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.     

Cultivation of wheat following pea and triticale/pea mixtures increases yields and nitrogen content

Abstract

An experiment was conducted in 2004–2007 at the University of Podlasie Zawady Experimental Station (52°06′N, 22°50′E), Siedlce, Poland, to examine the effect of either post-harvest residues or residues and straw of spring triticale (Triticale), field pea (Pisum sativum L.) and their mixtures containing the following proportions of both components: 75+25, 50+50, 25+75% on the subsequent crop of winter wheat (Triticum aestivum L.). A field experiment was designed as split-blocks with three replicates. Residue mass, straw mass as well as N, P, K, Ca and Mg amounts were determined in the residues and straw. The residue amount of spring triticale was the greatest. N, Ca and Mg amounts in the residues of spring triticale/field pea mixtures were similar or higher whereas P and K amounts were similar or lower compared with spring triticale residues. Spring triticale straw contained less N, P, Ca and Mg than the straw of either field pea or spring triticale/field pea mixtures. Grain yield, yield components, N content and N uptake in the grain of winter wheat following field pea and spring triticale/field pea mixtures were significantly higher compared with winter wheat following spring triticale. Increasing proportions of field pea in mixtures with spring triticale cultivated as previous crops significantly increased winter wheat grain yields as well as N content and uptake. The residues of the previous crops combined with the straw significantly increased winter wheat grain yield, number of ears per m², number of grains in an ear, thousand-grain weight and N content and uptake. The highest winter wheat grain yield and N uptake were determined following an application of residues and straw of field pea and 25+75% spring triticale/field pea mixture. The grain of winter wheat after field pea had the greatest N content.     

Contributions from carbon and nitrogen in roots to closing the yield gap between conventional and organic cropping systems

This study investigates the effect of different crop rotation systems on carbon (C) and nitrogen (N) in root biomass as well as on soil organic carbon (SOC ). Soils under spring barley and spring barley/pea mixture were sampled both in organic and conventional crop rotations. The amounts of root biomass and SOC in fine (250–253 μ m), medium (425–250 μ m) and coarse (>425 μ m) soil particulate organic matter (POM ) were determined. Grain dry matter (DM ) and the amount of N in harvested grain were also quantified. Organic systems with varying use of manure and catch crops had lower spring barley grain DM yield compared to those in conventional systems, whereas barley/pea showed no differences. The largest benefits were observed for grain N yields and grain DM yields for spring barley, where grain N yield was positively correlated with root N. The inclusion of catch crops in organic rotations resulted in higher root N and SOC (g C/m²) in fine POM in soils under barley/pea. Our results suggest that manure application and inclusion of catch crops improve crop N supply and reduce the yield gap between conventional and organic rotations. The observed positive correlation between root N and grain N imply that management practices aimed at increasing grain N could also increase root N and thus enhance N supply for subsequent crops.     

Yield,yield formation,and blackleg disease of oilseed rape cultivated in high-intensity crop rotations

The short-term economic benefit has in recent years prompted farmers to grow oilseed rape (OSR) (Brassica napus L.) and thus the frequency of this crop increased in German crop rotations. Here, we investigate the impact of high-intensity OSR crop rotations on yield, yield formation, and blackleg disease (Leptosphaeria maculans) in a rotation experiment in the Hercynian dry region of Central Germany over two seasons (2014/2015?–?2015/2016). The preceding crop combinations compared were winter wheat (WW) (Triticum aestivum L.)-WW, WW-OSR, OSR-OSR, and an OSR monoculture. Furthermore, the fertilizer treatments 120 kg N ha^?1 and 180 kg N ha^?1 were analyzed.

Higher OSR cropping intensity decreased seed yields, however, with a variation among years and oil yield was highest when OSR was following WW-WW over both years. Minor differences were observed among the yield components, but significantly less pods per m² were developed in a long-term OSR monoculture. The disease assessment clearly showed an increased blackleg incidence and severity when OSR was grown successively.

