Effects of tillage on deposition and utilization of 15N residual fertilizer

Differences in soil tillage can influence the utilization of fertilizer N. This study determined the effect of zero tillage (ZT) and conventional shallow tillage (CT), of three years duration, on the deposition and dynamics of residual ¹⁵N urea. The study was conducted on a Chernozemic soil in a semiarid region of the Canadian prairie. In the absence of tillage, microbial biomass N levels increased by 48% and mineral N levels decreased by 62%, at the 0–5-cm soil depth, compared to the CT soil. The ZT soil had 96% more residual N distributed in the non-biomass organic N, but 52% less in the mineral and microbial biomass forms of soil N, compared to the CT soil. These tillage induced changes affected the short-term availability of residual ¹⁵N as determined by N mineralization and plant utilization studies. Potentially mineralizable N (N₀) was higher, but release of ¹⁵N residual fertilizer was slower in the ZT soil, compared to CT soil. Initial plant uptake of soil N was similar between tillage systems, although three times as much residual fertilizer was derived from the CT as compared to the ZT soil. Mineralization or plant uptake reduced the differences in ¹⁵N residual fertilizer deposition between tillage soil samples. Tillage differences may influence the short-term N balance of soils receiving N fertilizer. Such changes are related to the greater level of microbial biomass in the surface of ZT soils.     

Tillage and nitrogen effects on growth,nitrogen content,and yield of corn

Abstract

The use of conservation tillage methods, including ridge tillage, has increased dramatically in recent years. At the present time, there is great concern that farmers are applying more nitrogen (N) fertilizer than is environmentally or economically sound. In order to determine if N requirement for optimum yield differs with tillage system, tests were initiated to study tillage and N effects on N content, soil moisture content, and yield of corn (Zea mays L.). The study was established in 1987 on two soil types, an Estelline soil (Pachic Haploboroll) and an Egan soil (Udic Haplustoll), located in eastern South Dakota. Five rates of N (0, 65, 130, 195, and 260 kg ha^?1) were applied to plots managed with 3 tillage systems: chisel plow, moldboard plow, and ridge. On the Estelline soil, in both 1988 and 1989, ridge‐tilled plots contained a greater amount of water in the soil profile at emergence and at mid silk than did plots in the other two tillage systems. Soil moisture content at mid silk was significantly correlated with earleaf N, total N uptake, and grain yield in 1988 and earleaf N and grain yield in 1989. However, the correlation coefficients were higher in 1988 than in 1989. On the Egan soil, there were no significant differences in soil moisture content among tillage systems. On the Estelline soil, corn grain yield was affected by a tillage x N‐rate interaction in 1988. Maximum yield within the ridge system was achieved with the 130 kg ha^?1 rate. In 1989 on the Estelline soil, yield was affected by tillage and N rate, but there was no interaction between factors. When averaged over N rates, yields were 7.1, 6.6, and 6.5 Mg ha^?1 in the ridge, moldboard, and chisel systems, respectively. In 1988 plant total N uptake was greater in the ridge system than the moldboard or chisel systems; in 1989 uptake was affected by N rate alone. On the Egan soil, tillage did not affect soil moisture, total N uptake or grain yield in either year. Corn grain yield increased with increasing N rate up to the 195 kg ha^?1 rate. This study indicates that, on some soil types, ridge tillage can improve soil water holding capacity, N utilization and yield of corn.     

Deep Tillage,Soil Moisture Regime,and Optimizing N Nutrition for Sustaining Soil Health and Sugarcane Yield in Subtropical India

A field experiment was conducted at ICAR-Indian Institute of Sugarcane Research, Lucknow, with three tillage practices (T₁: Control- two times ploughing with harrow and cultivator, each followed by planking before sugarcane planting; T₂: Deep tillage with disc plough (depth 25–30 cm) before planting followed by harrowing, cultivator, and planking; and T₃: Subsoiling at 45–50 cm and deep tillage with disc plough/moldboard plough (depth 25–30 cm) followed by harrowing, cultivator, and planking before planting, two soil moisture regimes (M₁: 0.5 irrigation water (IW)/cumulative pan evaporation (?CPE) ratio and M₂: 0.75 IW/CPE ratio) at 7.5 cm depth of IW, and four N levels (N₁- 0, N₂- 75, N₃- 150, and N₄-225 kg N ha^?1) in sugarcane plant crop. Deep tillage and subsoiling increased porosity and reduced bulk density in surface/subsurface soil. Further, these physical changes also improved soil biological and chemical properties responsible for higher crop growth and yield. Deep tillage and subsoiling reduced the compaction by 6.12% in 0–15 cm depth in sugarcane plant crop at maximum tillering stage. The highest N uptake (158.5 kg ha^?1) was analyzed with deep tillage and subsoiling compared to all other tillage practices. Maintaining suboptimal moisture regime with deep tillage and subsoiling showed the highest IW use efficiency (157.16 kg cane kg^?1 N applied). Mean soil microbial biomass carbon (SMBC) in ratoon crop was higher compared to plant crop. During initial tillering stage, ratoon crop showed higher SMBC with application of deep tillage and subsoiling (1209 mg CO₂-C g^?1 soil day^?1) at 0–15 cm depth and 1082.9 mg CO₂-C g^?1 soil day^?1 at 15–30 cm depth. Thus, it could be concluded that besides improving sugarcane yield, soil health could be sustained by adopting subsoiling (45–50 cm depth) and deep tillage (20–25 cm depth), with soil moisture regime of 0.75 IW/CPE and application of 150 kg N ha^?1 in sugarcane (plant crop).     

