K. Sieling

Yield, N uptake, and apparent N-use efficiency of winter wheat and winter barley grown in different cropping systems

Increasing the efficiency with which crops use supplied nitrogen (N) can minimize the impact on the environment. In the growing seasons 1990/91 to 1992/93, the effects of different cropping systems on yield, N uptake by the grain and apparent N-use efficiency (NUE) of the grain of winter wheat and winter barley were investigated in a factorial field experiment at Hohenschulen Experimental Station near Kiel in NW Germany. The crop rotation was oilseed rape-winter wheat-winter barley, and soil tillage (conservation tillage without ploughing, conventional tillage), application of pig slurry (none, autumn, spring, autumn + spring), mineral N fertilization (0-240 kg N ha -1 ) and application of fungicides (none, applications against pathogens of the stems, leaves and ears) were all varied. Each year, the treatments were applied to all three crops of the rotation and were located on the same plots. Averaged over all factors, wheat yield was > 7 t ha -1 dry matter in all years and N uptake of the harvested grain varied between 140 and 168 kg N ha 1 . Pig slurry application in autumn increased grain yield and N uptake more than spring slurry in two out of three years. Mineral N unfertilized wheat yielded only 5.3-6.3 t ha depending on the year, mineral N fertilization increased wheat yield up to 8 t ha -1 . Barley yield was lower than wheat yield, ranging from 4.5 t ha -1 in 1993 to 6.3 t ha -1 in 1992. Unlike wheat, spring slurry N affected barley yield and N uptake more than autumn slurry. Wheat apparently utilized 12-21 % and barley up to 13% of the applied slurry N for its grain development. In 1991, the highest apparent slurry N-use efficiency (SNUE) of wheat and barley occurred after the late spring slurry application. However, in the following years, autumn SNUE of wheat was similar to (1992) or higher than (1993) spring SNUE, presumably because of vigorous tiller growth before winter. Additionally applied mineral fertilizer N decreased SNUE. Apparent mineral fertilizer N-use efficiency (FNUE) was higher than SNUE and ranged in wheat from 40 to 59% and in barley between 19 and 37% of the applied mineral fertilizer N. FNUE decreased with increasing N fertilization. To improve the N-use efficiency of both slurry N and mineral fertilizer N, more information is needed about the combined use of both N sources, with special emphasis on split applications of slurry as is common practice for mineral N fertilizer.

Efficient N management using winter oilseed rape. A review.

During the last decades the acreage of winter oilseed rape has been increased considerably in Europe. Rapeseed can take up a large amount of nitrogen before winter (>100 kg N/ha) and thus prevent nitrate leaching and pollution. Winter wheat is often grown subsequently, using oilseed rape as a favorable preceding crop. However, under wheat large nitrogen losses via leaching are frequently observed in humid climates during winter, mainly due to high amounts of soil mineral N available in fall and the small N uptake in fall of wheat as a subsequent crop. The low N offtake by the seeds results in a lower N-use efficiency and increases the N surpluses (>90 kg N/ha) compared with winter wheat (c. 40 kg N/ha). In addition, a large soil N pool increases the risk of N2O emission, with its impact on climate change. In our review we discuss several options to increase nitrogen-use efficiency in oilseed rape-based cropping systems ranging from optimizing N fertilization practices to options arising from adopted tillage practices and crop rotation. N application in fall normally increases dry matter accumulation and N uptake before winter. However, because of its limited yield effects in most situations, fall N supply also boosts N surpluses. N fertilization in spring exceeding the need of the crop for optimal seed yield increases the risk of N leaching and decreases the farmer’s net revenue. Considering the amount of N taken up by the canopy before the first spring application improves the determination of the optimal spring N supply. Measuring canopy N in fall gave the best results. At the cropping system level, time and intensity of soil tillage after the harvest of oilseed rape has concurrent goals of controlling volunteer rape, and achieving a successful establishment of the following crop, but avoiding an increased N mineralization. Changing the crop rotation by growing catch crops which prevent N from leaching is very effective in reducing N losses from the system by >40%. However, the economic losses from growing a usually less profitable spring crop probably limit the acceptance by farmers. Despite the problems addressed above, looking at the whole cropping system, oilseed rape is indispensable because of its beneficial effects on yield levels and nitrogen-use efficiency of following cereals, especially wheat, because alternative crops are often not realistic alternatives.