Results of our study emphasize that high-intensity OSR production will very likely be unsustainable over the long term associated with yield losses and increased infestation levels of blackleg disease.     

Manganese relationships in spring wheat and spring barley production in Northern Idaho

Abstract

Manganese is often limiting in cereal crop production in the Kootenai River Valley of Northern Idaho; however, attempts to relate DTPA‐extractable Mn in soils to crop yield response have not been successful. Consequently, Mn plant tissue diagnosis may be an alternate diagnostic tool. The objectives of this study were to: (1) determine the critical nutrient concentration (CNC) of Mn in spring wheat and spring barley tissue in the Kootenai River Valley of northern Idaho, (2) examine yield response of spring wheat and spring barley to Mn fertilization, and (3) assess relative efficiencies of foliar and surface broadcast Mn applications to these crops. Paired plots with four replications consisting of a foliar Mn application rate of 1.5 kg ha^‐1 and a control were located at four sites in 1988 and at ten sites in 1989. Soil, plant tissue samples and grain yield data were evaluated by linear plateau regression to determine CNCs of Mn for spring wheat and spring barley tissue. In addition, five randomized complete block experiments were conducted in 1989 and 1990 to evaluate Mn fertilizer rates and sources (foliar vs. surface applied) on spring wheat and spring barley production. Tissue Mn was highly correlated by linear plateau regression to both spring wheat (r² = 0.74**) and spring barley (r² = 0.70**) grain yield. The Mn CNC was established at 11.0 mg Mn kg‐¹ plant tissue for spring wheat and 10.1 mg Mn kg^‐1 plant tissue for spring barley. The Mn CNCs were established at 92.4 and 93.0% of maximum yield for spring wheat and spring barley, respectively. DTPA‐extractable Mn was not significantly correlated to grain yield for either crop (r² = 0.02, NS). Based on study results, Mn analysis of spring wheat and spring barley plant tissue was diagnostic of eventual grain yield. When tissue diagnosis showed plants to be deficient in Mn, the deficiency was corrected by applying Mn fertilizer as a surface broadcast or a foliar spray. However, foliar application of Mn was more efficient than broadcast application.     

Nitrate leaching from an organic dairy crop rotation: the effects of manure type, nitrogen input and improved crop rotation

Abstract. Four management systems combining high and low livestock densities (0.7 and 1.4 livestock units ha⁻¹) and different types of organic manure (slurry and straw based FYM) were applied to an organic dairy crop rotation (undersown barley – grass–clover – grass–clover – barley/pea – oats – fodder beet) between 1998 and 2001. The effects of the management systems on crop yields and nitrate leaching were measured. In all four years, nitrate leaching, as determined using ceramic suction cups, was higher in the three crops following ploughing of grass–clover than under the barley or grass–clover. Overall, no significant differences in nitrate leaching were observed between the management systems. However, the replacement of the winter wheat crop used in the earlier experimental period (1994–97) by spring oats with catch crops in both the preceding and succeeding winters reduced nitrate leaching compared with the earlier rotation. Increasing the livestock density, which increased manure application by c. 60 kg total N ha⁻¹, increased crop yields by 7 and 9% on average for FYM and slurry, respectively. Yields were 3–5% lower where FYM was used instead of slurry. The experiment confirmed the overriding importance of grassland N management, particularly the cultivation of the ley, in organic dairy crop rotations.     

Stability analysis for grain yield of winter wheat in a long-term field experiment

The current study is based on a long-term field experiment that was conducted at the Rauischholzhausen field station of the University of Giessen (Germany). It includes six different crop rotation systems (CRSs), three mineral nitrogen (N) fertilization treatments and the varying annual weather conditions (AWCs) over 25 years (1993–2017). To ensure new insight into wheat cropping systems that have high yield stability, the dataset was assessed using different methods of stability analysis, including eco-valence, biplot and risk analysis. The results show that the factors which influence grain yield variation in winter wheat can be ranked in the following order: (1) N fertilization; (2) AWC; and (3) CRS. Compared to winter rye as the preceding cereal crop, field bean as the preceding legume crop had a clearly positive effect on the grain yield stability of winter wheat. Furthermore, the higher N fertilization level led to more stable grain yields of winter wheat for all investigated CRSs. Overall, in this study, crop rotation and N fertilization had a high impact on the yield stability of winter wheat. These are important factors to consider in agronomic management decisions under the increasingly difficult environmental conditions caused by climate change.     

