Relative yield and zinc uptake by rice from zinc sulphate and zinc oxide coatings onto urea

Zinc (Zn) deficiency is prevalent worldwide and is a barrier to achieving yield goals in crops. It is also now recognized as a leading risk factor for disease in humans in developing countries. In general, soil application of 5–17 kg of Zn ha⁻¹ year⁻¹ as zinc sulphate (ZnSO₄) or more is recommended. However, in developing rice growing countries of Asia, ZnSO₄ of desired quality is not readily available and is also quite expensive, so the farmers generally fail to apply Zn, resulting in rice crop yield loss. Availability of Zn-coated urea guarantees not only the availability of quality Zn but also ensures its application. Field experiments were therefore conducted during the rice seasons of 2005 and 2006 at the Indian Agricultural Research Institute, New Delhi, to evaluate the relative efficiency of 0.5, 1.0, 1.5 and 2.0% Zn as ZnSO₄- or zinc oxide (ZnO)-coated ureas for rice. Soil application of ZnSO₄ was also compared in 2006. Rice grain and straw yields, Zn concentrations in grain and straw, and Zn uptake by rice increased with the level of Zn coating onto urea. Crop response was the highest with 2.0% ZnSO₄-coated urea, and higher than with the same rate of ZnO-coated urea, possibly related to the higher water solubility of Zn in ZnSO₄. Crop response with ZnSO₄-coated urea was also higher than with the same rate of ZnSO₄ and urea applied separately to the soil. However, apparent recovery data suggest that 1.0% coating with ZnSO₄ may be a better choice from the point of view of the utilization of applied Zn. Increased Zn concentrations in rice grain due to application of Zn-coated urea is important from the point of view of Zn nutrition of humans, since rice is the staple food in developing countries of Asia. Also, increased Zn concentrations in rice straw is of importance as regards cattle nutrition since in developing countries of Asia rice straw is the major feed for farm cattle.     

Comparative study of a Zn-enriched post-methanation bio-sludge and Zn sulfate as Zn sources for a rice–wheat crop rotation

A field experiment was carried out during 2005–2007 to compare the efficacy of Zn-enriched post-methanation bio-sludge (ZEMB, 4.4% Zn) and ZnSO₄ (ZSH, 22% Zn) as Zn source to rice (Oryza sativa L.)—wheat (Triticum aestivum L.) rotation. A new Zn source (ZEMB) contained most of the Zn (98.4% of total Zn) in citrate-soluble form as compared to ZSH which had all Zn in water-soluble form. Chemical speciation of Zn in the aqueous solution of both fertilizers revealed that 85.8% of water-soluble Zn present in ZEMB existed as complexes of dissolved organic matter. In the field experiment, application of ZEMB at 5 kg Zn ha⁻¹ to I-year rice increased the grain yields of rice and wheat in both years significantly over the control while application of ZSH at 5 kg Zn ha⁻¹ to I-year rice increased only grain yields of I- and II-year rice (first year and second year, respectively). The magnitude of increase in grain yields was also higher with ZEMB than with ZSH. Application of ZEMB at 5 kg Zn ha⁻¹ to I-year rice maintained significantly higher concentrations of Zn in the flag leaves of rice and wheat in both years, in the grains of I- and II-year rice, and also in the straw of I-year rice than ZSH applied at an equivalent dose. Total Zn uptake values for I-year rice and wheat and II-year rice, apparent recovery of applied Zn and also DTPA-extractable Zn in soil were significantly higher with ZEMB at 5 kg Zn ha⁻¹ than with ZSH at an equivalent dose.     

Grain legume rotation benefits to maize in the northern Guinea savanna of Nigeria: fixed-nitrogen versus other rotation effects

The yield increases often recorded in maize following grain legumes have been attributed to fixed-N and ‘other rotation’ effects, but these effects have rarely been separated. Field trials were conducted between 2003 and 2005 to measure these effects on maize following grain legumes in the northern Guinea savanna of Nigeria. Maize was grown on plots previously cultivated to two genotypes each of soybean (TGx 1448-2E and SAMSOY-2) and cowpea (IT 96D-724 and SAMPEA-7), maize, and natural fallow. The plots were split into four N fertilizer rates (0, 30, 60 and 90 kg N ha⁻¹) in a split plot design. The total effect was calculated as the yield of maize following a legume minus the yield following maize, both without added N and the rotation effect was calculated as the difference between rotations at the highest N fertilizer rate. The legume genotypes fixed between 14 and 51 kg N ha⁻¹ of their total N and had an estimated net N balance ranging from −29.8 to 9.5 kg N ha⁻¹. Positive N balance was obtained only when the nitrogen harvest index was greater than the proportion of N derived from atmosphere. The results also indicated that the magnitude of the fixed-N and other rotation effects varied widely and were influenced by the contributions of the grain legumes to the soil N-balance. In general, fixed-N effects ranged from 124 to 279 kg ha⁻¹ while rotation effects ranged between 193 and 513 kg ha⁻¹. On average, maize following legumes had higher grain yield of 1.2 and 1.3-fold compared with maize after fallow or maize after maize, respectively.     

