The study investigated the prolonged impact of swine manure application on soil inorganic phosphorus (P) fractions over an 8-year continuous, randomized field trial involving rotating wheat (wet conditions) and rice (flooded conditions) crops. The trial comprised six treatments: triplicate control plots receiving only chemical fertilizers, and triplicate plots receiving chemical fertilizers and/or swine manure ranging from 150 to 1200 kg P2O5 ha- 1. The continuous application of swine manure increased soil P content and availability. Initially, P primarily accumulated in the soil as Fe-P during the first four years of manure application, transitioning to Ca8-P over the following four years. The main driver of these changes in P fractions was soil total organic carbon (TOC) was identified as the main driver of these changes in P fractions, contributing 31.5% to the observed variations. TOC increased steadily throughout the trial, with a faster rising in years 1-4 compared to years 4-8. Laboratoryscale soil incubation experiments were conducted, involving the addition of glucose or cellulose as exogenous carbon sources to test their effects on soil P dynamics and mitigate environmental damage from P leaching. The addition of cellulose to soil that had received high quantities of swine manure for eight years resulted in increased the moderately labile and moderately resistant organic P fractions while decreasing the Ca8-P and Olsen-P fractions. This promoted adsorption of high-activity inorganic P to organic matter, consequently limiting the accumulation of Ca8-P. The long-term application of swine manure altered soil P fractions and enhances P lability, enhancing P lability and availability. This study identified an optimized the risk of leaching of labile P from soil under a fertilization regime applying 10,300 kg ha- 1 yr- 1 swine manure. To further mitigate the risk of P leaching, the inclusion of additional cellulose-based organic matter (e.g., straw) in swine manure fertilization regimes is recommended.

Background Piglets are born with limited stores of iron, and with an increasing number of live-born piglets, there may be a risk that the sows cannot provide enough iron to their offspring. The iron content in soil may not meet the demands of today's piglet, born and reared in an outdoor setting. The study aimed to describe the blood haemoglobin (Hb) levels in pigs reared outdoors and to determine whether piglets have higher Hb levels at weaning when an iron supplement is administered intramuscularly at three days of age, as compared to pigs not given an iron supplement. The seasonal variation in Hb-levels was also to be investigated. The Hb concentration was analysed with a HemoCue 201 + Hb photometer. Results In total 56 litters (399 piglets) were included in the study and sampled at three days of age, while 378 piglets were sampled at weaning. The mean Hb level at three days of age was 91 g/L (48-154 g/L). In total 47% of the piglets had Hb levels < 90 g/L at three days of age. The mean Hb level at weaning was 127 g/L (76-176 g/L), with a lower level (122 g/L) in the group given the iron supplement than in the group not given an iron supplement (132 g/L). Only 1% of the piglets had Hb levels lower than 90 g/L at weaning. Results indicative of a seasonal effect on Hb levels at three days of age was demonstrated. Piglets born in spring had significantly lower Hb levels, and piglets born in autumn had significantly higher Hb levels. No seasonal effect could be demonstrated for Hb levels at day 33. Conclusions The results indicate that the natural uptake from the environment was sufficient, but that there was a seasonal effect on the Hb levels at three days of age. This indicates that there might be a need for different routines regarding iron supplementation in outdoor reared piglets depending on the climate and season.