Lena Engström

Reducing nitrate leaching after winter oilseed rape and peas in mild and cold winters

Nitrate leaching after winter oilseed rape and peas has not been studied at the most northern limits of oilseed rape cultivation where winters vary between being mild, with continuous drainage, and cold, with periods of frozen soil. Here, we studied the effect of N fertilisation to oilseed rape, catch crops after oilseed rape and peas and dired drilling of winter wheat after oilseed rape on N leaching in south-west Sweden. Nitrate leaching was determined in two field experiments, dated 2004–2006 and 2005–2007, respectively, on a sandy loam. Our results show that under oilseed rape nitrate leaching was low, at 16–23 kg N ha−1, in a mild winter with drainage from October to March. In the subsequent mild winter nitrate leaching under wheat was higher, amounting to 35–94 kg N ha−1. Nitrate leaching levels were similar, 32–58 kg N ha−1, for all crops in a cold winter with a long-lasting snow cover and main drainage occurring after snowmelt in March and April. Application of fertiliser N to oilseed rape at the optimum N rate, rather than 50 kg N ha−1 above optimum, reduced leaching in a following winter wheat crop by 25 and 27 kg N ha−1 in a cold and a mild winter, respectively. Spring undersowing of perennial ryegrass as a catch crop reduced leaching by 12 kg N ha−1 after optimally fertilised oilseed rape in a mild winter, despite only growing until mid-September when winter wheat was sown. An undersown catch crop of peas, then grown until November, reduced leaching by 15 kg N ha−1. Direct drilling of winter wheat after oilseed rape had no effect. These findings show that there are risks of enhanced leaching in early spring after a cold winter with a snow cover and superficially frozen soil. Optimising the spring N rate for oilseed rape was the most effective measure to decrease leaching in both mild and cold winters, and this effect was improved by an undersown catch crop in a mild winter.

Timing of organic fertiliser application to synchronise nitrogen supply with crop demand

Abstract To achieve high nitrogen (N)-use efficiency, N availability from organic fertilisers must be synchronised with crop uptake. In order to estimate when previously unmineralised N is plant-available in relation to fertilisation time-point, net N mineralisation was studied in incubations under natural temperature conditions. The fertilisers studied were meat and bone meal (Biofer), dairy slurry, dairy manure, chicken manure, and a by-product from yeast production (Vinasse). The fertilisers were mixed with soil and incubated in plastic bottles placed in topsoil in south-west Sweden on different dates throughout the year, simulating fertiliser application in autumn, early spring, spring, and early summer. Bottles were sampled for analysis of NH4-N and NO3-N on three to seven occasions until late autumn and the experiment was repeated in two consecutive years. Dairy slurry and dairy manure had a very slow, almost negligible, net N mineralisation after application. Slurry with rather high ammonium content should therefore be applied as close to crop demand as other circumstances allow, whereas dairy farmyard manure with very low mineral N content can be applied off-season. Chicken manure had a considerable proportion of mineral N initially, but released further mineral N after application. Vinasse and Biofer had almost no mineral N initially, but much of the N present mineralised rapidly. About 65% of total N in Biofer, Vinasse, and chicken manure was in mineral form within 30–50 days or 450 growing degree-days (GDD), after which net mineralisation ceased. This indicates that these three types of fertiliser should be applied at least one month before the end of crop N uptake and that autumn application is associated with a risk of N leaching unless a crop with high N uptake is present during winter.

Importance of soil mineral N in early spring and subsequent net N mineralisation for winter wheat following winter oilseed rape and peas in a milder climate