Influence of Long-term Tillage,Straw, and N Fertilizer Management on Crop Yield,N Uptake,and N Balance Sheet in Two Contrasting Soil Types

Field experiments (established in autumn 1979, with monoculture barley from 1980 to 1990 and barley/wheat–canola–triticale–pea rotation from 1991 to 2008) were conducted on two contrasting soil types (Gray Luvisol [Typic Haplocryalf] loam soil at Breton; Black Chernozem [Albic Agricryoll] silty clay loam soil at Ellerslie) in north-central Alberta, Canada, to determine the influence of tillage (zero tillage and conventional tillage), straw management (straw removed [S_Rem] and straw retained [S_Ret]), and N fertilizer rate (0, 50 and 100 kg N ha^?1in S_Ret, and only 0 kg N ha^?1in S_Rem plots) on seed yield, straw yield, total N uptake in seed + straw (1991–2008), and N balance sheet (1980–2008). The N fertilizer urea was midrow-banded under both tillage systems in the 1991 to 2008 period. There was a considerable increase in seed yield, straw yield, and total N uptake in seed + straw with increasing N rate up to 100 kg N ha^?1 under both tillage systems. On the average, conventional tillage produced greater seed yield (by 279 kg ha^?1), straw yield (by 252 kg ha^?1), and total N uptake in seed + straw (by 6.0 kg N ha^?1) than zero tillage, but the differences were greater at Breton than Ellerslie. Compared to straw removal treatment, seed yield, straw yield, and total N uptake in seed + straw tended to be greater with straw retained at the zero-N rate used in the study. The amounts of applied N unaccounted for over the 1980 to 2008 period ranged from 1114 to 1846 kg N ha^?1 at Breton and 845 to 1665 kg N ha^?1 at Ellerslie, suggesting a great potential for N loss from the soil-plant system through denitrification, and N immobilization from the soil mineral N pool. In conclusion, crop yield and N uptake were lower under zero tillage than conventional, and long-term retention of straw suggests some gradual improvement in soil productivity.     

Starter fertilizer effects on grain sorghum hybrids grown on a soil high in residual phosphorus in a no‐tillage environment

Conservation tillage crop production systems have become common in the central Great Plains because they reduce soil erosion and increase water‐use efficiency. The high residue levels associated with no‐tillage systems can cause soils to be cool and wet which can reduce nutrient uptake and growth of crops. Starter fertilizer applications have been effective in improving nutrient uptake even on soils high in available nutrient elements. Resent research indicates that corn (Zea mays L.) hybrids differ in their responses to starter fertilizer. No information is currently available concerning grain sorghum [Sorghum bicolor (L.) Moench] hybrid response to starter fertilizer. The objective of this study was to evaluate grain sorghum hybrid responses to starter fertilizer in a no‐tillage environment on a soil high in available phosphorus (P). This field experiment was conducted from 1995 to 1997 at the North Central Kansas Experiment Field, located near Belleville, on a Crete silt loam soil (fine, montmorillonitic, mesic, Pachic Arguistoll). Treatments consisted of 12 grain sorghum hybrids and two starter fertilizer treatments. Fertilizer treatments were starter fertilizer [34 kg nitrogen (N) and 34 kg P₂O₅ ha^‐1] or no starter fertilizer. Starter fertilizer was applied 5 cm to the side and 5 cm below the seed at planting. Immediately after planting, N was balanced on all plots to give a total of 168 kg N ha^‐1. In all three years of the experiment, grain yield, total P uptake (grain plus stover), grain moisture content at harvest, and days to mid‐bloom were affected by a hybrid x starter fertilizer interaction. Starter fertilizer consistently increased yields, reduced harvest grain moisture, improved total P uptake, and reduced the number of days needed from emergence to mid‐bloom of Pioneer 8505, Pioneer 8522Y, Pioneer 8310, Dekalb 40Y, Dekalb 48, Dekalb 51, Dekalb 55, and Northrup King 524, buthadno effect on Pioneer 8699, Dekalb 39Y, Northrup King 383Y, and Northrup King 735. When averaged over the three years, starter fertilizer increased grain yield of responding hybrids (hybrids in which the 3‐year average grain yield was significantly increased by the application of starter fertilizer) by 920 kg ha^‐1. In responding hybrids, starter fertilizer reduced grain moisture at harvest by 54 g kg¹ and also shortened the period from emergence to mid‐bloom by five days. Starter fertilizer increased V6 stage aboveground dry matter production and N and P uptake of all hybrids tested. Results of this work show that in high residue production systems even on soils high in available P, starter fertilizer can consistently increase yield of some hybrids, whereas other hybrids are not affected.     