The effect of different preceding crops on the development, growth and yield of winter wheat

Abstract The effects of different preceding crops on the growth, development and yield components of winter wheat (cv. « Kanzler ») were determined in field trials carried out over three seasons in a system with high inputs. The effects on grain yield were observed in a total of four seasons. At most of the sample dates after winter, wheat following wheat had a lower dry weight and a slightly lower number of shoots per unit area than the other treatments, but the differences were inconsistent within years. After winter in one season (1986/87) a large range in number of shoots per unit area was observed, but it diminished during the season and finally led to negligible differences in dry weight; in the succeeding seasons (1987/88 and 1988/89) there was a contrasting trend. Wheat after wheat compared with wheat after rapeseed yielded between 0.66 t ha -1 (1986/87) to 1.97 t ha -1 (1987/88) less, but in the last season (1989/90) the wheat following wheat outyielded wheat following rapeseed by 0.59 t ha -1 . This was attributed to the optimum of nitrogen fertilization being exceeded in the wheat after rapeseed. Considering all seasons, the differences in grain yield could not be accounted for in terms of any single yield component. Take-all was apparent in three seasons and the higher disease incidence in wheat after wheat was associated with differences in growth and yield in 1987/88 and 1988/89 but in 1986/87 the incidence of take-all was considerably lower. It is suggested that the harmful influences of the disease were mitigated by wet seasonal conditions. Averaging over seasons, it was not possible to compensate for the detrimental influences of the preceding wheat crop on the grain yield of the subsequent wheat by increasing the amount of nitrogen fertilization from 210 kg N ha -1 to 250 kg N ha -1 .

Effect of slurry application and mineral nitrogen fertilization on N leaching in different crop combinations

Nitrogen (N) fertilizer not used by the crop can increase the risk of nitrate leaching into the groundwater. In two growing seasons, 1990/91 and 1991/92, the relationships between N fertilization and yield, N uptake by the grain and the N leaching in the subsequent percolation period were investigated in a multifactorial field experiment at Hohenschulen Experimental Station near Kiel in NW Germany. The crop rotation was oilseed rape – winter wheat – winter barley, and effects of soil tillage (minimum tillage without ploughing, conventional tillage), application of pig slurry (none, application in autumn, application in autumn and in spring), mineral N fertilization (none, 80 or 200 kg N ha −1 to oilseed rape and 120 or 240 kg N ha −1 to cereals) and application of fungicides (none, intensive) were all tested. In each year, the rotation and the treatments were located on the same plots. Mineral N fertilization and fungicide application increased yield and N uptake by grain or seed in all crops. In contrast, the application of slurry, especially in autumn, had only small effects on yield and N uptake. Nitrogen losses by leaching (measured using porous ceramic cups) were affected mainly by the year and the crop. In 1992/93, averaged over all factors, 80 kg N ha −1 was leached compared with 28 kg N ha −1 the previous year. Oilseed rape reduced N losses, whereas under winter wheat up to 160 kg N ha −1 was leached. Due to a lower N-use efficiency, autumn applications of slurry increased N leaching, and mineral N fertilization of the preceding crop also led to higher N losses. Since the amount of leached N depends both on the nitrogen left by the preceding crop (unused fertilizer N as well as N in residues) and on N uptake by the subsequent crop, it is not possible to apportion the N losses to any particular crop in the rotation. The cropping sequence, together with its previous and subsequent crops, must also be considered. To minimize leaching, N fertilization must meet the needs of the growing crop. In order to improve the efficiency further, investigations must be conducted in order to understand the dynamics of N in the plant–soil system in conjunction with the weather and crop management practices.

Effect of preceding crop combination and N fertilization on yield of six oil-seed rape cultivars (Brassica napus L.)

Abstract Information about the effect of the cropping history on the seed yield of oil-seed rape is extremely scarce. In 1992/93 and 1994/95, the effects of different preceding crop combinations (winter barley and winter wheat as preceding crops, oil-seed rape and wheat as pre-preceding crops) on the yield of six double low oil-seed rape cultivars were examined in a field trial at Hohenschulen Experimental Farm, north-west Germany. In addition, eight nitrogen treatments (different amounts and distribution patterns) were tested for their potential to reduce negative effects of the preceding crops. Following the cropping sequence of oil-seed rape then wheat, oil-seed rape yielded only 3.12 t ha−1; after oil-seed rape then barley, the yield was 3.43 t ha−1 compared with 3.77 t ha−1 following wheat then barley and 3.71 t ha−1 following wheat then wheat. The number of seeds per m2 showed a similar pattern, whereas the thousand-seed weight partly compensated for the reduced seed number. It was highest if oil-seed rape was grown 2 years previously. The cultivars differed significantly in their yield potential. Express (3.79 t ha−1) yielded 0.6 t ha−1 more than Falcon (3.18 t ha−1). Increasing amounts of fertilizer-N (80–200 kg N ha−1) increased the seed yield from 3.21 t ha−1 to 3.84 t ha−1. Changes in the distribution pattern within one fertilizer amount had no effect on seed yield. In addition, no interactions between preceding crop combination and the different cultivars or N treatments occurred. It is concluded that crop management cannot totally eliminate the negative effects of an unfavourable cropping history on the seed yield of oil-seed rape.

