Potassium balances for arable soils in southern England 1986–1999

Abstract. The behaviour of potassium (K) in a range of arable soils was examined by plotting the change in exchangeable K of the topsoil (Δ K_ex) at the end of a 3–5 year period against the K balance over the same period (fertilizer K applied minus offtake in crops, estimated from farmers' records of yield and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops MAFF 2000) are valid averages, 10–50% of Δ K_ex was explained by the balance, relationships being stronger on shallow/stony soils. Excess fertilizer tended to increase K_ex and reduced fertilization decreased it, requiring between 1.2 and 5.4 kg K ha⁻¹ for each mg L⁻¹Δ K_ex. However, merely to prevent K_ex falling required an extra 20 kg K ha⁻¹ yr⁻¹ fertilizer on Chalk soils and soils formed in the overlying Tertiary and Quaternary deposits, despite clay contents >18%. Whereas, on older geological materials, medium soils needed no extra K and clays gained 17 kg K ha⁻¹ yr⁻¹. It is unlikely that the apparent losses on some soil types are anomalies due to greater crop K contents. Theory and the literature suggest leaching from the topsoil as a major factor; accumulation in the subsoil was not measured. Recommendations for K fertilization of UK soils might be improved by including loss or gain corrections for certain soil types.     

Crop and soil response to subsoil loosening, deep incorporation of phosphorus and potassium fertilizer and subsequent soil management on a range of soil types.: Part 2: Soil structural conditions

Abstract. In a series of experiments on 16 sites both a power-driven rotary-tine Wye Double Digger and a rigid tine winged subsoiler produced significant subsoil loosening and fissuring. The Double Digger consistently produced the greatest clod breakdown together with the least soil bulk densities and cone penetration resistances. Management strategies after loosening had an important influence on the longevity of the loosening effect. The rate of recompaction was least with controlled traffic and bed systems and increased with random traffic and with the growing of root crops. No significant differences in crop response were monitored between the two loosening treatments, yield response depending largely on the extent of moisture stress experienced by the crop. Loosening on silty soils reduced yields in wet seasons and this was associated with soil structural instability. Visual soil profile examination is necessary to support bulk density and cone penetration resistance measurements when assessing soil compaction.     

The influence of soil macroporosity on water retention, transmission and drainage in a clay soil

Abstract. Reductions in hydraulic conductivity and specific yield (drainable porosity) of large cores of Evesham clay soil were observed for periods up to 40 days under continuous ponding. A strong linear relationship ( r ²= 0.94) found between these two variables was used as parameter input to a layered drainage model for mole drained soils. Model results indicated that soils of lower drainable porosity and hydraulic conductivity produced higher peaked hydrographs widi faster recessions. These results are discussed in relation to the effects of soil loosening on drain response in heavy clay soils.     

Ability of some Norwegian soils to supply grass with potassium (K) - soil analyses as predictors of K supply from soil

Abstract. Uptake in grass crops of ammonium acetate lactate extractable K (K_AL) and reserve K (interlayer K + structural K) in soil was studied in 16 field experiments at different locations on a range of mineral soil types in Norway. The K uptake from soil, both from K_AL and reserve K, was considerable, often even at the highest level of K fertilizer. During three years, only on the sandy soils with a low level of acid soluble K (K_HNO3 minus K_AL) was there a yield response to K fertilization. The K_AL values declined rapidly and flattened off at a 'minimum level' which differed with soil type. This minimum level for K_AL is a useful parameter in fertilizer planning, because the grass usually took up the K in excess of the minimum level over two years. The minimum value of K_AL was significantly correlated with the content of clay + silt in soil. The decrease in K_AL during the growing season was closely correlated to the K_AL value in spring minus the minimum value and, therefore, the amount of K supplied to the grass from the K_AL fraction can be calculated. Furthermore, the K_AL value for the following spring may be estimated. The release from reserve K was partially related to acid soluble K.     