Residue Decomposition and Fate of Nitrogen‐15 in a Wheat Crop under Different Previous Crops and Tillage Systems

Abstract

Nitrogen (N) management may be improved by a thorough understanding of the nutrient dynamics during previous‐crop residue decomposition and its impact on fertilizer N fate in the soil–plant system. An experiment was conducted in the Argentine Pampas to evaluate the effect of maize and soybean as previouscrops and plow‐till and no‐till methods on N dynamics and ¹⁵N‐labeled fertilizer uptake during a wheat growing season. Maize and soybean residues released N under both tillage treatments, but N release was faster from soybean residues and when residues were buried by tillage. Net immobilization of N on decomposing residues was not detected. A regression model that accounted for 92% of remaining N variability included time, previous crop, and tillage treatment as independent variables. The rapid residue decomposition with N release was attributed to the high temperatures of the agroecosystem. The recovery of ¹⁵N‐labeled fertilizer in the wheat crop, soil organic matter, and decomposing residues was not statistically different between previous crop treatments or tillage systems. Crop uptake of fertilizer N averaged 52% across treatments. Forty percent of fertilizer N was removed in grains. Immobilization of labeled N on soil organic matter was substantial, averaging 34% of the ¹⁵N‐labeled fertilizer retained, but was very small on decomposing residues, averaging 0.2–3.0%. Fertilizer N not accounted for at harvest in the soil–plant system was 12% and was ascribed to losses. Previous crop or tillage system had no impact on wheat yield, but when soybean was the previous crop, N content of grain and straw+roots increased. Discussion is presented on the potential availability of N retained in wheat straw, roots, and soil organic matter for future crops.     

Traffic and residue management systems: effects on fate of fertilizer N in corn

Soil compaction has been recognized as a problem limiting crop production, especially in the Southern Coastal Plain of the USA. Development of tillage and residue management systems is needed to alleviate soil compaction problems in these soils. Fertilizer nitrogen (N) management is also an important factor in these management systems. In 1988, a study was initiated with a wide-frame (6.3 m) vehicle to determine the interactive effects of traffic, deep tillage, and surface residue management on the fate of fertilizer N applied to corn (Zea mays L.) grown on a Norfork loamy sand (fine-loamy, siliceous, Thermic, Typic Kandiudults). Corn was planted into a winter cover crop of ‘Tibbee’ crimson clover (Trifolium incarnatum L.). Treatments included: traffic (conventional equipment or no traffic); deep tillage (no deep tillage, annual in-row subsoiling, or one-time only complete disruption); residue management (no surface tillage or disk and field cultivation). The one-time only complete disruption was accomplished by subsoiling at a depth of 43 cm on 25 cm centers in spring 1988. In 1990–1991, fertilizer applications were made as ¹⁵N-depleted NH₄NO₃ to microplots inside each treatment plot. The 1990 and 1991 data are reported here. In 1990 an extreme drought resulted in an average grain yield of 1.8 Mg grain ha⁻¹, whereas abundant rainfall in 1991 resulted in 9.4 Mg grain ha⁻¹. Deep tillage increased corn dry matter production in both years. In 1991, grain yields indicated that corn was susceptible to recompaction of soil owing to traffic when residues were incorporated with surface tillage. In the dry year, plant N uptake was increased 27% with deep tillage and decreased 10% with traffic. In the wet year, a surface tillage × deep tillage × traffic interaction was observed for total N uptake, fertilizer N uptake, and total fertilizer N recovery in the plant-soil system. When combined with traffic, plant N uptake was reduced with the highest intensity tillage treatment (135 kg N ha⁻¹) because of rootrestricting soil compaction, and with the lowest intensity tillage treatment (129 kg N ha⁻¹) because of increased N losses. In these soils, leaving residues on the soil surface can reduce the detrimental effect of traffic on corn production, but if no surface tillage is performed, deep tillage is needed.     