Nitrogen and residue management effects on agronomic productivity and nitrogen use efficiency in rice–wheat system in Indian Punjab

Development of a sustainable and environment friendly crop production system depends on identifying effective strategies for the management of tillage and postharvest crop residues. Three-year (2004–2007) field study was initiated on two soil types to evaluate the effect of straw management (burning, incorporation and surface mulch) and tillage (conventional tillage and zero tillage) before sowing wheat and four nitrogen rates (0, 90, 120 and 150 kg N ha⁻¹) on crop yields, N use efficiency, and soil fertility in the northwestern India. Effect of tillage and straw management on nitrogen transformation in soils was investigated in a laboratory incubation study. In sandy loam, grain yield of wheat with straw mulch-zero-till (ZT) was 7% higher compared to when residues were burnt-ZT but it was similar to straw burnt-conventional till (CT), averaged across 3 years. In silt loam, grain yield of wheat with straw mulch-ZT was 4.4% higher compared to straw incorporated-CT, but it was similar to straw burnt-CT. Response to N application was generally observed up to 150 kg N ha⁻¹ except in 2004–2005 on sandy loam where N response was observed up to 120 kg N ha⁻¹, irrespective of straw and tillage treatments. In sandy loam, RE was lower (49%) for straw burnt-ZT than in other treatments (54–56%). In silt loam, RE was higher in straw mulch-ZT compared with straw incorporation-CT (65 vs. 58%). In sandy loam, AE was higher in straw burnt-CT and straw mulch-ZT compared with the other treatments (19.2 vs. 16.9 kg grain kg⁻¹ N applied). In silt loam, AE was lower in straw incorporation-CT than in other treatments (16.0 vs. 17.6 kg grain kg⁻¹ N applied). Rice yield and N uptake were not influenced by straw and tillage management treatments applied to the preceding wheat. Recycling of rice residue (incorporation and surface mulch) compared with straw burning increased soil organic carbon and the availability of soil P and K. There was more carbon sequestration in rice straw mulch with zero tillage (25%) than in straw incorporation with conventional tillage (17%). Soil N mineralization at 45 days after incubation was 15–25% higher in straw retention plots compared with on straw burnt plots.     

Yield and yield components of cowpea (<Emphasis Type="Italic">Vigna unguiculata</Emphasis> (L.) Walp.) as influenced by Sokoto phosphate rock and placement methods in the semi-arid zone of Nigeria

Phosphate rock with proper management could be a sustainable source of phosphorus for increased cowpea production on the Entisols of Sokoto Semi-arid zone. Therefore, field experiments were conducted in 2004 and 2005 rainy seasons to determine the influence of Sokoto phosphate rock (SPR) and placement methods on the yield of cowpea varieties. Treatments consisted of factorial combination of two varieties (Ba’adare and IAR48), three levels of SPR (25, 50 and 75 kg SPR ha⁻¹) along with a control (0 kg SPR ha⁻¹) and three placement methods (plough sole, broadcast and side-band) laid out in a randomized complete block design replicated 3 times. Results of phosphate rock and placement methods are presented in this paper. The study indicated significant (P < 0.01) response to applied SPR compared to control (1074 kg grain ha⁻¹) in most parameters studied. Application of 25 kg SPR ha⁻¹ significantly (P < 0.05) influenced higher pod yield and number of pods plant⁻¹ only in 2004 trial. But, shelling percentage, grain yield, stover yield, 1000-grain weight, harvest index (HI) and number of seeds pods⁻¹ were not influenced by SPR levels. Significantly (P < 0.05) higher pod yield in 2004, grain yield, 1000-grain weight and number of pods per plant in 2004 and 2005, HI, shelling percentage and number of seeds pod⁻¹ in 2005, were observed in plough-sole than broadcast and band-side methods of fertilizer placement. Therefore, from this study, it was concluded that SPR could be directly used as a source of P to sustain cowpea production (1527 kg grain ha⁻¹ with 25 kg SPR compared to 1074 kg ha⁻¹with 0 kg SPR). Application of 25 kg SPR ha⁻¹ (3.74 kg P ha⁻¹) using plough-sole method of fertilizer placement was most efficient under Sokoto semi-arid condition.     

Effect of organic and inorganic phosphate fertilizers and their combination on maize yield and phosphorus availability in a Yellow Earth in Myanmar