The influence of tillage on NO and N2O fluxes under spring and winter barley

Abstract. There is a lack of information about the influence of tillage and time of sowing on N₂O and NO emission in cereal production. Both factors influence crop growth and soil conditions and thereby can affect trace gas emissions from soils. We measured fluxes of NO and N₂O in a tillage experiment where grassland on clay loam soil was converted to arable by either direct drilling or ploughing to 30 cm depth. We made measurements in spring for 20 days after fertilizer application to spring-sown and to winter-sown barley. Both were the second barley crop after grass. Direct drilling enhanced N₂O emission primarily as a result of restricted gas diffusivity causing poor aeration after rainfall. Deep ploughing enhanced NO emission, because of the large air-filled porosity in the topsoil. NO and N₂O emissions were smaller from winter sown crops than from spring sown crops.   The three rates of N fertilizer application (40, 80 or 120 kg N ha^–1) did not produce the expected linear response in either soil available N concentrations or in NO and N₂O fluxes. We attributed this to the lack of rainfall in the ten-day period after fertilizer application and therefore very slow incorporation and movement of fertilizer into and through the soil.     

The effectiveness of cover crops during eight years of a UK sandland rotation

Abstract. Growing cover crops during the winter before spring-planted crops is often suggested as an effective method to decrease nitrate leaching. A four-course crop rotation (potatoes-cereal-sugarbeet-cereal) was followed through two rotations on a sandy soil in the English Midlands. Three management systems were imposed on the rotation to test their effects on nitrate loss. The effects of cover crops on nitrate leaching and crop yields were compared with the more conventional practice of over-winter bare fallow before potatoes and sugarbeet.
Cover crop N uptake was variable between years, averaging 25 kg ha⁻¹, which is typical of their performance on sandy soils in the UK. The cover crops usually decreased nitrate leaching but their effectiveness depended on good establishment before the start of drainage. Over 7 years, cover crops decreased the average N concentration in the drainage from 24 to 11 mg l⁻¹. Potato yield and tuber N offtake increased after cover crops. Ware tuber yield increased by an average of c . 8%; this was unlikely to be due to additional N mineralization from the cover crop because the potatoes received 220–250 kg fertilizer N ha⁻¹, and non-N effects are therefore implicated. Sugar yield was not increased following a cover crop.
After 8 years of nitrate-retentive practices, there were no measurable differences in soil organic matter. However, plots that had received only half of the N fertilizer each year contained, on average, 0.14% less organic matter at the end of the experiment.     

Subsoil loosening in a crop rotation for organic farming eliminated plough pan with mixed effects on crop yield

Compacted subsoil may reduce plant root growth with resulting effects on plant uptake of water and nutrients. In organic farming systems subsoil loosening may therefore be considered an option to increase nutrient use. We investigated the effect of subsoil loosening with a paraplow to ca. 35 cm depth within a four-crop rotation in an organic farming experiment at Foulum (loamy sand) and Flakkebjerg (sandy loam) in Denmark. In each of the years 2000–2003, half of four plots per site were loosened in the autumn bearing a young grass-clover crop (mixture of Lolium perenne L., Trifolium repens L. and Trifolium pratense L.) established by undersowing in spring barley (Hordeum vulgare L.). The grass-clover was grown for another year as a green manure crop and was followed by winter wheat (Triticum aestivum L.), lupin (Lupinus angustifolius L.):barley and spring barley in the following 3 years. On-land ploughing was used for all cereal and pulse crops. Penetration resistance was recorded in all crops, and the results clearly showed that subsoil loosening had effectively reduced the plough pan and that the effect lasted at least for 3.5 years. Measurements of wheat root growth using minirhizotrons at Foulum in 2002/2003 did not show marked effects of subsoil loosening on root frequency in the subsoil. Subsoil loosening resulted in reduced growth and less N uptake of the grass-clover crop in which the subsoil loosening was carried out, probably due to a reduced biological nitrogen (N) fixation resulting from a smaller clover proportion. This had a marked effect on the growth of the succeeding winter wheat. Negative effect of subsoil loosening on yield of winter wheat and spring barley was observed without manure application, whereas small positive yield effect of subsoil loosening was observed in crops with a higher N supply from manure. Yield decrease in winter wheat was observed in years with high winter rainfall. There was no significant effect of subsoiling on grain yield of the lupin:barley crops, although subsoiling had a tendency to increase crop growth and yield during dry summers. Our results suggest that subsoil loosening should not be recommended in general under Danish conditions as a measure to ameliorate subsoil compaction.     