深翻－旋耕轮耕与有机肥配施对黑土农田土壤物理性质的影响

针对东北松嫩平原中南部黑土区玉米带农田长期旋耕导致耕层变浅、容重增大等问题,开展深翻-旋耕轮耕模式改善土壤物理性质的研究。试验设置连年旋耕配施化肥（RT）、连年旋耕配施化肥与有机肥（RM）、深翻－旋耕轮耕配施化肥（DT）和深翻－旋耕轮耕配施化肥与有机肥（DM）4个处理,分析0 ~ 45 cm土壤含水量、容重、紧实度、团聚体的变化及10 cm、20 cm、30 cm各深度处土壤温度变化情况。结果表明,与RT处理相比,DT处理能够显著提高玉米苗期和拔节期20 cm、30 cm深度土壤温度,增加玉米各生育时期15 ~ 45 cm土层土壤含水量,并且显著降低土壤容重和紧实度,提高了30 ~ 45 cm土层 > 0.25 mm水稳性团聚体的比例;同时DM处理能够增加苗期、收获期各土层含水量,且对0 ~ 45 cm土壤容重均有显著降低作用;而RM处理仅使0 ~ 15 cm土层容重有降低,但并不显著,且对深层土壤容重无明显影响。相关分析表明,在0 ~ 15 cm土层中,土壤含水量、紧实度、容重与温度呈负相关关系（P < 0.05）;在0 ~ 45 cm土层中,土壤容重与土壤紧实度呈极显著正相关关系（P < 0.05）。DM的耕作模式能降低土壤容重和紧实度,有效提高土壤温度、土壤含水量以及 > 0.25 mm 水稳性团聚体的比例,能够较好的改善土壤耕层物理性质。     

Dryland corn response to tillage and nitrogen fertilization. I. Growth‐yield‐N relationships

Abstract

Crop response to fertilizer nitrogen (N) is dependent upon tillage management. This study was conducted to determine how tillage rotation influences non‐irrigated crop growth, N uptake and yield. The effects of tillage rotation, N rate and N timing schedule on early season dry matter production and N uptake, ear leaf N concentration at silking, and yield of corn [Zea mays (L.) Pioneer 3378] were investigated at Painter, VA, on an Altavista loam (fine‐loamy, mixed, thermic Aquic Hapludult). In 1986, maximum yields achieved in the 6‐year continuous no till (NT) [5.82 Mg/ha] and first year no till (AT) [5.64 Mg/ha] were significantly greater than that of the 6‐year continuous conventional till (CT) [3.67 Mg/ha], but no yield differences were obtained in the drier 1987 season. A higher rate of N fertilizer was required to obtain maximum yield in the first year no till (168 kg N/ha) than in the NT (112 kg N/ha) during 1986. Early 1986 N uptake and growth response with and without N at planting increased in the order CT < AT = NT and AT < CT < NT, respectively, indicating greatest immobilization of soil N occurred in the newly established no till soil. Lack of differences in critical ear leaf N values developed for NT and CT in each year imply that plant norms developed for one tillage system may accurately assess N status of corn grown under different tillage practices.     

Direct drilling and soil loosening for spring cereals on a fine sandy loam in Atlantic Canada

Changes in soil structure and properties, plant growth and diseases and agronomic aspects were determined, after 3 years, on a Charlottetown fine sandy loam, an Orthic Podzol with a perhumid soil moisture regime, subjected to three tillage systems for spring cereals. The tillage systems consisted of direct drilling, soil loosening with a “paraplow” followed by direct drilling and mouldboard ploughing.

Rate of plant growth and other crop measurements were not changed by the tillage systems, except for the depth of seeding. Direct drilling reduced the accumulation of N and K in the plant, and reduced grain N, compared with mouldboard ploughing. Soil loosening prior to direct drilling prevented the decline in N and K accumulation, and increased grain yield and N content, in comparison with mouldboard ploughing. Direct drilling caused changes in soil macro-aggregation and reduced the evaporation rate, and increased microbial biomass C and N, total organic C and N and extractable ions at the soil surface (0–5 cm), compared with mouldboard ploughing. In addition, earthworm numbers were increased under direct drilling. Root lesion and spiral nematodes were not influenced by tillage differences.

Soil loosening prior to direct drilling alleviated the significant reductions in soil macroporosity, and prevented the increase in soil bulk density, soil strength and percentage water-filled pore space (%WFPS) associated with direct drilling alone. Although soil permeability was optimum under direct drilling alone, the relative increase in %WFPS and reduction in soil aeration were associated with a concomitant increase in common root rot.     

