太湖地区水稻土的物理特性与少免耕法的关系

本文从土壤物理特性和作物生长的关系探讨了耕作的要求.土壤水分能量特性可被机械扰动改变,这是导致土壤粘闭的重要原因.水稻土的含水量和有效水均以表土高,而下层低,含水量和容重成线性负相关(n=62,r=-0.909^**).土壤扰动可提高持水量,长年免耕在干旱年份可能会出现水分不足问题.土壤含水量、气容量和机械强度三者的变化相互联系.由三个因素决定的小麦生长最佳范围是在水分吸力0.02-0.5巴内,而田间持水量大于塑性限,所以秋季耕作必然导致土壤粘闭.免耕土壤的容重一般在1-1.25g/cm₃之间,是稻麦生长的较佳环境,所以水稻土本身存在适合稻麦免耕生产的条件.根据水稻和三麦分别52和23组次对比试验,水稻免耕增产19斤/亩,三麦49斤/亩,均达到极显著水平(p=0.01).平田地区连续三年免耕土壤不恶化,囊水型土壤第二年开始有变差趋势,但产量不减低.免耕有保护土壤结构的作用,但不利于结构发展.     

Compaction and tillage depth combinations for water management and rice production in low-retentive permeable soils

Excessive percolation loss and low water retention adversely affect the production of rice in coarse-textured lateritic soils. A tillage scheme has been developed from long-term field experimentation during 1973–1978 to measurably reduce the percolation losses and enhance the productivity of rice in this soil under both lowland and upland conditions. Artificially compacted surface and subsurface layers were induced in soil by suitably combining level of compaction as obtained by one (D₁), two (D₂), four (D₃) or six (D₄) passes of a 800 kg iron roller at a load intensity of 0.21 kg cm⁻² and post-compaction tillage or puddling depth of o cm (T₀), 5 cm (T₁), 10 cm (T₂) or 15 cm (T₃). An additional no-compaction treatment (D₀) was included in lowland experiments. where the effect of either the depht or intensity of puddling was also studied. The utility of this tillage scheme in increasing the efficiency of nitrogen fertilizer use was characterized by a separate upland experiment in 1976 with a lower rate (60 kg N ha⁻¹) of N application than that (100 kg N ha⁻¹) applied in all other experiments.Rice yield was significantly increased on upland by artificially compacting the soil to D₂. However, with further compaction to D₃ and D₄, the yield decreased. When postcompaction tillage was adopted, the grain yield decreased at low compaction level (D₁, D₂) but increased at high compaction level (D₃, D₄) with increase in tillage depth from 0 to 15 cm. The maximum grain yield occurred at D₃T₁.Higher grain yield at D₃T₁, D₂T₀ and D₄T₂ is attributable to a more favourable soil bulk density profile, a lower infiltration rate and higher surface retention of water. The efficiency of applied nitrogen fertilizer was apparently increased at these compaction—tillage depth combinations, where the upland rice yield experienced insignificant reduction with decrease in nitrogen application rate from 100 to 60 kg ha⁻¹.Similar trends of yield response to compaction—tillage combinations were also observed under lowland conditions. When the soil was puddled (following high compaction) with a wedge plough or a power tiller, rice yields were increased by 48 and 56%, respectively, over yields using conventional puddling (without compaction). The yield increased further with the increase in intensity of puddling using a power tiller.     

Effect of tillage practices on irrigation requirement,weed control and yield of lowland rice

Dry soil bulk density increased from 1.42 g/cm³ with ordinary ploughing to 1.69 g/cm³ with puddling twice and to 1.80 g/cm³ with soil compaction. Consequently, saturated hydraulic conductivity decreased from 113 mm/day with ordinary ploughing to 48 mm/day with puddling twice and to 29 mm/day with soil compaction. The irrigation requirement was 2295 mm with ordinary ploughing compared with 1350 mm with soil compaction. Dry weight of weeds was only 0.6 and 0.7 t/ha with puddling twice and soil compaction, respectively, and 3.9 t/ha with ordinary ploughing. The highest grain yield of rice (4.5 t/ha) was obtained with puddling twice, due to effective weed control. Weeds shared 57 and 35% of the nutrient (N+P+K) with ordinary ploughing and puddling once, respectively, as compared with only 8 and 15% with puddling twice and soil compaction, respectively. The ratio of total biological yield (grain + straw + weeds) to total nutrient (N+P+K) uptake was 59.0 with puddling twice and soil compaction as compared with 53.5 with puddling once and 50.0 with ordinary ploughing. This suggests that tillage practices may affect the efficiency of the use of soil and applied nutrients by the rice crop.     