Effects of soil physical conditions on root growth and water use of barley grown in containers

The results of an experiment to study the effects of subsoil loosening on root growth and water use of barley plants grown in 1.0-m-deep, 65-mm-diameter plastic tubes are reported. Changes in the dry bulk density (1280–1530 kg m⁻³) of the 0.2-m-deep soil layer immediately below the plough layer hand disproportionate effects on rates of root growth, and following this on crop water use and dry matter yield. Increasing the number of large pores in the sieved sandy loam soil at a depth of between 0.2 and 0.4 m allowed roots to proliferate easily and at the same time to extract the water held at relatively low suctions. When no extra water was added, these plants came under water stress sooner than those grown in containers with relatively compacteds ubsoil. Reduced rates of root growth meant that water was made available over a longer period of time. The variable and unpredictable yield responses of crops to subsoil loosening reported in the literature must be owing in part to the patterns of rainfall distribution during the season in relation to root growth and the development stage of the crop. Under certain conditions subsoil loosening will increase crop water stress and reduce yield.

The validity of the techniques used for observing root growth was supported by the linear (β=1.09) relationship obtained at the end of the experiment between the length of root at the soil/plastic interface and the corresponding number of root ends observed at the centre of the soil core (r²=70%, N=216), although there was still a considerable degree of scatter in the position of individual points.     

The effect of soil texture and soil drainage on emissions of nitric oxide and nitrous oxide

Abstract. Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N₂O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N₂O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N₂O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 μg NO-N m^–2 h^–1, with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 μg N₂O-N m^–2 h^–1. Seasonal shifts in soil aeration caused maximum N₂O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N₂O emission was best related to a combination of bulk density and clay content and the NO/N₂O ratio decreased logarithmically with increasing water filled pore space.     

In-row tillage methods for subsoil amendment and starter fertilizer application to conservation-tilled grain sorghum

Acid subsoils and tillage pans limit crop yields on sandy soils of the Southern Coastal Plain of the United States. Studies were conducted for 3 years on two soils with acid subsoils and tillage pans to determine the effect of starter fertilizer (22 kg N, 10 kg P ha⁻¹ and fluid lime (1350 kg ha⁻¹) placement with in-row tillage methods on growth and yield of grain sorghum (Sorghum bicolor (L.) Moench) grown in a conservation-tillage system. Fertilizer and lime were applied in factorial combinations in the in-row subsoil channel, in a narrow (4-mm) slit 18 cm below the tillage pan (slit-tillage), or 7 cm to the side of the row incorporated 7 cm deep. Slit-tillage was as effective as subsoiling in two of the four tests where plant growth and grain yield responded to deep tillage. Of the other two tests where there was a response to deep tillage, slit-tillage resulted in a 6% decrease in grain yield compared to subsoiling in one test, and an 8% yield increase in the other. Starter fertilizer placement was not critical, but response to starter fertilizer occurred only when deep tillage, either in-row subsoiling or slit-tillage, was used in conjunction with the fertilizer. Starter fertilizer consistently increased early-season plant growth; however, yield response to starter fertilizer was highly dependent on rainfall. Starter fertilizer application increased yield in only one of five tests. There was no benefit from injecting lime.     

Subsoil strength and yield of vegetable crops

Abstract. In a field experiment over two years, broad beans ( Vicia faba ), cabbage ( Brassica oleracea var. capitata ), leeks ( Allium porrum ) and red beet ( Beta vulgaris var. esculenta ) were grown on a sandy clay loam soil in which a range of bulk densities and penetration resistances had been established by (1) thorough loosening to 0.9 m by trenching, (2) artificially compacting with tractor wheelings or (3) leaving unloosened.
Loosening the soil substantially increased, and compacting it decreased, yields of all four crops. The mean penetration resistance of the subsoil at field capacity correlated negatively with dry matter production. The relationship was broadly similar for all crops and years, showing a decrease in dry matter production of about 1 t ha^-1 per 0.5 MPa increase in resistance over the range examined.     

