The effects of soil moisture levels on organic phosphorus mineralization and rate constant of decomposition

Plant residues, due to having amounts of nutrients that required by plants, plays an important role in the natural cycle of this elements. Due to the role of plant residues in the improvement of soil fertility, understanding the various management practices and choose the best method of management is necessary. A combination of environmental and biological factors are involved in organic phosphorus mineralization. Microbes are agents responsible for litter degradation and abiotic factors such as temperature, soil type, bulk density, soil moisture and irrigation water quality influence organic phosphorus mineralization rates since microbial activities are affected by these factors. The rate of organic phosphorus mineralization is higher in warm and moist environments than in cold or dry sites. Due to the inverse relationship between soil moisture and aeration this experiment was performed to evaluate the effects of soil moisture levels on organic phosphorus mineralization and rate constant of decomposition.
This experiment was performed to evaluate the effects of soil moisture on organic phosphorus mineralization and degradation rate constant of phosphorus from alfalfa and barley residues. For this purpose, a split – split plot experiment with three replications was conducted using litter bag method in greenhouse. Factors examined were types of plant residue (barley and alfalfa), soil moisture levels (10, 25, 50, 75 and100% saturation) and incubation time intervals (1, 2, 3 and 4 months). At the end of incubation periods, the litter bags were pulled of the pots and the weights of plant residues remained in bags were measured. The plant residues were also analyzed for organic phosphorus using colorimetry method. Organic phosphorus mineralization were calculated by subtracting the remaining amounts of organic phosphorus in one incubation time interval from those of the latter incubation.
The results showed that the amounts of organic phosphorus mineralization after 4 months were 25.24, 36.38, 43.40, 36.87 and 31.25% for plant residues when the soil moisture levels were adjusted at 10, 25, 50, 75 and 100% of saturation percentage (sp) respectively. The corresponding amounts for degradation rate constant of phosphorus were also 0.13, 0.20, 0.26, 0.21 and 0.16 Mounth-1 for plant residues.
The rate of organic phosphorus mineralization in the first month of incubation were higher than the sum of those mineralization in the other months of incubation. maximum amounts of phosphorus mineralization observed at 50% sp. The results also showed that in the case of organic phosphorus, soil moisture abound is a strong limiting factor for phosphorus mineralization same as soil moisture deficit and in saturated soils the amount of organic phosphorus mineralization was same to low levels of soil moisture.