Phosphorus (P) deficiency is a major constraint for crop production in many parts of the world including Myanmar and field research into management of P fertilizers and P responsiveness of crops on infertile soils has been limited. The purpose of this study is to determine maize yield response to different forms of P fertilizers on an acidic (pH 4.9) P deficient (Olsen-P 8 mg kg⁻¹) Yellow Earth (Acrisol) in Southern Shan State, Myanmar and to establish relationships between soil Olsen-P test values (0.5 M sodium bicarbonate extracted P) and maize yield. Field experiments were conducted during two cropping seasons. There were 15 treatments in total: P was applied at seven rates of a soluble P fertilizer as Triple superphosphate (TSP) (0–120 kg P ha⁻¹) to establish a P response curve; one rate of a partially soluble P fertilizer (Chinese partially acidulated phosphate rock, CPAPR) and two organic P fertilizers (farmyard manure (FYM) and Tithonia diversifolia) at 20 kg P ha⁻¹; combination of TSP and CPAPR at 20 kg P ha⁻¹ with FYM and Tithonia at 20 kg P ha⁻¹; an additional treatment (TSP 20 kg P ha⁻¹ plus 2.5 t ha⁻¹ dolomite) for assessing the liming effect of a local dolomite. In Year 1, applications of TSP at 40–60 kg P ha⁻¹ produced near maximum grain yields, whereas in Year 2 this could be achieved with a reapplication of 20–30 kg P ha⁻¹ on top of the residual value of the Year 1 application. In both years, CPAPR, TSP and Tithonia at 20 kg P ha⁻¹ significantly increased maize grain yield, but FYM failed to increase grain yield. In Year 1, CPAPR and TSP effects on grain yield were higher than that of Tithonia but in Year 2 the effects were same for all these three treatments. In both years the combination of FYM (20 kg P ha⁻¹) with TSP (20 kg P ha⁻¹) produced significantly higher grain yield than TSP at 20 kg P ha⁻¹ whereas 40 kg P ha⁻¹ of TSP application did not significantly increase grain yield over the TSP application at 20 kg P ha⁻¹. Similar results were obtained when half the P applied as CPAPR was substituted with P from Tithonia and FMP during the first year. The combined data from the two years experiment suggests that 90% of maximum maize grain yields can be obtained by raising the Olsen-P to 30–35 mg P ha⁻¹ soil at the silking stage of growth. Olsen-P for the treatments at silking in Year 1 was: Control < FYM, Tithonia < TSP, CPAPR and in Year 2 was: Control < FYM < Tithonia < TSP, CPAPR. The results showed that for a long-term approach, repeated annual applications of Tithonia can be considered as a potential P source for improving soil P status in P deficient Yellow Earths.     

Effects of mulch,N fertilizer,and plant density on wheat yield,wheat nitrogen uptake,and residual soil nitrate in a dryland area of China

Understanding mulching influences on nitrogen (N) activities in soil is important for developing N management strategies in dryland. A 3 year field experiment was conducted in the Loess Plateau of China to investigate the effects of mulching, N fertilizer application rate and plant density on winter wheat yield, N uptake by wheat and residual soil nitrate in a winter wheat-fallow system. The split plot design included four mulching methods (CK, no mulch; SM, straw mulch; FM, plastic film mulch; CM, combined mulch with plastic film and straw) as main plot treatments. Three N fertilizer rates (N0, 0 kg N ha⁻¹; N120, 120 kg N ha⁻¹; N240, 240 kg N ha⁻¹) were sub-plot treatments and two wheat sowing densities (LD, low density, seeding rate = 180 kg ha⁻¹; HD, high density, seeding rate = 225 kg ha⁻¹) were sub-subplot treatments. The results showed that wheat yield, N uptake, and N use efficiency (NUE) were higher for FM and CM compared to CK. However, soil nitrate-N contents in the 0–200 cm soil profile were also higher for FM and CM compared to CK after the 3 year experiment. Wheat grain yields were higher for SM compared to CK only when high levels of nitrogen or high planting density were applied. Mulching did not have a significant effect on wheat yield, nitrogen uptake and NUE when soil water content at planting was much high. Wheat yield, N uptake, and residual nitrate in 0–200 cm were significantly higher for N240 compared to N120 and N0. Wheat yield and N uptake were also significantly higher for HD compared to LD. When 0 or 120 kg N ha⁻¹ was applied, HD had more residual nitrate than LD while the reverse was true when 240 kg N ha⁻¹ was applied. After 3 years, residual nitrate-N in 0–200 cm soil averaged 170 kg ha⁻¹, which was equivalent to ~40% of the total N uptake by wheat in the three growing seasons.     

Long-term tillage,straw management and N fertilization effects on quantity and quality of organic C and N in a Black Chernozem soil