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.     

Water storage,water use and maize yield for tillage systems on a tropical alfisol in Nigeria

Water storage, water use, and maize yields were studied on a tropical alfisol derived from basement complex rocks in Western Nigeria. The objective was to determine the effects of tillage practices on these factors over a long period since a short term yield record may not be a good basis to evaluate the performance of tillage systems.The study, which lasted for five years (1976–1980) with two growing seasons per year, involved four tillage practices, namely: zero-tillage with mulch; conventional tillage (ploughing and harrowing); plough only and “manual” system which was an imitation of the local peasant practice. The experimental design was randomised complete block with four replications.Results show that in the early seasons the cultivated treatments, namely conventional and ploughing, out-yielded the zero-tillage in the first two years of the study (1976 and 1977). Yields ranged from 2639 kg ha^?1 in the zero-tillage to 5240 kg ha^?1 in the conventional tillage. However from 1978, the zero-tillage yields were significantly higher (P < 0.05) than yields from the cultivated treatments with the figures ranging from 4998 kg ha^?1 to 5949 kg ha^?1 in the cultivated plots and zero-tillage, respectively.The late season yields were also significantly higher in the zero-tillage throughout the study period. The late season is usually a period of low rainfall and the plants go through periods of stress, especially during the critical tasseling and silking period.Water use was similar for plants under the different tillage practices but water use efficiency (WUE), which for the early season ranged between 76.34 kg ha^?1 cm^?1 in 1980 to 118.65 kg ha^?1 cm^?1 in 1978, was significantly higher in the zero-tillage most of the time.The leaf stomatal resistances averaged over the measuring periods were 9.2, 9.5, 9.7 and 10.6 s per cm for plants under the zero-tillage, conventional, manual, and plough respectively. These figures were, however, not significant at five percent.There was also no significant difference (P < 0.05) in the flag leaf water potentials. The average values were ?1.39, ?1.42, ?1.49 and ?1.80 MPa for conventional, plough, zero-tillage and manual techniques, respectively.     

Water use efficiency of rice (Oryza sativa L.) under intermittent ponding and different intensity of puddling

Abstract

To increase the water use efficiency (WUE) of rice, two sets of experiments were carried out from 1997 – 1999. Experiment one: Irrigation period of rice was divided into three stages: early (S₁, 10 – 35 days after transplanting, [DAT]); middle (S₂, 36 – 60 DAT) and late (S₃, 61 – 85 DAT). Intermittent ponding (IP) was imposed at single, two stages or the entire growing period. Continuous ponding (CP) in all three stages was taken as control. Though the highest grain yield (6.71 mg ha^?1) was obtained under control, this regime was responsible for the lowest WUE. In contrast, IP in all stages was responsible for maximum WUE with minimum yield level. Imposition of IP in S₁ resulted in higher (0.529 kg m^?3) WUE along with insignificant reduction in yield over control. Experiment two: Three puddling practices were: (i) High intensity puddling (HIP); (ii) Moderate intensity puddling (MIP); and (iii) Low intensity puddling (LIP). On average, HIP resulted in the lowest value (6.5 mm d^?1) of percolation rate. Both grain yield (6.93 mg ha^?1) and WUE (0.597 kg m^?3) attained highest value under HIP. A decrease in puddling intensity under MIP and LIP lowered the yield by 2.97 and 17.75% respectively. In the case of WUE, the reduction was 16.27 and 54.66%.     