Changes in N leaching and crop production as a result of measures to reduce N losses to water in a 6‐yr crop rotation

The effects of various measures introduced to increase nitrogen (N)‐use efficiency and reduce N losses to water in a 6‐yr crop rotation (winter wheat, spring barley, green manure, winter wheat, spring barley, spring oilseed rape) were examined with respect to N leaching, soil mineral N (SMN) accumulation and grain yield. An N‐use efficient system (NUE) with delayed tillage until late autumn and spring, direct drilling of winter wheat, earlier sowing of winter and spring crops and use of a catch crop in winter wheat was compared with a conventional system (CON) in a field experiment with six separately tile‐drained plots in south‐western Sweden during the period 1999–2011 (two crop rotation cycles). Total leaching of NO₃‐N from the NUE system was significantly 46 and 33% lower than in the CON system during the first and second crop rotation cycle, respectively, with the most pronounced differences apparently related to management strategies for winter wheat. Differences in NO₃‐N leaching largely reflected differences in SMN during autumn and winter. There was a tendency for lower yields in the NUE system, probably due to problems with couch grass. Overall, the measures for conserving N, when frequently used within a crop rotation, effectively reduced NO₃ concentrations in drainage water and NO₃‐N leaching losses, without severely affecting yield.     

The effects of shelter for cereal crops in an exposed area of Cleveland, North-East England

Abstract. Plots of spring barley, winter wheat and winter barley were sheltered with netting in a coastal area of North-East England. Crop height, yield components and grain yield were measured and compared with unsheltered crops receiving the same agronomic treatments. Plant height, ears m^-2, 1000 grain weight and grain yield were increased by shelter in seasons with windy, dry weather during the tillering and stem extension phases. Negligible response was found in a wet season. One experiment suggests that greater applications of nitrogen fertilizer can counteract the effects of exposure.     

Yields of wheat and soil carbon and nitrogen contents following long-term incorporation of barley straw and ryegrass catch crops

Abstract. Three successive crops of winter wheat were grown on a sandy loam to test the residual effect of long‐term annual incorporation of spring barley straw at rates of 0, 4, 8 and 12 t ha^?1, and ryegrass catch crops with or without additions of pig slurry. Soil receiving 4, 8 and 12 t ha^?1 of straw annually for 18 years contained 12, 21 and 30% more carbon (C), respectively, than soil with straw removal, and soil C and nitrogen (N) contents increased linearly with straw rate. The soil retained 14% of the straw C and 37% of the straw N. Ryegrass catch‐cropping for 10 years also increased soil C and N concentrations, whereas the effect of pig slurry was insignificant. Grain yield in the first wheat crop showed an average dry matter (DM) increase of 0.7 t ha^?1 after treatment with 8 and 12 t straw ha^?1. In the two subsequent wheat crops, grain yield increased by 0.2–0.3 t DM ha^?1 after 8 and 12 t straw ha^?1. No grain yield increases were found after 4 t straw ha^?1 in any of the three years. Previous ryegrass catch crops increased yields of wheat grain, but effects in the third wheat crop were significant only where ryegrass had been combined with pig slurry. Straw incorporation increased the N offtake in the first wheat crop. In the second crop, only 8 and 12 t straw ha^?1 improved wheat N offtake, while the N offtake in the third wheat crop was unaffected. Ryegrass catch crops increased N offtake in the first and second wheat crop. Again, a positive effect in the third crop was seen only when ryegrass was combined with slurry. Long‐term, annual incorporation of straw and ryegrass catch crops provided a clear and relatively persistent increase in soil organic matter levels, whereas the positive effects on the yield of subsequent wheat crops were modest and transient.     