Soil, crop and fertilizer management practices may affect the amount and quality of organic C and N in soil. A long-term field experiment (growing barley, wheat, or canola) was conducted on a Black Chernozem (Albic Argicryoll) loam at Ellerslie, Alberta, Canada, to determine the influence of 19 (1980 to 1998) or 27 years (1980 to 2006) of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [S_Rem]and straw retained [S_Ret]) and N fertilizer rate (0, 50 and 100 kg N ha⁻¹ in S_Ret and 0 kg N ha⁻¹ in S_Rem plots) on total organic C (TOC) and N (TON), and light fraction organic C (LFOC) and N (LFON) in the 0–7.5 and 7.5–15 cm or 0–5, 5–10 and 10–15 cm soil layers. The mass of TOC and TON in soil was usually higher in S_Ret than in S_Rem treatment (by 3.44 Mg C ha⁻¹ for TOC and 0.248 Mg N ha⁻¹ for TON after 27 years), but there was little effect of tillage and N fertilization on these parameters. The mass of LFOC and LFON in soil tended to increase with S_Ret (by 285 kg C ha⁻¹ for LFOC and 12.6 kg N ha⁻¹ for LFON with annual rate of 100 kg N ha⁻¹ for 27 years)_, increased with N fertilizer application (by 517 kg C ha⁻¹ for LFOC and 36.0 kg N ha⁻¹ for LFON after 27 years), but was usually higher under CT than ZT (by 451 kg C ha⁻¹ for LFOC and 25.3 kg N ha⁻¹ for LFON after 27 years). Correlations between soil organic C or N fractions were highly significant in most cases. Linear regressions between crop residue C input and soil organic C or N were significant in most cases. The effects of tillage, straw management and N fertilizer on soil were more pronounced for LFOC and LFON than TOC and TON, and also in the surface layers than in the deeper layers. Tillage and straw management had little or no effect on C:N ratios, but the C:N ratios in light organic fractions significantly decreased with increasing N rate (from 20.06 at zero-N to 18.91 at 100 kg N ha⁻¹). Compared to the 1979 results, in treatments that did not receive N fertilizer (CTS_Rem0, CTS_Ret0, ZTS_Rem0 and ZTS_Ret0), CTS_Rem0 resulted in a net decrease in TOC concentration (by 1.9 g C kg⁻¹) in the 0–15 cm soil layer in 2007 (after 27 years), with little or no change in the CTS_Ret0 and ZTS_Rem0 treatments, while there was a net increase in TOC concentration (by 1.2 g C kg⁻¹) in the ZTS_Ret0 treatment. Straw retention and N fertilizer application at 50 and 100 kg N ha⁻¹ rates showed a net positive effect on TOC concentration under both ZT (ZTS_Ret50 by 2.3 g C kg⁻¹ and ZTS_Ret100 by 3.1 g C kg⁻¹) and CT (CTS_Ret50 by 3.5 g C kg⁻¹ and CTS_Ret100 by 1.6 g C kg⁻¹) treatments in 2007 compared to 1979 data. In conclusion, the findings suggest that retention of straw, application of N fertilizer and elimination of tillage would improve soil quality, and this might increase the potential for N supplying power of the soil and sustainability of crop productivity.     

Long-term effect of continuous cropping of irrigated rice on soil and yield trends in the Sahel of West Africa

The effects of 18 years continuous cropping of irrigated rice on soil and yields were studied in two long-term fertility experiments (LTFE) at Ndiaye and Fanaye in the Senegal River Valley (West Africa). Rice was planted twice in a year during the hot dry season (HDS) and wet season (WS) with different fertilizer treatments. Soil organic carbon (SOC) under fallow varied from 7.1 g kg⁻¹ at Fanaye to 11.0 g kg⁻¹ at Ndiaye. Rice cropping maintained and increased SOC at Ndiaye and Fanaye, respectively and fertilizer treatments did not affect SOC. Soil available P and exchangeable K were maintained or increased with long-term application of NPK fertilizers. Without any fertilizer, yields decreased by 60 kg ha⁻¹ (1.5%) and 115 kg ha⁻¹ (3%) per year at Fanaye and Ndiaye, respectively. The highest annual yield decreases of 268 kg ha⁻¹ (3.6%) and 277 kg ha⁻¹ (4.1%) were observed at Fanaye and Ndiaye, respectively when only N fertilizer was applied. Rice yields were only maintained with NPK fertilizers supplying at least 60 kg N, 26 kg P and 50 kg K ha⁻¹. It was concluded that the double cropping of irrigated rice does not decrease SOC and the application of the recommended doses of NPK fertilizer maintained rice yields for 18 years.     

Interactive effects of selected nutrient resources and tied-ridging on plant growth performance in a semi-arid smallholder farming environment in central Zimbabwe

Crop production in sub-Saharan Africa is constrained by numerous factors including frequent droughts and periods of moisture stress, low soil fertility, and restricted access to mineral fertilisers. A 2 year (2005/6 and 2006/7) field study was conducted in Shurugwi district, central Zimbabwe, to determine the effects of different nutrient resources and two tillage practices on the grain yield of maize (Zea mays L.) and soybean (Glycine max (L.) Merr). Six nutrient resource treatments (control, pit-stored manure, leaf litter, anthill soil, mineral fertiliser, mineral fertiliser plus pit-stored manure) were combined with two tillage practices (conventional tillage and post-emergence tied ridging). Basal fertilisation was done with 0 kg ha⁻¹ as control, 240 kg ha⁻¹ PKS fertiliser, 18 t ha⁻¹ manure, 10 t ha⁻¹ manure plus 240 kg ha⁻¹ PKS fertiliser, 35 t ha⁻¹ leaf litter, 52 t ha⁻¹ anthill soil. About 60 kg N/ha was applied to fertiliser only and fertiliser plus manure treatments as top dressing in the form of ammonium nitrate (34.5%N). A split-plot design was used with nutrient resource as the main plot and tillage practice as the subplot, and five farmers’ fields were used as replicates. Grain yield was determined at physiological maturity (140 and 126 days after planting for maize and soybean, respectively) and adjusted to 12.5% moisture content for maize and 11% for soybean. In the first season (2005/06), addition of different nutrient resources under conventional tillage increased (P < 0.05) maize grain yield by 102–450%, with leaf litter and manure plus fertiliser treatments, giving the lowest (551 kg ha⁻¹⁾ and highest (3,032 kg ha⁻¹) increments, respectively, compared to the control. For each treatment, tied-ridging further increased maize grain yield. For example, for leaf litter, tied-ridging further increased grain yield by 96% indicating the importance of integrating nutrient and water management practices in semi-arid areas where moisture stress is frequent. Despite the low rainfall and extended dry spells in the second season, addition of the different nutrient resources still increased yield which was further increased by tied-ridging in most treatments. Besides providing grain, soybean had higher residual effects on the following maize crop compared to Crotalaria gramiana, a green manure. It was concluded that the highest benefits of tied-ridging, in terms of grain yield, were realised when cattle manure was combined with mineral fertiliser, both of which are available to resource-endowed households. Besides marginally increasing yield, leaf litter and anthill which represent resources that can be accessed by very poor households, have a positive effect of the soil chemical environment.     