Mineral and slurry nitrogen effects on yield, N uptake, and apparent N-use efficiency of oilseed rape (Brassica napus)

In NW Europe, autumn-grown oilseed rape normally receives nitrogen (N) in autumn as seedbed N and in the spring as a split application at the beginning of growth and at stem elongation. In the growing seasons 1990/91 to 1992/93, the effects of slurry and mineral N fertilization on yield, N uptake by the seed and apparent N-use efficiency (NUE) by oilseed rape ( Brassica napus ) were investigated in a factorial field experiment at Hohenschulen Experimental Station near Kiel, NW Germany. The crop rotation was oilseed rape–winter wheat–winter barley, and soil tillage (conservation tillage without ploughing, conventional tillage), application of pig slurry (none, autumn, spring, autumn+spring) and mineral N fertilization (0 to 200 kg N ha −1 ) were all varied. Each year, the treatments were applied to all three crops of the rotation and were located on the same plots. Between the years, average seed yield ranged from 3·04 to 3·78 t ha −1 , while the corresponding N uptake by the seed varied from 107 to 131 kg N ha −1 . Slurry application in spring increased the seed yield and N uptake by the seed in all years, whereas the effect of autumn slurry alone or in combination with spring slurry was negligible. Mineral N fertilizer increased seed yield and N uptake by the seeds except in 1991/92, when N amounts exceeded 160 kg N ha −1 . No significant slurry×mineral N interaction occurred. Apparent NUE of mineral N was larger than that of slurry N, but decreased with increasing mineral fertilizer N rates. Only 5% of the autumn slurry N was apparently utilized by the seeds, compared with 24% of the spring slurry N. Despite its ability to take up substantial quantities of N before the winter, oilseed rape utilized very little autumn slurry N for seed production. To minimize environmental impacts, slurry should be applied in the spring, when plants are more able to use N for yield formation, even if NUE of slurry N is lower than that of mineral N. However, since NUE changes with the amount of applied N, it is difficult to find the best combination of slurry and mineral N fertilization to avoid negative environmental effects.

Impact of uncertainty on the optimum nitrogen fertilization rate and agronomic, ecological and economic factors in an oilseed rape based crop rotation

Crop yield and optimum nitrogen fertilization rates (Nopt) are often calculated ex post by specific functions of the nitrogen fertilization rate, but in doing this, uncertainties in terms of model choice, annual nitrogen response variations and parameter estimation are neglected. In the present study, Nopt, grain yields, net revenues and N balances were estimated for the three crops of an oilseed rape (OSR)–winter wheat–winter barley rotation. The effects of uncertainties were considered using three different statistical models, estimating an identical Nopt over the years and carrying out Monte-Carlo simulations where model parameters were varied according to their estimated standard errors. The statistical models used were the quadratic (Q) polynomial function, the linear response and plateau (LRP) function and the quadratic response and plateau (QRP) function. The Q model tended to estimate the highest Nopt values for the three crops, followed by the QRP and the LRP model in an initial ex post analysis. The highest corresponding mean net revenues in the rotation were estimated by the LRP model, followed by the Q and QRP model; mean N balances increased in the order LRP, QRP and Q. In the comparison of the crops, OSR showed the highest N balances followed by wheat and barley. Considering the protein concentration in wheat, Nopt values estimated by the Q model were considerably higher than without the economic effects of grain quality. In order to consider uncertainties in annual nitrogen response, an ex ante Nopt over the years was determined by maximizing the cumulated net revenues over all years in the rotation. Ex ante Nopt was higher as the mean of the ex post Nopt values for the QRP and LRP model. Average grain yields and net revenues were lower, N balances were higher. Running the Monte-Carlo simulations, ex post Nopt was obtained by 10 000 generated functions in each year and ex ante Nopt by 50 000 generated functions of years 1996, 1997, 1998, 1999 and 2002. This led to an increase in Nopt especially for the LRP model, while effects on the estimation of Nopt by the Q model were rather small. For the LRP model, corresponding mean net revenue decreased and mean N balance rose. In contrast, due to marginal changes in Nopt, the consideration of uncertainties in the estimations had only a small effect on net revenue and N balance in the Q model. In general, all kinds of uncertainty tended to increase Nopt but this effect was much higher for the LRP model as compared to the Q model. This increase in Nopt was associated with decreasing net revenues and increasing N balances. Exceptionally in OSR using the Q model, however, the ex ante approaches considering uncertainty led to slightly lower Nopt values compared to the ex post value.

Effects of previous cropping on seed yield and yield components of oil-seed rape (Brassica napus L.)