Barley yield and weed development as affected by crop sequence and tillage systems in a semi‐arid environment

Abstract

In order to monitor barley and weed development on a loamy sand soil subjected to different agronomic practices, field experiments were conducted for three growing seasons (1992–95) in a semi‐arid agrosystem in central Spain. For eight years, independent plots were managed with three crop sequences: barley (Hordeum vulgare L.)?vetch (Vicia sativa L.); barley? sunflower (Helianthus annuus L.); and a barley monoculture. In all cases, two tillage systems were implemented: no‐tillage and conventional tillage. In the years with standard rainfall (400 mm) an improvement in growth‐related cultivation variables and yield components of barley were observed in plots under barley?vetch rotation and/or conventional tillage. In drier conditions (<350 mm) the growth rate, crop yield and yield components of barley tended to improve under the no‐tillage system. Barley?vetch rotation and/or conventional tillage increased nitrate‐nitrogen (NO₃‐N) content in barley plants. Similar results were found for the concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg). In addition, the plots under crop rotation showed a weed biomass with a high concentration of N, K, and Ca in comparison with plots under monoculture. The lack of spring herbicide treatment in the no‐tillage plots led to a 3‐fold increase in weed density compared with the plots under conventional tillage.     

Weed levels did not alter rice grain yield response to nitrogen

Abstract

Rice (Oryza sativa L.) research field plots are likely to have nearly complete weed control whereas normal farmer field‐grown rice often have considerably greater weed populations. Consequently, a disparity might exist between nitrogen (N) requirements for producing maximum yields, in weedy (such as in some farmer fields) versus weed‐free rice (such as field research plots). We conducted a 2‐year field study at Keiser, AR. Using paired plots, we compared weed control effects, at several preflood ? rates (0–112 kg ? ha^‐1) on yield, yield components, harvest index and weed weights. Rice yield responses to preflood ? fertilization were similar with and without weed pressure. Consequently, ? fertilization recommendations based on research plots with little or no weed pressure are valid for research plots and grower fields with much greater levels of weed pressure.     

Effects of tillage, weed control method and row spacing on soybean yield and certain soil properties

Soybean (Glycine max (L.) Merr.) is an important crop in the southeastern United States, and thus there is a need for additional information on the effects of tillage, weed control methods and row spacing on soybean yields, weed populations and soil properties. The objective of this study was to determine the effects of three weed control methods (none, cultivation, and herbicide) and three row spacings (45, 60 and 90 cm) on soybeans planted in a conventionally prepared seedbed or planted in wheat stubble (no-till (NT)) on a Decatur silty clay loam (Rhodic Paleudult) soil during the 1987 and 1988 growing seasons. Following NT planting, soybean plots produced a seed yield of 3102 kg ha⁻¹ with herbicide, 2911 kg ha⁻¹ with cultivation and 2216 kg ha⁻¹ with no weed control. On a conventionally prepared seedbed, herbicide and cultivation resulted in almost equal seed yields (3898 kg ha⁻¹ and 3954 kg ha⁻¹ respectively) which were significantly higher than those from the no weed control plots (3151 kg ha⁻¹). Soybeans in narrow (45 cm) rows (3997 kg ha⁻¹) consistently out-yielded those in the wider 60 cm rows (3130 kg ha⁻¹) and 90 cm rows (2490 kg ha⁻¹) in both growing seasons, results averaged across years showed that conventionally planted soybeans produced higher yields (3668 kg ha⁻¹) than NT planted soybeans (2743 kg ha⁻¹). The weed infestation was significantly less with herbicide or cultivation than with no weed control and also less in narrow rows (45 cm) than in wider rows (60 and 90 cm). Data on the soil properties (from a depth of 0–15 cm) showed that moisture content, organic matter content and total soil nitrogen were higher in NT plots than in conventional plots. Similarly, disease ratings and infestation of bacterial blight of soybean were significantly higher in NT than in conventional tillage systems.     

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.     

Short-term responses of soil nutrients and corn yield to tillage and organic amendment

Field experiments were conducted in 2010 and 2011 at the Agricultural College of Shiraz University to evaluate the effects of cattle manure and nitrogen (N) fertilizers on soil properties such as soil organic carbon (SOC), soil organic nitrogen (SON), soil electrical conductivity, soil pH and corn yield under two tillage systems. Treatments included tillage systems in two levels as conventional tillage and reduced tillage as subplots, cattle manure (0, 25 and 50 tons ha^?1) and N fertilizer (0, 125 and 250 kg N ha^?1) as sub-subplots. Results showed that SOC and SON were significantly affected by tillage system in both years of the experiment. SOC and SON were higher in reduced tillage compared to conventional tillage. Tillage system had no significant effect on grain yield, plant height and 1000 seed weight. Increased cattle manure rates at 25 and 50 tons ha^?1 increased grain yield by 27% and 38%, respectively, in 2010 and 25% and 25% in 2011. The results showed that application of cattle manure combined with N fertilizer might be an efficient management to increase soil productivity in southern Iran, in soils with poor organic content. Additionally, reduced tillage showed to be an efficient method to increase soil organic matter.     