Influence of Residue Management and Tillage Systems on Carbon Sequestration and Nitrogen,Phosphorus, and Potassium Dynamics of Soil and Plant and Wheat Production in Semi-arid Region

Reducing the tillage and application of mulch are important strategies for soil and water conservation and sustainability of agricultural systems. Soil can be a source or sink for carbon (C) depending on management strategies and plays a major role in the global C cycle. These interacting practices can alter nutrient movement and availability to the crops, reduce water loss, slow down organic-matter (OM) decomposition, and thus enhance C sequestration. A 2-year field study was conducted to quantify the tillage and mulching effect on soil organic C (SOC), OM, nitrogen (N), phosphorus (P), and potassium (K) at two depths (i.e., 0–15 and 15–30 cm deep) in the soil profile and N, P, and K concentrations (g kg^?1) in plant shoots at harvest on a Typic Calciargids in wheat–maize rotation. The four tillage systems used were zero tillage (ZT), minimum tillage (MT), conventional tillage (CT), and deep tillage (DT), and four mulch rates [control, 2 (M₂), 4 (M₄), and 6 (M₆) Mg ha^?1 year^?1 wheat (Triticum aestivum L.) straw] were applied in combination with each tillage system, keeping recommended rates of fertilizers. There was a linear positive response of mulch application on SOC for both years, but it was more pronounced during the second year. Greater values were found in ZT and the lowest in CT at all depths, although greater SOC content was found in upper layers than in deeper ones. Greater shoot N, P, and K concentrations were found in MT, CT, and DT, whereas the lowest concentration was found in ZT. Mulch application has no effect on N, P, and K concentrations in shoots. The soil N concentration was not affected by tillage and mulch, yet greater soil N content was found at 0–15 cm than 15–30 cm deep. There was significant effect of tillage on soil P and K during one year as greater P and K concentrations were found under MT, CT, and DT compared to ZT. More N, P, K, and OM concentrations were found at 0–15 cm deep than at 15–30 cm deep during the whole study period. Mulch effect was significant on K, and significantly greater amounts were found at greater levels of mulch application. The increases in the soil OM were 34.5, 35.75, and 24% at 0–8, 8–16, and 16–24 cm deep respectively from the first year to the second year. Tillage effect on soil organic-matter content was not significant. Tillage increased grain production for both years. For the first year, 22.9 and 27% greater yields were found in CT and DT, whereas in the second year yields were 10.6, 17.9, and 57% greater, respectively, in MT, CT, and DT as compared to ZT. Grain production was increased at a result of mulch application by 12.9, 20.3, and 10.6% during the first year and 11.45, 23.74, and 10.9% during the second year as compared to control (i.e., without mulch). Results show the importance of mulch application and crop residue retention. Both can increase the SOC content and water-holding capacity, which will result in improved production and soil physical health over long and continuous use of mulch.     

Long-term effects of tillage systems and rotations on soil structural stability and organic carbon stratification in semiarid central Spain

Under semiarid Mediterranean climatic conditions, soils typically have low organic matter content and weak structure resulting in low infiltration rates. Aggregate stability is a quality indicator directly related to soil organic matter, which can be redistributed within soil by tillage. Long-term effects (1983–1996) of tillage systems on water stability of pre-wetted and air dried aggregates, soil organic carbon (SOC) stratification and crop production were studied in a Vertic Luvisol with a loam texture. Tillage treatments included conventional tillage (CT), minimum tillage (MT) and zero tillage (ZT) under winter wheat (Triticum aestivum L.) and vetch (Vicia sativa L.) rotation (W–V), and under continuous monoculture of winter wheat or winter barley (Hordeum vulgare L.) (CM). Aggregate stability of soil at a depth of 0–5 cm was much greater when 1–2 mm aggregates were vacuum wetted prior to sieving (83%) than when slaked (6%). However, slaking resulted in tillage effects that were consistent with changes in SOC. Aggregate stability of slaked aggregates was greater under ZT than under CT or MT in both crop rotations (i.e., 11% vs. 3%, respectively).

SOC under ZT tended to accumulate in the surface soil layer (0–5 and 5–10 cm) at the expense of deeper ones. At depths of 10–20 and 20–30 cm no differences in SOC were encountered among tillage systems, but CT exhibited the highest concentration at 30–40 cm depth. Nevertheless, when comparisons were made on mass basis (Mg ha⁻¹), significant differences in stocked SOC were observed at depths of 0–10 and 0–20 cm, where ZT had the highest SOC content in both rotations. The stock of SOC to a depth of 40 cm, averaged across crop rotations, was greater under ZT (43 Mg ha⁻¹) than under CT (41 Mg ha⁻¹) and MT (40 Mg ha⁻¹) although these figures were not significantly different. Likewise, no significant differences were encountered in the stock of SOC to a depth of 40 cm among crop rotations (i.e., 42 Mg ha⁻¹ for W–V vs. 40 Mg ha⁻¹ for CM).