Nitrogen fertilizer requirements of cereals following grass

Abstract. The effect of increasing rates of nitrogen (N) fertilizer on the yield response of 3 or 4 consecutive winter cereal crops after ploughing out grass was investigated at six field sites on commercial farms in England and Wales. Amounts of N required for an economically optimum yield (>3 kg of grain for each kg of fertilizer N applied) ranged from 0 to 265 kg ha⁻¹ and were dependent on soil N supply, but not on crop yield. Optimum N rates were large (mean 197 kg N ha⁻¹) at three sites: two sites where cereals followed 2-year grass leys receiving low N inputs (<200 kg N ha⁻¹), and at one site where a cut and grazed 4-year ley had received c . 315 kg N ha⁻¹ of fertilizer N annually. At the other three sites where 4 and 5-year grass leys had received large regular amounts of organic manures (20–30 t or m³ ha⁻¹) plus fertilizer N ( c . 300 kg ha⁻¹ each year), optimum N rates were low (mean 93 kg N ha⁻¹) and consistently over-estimated by the farmer by an average of 107 kg N ha⁻¹. Optimum N rates generally increased in successive years after ploughing as the N supply from the soil declined. Determination of soil C:N ratio and mineral N (NO₃N+NH₄N) to 90 cm depth in autumn were helpful in assessing fertilizer N need. The results suggest there is scope to improve current fertilizer recommendations for cereals after grass by removing crop yield as a determinant and including an assessment of soil mineralizable N during the growing season.     

Effects of sorbed orthophosphate on zinc status in three soils of eastern Canada

P-Zn interactions can affect fertilizer use and produce Zn deficiencies with certain crops. Phosphorus-Zn sorption-desorption reactions were studied in topsoil and subsoil samples from three Quebec soils. Soils were equilibrated with P solutions, then with Zn solutions, and finally with solutions containing no P or Zn. The first equilibration evaluated P sorption (P_s), the second evaluated Zn sorption (Zn_s) after P sorption (P_s), and the third evaluated Zn desorption (Zn_D) as related to added P. Subsequently, Zn fractions were extracted sequentially with KNO₃ (Zn _{kno 3}), NaOH (Zn_NaOH) solutions and concentrated HN0₃+ H₂0₂(Zn_HNO,).
One mmole sorbed P resulted in increases of 0.5 to 1.0 meq (mean = 0.72) increases in cation exchange capacity (CEC). Increased Zn_s with added P was equivalent to 4 to 5% of the increase in CEC induced by P_s in the Uplands (sand) and St. Bernard (loam) soils, and 0.4 to 0.9% in the Dalhousie (clay) soils, while one meq increase in CEC resulted in 1.5-3.5% decrease in Zn_D. There existed positive correlations between P_s and extractable soil Fe materials. Phosphate sorption enhanced associations between Zn_s, Zn_D or Zn fractions and soil organic or crystalline Fe contents, confirming that P addition increased specific sorption of Zn on Fe components. Other mechanisms including precipitation, P-induced negative charge and 'bridge' effects are also discussed.     

Sequential extraction methods for soil organic nitrogen

(pp. 825–831)
This study was carried out to clarify the effects of soil nitrate before cultivation and amounts of basal-dressed nitrogen on additional N application rate and yields of semi-forced tomato for three years from 1998 to 2000. The amounts and timing of additional N dressing were determined based on diagnosis of petiole sap nitrate. The top-dressing was carried out with a liquid fertilizer when the nitrate concentration of a leaflet's petiole sap of leaf beneath fruit which is 2–4 cm declined below 2000 mg L⁻¹.
For standard yield by the method of fertilizer application based on this condition, no basal-dressed nitrogen was required when soil nitrate before cultivation was 150 mg kg⁻¹ dry soil or higher in the 0–30 cm layer; 38 kg ha⁻¹ of basal-dressed nitrogen, which corresponds to 25% of the standard rate of fertilizer application of Chiba Prefecture, was optimum when soil nitrate before cultivation was 100150 mg kg⁻¹ dry soil; 75 kg ha⁻¹ of basal-dressed nitrogen, which corresponds to 50% of the standard, was optimum when soil nitrate before cultivation was under 100 mg kg⁻¹ dry soil. A standard yield was secured and the rate of nitrogen fertilizer application decreased by 49–76% of the standard by keeping the nitrate concentration of tomato petiole sap between 1000–2000 mg L⁻¹ from early harvest time to topping time under these conditions.     

