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Predicting the changes in environmentally and agronomically significant phosphorus forms following the cessation of phosphorus fertilizer applications to grassland
Author(s) -
Dodd R. J.,
Mcdowell R. W.,
Condron L. M.
Publication year - 2012
Publication title -
soil use and management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.709
H-Index - 81
eISSN - 1475-2743
pISSN - 0266-0032
DOI - 10.1111/j.1475-2743.2012.00390.x
Subject(s) - phosphorus , zoology , fertilizer , grassland , chemistry , agronomy , biology , organic chemistry
Phosphorus (P) loss from soil can impair surface water quality. Losses from soil are related to soil P concentrations, but agronomic measures such as Olsen P do not in many cases predict the potential for P loss. One possible strategy to decrease P loss is to stop applying P fertilizers. We examined the changes in both agronomic (Olsen P) and environmental [water‐extractable P (WEP) and calcium chloride‐extractable P (CaCl 2 ‐P)] P tests, and the potential implications following a halt to P fertilizer application to four long‐term grassland field trials on different soil types. Exponential decreases in Olsen P and WEP concentration over time were observed in three of the four trials, but only in one trial for CaCl 2 ‐P. The rates of decrease in Olsen P (OP) and WEP concentration were best correlated with initial WEP (WEP i ) concentration and the quotient of Olsen P i /P retention (PR, a measure of Al‐ and Fe‐oxides), respectively. The equation t = 1/(−0.035 × ln OP i /PR − 0.0455) × (ln WEP t − ln WEP i ) was used to predict the time ( t ) taken for WEP concentrations at the sites to decrease to 0.02 mg/L (WEP t ), which is proposed as a limit for dissolved reactive phosphorus in overland flow, and the result was 23–44 yr. Results from a similar equation for Olsen P predicted a quicker rate of WEP. A significant decline in dry matter (DM) yield was observed at one trial site. For this site, the rate of decline in DM yield was of a similar magnitude to the rate of decline in WEP concentration. This suggests that halting P fertilizer application to decrease P loss as measured by WEP concentration may decrease farm productivity. An alternative, more financially acceptable, strategy is required, such as a negative P balance while maintaining yields with N fertilizer, but further work is required to assess both the agronomic and environmental implications of this strategy.