Crop production with wheat–vetch and continuous cereal showed no differences among tillage systems. Yields were strongly limited by the environmental conditions, particularly the amount of rainfall received in the crop growth season and its distribution. Similar yield and improved soil properties under ZT suggests that it is a more sustainable system for the semiarid Mediterranean region of Spain.     

Physical and mechanical properties of a clayey soil as affected by tillage systems for wheat growth

Abstract

The effect of tillage systems on soil physical properties of a clayey soil was studied. Tillage systems consisting of conventional tillage I (CT₁), conventional tillage II (CT₂), reduced conventional tillage (RCT), reduced tillage (RT) and no tillage (NT) were carried out in autumn after harvest of sugar beet. Significant differences between tillage systems were recorded on the measured properties, apart from moisture content, at 15–30 cm soil layer. The CT₁, CT₂ and RCT systems resulted in similar penetration resistance and bulk density values below the 15 cm soil depth, while the RT and NT systems resulted in higher but similar values. The mean penetration resistance values were less than 1 MPa in the CT₁, CT₂ and RCT systems at the 0–15 cm depth, while they were 1.41, 1.84 MPa in RT and NT, respectively. The mean total porosity increased with tillage from 8.2 to 28% when compared with NT. The CT₁, CT₂ and RCT systems resulted in lower moisture content at the 0–15 cm depth. The lowest moisture content occurred in RCT (24.4%) and the highest in NT (30.9%), while it was 30.3% in RT system. The lowest and highest mean weight diameter values were reported for the RT (1.36 mm) and NT (2.37 mm) systems, respectively. The lowest wheat grain yield was obtained in NT (4.14) and the highest in CT₁ (5.24 Mg ha^?1). A significant difference occurred between only NT and the other systems. When both grain yield and advantages of reduced tillage are considered, the RT system is recommended.     

Nitrogen balance in a soil‐wheat system under plow‐ and no‐tillage in the argentine humid pampa

Abstract

Changing conventional tillage to conservation tillage systems affects nitrogen (N) cycling in agroecosystems. Our objective was to evaluate the role of soil organic pools, specially plant residues, as sources‐sinks of nitrogen in an humid and warm temperate environment cropped to wheat, under plow‐ and no‐tillage. The experimental site was in the Argentine Pampa on a Typic Hapludoll. A balance‐sheet method was used: Nupt+Nres=Nsow+Nmin, where Nupt=N uptake by the crop at harvest; Nsow=soil mineral N as NH₄ and NO₃ at 0–90 cm depth, one month before sowing, plus N added as fertilizer; Nres=residual soil mineral N as NH₄ and NO₃ at 0–90 cm depth, at harvest; Nmin=N mineralized from humus and plant residues during wheat growing period. Nupt did not differ between tillage systems. Nitrogen supply by the mineral N pool, estimated by the difference Nsow‐Nres, was ca. 150 kg N ha^‐1 in both tillage systems. Plant residues decomposed and released N under both treatments. This organic N pool decreased 77% along the crop cycle. Nmin, calculated using the balance equation was 83 kg N ha^‐1, and did not differ between tillage managements, representing 35% of Nupt. This results highlight the importance of the organic pools as sources of N for wheat in the Humid Pampa. They also brink our attention on the importance for evaluate residue decomposition and humus mineralization in warm‐temperate regions when fertilizer requirements are determined, in order to minimize environmental hazard and economic losses by overfertilization.     

Influence of long-term tillage, straw and N fertilizer on barley yield, plant-N uptake and soil-N balance

Long-term influence of N fertilizer, tillage and straw on crop production and soil properties are not well known in central Alberta. Field experiments were established in autumn 1979, on a Black Chernozemic soil and on a Gray Luvisolic soil in north-central Alberta to determine the long-term effect of tillage, straw and N fertilizer on yield and N uptake of barley (Hordeum vulgare L.). Fertilizer N was applied annually at 56 kg ha⁻¹. The 11 year averages of barley yields and N uptake under zero tillage were lower than under conventional tillage. Retention rather than removal of straw tended to reduce barley yield for the initial 6 years and 2 year at Site 1 and Site 2, respectively. A simple mathematical model of average annual plant N uptake and grain yield could account for most of the variation in the data observed at both sites (R² = 0.907; P < 0.01). Final values of soil N, calculated using a mass balance approach, agree closely with values measured at the end of the eleventh year. Conventional tillage and zero tillage, with addition of fertilizer N and retention of straw, were the only treatments with apparent but small net addition of N to soil at Site 1 (40 kg ha⁻¹ and 117 kg ha⁻¹, respectively). At Site 2, only the zero tillage treatment with addition of fertilizer and retention of straw gained soil N (29 kg ha⁻¹). In conclusion, soil ecosystems functioning in subhumid environments with slight to moderate heat limitations such as those in central Alberta can adapt, within a few years, to zero tillage practices with full retention of straw.     