Cover crop growth and impact on N leaching as affected by pre‐ and postharvest sowing and time of incorporation

In Northern Europe, cover crops are traditionally established before spring crops by undersowing, but some cover crops might also have an effect if preharvest sown before spring crops and even winter crops. The effects of cover crop sowing date, sowing technique and succeeding main crop on biomass production, N uptake, nitrate leaching and soil inorganic N were tested in lysimeters and in the field. Cruciferous cover crops (oil radish, white mustard) were sown preharvest by broadcasting into winter wheat in July and were allowed to grow until a following winter wheat was established in September. Other preharvest cover crops were left in place until late autumn. For comparison, the same cruciferous cover crops were established postharvest after light harrowing. Perennial ryegrass undersown in spring barley was also included. Aboveground N uptake in preharvest cover crops amounted to a maximum of 24 kg N/ha in September before sowing winter wheat. When left until late autumn, preharvest oil radish took up a maximum of 66 kg N/ha, and ryegrass and postharvest cover crops 35 kg N/ha. Preharvest establishment of cruciferous cover crops before a spring‐sown crop thus seems promising. The soil was depleted of inorganic N to the same extent in late autumn irrespective of cover crop type, sowing time and technique within winter wheat or spring barley. However, the reduction in nitrate leaching of preharvest cover crops incorporated after 2 months and followed by winter wheat was only half of that achieved by cover crops left until late autumn or spring.     

Long-term continuous cropping in the Pacific Northwest: Tillage and fertilizer effects on winter wheat, spring wheat, and spring barley production

Conventional tillage winter wheat (Triticum aestivum) (WW)–summer fallow reduces soil productivity and increases soil erosion. Conservation tillage management, together with intensive cropping may have the potential to reverse these sustainability concerns. The objective of this study was to determine the effects of conventional tillage (CT) and no-tillage (NT) systems on grain yield of long-term annual cropping of monoculture WW, spring wheat (SW), and spring barley (Hordeum vulgare) (SB) grown with or without fertilizer, in the Pacific Northwest region of the USA. In unfertilized crops, grain yield of WW, SW, and SB was 15%, 25%, and 50% higher, respectively, in CT than in NT plots, an indication of the involvement of yield limiting factors under the NT cropping system. When fertilized, there were no significant differences in grain yield of WW. Yields of SW and SB, however, remained 21% and 15% higher, respectively, in CT than in NT, an indication that factors other than fertility were involved. These results suggest that in order for NT management to be widely adopted by area growers, the yield-limiting factors need to be addressed.     

Changes in Grain Production,Mechanisms for Sale of Grain and Possible Effects on Grain Quality in Lithuania in the Period 1990-1999

The main objective was to compare the response of grain yield to fertiliser N in a winter wheat-white clover intercropping system with the response in wheat alone. Clover was undersown in spring barley and remained established in two consecutive crops of wheat in two field experiments. Clover reduced grain yield in the first crop of wheat and increased it in the second. There was more inorganic N in the soil and a higher concentration of N in the grains in the intercropping system. The grain and N yield response to fertiliser N was equal or less with intercropped than with wheat alone. The reduction of clover biomass with a herbicide increased grain yield of the first crop of wheat without reducing the clover biomass or the positive residual effect in the second wheat crop. It was concluded that in order to produce large grain yields, competition from clover needs to be kept small when wheat is at the tillering stage.     