Relative efficiency of zinc oxide and zinc sulphate-enriched urea for spring wheat

Field experiments conducted at the Indian Agricultural Research Institute, New Delhi during 2005–2007 showed that the application of small amounts of zinc (Zn) in the form 0.5–2.0% of Zn-enriched urea significantly increased yield attributes, grain and straw yield, Zn concentrations in the grain and straw and Zn uptake by spring wheat. The agronomic and crop recovery efficiency of applied Zn decreased as the level of Zn-enrichment was increased from 0.5 to 2%. Zinc sulphate (ZnSO₄) and zinc oxide (ZnO) were equally effective in increasing the grain yield of wheat. Based on these results, we recommend the application of a 0.5–1.0% Zn enrichment of urea with ZnSO₄ or a 1.0% Zn-enrichment with ZnO.     

Influence of organic amendments on growth, yield and quality of wheat and on soil properties during transition to organic production

A transition period of at least 2 years is required for annual crops before the produce may be certified as organically grown. The purpose of this study was to evaluate the effects of three organic amendments on the yield and quality of wheat (Triticum aestivum L.) and on soil properties during transition to organic production. The organic amendments were composted farmyard manure (FYMC), vermicompost and lantana (Lantana spp. L.) compost applied to soil at four application rates (60 kg N ha⁻¹, 90 kg N ha⁻¹, 120 kg N ha⁻¹ and 150 kg N ha⁻¹). The grain yield of wheat in all the treatments involving organic amendments was markedly lower (36–65% and 23–54% less in the first and second year of transition, respectively) than with the mineral fertilizer treatment. For the organic treatments applied at equivalent N rates, grain yield was higher for FYMC treatment, closely followed by vermicompost. In the first year of transition, protein content of wheat grain was higher (85.9 g kg⁻¹) for mineral fertilizer treatment, whereas, in the second year, there were no significant differences among the mineral fertilizer treatment and the highest application rate (150 kg N ha⁻¹) of three organic amendments. The grain P and K contents were, however, significantly higher for the treatments involving organic amendments than their mineral fertilizer counterpart in both years. Application of organic amendments, irrespective of source and rate, greatly lowered bulk density (1.14–1.25 Mg m⁻³) and enhanced pH (6.0–6.5) and oxidizable organic carbon (13–18.8 g kg⁻¹) of soil compared with mineral fertilizer treatment after a 2-year transition period. Mineral fertilized plots, however, had higher levels of available N and P than plots with organic amendments. All the treatments involving organic amendments, particularly at higher application rates, enhanced soil microbial activities of dehydrogenase, β-glucosidase, urease and phosphatase compared with the mineral fertilizer and unamended check treatments. We conclude that the application rate of 120 kg N ha⁻¹ and 150 kg N ha⁻¹ of all the three sources of organic amendments improved soil properties. There was, however, a 23–65% reduction in wheat yield during the 2 years of transition to organic production.     

Nitrogen-15 balance as affected by rice straw management in a rice-wheat rotation in northwest India

The sustainability of the productive rice-wheat systems of Northwest India is being questioned due to the complete removal of straw for animal consumption and fuel, or the burning of straw which has reduced the soil organic matter contents. However, straw incorporation at planting can temporarily reduce the availability of fertilizer-N and reduce crop yields. In a field study on a loamy sand soil, the effect of 6 mg ha⁻¹ rice straw incorporated into the soil 20 or 40 days before sowing (DBS) the wheat was compared with removal or burning of rice straw on the fate and balance of 120 kg ha⁻¹ of 5 atom% ¹⁵N-urea applied to wheat and to a following crop of rice. Wheat grain yield and agronomic efficiency (AE) of applied N (kg grain/kg N applied) were not influenced by rice straw management. However, N uptake (NU), and recovery efficiency (RE) of N by the difference method were lower with rice straw incorporation than with burning. Nitrogen-15 recovery by wheat was highest (41%) when the rice straw was removed or burned and lowest (30.4%) when 30 of the 120 kg N ha⁻¹ was applied at the time of straw incorporation at 20 DBS of wheat. However, this strategy of adding 25% of the urea-N dose at the time of straw incorporation resulted in the highest ¹⁵N losses (45.2%). Inorganic N remaining at harvest in the 0 to 60 cm soil profile, mostly NO₃ ⁻, was 5.5% after wheat and 4.2% after rice. Rice grain yields, NU, and RE were not influenced by rice straw management. Nitrogen-15 losses were similar in rice and wheat (31% with straw removed) despite total irrigation and rainfall inputs of 340 and 32 cm to rice and wheat, respectively. These results suggest to the farmers of northwest India that straw incorporation does not necessarily hurt grain yields, and indicates to researchers that work is still needed to improve N use efficiency in rice and wheat. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of fertilization on nutrient budget and nitrogen use efficiency of farmland soil under different precipitations in Northeastern China

