Some Factors Influencing the Utilization of Phosphorus from Crop Residues

Abstract

A large proportion of phosphorus of crop residues was found to be readily available to succeeding crops. Some of the factors that influence the rate of release of phosporus from plant residues added to soils for use by succeeding plants were studied. They were: (a) maturity of the crop residue, (b) phosphorus content of the residue, (c) rate of application of the residues, (d) time of contact of the crop residue with the soil, (e) kind of crop residue, and (f) plant part involved. The study was conducted under greenhouse conditions in large glazed pots that held 1 kg. or more of soil. The influence of the above factors on the utilization of phosphorus by several test crops is less pronounced in soils well supplied with available phosphorus than in soils low in available phosphorus. The rate of availability of the phosphorus of the crop residues to the test crops, ryegrass and tomato, was inversely related to the stage of growth of the residues. For example, green manures cut prior to blooming supplied plants with about as much phosphorus as did liquid H3PO4 fertilizer. The phosphorus of straw, on the other hand, was absorbed by plants to a lesser extent than that of the liquid H3PO4. The phosphorus of residues high in total phosphorus was more readily available to plants than was that of residues low in phosphorus. The threshold phosphorus content of the crop residue above which the phosphorus of the residue was not wholly immobilized by microorganisms for use in decomposition was found to be about 0.2%. Phosphorus from root residues was less readily available than that from top residues only if the residues came from fully mature plants.

The potential for phosphorus loss in relation to nitrogen fertiliser application and cultivation

“…This would suggest that it was the loss of organic P from the soil and not from plant residues (as in the cultivated soils) that was the predominant pool involved, and furthermore that this pool of organic P is highly labile (water soluble). This is consistent with the wide C:P ratio of the plant residues, as it is suggested that for ratios > 300:1 (C:P) immobilisation occurs and for ratios < 200:1 (C:P) mineralisation occurs (Fuller et al 1956;Dalal 1977). Phosphorus from plant residues in our study would likely be immobilised (C:P ratio > 300, Table 3) before any mineralisation or release to drainage occurred.…”

Isotopic tracing of phosphorus uptake in corn from 33P labelled legume residues and 32P labelled fertilisers applied to a sandy loam soil

“…Further, earlier studies reported up to 40 % (McLaughlin et al 1988c) and 50 % (Friesen and Blair 1988) mineralisation of P from organic residues at 7 and 11 days. Although these earlier studies indicate that P release from young residues will be rapid (Fuller and Dean 1949;Fuller et al 1956), low mineralisation and release of P from the two legume residues (which were just 22 days older) in this study could possibly be due to the lack of distinct drying and wetting cycles (Chepkwony et al 2001). Transpirational demand was low and soil water content was permanently high, potentially slowing mineralisation significantly.…”

The effect of C:P ratio of plant residues added to soils of contrasting phosphate sorption capacities on P uptake by Panicum maximum (Jacq.)

“…Crop residues also contain a significant proportion of the nutrients taken up by the crop and, when returned to the soil, contribute to the maintenance of soil fertility. Several studies have shown that such materials can be an important supply of phosphorus (P) to subsequent crops (Blair and Boland, 1978;Dalal, 1979;Friesen and Blair, 1988;Fuller et al, 1956;Till and Blair, 1978). The rate and extent of reutilization of P from crop residues can be influenced by a number of factors including the amount and type of residues, their carbon : P (C : P) ratio and the prevailing soil and climatic conditions (Dalal, 1977).…”