Influence of nitrogen and weed management on the productivity of upland rice

Nitrogen and weeds are two important factors that influence the productivity of rainfed upland rice (Oryza sativa L.) in tropical Asia. A low recovery of applied fertilizer N in rainfed uplands is generally associated with high nitrate leaching losses and weed interferences. Field experiments were conducted during the wet seasons of 2002 and 2003 at the research farm of Central Rainfed Upland Rice Research Station, Hazaribag, Jharkhand, India, to determine the response of upland rice to nitrogen applied at 60 kg N ha^–1 as different forms of urea (single pre‐plant application of controlled‐release urea, single pre‐plant application of urea supergranules, and split application of prilled urea with or without basal N) against no N application under three weed‐control regimes (unweeded, pre‐emergence application of butachlor at 1.5 kg a.i. ha^–1 supplemented with one single hand weeding or two hand weedings). The response of rice to applied N varied greatly among the three weed‐control regimes. Across the different N treatments, the application of 60 kg N ha^–1 resulted in a grain‐yield increase above the unfertilized control of only 0.24 Mg ha^–1 in unweeded treatments, whereas yields increased by 1.07 Mg ha^–1 when butachlor application was supplemented with a single hand weeding and by 1.28 Mg ha^–1 with two hand weedings. Among the weed‐control measures, hand weeding twice produced highest grain yield in both years. The comparison of different forms of urea showed that a single pre‐plant application of controlled‐release urea resulted in average grain yields of 1.57 and 1.87 Mg ha^–1 compared to 1.32 and 1.30 Mg ha^–1 in the case of the recommended practice of split‐applied prilled urea in the years 2002 and 2003, respectively. The highest agronomic N use efficiency of 15–20 kg grain per kg N applied and the highest apparent N recovery of 39%–45% were attained with controlled‐release urea, suggesting that this N form is particularly beneficial for upland‐rice cultivation under variable rainfall conditions, provided weeds are controlled.     

Weed abundance and soil seedbank responses to tillage systems in continuous maize crops

Weed abundance in crops undergoes frequent changes, often due to changes in tillage practices. Annual species, with quick germination, a short vegetative stage, profuse seed production and long-lived seeds become problematic under zero-tillage systems. Portulaca oleracea L. and Amaranthus blitoides L. are widespread weeds in the Mediterranean area, prominent in irrigated crops. We studied the total weed abundance in the field, and specifically these two species (Portulaca oleracea and Amaranthus blitoides) with high frequency of occurrence in monoculture maize, from 2012 to 2014, in the field and soil seedbank. Results showed significant differences between zero-tillage (ZT) and conventional tillage (CT) systems on total weed abundance and relative abundance of Portulaca oleracea. Total weed abundance decreased in ZT plots (from 136 plants m^?2 to 25 and 46 plants m^?2, in 2013 and 2014 respectively). The same trend was observed in Portulaca oleracea recorded in ZT plots, but the abundance of Amaranthus blitoides did not vary in this system. Weed seedling germination and weed seed numbers both of total weed seedbank and Portulaca oleracea, were greater in ZT plots compared to CT, regarding Amaranthus blitoides seedling germination and seed count, the values did not increase with ZT, in continuous maize crops.     

Reduced tillage techniques for wetland rice as affected by herbicides

Two experiments on land preparation practices, consisting of zero, minimum and conventional tillage treatments, revealed that conventional tillage was the best practice in terms of grain yield, tiller number and weed yield. It was followed by minimum and zero tillage, respectively. A third experiment where zero tillage was associated with dry-seeding with a rolling-injection planter produced yields which were similar to minimum and conventional tillage. Compared to paraquat and SC-0224, glyphosate performed better both in zero and in minimum tillage when followed by harrowing. Application time of paraquat or glyphosate did not affect the grain yield. Butachlor (0.8) application 6 days after seeding significantly increased the grain yield and tiller number. Of the crop establishment methods tested, dry-seeding with a rolling-injection planter in zero tillage, broadcast wet-seeding by hand in minimum tillage and wet-seeding with a low land-seeder in conventional tillage proved to be most suitable. Dry-seeding with a rolling-injection planter proved better in the dry-season, than in the wet-season experiment.     

