No abstract

A better appraisal of the plant availability of soil phosphorus (P) added with animal manure is crucial to alleviate environmental impacts from over-application of P. This study compares the availability of P to maize in the Askov long-term experiments using unmanured plots and plots receiving corresponding rates of nitrogen (N), P and potassium (K) in mineral fertilizers or manure. Total-P and water extractable P (Pw) in soil, and plant height, dry weight, P concentration and P uptake were determined in early August. Final yields were determined in late October. Soil Pw was similar for plots receiving corresponding rates of P in mineral fertilizer or manure form. With a strong relationship between Pw, and maize growth and final yields, Pw was a reliable indicator of P availability to maize. Plant dry weight, P concentration and P uptake in early August were 23%, 8% and 31% higher, respectively, for maize grown on soil receiving manure compared with mineral fertilizer, while final maize yield in late October was 13% higher. Plant height and dry weight determined in early August suggested that maize development at this growth stage defined final maize yield. We conclude that the availability of P was similar after long-term application of corresponding rates of P in animal manure and mineral fertilizers, and that animal manure improves the growth of maize compared to mineral fertilizers. This is ascribed to micronutrients and residual N effects from previous additions of manure. K E Y W O R D Scattle slurry, long-term experiment, maize, mineral fertilizer, water extractable P 324 | JING et al.

Silage maize (Zea mays L.) is an important crop for forage on Northwestern European dairy cattle farms. We examined the effect of readily available soil phosphorus (P) on early maize growth and linked in-season height growth to final harvest yield using field plots with contrasting P supply in a one-year study embedded in a long-term experiment. Water-extractable P (Pw) was used as a proxy for readily available P in soil. Plant height, dry matter (DM) accumulation, P and nitrogen (N) uptakes were determined eight times from the two-leaf stage until final whole-crop harvest and fitted to logistic growth models. The models revealed that the final yield was significantly related to the time required to reach the maximum rate of height growth (occurring from 330 to 485 accumulated growing degree units, GDU), but not the time required to reach the maximum rate of DM accumulation (occurring from 561 to 649 GDU). Furthermore, plant height at the four-leaf stage and onwards was significantly related to the final harvest yield. Soil Pw linked closely to height growth parameters; higher levels of Pw gave earlier peaks in height growth. For this light sandy loam with a wide gradient in P content, we conclude that suboptimal P supply postpones height growth and reduces final yields. A sufficient P supply links to an early rapid increase in plant height and forms the potential for optimum nutrient uptake and high forage yields. Thus, early-season plant height may serve as a simple morphometric indicator for final yields.

Summary Lime and phosphorus (P) applications are common agricultural management practices. Our aim was to quantify the effects of long‐term application practices on root growth and abundance of arbuscular mycorrhizal fungi (AMF) under field conditions. We assessed the effects of lime and P fertilizer applications on barley yield, root growth and AMF abundance in 2016. Treatments were no, low, medium and high liming rate corresponding to application of 0, 4, 8 and 12 Mg lime ha−1 every 5–9 years since 1942 combined with no or yearly application of 15.6 kg P ha−1 since 1944. At harvest, grain yield, root intensity (core‐break) and AMF abundance at different soil depths were estimated. Root development was monitored during early growth with minirhizotrons in treatments receiving low, medium and high liming rates and P fertilization. A quadratic model relating grain yield to liming rate estimated yields to peak at 6.4 Mg lime ha−1 with yields of 4.2 and 3.2 Mg grain ha−1 with and without P fertilization, respectively. Low and medium liming rates resulted in greater AMF abundance, especially in the no P treatments. During early growth in P‐fertilized treatments, 77% and 65% more roots developed in the soil profile when treated with medium and high liming rate, respectively, compared to low liming rate. We conclude that long‐term application of lime in soils receiving yearly P fertilization improved conditions for root growth in soil layers below 30 cm, but at the high liming rate, this did not translate into higher yield.

Background Cover crops (CC) introduced to reduce leaching of nitrate may also improve soil microbial properties and phosphorus (P) uptake in crops that follow. These effects may depend on soil P status and the quality of the CC residues. Aim Our aim was to quantify the more persistent effects of incorporation of residues of three different CC species on barley growth and P uptake and whether any response in growth and P uptake was related to soil P status and changes in soil microbial properties. Methods We examined the impact of soil P status, CC species, and residue fraction (shoots and/or roots) on the growth of winter barley (Hordeum vulgare) and soil microbial properties. Shoot and root residues from three contrasting CC (oats, Avena sativa; corncockle, Agrostemma githago; lupine, Lupinus angustifolius) were incubated for 2 months in soil with low and medium P status. Dry matter yield and P offtake characterized effects of CC residues on barley while phospholipid fatty acids (PLFAs), neutral lipid fatty acids (NLFAs), and enzyme activity characterized soil microbial properties after barley harvest. Results Effects of shoot residues on barley yield and P offtake appeared neutral or positive and not affected by soil P status, while the effect of root residues appeared negative for medium P soil and neutral for low P soil. With lupine shoot biomass, however, barley yield and P offtake increased in both soils. Neither CC treatments nor soil P status affected the microbial community composition (bacterial and fungal specific PLFAs). Lupine roots increased phosphomonoesterase, and lupine residues generally stimulated microbial abundance (total microbial PLFAs) compared to other CC treatments. Conclusion We conclude that the effect of CC residues on the following crop and soil microorganisms depends on soil P status and that lupine had the largest positive impact on barley growth.