Based on a consecutive 16-year field trial and meteorological data, the effects of fertilization on the nutrient budget and nitrogen use efficiency in farmland soil under different precipitation years were studied. With no fertilization treatment, the grain yield of maize was 3,520 kg ha⁻¹ (mean yield over 13 years). But the maximum yield increased to 7,470 kg ha⁻¹ when treated with mineral N, P and K fertilizers and recycled manure. The nutrient uptake also increased by twofold to threefold in NPKM treated field compared with that in the control treatment. The highest yields were obtained in years with normal precipitation, despite the different fertilization schemes. The lowest yields were obtained in drought or waterlogging years, which were 44.7–58.5% of the yields in years with normal precipitation. It also appeared that the deficits of N, P and K were greater in the years with proper precipitation than those in arid or flood years, because more production was removed from the field. Soil total N decreased significantly when treated with mineral fertilizer or recycled manure alone. The maximum deficit of soil total N was observed in control treatment (557 kg ha⁻¹) from 1990 to 2005. The N treatment resulted in a significant negative balance of P, due to the high yield of the crop in response to applied N. The application of NP or N to soils resulted in a greater negative K balance than that of the control. The greatest negative balance of total P and available P were obtained under the control and N treatment, and the highest deficit of soil total K and exchangeable K were obtained under NP treatment. We found that the rate of 150 kg N ha⁻¹ year⁻¹ was inadequate for maintaining soil N balance, and amendment of soil with organic source could not stop the loss of soil P and K. The applying rates of 150 kg N ha⁻¹ year⁻¹, 25 kg P ha⁻¹ year⁻¹, and 60 kg K ha⁻¹ year⁻¹ combined with 2–3 t ha⁻¹ organic manure were recommended to maintain soil fertility level. The nitrogen use efficiency (NUE) was greatly improved in the years with proper precipitation and balanced fertilization. Higher NUE and grain yields were achieved under NPK and NPKM treatments in years with normal precipitation. The results clearly demonstrated that both organic and mineral fertilizers were needed to increase crop production, improve NUE and maintain soil fertility level.     

Rice yield,potassium uptake and apparent balance under long-term fertilization in rice-based cropping systems in southern China

Potassium (K) imbalances are of growing concern in southern China, where rice (Oryza sativa L.) is the primary food resource for a growing population. This study examined rice yield, K uptake and apparent balance under long-term fertilization in rice-based systems at four experimental sites, including both rice-rice as well as rice–wheat rotations. The experiments consist of four treatments: control (no fertilizer), nitrogen and phosphorus (NP), nitrogen, phosphorus and potassium (NPK), and NPK plus manure (NPKM). Across all sites, rice yields increased by 3–20% due to K fertilization (NPK vs. NP) and 4–20% due to manure application (NPKM vs. NPK). The mean internal K use efficiency (IE) was lower (32–56 kg kg⁻¹) in treatments receiving K (NPK and NPKM) than in those without K application (36–91 kg kg⁻¹—control and NP). Estimated from the logarithmic model, a total K uptake of 38–212 kg ha⁻¹ was needed to produce 3–7 Mg ha⁻¹ of rice grain. The annual apparent K balances were negative (17–245 kg ha⁻¹ year⁻¹), irrespective of mineral K application and site. But the negative K balance reduced by 27–88 kg ha⁻¹ year⁻¹ through application of mineral K in combination with manure. The higher negative apparent K balances under rice–wheat cropping system were related to the lower K application rate and the soils rich in K-bearing minerals, while the lower negative apparent K balances under rice–rice cropping system were related to the higher K application rate and the soils low in K-bearing minerals. We conclude that a re-adjustment of the current K application rate is needed to improve the long-term rice production in southern China.     