Improvement of rice (Oryza sativa L.) growth in upland conditions with deep tillage and mulch

The productivity of upland rice in Japan as well as in the world is low and unstable owing to scarce and unpredictable rainfall. The objective of this study was to examine whether agronomic methods could enhance grain yield of upland rice. Four field experiments were conducted from 2001 to 2003 in Nishitokyo, Japan, under upland conditions with different water supplies, in order to quantify the effects of deep tillage combined with deep placement of manure (50-cm depth), straw mulch (6 t ha⁻¹), or their combinations on the growth and grain yield of rice. Mulch kept surface soil moisture higher than without mulch even at reproductive stage, and it increased yield to the greatest extent under the most favourable conditions with much rainfall before heading (i.e., 2003). Deep tillage with deep placement of manure induced deep root proliferation and higher nitrogen uptake, increasing biomass production, and panicle number, and consequently grain yield was enhanced under the two lowest yielding environments with less rainfall before heading. Rice plants with deep tillage with deep manure application without mulch tended to have lower leaf water potential and higher diffusion resistance during drought, and negative effects on grain filling and harvest index in some experiments compared with the control. When deep tillage with deep placement of manure was combined with mulching in two experiments in 2002 and 2003, grain yield always enhanced compared with the control (P < 0.10, 6.0 t ha⁻¹ versus 5.4 t ha⁻¹ on average), suggesting their synergetic mechanisms for yield increase and stabilization. The results showed that deep tillage or mulching can improve grain yield of rice under drought-prone rainfed upland conditions in a temperate climate on an Andosol, and their combination had more consistent and greater positive effects.     

Effect of tillage and fertilizer levels on wheat yield, nitrogen uptake and their correlation with carbon isotope discrimination under rainfed conditions in north-west Pakistan

Appropriate cultural practices need to be determined for enhancing crop yields with low inputs under rainfed conditions. A field experiment was conducted to study the effect of tillage practices and fertilizer levels on yield, nitrogen (N) uptake and carbon (C) isotope discrimination in wheat (Triticum aestivum L.) grown under semi-arid conditions at three sites in north-west Pakistan: NIFA, Urmar and Jalozai. Two fertilizer levels, 60 kg N ha⁻¹+30 kg P ha⁻¹ (L1) and 60 kg N ha⁻¹+60 kg P ha⁻¹ (L2), were applied to wheat grown under conventional tillage (T1) and no-tillage (T0) practices. Labeled urea having 1% ¹⁵N atom excess at 60 kg N ha⁻¹ was applied as aqueous solution in microplots within each treatment plot. A pre-sowing irrigation of 60 mm was applied and during the growing season, the crop relied entirely on rainfall (268 mm). Biomass yield, N uptake and stable C isotope composition (δ¹³C) of plants were determined at maturity. Yield of wheat was improved by tillage at two sites (Sites 1 and 2), while at the third site yield was reduced by tillage as compared with the no-tillage treatment. At Sites 1 and 2, nutrient addition (L2, 60 kg N ha⁻¹+60 kg P ha⁻¹) increased the yield of all plant parts (straw, grain and root) in contrast to Site 3 where only grain yield was increased significantly. Maximum grain yield of wheat was observed with tillage under nutrient level L2 at all sites. Generally, the tillage treatment did not affect the N content in plant parts compared with no-tillage (T0) treatment at all three sites. However, fertilizer N uptake by wheat was variable under different fertilizer levels and tillage practices. Nitrogen derived from fertilizer (Ndff) for grain at Site 2 was higher in tilled plots but was not affected by tillage practice at the other sites. The C isotope (δ¹³C) values varied from −28.96 to −26.03‰ under different treatments at the three sites. The δ¹³C values were less negative indicating more effective water use at Sites 2 and 3 compared to Site 1. The C isotope discrimination (Δ) values were positively correlated with yield of wheat straw (r=0.578^*), grain (r=0.951^**) and root (r=0.583^*). Further, the Δ in grain had significant negative relationship (r=0.912^**) with Ndff (%). The tillage practice exerted a positive effect on yield, N uptake and plant N derived from fertilizer by wheat compared to no-tillage. The positive correlation of Δ with grain, straw and root yields and negative correlation with the Ndff (%) by wheat suggest that this value (Δ) could be used to predict these parameters. However, further studies on different crops under varied environmental conditions are necessary.     

