Nutrient Disorders of Sweet Potato

Crop Production/Industries,

Acid soil infertility effects on peanut yields and yield components

The interpretation of soil amelioration experiments with peanuts is made difficult by the unpredictability of the crop and by the many factors altered when ameliorating acid soils. The present study was conducted to investigate the effects of lime and gypsum applications on peanut kernel yield via the three first order yield components, pods per ha, kernels per pod, and kernel mass. On an acid medium sandy loam soil (typic Plinthustult), liming resulted in a highly significant kernel yield increase of 117% whereas gypsum applications were of no significant benefit. As indicated by path coefficient analysis, an increase in the number of pods per ha was markedly more important in increasing yield than an increase in either the number of kernels per pod or kernel mass. Furthermore, exch. A1 was found to be particularly detrimental to pod number. It was postulated that poor peanut yields

In vitro evidence of aluminum effects on solution movement through root cell walls

Little is known about the primary effects of aluminum (Al) in reducing root growth. However, the sorption of Al by the root cell wall, particularly by calcium (Ca) pectate, has been suggested as being important in the expression of Al toxicity in plants. To overcome problems arising from the close proximity of root cell components that may react with Al, a synthetic Ca pectate membrane was prepared as a model system for Al studies. Solution containing 1 mM Ca (as CaCl2) was passed through the membrane, and the flow rate measured. Solution containing 29 μM Al (as A1C13) and 1 mM Ca reduced solution flow rate by > 80% from c. 3.5 to c. 0.6 mL/min within 2 min, with a further slight decline over the next 4 min. The Al concentration in solution proximate to the inlet side of the membrane decreased to 15 μM within 10 min, and only 3 μM Al was measured in solution that had passed through the membrane. These results suggest that an important primary effect of toxic Al is a reduction in water movement into the root, with consequent effects on water relations in the plant

Timing, magnitude, and location of initial soluble aluminum injuries to mungbean roots

Despite a century's knowledge that soluble aluminum (Al) is associated with acid soils and poor plant growth, it is still uncertain how Al exerts its deleterious effects. Hypotheses include reactions of Al with components of the cell wall, plasmalemma, or cytoplasm of cells close to the root tip, thereby reducing cell expansion and root growth. Digital microscopy was used to determine the initial injuries of soluble Al to mungbean (Vigna radiata L.) roots. Roots of young seedlings were marked with activated carbon particles and grown in 1 mm CaCl2 solution at pH 6 for ca. 100 min (control period), and AlCl3 solution was added to ensure a final concentration of 50 muM Al (pH 4). Further studies were conducted on the effects of pH 4 with and without 50 muM Al. Four distinct, but possibly related, initial detrimental effects of soluble Al were noted. First, there was a 56-75% reduction in the root elongation rate, first evident 18-52 min after the addition of Al, root elongation continuing at a decreased rate for ca. 20 It. Decreasing solution pH from 6 to 4 increased the root elongation rate 4-fold after 5 min, which decreased to close to the original rate after 130 min. The addition of Al during the period of rapid growth at pH 4 reduced the root elongation rate by 71% 14 min after the addition of Al. The activated carbon marks on the roots showed that, during the control period, the zone of maximum root growth occurred at 2,200-5,100 mum from the root tip (i.e. the cell elongation zone). It was there that Al first exerted its detrimental effect and low pH increased root elongation. Second, soluble Al prevented the progress of cells from the transition to the elongation phase, resulting in a considerable reduction of root growth over the longer term. The third type of soluble Al injury occurred after exposure for ca. 4 h to 50 mum Al when a kink developed at 2,370 mum from the root tip. Fourth, ruptures of the root epidermal and cortical cells at 1,900-2,300 mum from the tip occurred greater than or equal to4.3 h after exposure to soluble Al. The timing and location of Al injuries support the contention that Al initially reduces cell elongation, thus decreasing root growth and causing damage to epidermal and cortical cells