施磷量与小麦产量的关系及其对土壤、气候因素的响应

【目的】分析在有效磷含量不同的土壤中磷肥施用量对小麦籽粒产量的影响,探明在保证小麦高产的前提下,不同有效磷含量土壤中施磷量与小麦籽粒产量之间的关系,为小麦生产中合理施用磷肥、改善农田生态环境提供理论依据。【方法】本研究根据1990—2017年间已公开发表的有关中国磷肥田间试验的文献,建立土壤有效磷、施磷量和小麦籽粒产量的数据库。采用数据整合分析方法(Meta-analysis),研究在3个土壤有效磷梯度(< 10、10～20、> 20 mg/kg)下,不同施磷(P₂O₅)量(< 60、60～90、90～120、120～150、> 150 kg/hm2)对小麦籽粒产量的影响,分析施磷量与小麦籽粒产量之间的关系及其对环境因素的响应。【结果】1)除在有效磷 > 20 mg/kg的土壤上施用P₂O₅ > 90 kg/hm2的高量磷肥外,在其它有效磷含量土壤上施用磷肥对小麦籽粒产量的提高均具有正影响。具体表现为:在有效磷 < 10 mg/kg的土壤上,小麦籽粒产量随施磷量的升高而呈直线上升趋势,其中施P₂O₅ > 150 kg/hm2的磷肥对小麦的增产作用最强(36.6%);在有效磷含量为10～20 mg/kg的土壤上,90～120 kg/hm2的P₂O₅施用量对小麦的增产作用最强(25.8%);在有效磷含量 > 20 mg/kg的土壤上,小麦籽粒产量与施磷量的关系符合米歇里西方程,即小麦籽粒产量随施磷量先增加后达到平衡,且磷肥施用对小麦的有效增产作用相对较弱(< 8%)。2)在不同的环境因素下磷肥施用对小麦籽粒产量的提高均为正影响。具体表现为:在不同的气候类型条件下,亚热带季风气候条件下施用磷肥对小麦籽粒产量的提高幅度为19.4%,高于亚热带季风气候区(10.7%);在不同土壤类型条件下,黑垆土中磷肥施用对小麦籽粒产量的提高幅度为34.4%,显著高于黄棕壤(10.3%)、棕壤(9.2%)和褐土(15.6%);在不同小麦种植区中,春小麦区中磷肥施用对小麦籽粒产量的提升幅度为32.9%,显著高于北方冬小麦区(13.9%)和南冬小麦区(10.8%)。【结论】在试验前初始有效磷含量不同的土壤中,磷肥施用量对小麦籽粒产量的影响程度不尽相同,其中在亚热带季风气候、黑垆土、春小麦区条件下施磷的增产作用较强。因此,在小麦生产过程中施用磷肥时应充分考虑当地的土壤有效磷含量,适量施肥,减少磷素浪费,保护农业生态环境。     

Cotton response to in-row subsoiling and potassium fertilizer placement in Alabama

In the USA a suggested method for correcting late season K deficiencies in cotton (Gossypium hirsutum L.) is by in-row deep placement of K fertilizer. Experiments were conducted on three Alabama soils (southeastern USA) for 3 years to evaluate cotton response to K fertilizer when surface broadcast with and without in-row subsoiling (to 38 cm depth) or deep placed in the in-row subsoil channel. Potassium was applied at rates ranging from 0 to 84 kg K ha⁻¹. Deep placement was achieved with a fertilizer applicator developed to distribute dry fertilizer at three depths down the back of the subsoil shank. All three soils also had deep placement treatments of 1680 kg ha⁻¹ agricultural limestone with and without 84 kg K ha⁻¹. Soils were an Emory silt loam (fine-silty, siliceous Fluventic Umbric Dystrochrepts), a Norfolk sandy loam (fine-loamy, siliceous Typic Kandiudults), and a Lucedale sandy clay loam (fine-loamy, siliceous Rhodic Paleuduts). All three soils had medium soil test K concentrations in the plow layer and medium or low concentrations of K at greater depths. The Norfolk soil had a well-developed traffic pan and in-row subsoiling increased seed cotton yields by an average of 22% during the 3 years of the study. Cotton responded to K fertilization in 2 out of 3 years at each location (6 out of 9 site-years) regardless of the method of K application. Annual applications of 84 kg K ha⁻¹ increased 3 year average seed cotton yields by 17%, 10% and 19% on the Emory, Norfolk and Lucedale soils, respectively. Deep placement of agricultural limestone with or without K fertilizer for cotton did not increase cotton yields.     