Abstract Nine biennial field experiments, 2000–2004, in south Sweden, 55–56°N, with winter wheat following winter oilseed rape, peas, and oats, were used to estimate the impact of a future milder climate on winter wheat production in central Sweden, 58–60°N. The trials included studies 1) on losses during winter of soil mineral nitrogen (Nmin, 0–90 cm soil), accumulated after the preceding crops in late autumn, 2) on soil N mineralisation (Nnet) during the growing season of the wheat (early spring to ripeness) and 3) on grain yield and optimum N fertilisation (Opt-N rate) of the wheat. Average Nmin in late autumn following winter oilseed rape, peas, and oats was 68, 64, and 45 kg ha−1, respectively, but decreased until early spring. Increased future losses of Nmin during the winter in central Sweden due to no or very short periods with soil frost should enhance the demand for fertiliser N and reduce the better residual N effect of winter oilseed rape and peas, compared with oats. Their better N effect will then mainly depend on larger Nnet (from March to maturity during the winter wheat year). Owing to more plant-available soil N (mainly as Nnet) Opt-N rates were lower after oilseed rape and peas than after oats despite increased wheat yields (700 kg ha−1) at optimum N fertilisation. In addition to these break crop effects, a milder climate should increase winter wheat yields in central Sweden by 2000–3000 kg ha−1 and require about 30–45 kg ha−1 more fertiliser N at optimum N fertilisation than the present yield levels. Increased losses and higher N fertilisation to the subsequent winter wheat in future indicates a need for an estimation of the residual N effect at the individual sites, rather than using mean values as at present, to increase N efficiency.

Effects of three N strategies on tillering and yield of low shoot density winter wheat

Abstract Application of nitrogen (N) in early spring is often recommended for low shoot density winter wheat in northern temperate areas such as Sweden. Regional N-strategy field trials in such areas generally show no relationship between early N and grain yield but the effects on shoot numbers and other yield components are seldom investigated. This study quantified the effect of three N fertilization strategies on the number of tillers at GS30-31 and the grain yield of winter wheat with low shoot density in early spring, in order to evaluate the importance of early N application. The investigations were carried out from 1999–2002 in four annual field experiments on a clay soil in south-west Sweden using winter wheat (cvs. Kosack and Tarso) with shoot densities in early spring ranging from 360–850 shoots m−2. A positive relationship between time of first N application as number of days before GS30 and increase in number of shoots from GS20-21 to GS30-31 was observed. The relationship was strongest in experiments with the lowest shoot density in early spring (360–560 shoots m−2) and the additional increase with each day of earlier availability of N before GS30 was 11 shoots m−2. In wheat with this low shoot density in early spring, N was needed before GS30 to avoid yield reductions. Whether N was applied and available 24 or 13 days before GS30 did not affect yield, despite significantly more shoots being present at GS30-31 with earlier N application.

Optimal Placement of Meat Bone Meal Pellets to Spring Oats

New technology makes it possible to apply organic fertilizers with higher precision, and organic producers want to know how to exploit these new possibilities to make their production more efficient. This study investigated the effect of band application (in different positions) of pelleted organic fertilizer, compared with broadcasting, on grain yield and weed density in spring oats (Avena sativa L.). Six microplot field experiments were carried out on silty clay and sandy loam in Sweden during the growing season of 2014-2016. In oats seeded at 25 cm row spacing, pelleted meat bone meal was band-applied at one of three distances from the crop row (0, 4, and 12.5 cm) and at two or three incorporation depths (1 and 4 cm on silty clay and 1, 4, and 6 cm on loamy sand). These treatments were compared with broadcast spreading, mineral nitrogen fertilizer, and an unfertilized control. On both soil types, fertilizer placement 4 cm from the crop and 4-6 cm incorporation depth gave the highest yield and crop nitrogen uptake. Yield in this treatment was 800 kg ha-1 higher on clay soil and 1100 kg ha-1 higher on sandy loam compared with the same organic fertilizer applied by broadcasting, an 80-150% yield increase. On the sandy loam, distance from the crop row had a more significant effect on grain yield (p<0.001) than soil incorporation depth (p=0.07). On the silty clay, crop yield was significantly influenced by incorporation depth (p=0.003) and distance from the crop row (p=0.04). In five experiments, mineral N fertilizer equivalent (MFE) increased from on average 63% with broadcasting to 85% with placement 4 cm from the crop row and 4 cm incorporation depth. Weed biomass was significantly affected by fertilizer placement on the clay soil, with higher weed biomass with deeper incorporation (p=0.045) and greater distance from the crop row (p=0.049). On the sandy loam, there was a tendency for larger weed plants at greater distance from the crop row (p=0.13) except when seeds and pellets were placed together, which gave the highest weed weight, probably due to lower competition from the crop in this treatment.