Tilth index: an approach to optimize tillage in rice–wheat system

This study was conducted to determine a tilth index from tillage induced soil physical properties and grain yield to optimize tillage in rice–wheat system. The experiment was conducted in a silty clay loam (Aquic hapludoll) associated with a shallow water table fluctuating between 0.02 and 0.96 m from the surface. Tillage treatments for rice were puddling by four passes of rotary puddler (PR), reduced puddling (ReP), conventional puddling (CP) and direct seeding without puddling (DSWP) in four replications. Tillage treatments for wheat were zero tillage (ZT) and conventional tillage (CT) superimposed over the plots of rice tillage treatments. Measurements were made of puddling index and specific volume (only in the rice season), bulk density, saturated hydraulic conductivity, infiltration rate, plasticity index, porosity and organic carbon in the rice and wheat seasons. Rice yield in the PR plots was highest and statistically equal to that in the ReP plots but wheat yield was highest in the DSWP plots under ZT condition and was statistically equal to that in the ReP plots.Tilth index (TI) was determined in two ways: one by the model suggested by Singh et al. [Trans. ASAE 35 (6) (1992) 1777] and the second by a proposed regression model. The proposed regression model utilizes soil physical properties having significant influence on crop yield. As per the Singh et al. model, wheat yield increased linearly with increasing TI from 0.75 to 0.89 but rice yield decreased with increasing TI from 0.67 to 0.81. Both TI and its relation with rice yield were contrary to their observations. The proposed regression model showed a value of TI in the range of 0.74–0.87 for rice soils and 0.86–1.0 for wheat soils as indicators of TI for optimum yields of rice and wheat. A high TI corresponds to low tillage both for rice and wheat. The optimum yield with minimum tillage operations coincided with TI obtained in ReP plots of rice and in ZT plots of wheat under ReP conditions. Results thus show that the quality of soil puddle obtained by half the efforts in PR and CP was sufficient for optimum yields of rice. Similarly, wheat sowing by zero-till drill in such a reduced puddling plots of rice was sufficient for optimum yields of wheat in Tarai soils associated with shallow water tables. The proposed regression model is simple and compatible to use in the existing crop growth models, such as in DSSAT 3.5, with suitable alterations.     

尼日利亚两个农业生态区施用氮肥和杂草干扰对热带玉米基因型的影响

Low soil nitrogen (N) and weed infestations are some of the major constraints to maize production in Nigeria.A split-split plot experiment in a randomized complete block design with three replicates was established at two sites with different agroecological zones,Ikenne (Typic Paleudalf) and Shika (Typic Tropaquept),in Nigeria in 2002 and 2003 rainy seasons to investigate the responses of four maize genotypes (Oba super II,Low N pool C2,TZB-SR,and ACR 8328 BN C7) to N fertilizer applied at four rates,0,30,60,and 90 kg N ha^-1,and three weed pressure treatments,no weed pressure (weekly weeding),low weed pressure (inter-row weekly weeding),and high weed pressure (no weeding throughout the growing season).Growth and yield parameters of maize and weeds were taken at flwering and harvest.The results indicated that there was a significant reduction in maize leaf area,leaf area index,and photosynthetically active radiation due to weed interference at both sites.The application of nitrogen at 90 kg N ha^-1 significantly increased maize leaf area.Reductions in maize growth and yield at flowering and harvest were significant due to weed interference at both Ikenne and Shika,thus showing that the reductions in maize growth and yield due to weed interference were not ecological zone specific even though weed species and their seed banks may differ.Ameliorative management options could thus be the same in the two agroecological zones.Application of 90 kg N ha^-1 led to a significant increase in maize grain yield at Shika while there was no fertilizer effect at Ikenne on grain yield.There was no significant difference between 60 and 90 kg N ha^-1,suggesting that 60 kg N ha^-1 could be a possible replacement for the higher fertilizer rate at least for the identified maize genotypes.Low weed pressure treatment led to 26% and 35% reductions in maize grain yield at Ikenne and Shika,respectively,while 22% and 51 % reductions,respectively,were observed due to high weed pressure.Generally,maize grain yield was higher at Ikenne than Shika.The maize genotypes Low N pool C2 and ACR 8328 BN C7 performed better than the other genotypes at Ikenne while the maize genotype Oba super II had the best performance at harvest at Shika.Application of nitrogen increased weed biomass at flowering at Ikenne.The maize grain yield was highest in the N-efficient genotypes,Oba super II and Low N pool C2;the susceptible genotype TZB-SR had the least yield at Shika.There existed a negative and significant correlation between maize grain yield and weed biomass at both sites.     