Effect of zinc-enriched urea on productivity,zinc uptake and efficiency of an aromatic rice–wheat cropping system

Zinc deficiency is prevalent worldwide and is a barrier in achieving yield targets in crops. It is also now recognized as a leading risk factor for disease in humans in developing countries. Generally, soil application of 5–17 kg Zn ha⁻¹ y⁻¹ (25–85 kg zinc sulphate heptahydrate ha⁻¹ y⁻¹) or more is recommended for rice. However, in the developing rice-growing countries of Asia, zinc sulphate of desired quality is not readily available and is also quite expensive, and the farmers generally fail to apply Zn, resulting in crop yield loss in rice. Availability of zinc-enriched urea (ZEU) makes possible not only the availability of quality zinc, but also assures its application. Therefore, field experiments were conducted for two consecutive years at the research farm of Indian Agricultural Research Institute, New Delhi, India, during rainy (rice) and winter (wheat) seasons of 2004–2006 on a sandy clay-loam soil to study the effect of various concentrations of zinc enrichment of urea on productivity, zinc concentrations, its uptake and use indices of aromatic rice–wheat cropping system. Eight treatments comprising prilled urea (PU) and 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5% zinc-enriched urea, replicated three times, were compared in a randomized block design. The enrichment of PU was done through zinc oxide containing 80% zinc. The results of this study revealed that the zinc-enriched urea (ZEU) had a significant effect on growth, yield attributes and yields of aromatic rice. Highest values for all these attributes and yields were recorded at the highest enrichment (3.5%) of the PU with zinc. The highest zinc concentration and uptake in rice grain and straw were also significantly higher with the highest level (3.5%) of zinc enrichment. The highest total zinc uptake recorded was 1,168 and 1,353 g ha⁻¹, during 2004 and 2005, respectively, with 3.5% ZEU. However, a major increase in grain yield of rice was recorded up to 1.0% zinc enrichment. The residual effect of zinc-enriched urea on succeeding wheat yield and zinc uptake was significant only at a higher level of zinc-enriched urea and only in the second year of study. Overall, 1.0% zinc-enriched urea recorded significantly higher productivity and zinc uptake over PU in the rice–wheat cropping system and is recommended for Delhi and adjoining areas. The recommendation is also made keeping in view the fact that with increased levels of zinc enrichment of urea, the partial factor productivity, agronomic efficiency, apparent recovery and physiological efficiency of applied zinc in a rice–wheat system decreased significantly. Considering all the economic parameters (benefit, benefit:cost ratio, IR gained IR⁻¹ invested in zinc), 1.0% ZEU proved the most economic source for aromatic rice–wheat cropping system and therefore is recommended for rice–wheat cropping system in Delhi and adjoining areas of north India.     

Soil nitrate-N levels required for high yield maize production in the North China Plain

High profile nitrate-nitrogen (N) accumulation has caused a series of problems, including low N use efficiency and environmental contamination in intensive agricultural systems. The key objective of this study was to evaluate summer maize (Zea mays L.) yield and N uptake response to soil nitrate-N accumulation, and determine soil nitrate-N levels to meet N demand of high yield maize production in the North China Plain (NCP). A total of 1,883 farmers’ fields were investigated and data from 458 no-N plots were analyzed in eight key maize production regions of the NCP from 2000 to 2005. High nitrate-N accumulation (≥172 kg N ha⁻¹) was observed in the top (0–90 cm) and deep (90–180 cm) soil layer with farmers’ N practice during maize growing season. Across all 458 no-N plots, maize grain yield and N uptake response to initial soil nitrate-N content could be simulated by a linear plus plateau model, and calculated minimal pre-planting soil nitrate-N content for maximum grain yield and N uptake was 180 and 186 kg N ha⁻¹, respectively, under no-N application conditions. Economically optimum N rate (EONR) decreased linearly with increasing pre-planting soil nitrate-N content (r ² = 0.894), and 1 kg soil nitrate-N ha⁻¹ was equivalent to 1.23 kg fertilizer-N ha⁻¹ for maize production. Residual soil nitrate-N content after maize harvest increased exponentially with increasing N fertilizer rate (P < 0.001), and average residual soil nitrate-N content at the EONR was 87 kg N ha⁻¹ with a range from 66 to 118 kg N ha⁻¹. We conclude that soil nitrate-N content in the top 90 cm of the soil profile should be maintained within the range of 87–180 kg N ha⁻¹ for high yield maize production. The upper limit of these levels would be reduce if N fertilizer was applied during maize growing season.     

Agro-ecological nitrogen management in soils vulnerable to nitrate leaching: a case study in the Lower Suwannee Watershed

