR Leaf. Manganese accumulation rate exceeded plant growth rate, leaf Mn increased with time and growth treatments did not affect growth rate unless soil pH was increased to eliminate excessive Mn in the soil. Field experiments were conducted in Rugao series, an acid Alfisol in Northern Philippines. The soil is acid (pH 4.40) with abundant Fe-Mn concretions within the surface 20-cm. Preliminary field experiment showed Mn phytotoxicity in local soybeans cv. PSB Sy2 and PSB Sy6 as leaf symptoms in addition to low plant growth rates and grain yields associated with leaf Mn exceeding a critical value of 500 mg kg-1. Results of a second field experiment showed that cultivar, liming, and the management of phosphorus (P), manure and mulching modified plant growth rate and enhanced tolerance to excess soil Mn. Lime control (2 t ha-1) neutralized half of the exchangeable AI while keeping saturated paste Mn in excess. Mulching did not affect saturated paste-and increased RAR Mn without affecting RGR Leaf. Increases in RGR Leaf due to P and manure were accompanied by increases in RAR Mn. This increase in RGR Leaf translated to increased yields even when RAR Mn and soil solution Mn were increased as in the case of manure addition. Increases in grain yield due to manure exceeded the increases due to lime or P. Chicken manure was more effective than green manure in increasing grain yield. Plant growth rate exceeded Mn accumulation rate, leaf Mn decreased with time and manure treatments alleviated Mn phytotoxicity despite an increase in soil Mn.
| Identifer | oai:union.ndltd.org:UHAWAII/oai:scholarspace.manoa.hawaii.edu:10125/996 |
| Date | 12 1900 |
| Creators | Bajita, Jocelyn |
| Contributors | Yost, Russell |
| Publisher | University of Hawaii at Manoa |
| Source Sets | University of Hawaii at Manoa Libraries |
| Language | en-US |
| Detected Language | English |
| Type | Thesis, Text |
| Rights | All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner., https://scholarspace.manoa.hawaii.edu/handle/10125/586 |
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