Effects of tillage methods and water regimes on soil properties and yield of lowland rice from a sandy loam soil in Southwest Nigeria

Field experiments were conducted on a sandy loam soil (Aeric Tropaquent) during 1981 adn 1982 to assess the effects of compaction, puddling and no-till systems on soil physical properties and on rice growth and yield with and without supplementary irrigation. Soil compaction decreased macro- and micro-pores more than puddling or no-till treatments. The equilibrium infiltration rates were 0.12, 0.15 and 1.65 μm s⁻¹ in compacted, ploughed and no-till treatments, respectively. The saturated hydraulic conductivity, void ratio and moisture content at −0.01 and −1.5 MPa water potential followed a similar trend. The mean weight diameters were 2.40, 2.36 and 2.09 mm for compacted, puddled and no-till treatments, respectively. The mean grain yields for 4 consecutive crops were 6.4, 5.1 and 4.9 Mg ha⁻¹, the compacted being significantly greater than the puddled and no-till treatments. Compared with both puddling and no-till treatments, soil compaction resulted in significant yield increases of about 20% under the rain-fed regime and from 34 to 40% in the flooded moisture regime. There was about 26% increase in rice grain yield by continuous flooding over the rain-fed treatments, with the rice producing greater dry matter and biological yields due to a higher uptake of P, Ca, Mg, K, Na, Mn, Fe and Zn.     

SOIL POTASSIUM FRACTIONS IN RICE-WHEAT CROPPING SYSTEM AFTER TWELVE YEARS OF LANTANA RESIDUE INCORPORATION IN A NORTHWEST HIMALAYAN ACID ALFISOL

A long-term field experiment with rice-wheat cropping was started in the wet season of 1988 with four levels of lantana (Lantana camara L.) (0, 10, 20, and 30 Mg ha^?1 on fresh weight basis) and three tillage practices (No puddling, puddling, and soil compaction). From wet season of 1997, however, three tillage practices were replaced with three levels of nitrogen (N) and potassium (K) to rice (33, 66, and 100% of recommended) and 66% of recommended N, phosphorus (P), and K to wheat. Phosphorus was totally omitted for the rice crop. The recommended N and K for rice was 90 and 40 kg ha^?1, whereas the recommendations for N, P, and K for wheat were 120, 90 and 30 kg ha^?1. Organic amendments are known to improve soil productivity under rice-wheat cropping by improving physical conditions and nutrient status of the soil, but their availability is restricted. There is a need to identify locally available and cost-effective organic materials that have minimal alternate uses as fodder and fuel. We evaluated Lantana camara L. residues, a fast-growing weed in nearby wastelands, as a potential soil organic amendment. Among the different fractions of K, nonexchangeable K was dominant followed by exchangeable and water soluble K. The incorporation of lantana (10 to 30 Mg ha^?1) over the last 12 years has resulted in a significant build-up of all the K fractions, the maximum being in water-soluble K (10 to 32%) followed by exchangeable K (18 to 27%) and least in nonexchangeable K (5 to 7%) over no lantana incorporation. The increasing levels of these two inputs significantly and consistently increased ammonium acetate (NH₄OAc)- extracted K (available K) content in soil and also resulted in significantly higher accumulation of K by the crops during the years of experimentation. Among different K fractions, exchangeable K was observed to be the most important K fraction contributing towards wheat and rice yields as well as K accumulation by wheat and rice. Stepwise multiple regression equations indicated that exchangeable K was the most important variable contributing towards total variation in grain yield and K accumulation by wheat or rice.