Environmental benefits associated with reduced rates of nitrogen (N) application, while maintaining economically optimum yields have economic and social benefits. Although N is an indispensable plant nutrient, residual soil N could leach out to contaminate groundwater and surface water resources, particularly in sandy soils. A 2-year field study was conducted in an established bermudagrass (Cynodon dactylon) pasture in the Lower Suwannee Watershed, Florida, to evaluate N application rates on forage yield, forage quality, and nitrate (NO₃-N) leaching in rapidly permeable upland sandy soils. Four N application rates (30, 50, 70, and 90 kg N ha⁻¹ harvest⁻¹) corresponding to 0.33, 0.55, 0.77 and IX, respectively, of recommended N rate (90 kg N ha⁻¹ harvest⁻¹) for bermudagrass hay production in Florida were evaluated vis-à-vis an unfertilized (0 N) control. Suction cups were installed near the center of each plot at two depths (30 and 100 cm) to monitor NO₃-N leaching. The grass was harvested at 28 days intervals to determine dry matter yield, N uptake, and herbage nutritive value. Nitrogen application at the recommended rate produced the greatest total dry matter yield (~18.4 Mg ha⁻¹ year⁻¹), but a modeled economically optimum N rate of ~57 kg N ha⁻¹ harvest⁻¹ (~60% of the recommended N rate) projected an average dry matter yield of ~17.3 Mg ha⁻¹ year⁻¹, which represents >90% of the observed maximum yield. Nitrogen application increased nutritive quality of the grass, but increases in N application rate above 30 kg N ha⁻¹ did not result in significant increases in in vitro digestible organic matter concentration, and tissue crude protein was not significant above 50 kg N ha⁻¹. Across the sampling period, treatments with N rates ≤50 kg N ha⁻¹ harvest⁻¹ had leachate NO₃-N concentration below the maximum contaminant limit of <10 mg l⁻¹. Conversely, applying N at rates ≥70 kg N ha⁻¹ harvest⁻¹ resulted in leachate N concentration that exceeded the maximum contaminant limit, and suggest high risk of impacting groundwater quality, if such rates are applied to soils with coarse (sand) textures. The study demonstrates that recommendation of a single N application rate may not be appropriate under all agro-climatic conditions and, thus, a site-specific evaluation of best N management strategy is critical.     

Recent trends in phosphate balance nationally and by region in Japan

A reduction in chemical phosphate (P) fertilizer application to farmland from 137.6 kg P ha⁻¹ in 1985 to 99.0 kg P ha⁻¹ in 2005 and in manure application from 42.4 kg P ha⁻¹ in 1985 to 32.8 kg P ha⁻¹ in 2005 did not reduce crop P uptake, which averaged 27 kg P ha⁻¹ over the period. Phosphate balance on farmland declined from 153.0 kg P ha⁻¹ in 1985 to 105.4 kg P ha⁻¹ in 2005 while livestock excreta disposal increased from 12.7 kg P ha⁻¹ in 1985 to 23.7 kg P ha⁻¹ in 2005. As a result, residual P associated with agriculture declined from 165.8 kg P ha⁻¹ in 1985 to 129.1 kg P ha⁻¹ in 2005. Phosphate utilization efficiency increased from 15.7% in 1985 to 20.1% in 2005. Median, minimum and maximum values of P flows by region showed similar trends. Phosphate input and withdrawal through crop production by region were not related to regional nitrogen (N) input and withdrawal through crop production. Although non-utilized P associated with agriculture has declined nationally and regionally, it is still higher than that in foreign countries, because of high chemical P fertilizer inputs and low crop yield withdrawal. Because soil P fertility was often sufficiently high previous large P surpluses, reducing P applications did not affect crop yields. Crop P uptake was less than half that of crop N yield. These results indicate that P inputs, especially by chemical fertilizer, for crop production could be reduced, thereby reducing negative environmental effects such as eutrophication of soil and water and conserving limited P resources.     

Soil organic carbon fractions after 16-years of applications of fertilizers and organic manure in a Typic Rhodalfs in semi-arid tropics

Agricultural soils can act as a potential sink of the increased carbon dioxide in the atmosphere if managed properly by application of organic manures and balanced fertilizers. However, the rate of carbon (C) sequestration in soils is low in warm climates and thus the short term changes in soil organic carbon (SOC) contents are almost negligible. Therefore, the knowledge about other C fractions that are more sensitive or responsive and indicative of the early changes in SOC can help to determine the effect of the management practices on soil C sequestration. The objective of this study was to determine the soil C sequestration after 16-years of applications of chemical fertilizers and farmyard manure (FYM) to rice (Oryza sativa)—cowpea (Vigna unguiculata) rotation system in a sandy loam soil (Typic Rhodalfs). The treatments were—(1) one control (no fertilizer or FYM); (2) three chemical fertilizer treatments [100 kg N ha⁻¹ (N), 100 kg N ha⁻¹ + 50 kg P₂O₅ ha⁻¹ (NP), 100 kg N ha⁻¹ + 50 kg P₂O₅ ha⁻¹ + 50 kg K₂O ha⁻¹ (NPK)]; (3) one integrated treatment [(50 kg N ha⁻¹ + 25 kg P₂O₅ ha⁻¹ + 25 K₂O ha⁻¹) + (50 kg N ha⁻¹ from FYM)]; and (4) one organic treatment at10 Mg ha⁻¹ FYM. Compared to the control treatment, the increase in SOC was 36, 33, and 19% greater in organic, integrated, and NPK treatments. The 16-years application of fertilizers and/or FYM resulted in much greater changes in water soluble C (WSC), microbial biomass C (MBC), light fraction of C (LFC), and particulate organic matter (POM) than SOC. Of the SOC, the proportion of POM was highest (24–35%), which was followed by LFC (12–14%), MBC (4.6–6.6%), and WSC (0.6–0.8%). The application of fertilizers and/or FYM increased the mean weight diameter of soil aggregates; thus provided physical protection to SOC from decomposition. Our results suggests that the application of fertilizers and/or FYM helps to sequester C in the soil and that the labile fractions of C can be used as indicators to determine the amount of C sequestered as a result of different management practices.