限量单次灌溉对套作冬小麦和春玉米产量的影响

A field experiment was conducted during the 2002/2003 cropping season of winter wheat (Triticum aestivum) and spring maize (Zea mays) to evaluate the effect of limited single drip irrigation on the yield and water use of both crops under relay intercropping in a semi-arid area of northwestern China. A controlled 35 mm single irrigation, either early or late, was applied to each crop at a certain growth stage. Soil water, leaf area, final grain yield and yield components such as the thousand-grain weight, length of spike, fertile spikelet number, number of grains per spike, and grain weight per spike were measured, and water use efficiency and leaf area index were calculated for the irrigated and non-irrigated relay intercropping treatments and sole cropping controls. The results showed that yield, yield components, water use efficiency, and leaf area index in the relay intercropping treatments were affected by limited single drip irrigation during various growth stages of wheat and maize. The total yields in the relay intercropping treatment irrigated during the heading stage of wheat and the heading and anthesis stage of maize were the highest among all the treatments, followed by that irrigated during the anthesis stage of wheat and silking stage of maize;so was the water use efficiency. Significant differences occurred in most yield components between the irrigated and non-irrigated relay-intercropping treatments. The dynamics of the leaf area index in the relay-intercropped or solely cropped wheat and maize showed a type of single-peak pattern, whereas that of the relay intercropping treatments showed a type of double-peak pattern. Appropriately, limited single irrigation and controlled soil water content level could result in higher total yield, water use efficiency, and leaf area index, and improved yield components in relay intercropping. This practice saved the amount of water used for irrigation and also increased the yield. Therefore, heading stage of wheat and heading and anthesis stage of maize were suggested to be the optimum limited single irrigation time for relay-intercropped wheat and maize in the semi-arid area.     

The impact of soil and crop management practices on soil-borne root diseases and wheat yields

Abstract. The most important root diseases of wheat in southern Australia are take-all, rhizoctonia bare patch and cereal cyst nematode. Control of grasses in annual pastures in the year preceding wheat crops decreased take-all on wheat and the amount of the take-all fungus in soil, decreased the damage caused by Rhizoctonia , and gave yield increases. Fumigation of cereal-growing soils gave yield increases in wheat of 0.75 to 2.8 tonnes per hectare, indicating that in southern Australia soil-borne root diseases impose a major constraint on productivity. Residues of the herbicide chlorsulfuron one year after application to an alkaline soil increased root damage by Rhizoctonia in barley and decreased grain yields by 1.5 tonnes per hectare. Root damage by cereal cyst nematode was decreased by direct drilling wheat and also by having a barley cultivar resistant to the pathogen as a preceding crop. The number of cysts of cereal cyst nematode on wheat roots was increased by the application of superphosphate in bands with the seed. These results show that in southern Australia soil management strategies which decrease the levels of root disease greatly increase grain yields.     

The effects of pure and undersowing green manures on yields of succeeding spring cereals

Abstract

A field experiment was conducted in 2004–2006 to investigate the effect of green manure treatments on the yield of oats and spring barley. In the experiment, different green manure crops with undersowing and pure sowing were compared for amounts of N, C, and organic matter driven into soil and their effect on cereal yield. The spring barley field had a total of 41.7–62.4 kg N ha^?1 and 1.75–2.81 Mg C ha^?1 added to the soil with straw, weed, and roots, depending on the level of fertilisation; with red clover, and both common and hybrid lucerne undersowing, with barley straw and roots, the values were 3.45–3.96 Mg C ha^?1 and 139.9–184.9 kg N ha^?1. Pure sowings of these three leguminous green manure crops had total applications of 3.37–4.14 Mg C ha^?1 and 219.7–236.8 kg N ha^?1. The mixed and pure sowing of bird's-foot trefoil provided considerably less nitrogen and carbon to the soil with the biomass than with the other leguminous crops. Application of biomass with a high C/N ratio reduced the yield of the succeeding spring cereals. Of the green manures, the most effective were red clover and both common and hybrid lucerne, either as undersowing or as pure sowing. Undersowings with barley significantly increased the N supply for the succeeding crop without yield loss of the main crop compared with the unfertilised variant. Compared with ploughing-in of green manure in autumn, spring ploughing gave a 0.2–0.57 Mg ha^?1 larger grain yield.     