陕西省关中地区石灰性土壤上影响磷肥肥效因素的探讨 Ⅰ.土壤的某些农化性质对磷肥肥效的影响

我国北方石灰性土壤上磷肥的肥效,很不稳定。近年来各地围绕着这一问题,进行了一些工作。大体看来,着重在肥料配合、施用方法、磷肥品种和作物种类对磷肥肥效影响的报道较多。至于土壤本身对于磷肥肥效的影响,研究的还少。     

Yield and uptake of fertilizer nitrogen by direct-drilled winter barley growing on a chalk soil

Abstract. This paper reports the growth and yield of grain and the utilization of fertilizer nitrogen applied on either one or two occasions in spring to a crop of winter barley established by direct drilling on a chalk soil in southern England. Nitrogen, as ammonium nitrate, was applied at rates of 0 to 140 kg N ha⁻¹ in a range of proportions on two occasions (March and April 1981); nitrogen-15 was used to facilitate study of the nitrogen utilization by the crop.
When sampled before the second top-dressing in April, the greatest number of tillers were found on plants treated with 70 and 100 kg N ha⁻¹ in March. The total above ground dry matter production at harvest was greatest when the split nitrogen dressing totalled more than 100 kg N ha⁻¹, although the apparent efficiency of nitrogen usage (kg DM per kg N applied) was greatest when 60 kg N ha⁻¹ was divided equally between the two application dates. Grain yield was heaviest (6.471 ha⁻¹) at the largest rate of nitrogen applied (140 kg N ha⁻¹); the lightest yield from the nitrogen treated crops was recorded from 100 kg N ha⁻¹ applied as a single dressing in April that stimulated shoot production and decreased individual grain weight. The recovery in grain and straw of labelled fertilizer nitrogen applied only in March averaged 42.2% and was 49.8% when the nitrogen was applied only in April. The recovery of nitrogen applied in both March and April at the total rate of 100 kg N ha⁻¹ but split 30/70 or 70/30 was 44.5% and 42.5% respectively. Non-fertilizer sources of nitrogen contributed 60.7–71.7% of the total nitrogen uptake by the crop at harvest.     

The impact of pasture improvement on the soil solution chemistry of some stagnopodzols in mid-Wales

Abstract. The impact of three methods of pasture improvement on soil water chemistry were studied: ploughing plus 15 t ha^-1 lime c. 40 years ago, 5 t ha^-1 surface spread lime c. 20 years ago and surface cultivation with 7 t ha^-1 lime plus compound fertilizer 10 years ago. Soil solution was sampled using tensionless lysimeters and porous ceramic cups. Concentrations of several solutes were higher in the treated soils than a control, including solutes not added in lime or fertilizers. Calcium, magnesium and bicarbonate concentrations showed the largest increases; these were apparent in all horizons, and all treatments. Bicarbonate had become the dominant anion. Solute concentrations varied between treatments and were related to the amount of an element added rather than time since treatment. Highest mean calcium concentrations, 6.25 mg l^-1 were still low compared with drainage from lowland arable soils but could have a significant impact on the calcium-poor surface waters of the uplands.     

Previous cropping and soil mineral nitrogen as predictors of yield response of winter wheat to nitrogen on silt soils in United Kingdom

Abstract. The fertilizer nitrogen requirement of winter wheat was assessed in sixteen experiments on marine silt soils in Eastern England. Eight experimental sites followed potatoes ( Solanum tuberosum ), six vining peas ( Pisum sativum ) and two wheat ( Triticum aestivum ). The yield response to nitrogen fertilizer was much less following peas than potatoes or wheat, five sites following peas showed little response to more than 30 kg N ha^–1. Previous crop explained some 79.7% of the variation in nitrogen optima. When autumn soil mineral nitrogen was also taken into account 81.9% of the variation in optimum nitrogen rate was explained ( P <0.001). The study revealed noticeably higher levels of autumn soil mineral nitrogen following vining peas on some sites than those found elsewhere in the UK and as assumed in the standard national fertilizer recommendation system.