Response of organic matter to reduced tillage and animal manure in a temperate loamy soil

The impacts of tillage and organic fertilization on soil organic matter (SOM) are highly variable and still unpredictable, and their interactions need to be investigated under various soil, climate and cropping system conditions. Our work examined the effect of reduced tillage and animal manure on SOM stocks and quality in the 0–40 cm layer of a loamy soil under mixed cropping system and humid temperate climate. The soil organic carbon (SOC) and N stocks, particulate organic matter (POM), and C and N mineralization potential (301 days at 15 °C) were measured in a 8‐yr‐old split‐plot field trial, including three tillage treatments [mouldboard ploughing (MP), shallow tillage (ST), no tillage (NT)] and two fertilization treatments [mineral (M), poultry manure 2.2 t/ha/yr C (O)]. No statistically significant interactive effects of tillage and fertilization were measured except on C mineralization. NT and ST showed greater SOC stocks (41.2 and 39.7 t/ha C) than MP (37.1 t/ha C) in the 0–15 cm increment, while no statistical differences were observed at a greater depth. N stocks exhibited similar distribution patterns with regard to tillage effect. Animal manure, applied at a rate representative of typical field application rates, had a smaller impact on SOC and N stocks than tillage. The mean SOC and N stocks were higher under O than M, but the differences were statistically significant only in the 0–5 cm increment. MP showed lower C‐POM stocks than NT and ST in the 0–5 cm increment, whereas greater C‐POM stocks were measured under MP than under NT or under ST in the 20–25 cm increment. Organic fertilization had no impact on C‐POM or N‐POM stocks. In the 0–25 cm increment, NT showed a lower C and N mineralization potential than MP. Our work shows that the sensitivity of SOM to reduced tillage for the whole soil profile can be relatively small in a loamy soil, under humid‐temperate climate. However, POM was particularly sensitive to the differential effects of tillage practices with depth, and indicative of differentiation in total SOM distribution in the soil profile.     

Soil properties and yam yield under different tillage systems in a tropical Alfisol

In Nigeria, information is lacking regarding the most suitable tillage method in extensive yam production. Hence, five tillage methods were compared at two sites in 2008–2010 with reference to their effects on soil physical and chemical properties, leaf nutrient concentrations, growth and tuber yield of yam (Dioscorea rotundata Poir) on Alfisols at Owo (site A) and Akure (site B), south-west Nigeria. The tillage methods were: zero tillage (ZT), manual ridging (MR), manual mounding (MM), ploughing + harrowing (P + H) and ploughing + harrowing + ridging (P + H + R). P + H + R had lower soil bulk density than other tillage methods and resulted in higher leaf N, P, K, Ca and Mg and yam tuber yield. In ZT, bulk density, soil moisture content, soil organic C, N, P, K, Ca and Mg were significantly higher and temperature lower than other tillage methods. Results of multiple regressions revealed that bulk density significantly influenced the yield of yam rather than soil chemical properties. Compared with MR, MM, P + H and ZT, and averaged across years, P + H + R increased yam tuber yield by 12.3, 12.8, 34.9 and 50.7%, respectively, in site A and 12.9, 13.5, 25.2 and 44.5%, respectively, in site B. P + H + R was found to be most advantageous and is therefore recommended for yam cultivation.     

Corn response to potassium placement in conservation tillage

Improvements in the yield potential of corn (Zea mays L.) grown using conservation-tillage may depend, in part, on K fertility management. Field research was conducted in 1997 and 1998 on a field which had been in continuous no-tillage (NT) for the previous 12 years near Paris, Ont., Canada to evaluate potassium (KCl) placement effects on corn growth and yields in NT, spring zone-tillage (ZT) and spring mulch-tillage (MT) systems. Soils were classified as moderately well drained and had low soil-test K levels. Potassium was spring-applied (1 day prior to corn planting) at either 0 or 100 kg K ha⁻¹. Potassium was either broadcast applied, deep in-row banded (15 cm deep), or half broadcast applied and half shallow-banded (5 cm beside the row, 5 cm below seeding depth). Early season and mid-season corn ear-leaf K concentrations indicated that spring-applied K fertilizer was available for uptake by corn in conservation-tillage systems. Potassium application sometimes significantly increased corn yields compared to the zero K control in the NT and ZT systems. However, MT corn yields did not show any response to K fertilization in either season despite the low soil-test K levels. There were no significant corn yield increases with deep banding of K fertilizer relative to shallow placement in any tillage system. This study suggests that, for similar low-testing K soils, alternate K placements will have greater impacts on corn plant nutritional status than on final yields. Surface broadcasting of K fertilizer is appropriate for continuous NT corn despite evident K stratification present after long-term NT. MT may improve corn K nutrition after long-term NT.     