渭北旱塬不同田间管理措施下冬小麦产量及水分利用效率

水分是限制旱地作物产量最主要的因素,提高自然降水利用效率是增加旱地作物产量的有效途径。2001～2003年在渭北旱塬粉砂壤土上的田间试验研究表明,不同田间管理措施对冬小麦的产量及水分利用效率有显著的影响。秸秆覆盖不仅增加雨水入渗,提高上层土壤含水量,而且促进水分向下运输。在覆盖第二年小麦产量较常规种植显著增加,同时覆盖下土壤有机质含量有较快增加的趋势。夏季休闲期种植填闲作物将不影响下一季作物的水分状况,短期内填闲作物对土壤有机质,小麦产量及水分利用效率也没有影响。     

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 (N_min, 0–90 cm soil), accumulated after the preceding crops in late autumn, 2) on soil N mineralisation (N_net) 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 N_min 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 N_min 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 N_net (from March to maturity during the winter wheat year). Owing to more plant-available soil N (mainly as N_net) 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.     

Crop yield forecasting on the Canadian Prairies using MODIS NDVI data

Although Normalised Difference Vegetation Index (NDVI) data derived from the advanced very high resolution radiometer (AVHRR) sensor have been extensively used to assess crop condition and yield on the Canadian Prairies and elsewhere, NDVI data derived from the new moderate resolution imaging spectroradiometer (MODIS) sensor have so far not been used for crop yield prediction on the Canadian Prairies. Therefore, the objective of this study was to evaluate the possibility of using MODIS-NDVI to forecast crop yield on the Canadian Prairies and also to identify the best time for making a reliable crop yield forecast. Growing season (May-August) MODIS 10-day composite NDVI data for the years 2000-2006 were obtained from the Canada Centre for Remote Sensing (CCRS). Crop yield data (i.e., barley, canola, field peas and spring wheat) for each Census Agricultural Region (CAR) were obtained from Statistics Canada. Correlation and regression analyses were performed using 10-day composite NDVI and running average NDVI for 2, 3 and 4 dekads with the highest correlation coefficients (r) as the independent variables and crop grain yield as the dependent variable. To test the robustness and the ability of the generated regression models to forecast crops grain yield, one year at a time was removed and new regression models were developed, which were then used to predict the grain yield for the missing year. Results showed that MODIS-NDVI data can be used effectively to predict crop yield on the Canadian Prairies. Depending on the agro-climatic zone, the power function models developed for each crop accounted for 48 to 90%, 32 to 82%, 53 to 89% and 47 to 80% of the grain yield variability for barley, canola, field peas and spring wheat, respectively, with the best prediction in the semi-arid zone. Overall (54 out of 84), the % difference of the predicted from the actual grain yield was within ±10%. On the whole, RMSE values ranged from 150 to 654, 108 to 475, 204 to 677 and 104 to 714 kg ha⁻¹ for barley, canola, field peas and spring wheat, respectively. When expressed as percentages of actual yield, the RMSE values ranged from 8 to 25% for barley, 10 to 58% for canola, 10 to 38% for field peas and 6 to 34% for spring wheat. The MAE values followed a similar trend but were slightly lower than the RMSE values. For all the crops, the best time for making grain yield predictions was found to be from the third dekad of June through the third dekad of July in the sub-humid zone and from the first dekad of July through the first dekad of August in both the semi-arid and arid zones. This means that accurate crop grain yield forecasts using the developed regression models can be made one to two months before harvest.     

Nitrogen effects of non-legume catch crops

Nitrate leaching during the winter period can be reduced and often prevented by growing catch crops after the harvest of a main crop. However, catch crops which effectively take up residual nitrogen do not necessarily show good nutrient effects on a succeeding main crop. The objective of this experiment was to investigate how the content of soil mineral nitrogen in spring was affected by the time of incorporation of non-legume catch crops and how the yield and nitrogen uptake of a succeeding main crop was influenced. The yield of spring sown onion and white cabbage was significantly increased by catch crop growing the previous autumn. The nitrogen effect of Italian ryegrass corresponded to 50–100 kg N per ha in the vegetables. However, the yield of spring barley was not significantly affected by the nitrogen released from decomposing catch crops. During decomposition of non-legume catch crops, grown at a high level of nitrogen fertility, nitrogen immobilization did not occur.