Abstract Information about the effect of the preceding crop or crop combination on the seed yield of oil-seed rape is extremely scarce. Experiments were carried out in northwest Germany to investigate the effect of different preceding crops on the growth, seed yield and yield components of oil-seed rape. The two directly preceding crops, wheat and oil-seed rape, had only a negligible and non-significant effect on the seed yield of the following oil-seed rape crop. Oil-seed rape grown after wheat had more pods per plant, due to an increase in the number of pods on the higher category branches. In contrast, the seed yield and yield components were more affected by the cropping sequence, i.e. the crops 2 years before. Averaged over two experimental years, the greatest yields were observed in oil-seed rape following the sequence peas-wheat (694 g m −2 ), whereas the smallest seed yield occurred after 2 years of oil-seed rape cropping (371 g m −2 ). The differences in the seed yield were again associated with more pods per plant, which compensated for the lower number of plants m −2 , whereas the number of seeds per pod and the mean seed weight were almost unaffected by the previous cropping. It was not possible to relate the described differences to the crop development, since differences in the biomass caused by the previous cropping were only significant at maturity. Oil-seed rape grown after 2 years of oil-seed rape had the highest ratings of stem canker ( Leptosphaeria maculans ) as well as verticillium wilt ( Verticillium dahliae ). But the general level of the diseases was low, and therefore other causes for the effects described must be considered.

Analysing soil and canopy factors affecting optimum nitrogen fertilization rates of oilseed rape ( Brassica napus )

Implementation of the EU Nitrate Directive in Germany will result in nitrogen (N) balance surpluses being restricted to 60 kg N/ha averaged over 3 years, starting in 2009. With N surpluses of more than 100 kg N/ha, winter oilseed rape (OSR) is a main contributor to N balance surpluses in OSR-based crop rotations in northern Germany. The exact calculation of N fertilization rates therefore becomes increasingly important in order to meet the target of less than 60 kg N/ha N balance average surplus over 3 years at a farm level. Currently, soil mineral nitrogen (SMN) at the beginning of spring growth is commonly used as an indicator for calculation of N fertilization rates in spring. However, amounts of SMN at the beginning of spring growth under OSR are usually low and canopy N is only taken into account to a very limited extent. This might lead to N fertilization rates exceeding the optimum N fertilization rate (N opt ). In the present study, the effects of SMN in spring and of canopy N in autumn and spring on N opt were investigated. Multi-site field trials producing different crop canopies, as a result of two sowing dates and two autumn N fertilization levels, with five spring N fertilization levels (0–280 kg N/ha) were carried out in 2005/06 and 2006/07. N opt in spring was estimated by quadratic response functions using the combine-harvested seed yield data from the spring N fertilization treatments. Regression analyses revealed no relationship between N opt and SMN at the beginning of spring growth or canopy N at the beginning of spring growth. In contrast, a significant negative correlation between N opt and canopy N at the end of autumn growth was found. Based on the results of the present study, it is sensible to take autumn canopy N into account when calculating N fertilization rates in spring. If canopy N in autumn is high (>50 kg N/ha), as a consequence, N fertilization rates should be reduced.

Short-term effects of biogas residue application on yield performance and N balance parameters of maize in different cropping systems

The expansion of biogas production in Germany poses a challenge in terms of the production of substrates for co-fermentation and the efficient use of biogas residues as fertilizers. At present there is limited information on the fertilizer value of biogas residues from energy-cropping systems. A 2-year field experiment was conducted at two sites in northern Germany to quantify the yield, nitrogen (N) concentration and the N balance of maize ( Zea mays L.) grown in different crop rotations: (i) maize monoculture (R1), (ii) maize – whole-crop wheat followed by Italian ryegrass as catch crop (R2) and (iii) maize – grain wheat followed by mustard as catch crop (R3). Crops were fertilized with different levels of biogas residues, cattle slurry, pig slurry, or mineral N fertilizer, which allowed quantification of the apparent N recovery (ANR) of the fertilizer types tested. The results revealed that crop rotation in interaction with N amount had a pronounced effect on the yield of maize. Maximum yield of 19·1 t dry matter (DM)/ha, corresponding to biogas production of 6685 m 3 N CH 4 /ha, was achieved in maize monoculture on a sandy loam site. Maize grown in R3 showed the lowest N response but had the highest yield under low N supply, whereas R2 generally had the lowest yield and N content. Differences in yield performance were reflected in the N balances, differing by 50 kg N/ha between R1 and R2, whereas R3 produced the lowest yield at low N supply. The carry-over effects from the preceding catch crops in R2 and R3, however, reduce the meaningfulness of the simple N balance. Nitrogen fertilizer type showed no interaction with crop rotation. Biogas residue application resulted in similar maize yielding performance to pig slurry and cattle slurry. However, relative N fertilizer value (RNFV) was 30% higher for biogas residue at optimal N supply, i.e. the minimum N input to achieve maximum DM yield.