Wheat yield and weed population as influenced by three tillage systems on a clay soil in temperate continental climate

The potential benefits of conservation tillage practices depend mainly on the soil and climatic conditions of the site. A study was conducted to determine the effects of three tillage systems (conventional, CT; reduced, RT; zero, ZT) on spring wheat (Triticum aestivum L.) and weed growth on a clay soil in temperate continental climate, northern Alberta (55°43′N, 118°41′W), Canada. A medium duty cultivator with 25 cm sweeps spaced 22 cm apart and a working depth of 8–10 cm was used for tillage in the CT (once in fall and twice in spring) and RT (once in spring) plots. The ZT plots received a harrowing to spread straw and a preseeding application of Roundup (glyphosate) to control weeds. Experimental design was a randomized complete block with four replications and the tillage systems were fixed in space for the 1989, 1990 and 1991 seasons. The RT treatment resulted in higher yields than the CT or ZT treatments. However, the differences were not always significant. The ZT treatment produced higher yields than CT in 1989 and 1991, whereas its yields were lower than CT in 1990. The 3 year means of total dry matter (TDM) were 3899 kg ha⁻¹, 3640 kg ha⁻¹ and 3331 kg ha⁻¹ for the RT, ZT and CT treatments, respectively. The corresponding grain yields were 1728 kg ha⁻¹, 1573 kg ha⁻¹ and 1530 kg ha⁻¹. The concentration of total N in plants and grains of wheat, amounts of extractable NO₃-N, NH₄-N and P in soil and soil moisture and bulk density were not significantly affected by tillage. The mean weight diameter of aggregates in surface soil was significantly greater under ZT than under the other systems. Wild buckwheat (Polygonum convolvulus L.) was more abundant under CT, but common groundsel (Senecio vulgaris L.), dandelion (Taraxacum officinale Weber), hemp nettle (Galeopsis tetrahit L.), field horsetail (Equisetum arvense L.) and smartweed (Polygonum scabrum Moench) tended to have higher populations under the ZT system. The populations of foxtail barley (Hordeum jubatum L.) wild rose (Rosa sp.), stinkweed (Thlaspi arvense L.) and wild oats (Avena fatua L.) showed no consistent effect of tillage. Tillage or preseeding application of glyphosate did not provide an effective control of all weed species. The spring tillage of the RT system improved crop yields and weed control relative to ZT, whereas the fall tillage of the CT system (in addition to spring tillage) reduced crop yields and had no significant effect on weed population relative to RT. The overall results showed that tillage intensity could be reduced to the level of RT without any adverse influence on crop yields, soil properties or weed populations. The RT system is also economical and environmentally desirable owing to lower tillage and herbicide requirements.     

No‐tillage corn response to placement of fertilizer nitrogen,phosphorus, and potassium

Abstract

Fertilizer placement for corn (Zea mays L.) has been a major concern for no‐tillage production systems. This 3‐yr study (1994 to 1996) evaluated fertilizer phosphorus (P) or potassium (K) rates and placement for no‐tillage corn on farmers’ fields. There were two sites for each experiment involving fertilizer P or K. Treatments consisted ofthe following fertilizer rates: 0,19,and 39 kg P ha^‐1 or 0, 51, and 102 kg K ha^‐I. The fertilizer was broadcast or added as a subsurface band 5 cm beside and 5 cm below the seed at planting. Early plant growth, nutrient concentrations, and grain yields were measured. At the initiation of the study, soil test levels for P and K at the 0–1 5 cm depths ranged from optimum (medium) to very high across sites. Effects of added fertilizer and placement on early plant growth and nutrient concentrations were inconsistent. Added fertilizer had a significant effect on grain yields in two of twelve site‐years. Therefore, on no‐tillage soils with high fertility, nutrient addition, and placement affected early plant growth and nutrient utilization, but had limited effect on grain yield. Consequently, crop responses to the additions of single element P or K fertilizers under no‐tillage practices and high testing soils may not result in grain yield advantages for corn producers in the Northern cornbelt regardless of placement method.