Agronomy Journal

Timsina, Jagadish; Singh, Upendra; Badaruddin, Mohammed; Meisner, Craig

doi: 10.2134/agronj1998.00021962009000020001xpmid: N/A

Rice (Oryza sativa L.) followed by wheat (Triticum aestivum L.) is a dominant cropping sequence under a range of management regimes in South Asia, with variable productivity. Simulation models can be used to extrapolate experimental results to other sites of interest in variable environments. Experiments were conducted to quantify the responses of two rice cultivars to three N regimes and two soil moisture regimes, followed by the responses of the succeeding two wheat cultivars to three N regimes, two soil moisture regimes, and two dates of planting, on a Haplaquept noncalcareous brown floodplain soil at the Wheat Research Center, Nashipur, Bangladesh. CERES‐Rice and CERES‐Wheat models were validated using the experimental data set, and then were used to estimate the grain yields at two other sites in Bangladesh. In rainfed plots, grain yields of ‘BR14’ rice were reduced by 48.8, 43.4, and 39.3% relative to irrigated plots, and those of ‘BR11’ were reduced by 49.1, 43.8, and 42.2% (P < 0.05), for 0, 90, and 135 kg N ha−1, respectively. The optimum N rate was between 90 and 135 kg ha−1. In the succeeding wheat crop, at 0 N, there were no significant differences between the two moisture regimes but, at high N (180 kg ha−1), irrigation promoted greater yield. Relative to the high‐N treatment, grain yields of irrigated ‘Kanchan’ wheat at 0 N were reduced by 73.0 and 71.6%, and of ‘Sowgat’ by 75.2 and 73.5%, for early and late plantings, respectively. Simulation investigated year‐to‐year variation in grain yields of both crops under their several N regimes. Rice yields tended to increase over years, but wheat yields had no definite trend. The simulation results indicated that, without N fertilizer application, N will be limiting across sites and long‐term weather conditions for both rainfed and irrigated crops. Field experimentation quantified actual crop responses to a range of management practices and allowed validating the models for the rice‐wheat sequence. The models were then used to extrapolate and generalize the results for two other sites in Bangladesh.

Vyn, Tony J.; Opoku, George; Swanton, Clarence J.

doi: 10.2134/agronj1998.00021962009000020002xpmid: N/A

The acceptance of no‐till systems for soybean [Glycine max (L.) Merr.] production following winter wheat (Triticum aestivum L.) on fine‐textured soils in Ontario has been hampered by soybean yield reductions due to unfavorable seedbed conditions. This research was conducted to identify alternative tillage and residue management systems that will enhance emergence, growth, and yield of soybean following winter wheat. Seven tillage and residue management systems, comprising fall moldboard plow, fall chisel plow, fall disk only, fall zone‐till, no‐till, no‐till (with wheat straw baled), and no‐till (with wheat straw and stubble removed), were evaluated following winter wheat on fine‐textured soils from 1994 to 1996 at six different sites near Centralia and Wyoming in southwestern Ontario. Spring soil moisture was lower in the fall tillage treatments than in no‐till with wheat residue, but moisture differences did not vary among fall tillage treatments. No‐till seedbeds had the highest soil moisture contents, the lowest proportion of fine soil aggregates (<5 mm in diameter), and the greatest penetrometer resistance. No‐till soybean growth was delayed and yields were reduced as the level of wheat residue left after planting increased. Soybean seed yield was negatively correlated with surface residue cover, but positively correlated with soil aggregates <5 mm in diameter at all sites. Fall zone‐till and fall disk systems generally improved in‐row seedbed conditions (higher fine soil aggregates and lower soil resistance), and increased seed yields by 5 to 29% relative to no‐till treatments. Fall zone‐till and fall tandem disk systems were the best conservation tillage alternatives to fall moldboard plowing.

Alvarez, Roberto; Russo, Miguel E.; Prystupa, Pablo; Scheiner, Javier D.; Blotta, Luis

doi: 10.2134/agronj1998.00021962009000020003xpmid: N/A

The Rolling Pampa is the most important cropping region of Argentina, and its soils are subjected to degradation. No‐tillage has been proposed to replace the use of the moldboard plow to reduce soil C losses. The effects of no‐tillage and plow tillage with and without N fertilization (0 or 90 kg N ha−1) on C inputs and outputs of a Typic Argiudoll and on organic C level and density fractions were studied in a field experiment at the end of 15 yr under a corn (Zea mays L.)‐wheat (Triticum aestivum L.)‐soybean [Glycine max (L.) Merr.] rotation. Microbial biomass and the rate of organic C mineralization during laboratory incubations were also determined. Nitrogen fertilization had no significant influence on C emission in the field, soil organic matter level or microbial biomass and activity. The annual C budget was negative under both tillage systems, but no‐tillage lost about 0.7 to 1.5 Mg ha−1 yr−1 more C than did plow tillage. Carbon in the medium‐density fraction (density = 1.6‐2.0 g mL−1) of the 0‐ to 20‐cm soil layer was 30% higher (P ≤ 0.05) under no‐tillage. Light (density < 1.6 g mL−1) and heavy (density > 2.0 g mL−1) organic fractions, total C, and microbial biomass and activity in the 0‐ to 20‐ cm layer were not different in no‐tilled and plowed soils, despite different patterns of distribution with depth. The rates of organic C mineralization during laboratory incubations were the same for both tillage systems. We propose that, after an accumulation phase, soil under no‐tillage loses higher amounts of CO2‐C than under plowing. The use of no‐tillage would not significantly affect soil organic matter pools of the region in situations with low erosion losses.

Gwathmey, C. Owen; Howard, Donald D.

doi: 10.2134/agronj1998.00021962009000020004xpmid: N/A

Earliness of maturity is essential for adaptation of cotton (Gossypium hirsutum L.) to regions with short growing seasons, and it may be influenced by potassium nutrition. Our objectives were to determine effects of K fertilization on interception of photosynthetically active radiation and earliness, and to describe the relationship between earliness and light interception at different in‐canopy heights. Research was conducted with no tillage on a Memphis silt loam (fine‐silty, mixed, active, thermic Typic Hapludalf) with low extractable K. Using a split‐plot randomized complete block design, 0 and 112 kg K ha−1 were soil‐applied before planting each year as mainplot treatments, and 0 and 4.1 kg K ha−1 were foliar applied four times per season as subplot treatments. Canopy interception of photosynthetic photon flux density (PPFD) was measured at 23‐cm vertical increments in 1993 and 1994. Plots were spindle‐picked twice each year. Earliness was measured as the percent of total yield picked at first harvest. Relative to no fertilizer K, soil‐applied K increased canopy PPFD interception at all heights measured. Neither soil‐applied nor foliar K affected earliness in 1993, a drought year, but soil‐applied K decreased percent first harvest from 78 to 65% in 1994. Foliar K did not affect canopy light interception in 1993, and it increased interception in 1994 only with no soil‐applied K. At 111 d after planting, percent first harvest was negatively correlated with PPFD interception at all measured heights in the canopy, suggesting that higher K fertility delayed maturity as it increased upper‐canopy light interception. In short‐season environments, optimum K fertilization needs to be accompanied by cultivar selection and management that promote earliness of maturity.

Clément, Alain; Ladha, Jagdish K.; Chalifour, François‐P.

doi: 10.2134/agronj1998.00021962009000020005xpmid: N/A

Green manure (GM) is an alternative to mineral fertilizers, particularly for subsistence farmers whose resource base is small. Published information on the influence of the chemical composition of GM on N dynamics in lowland rice (Oryza sativa L.) is scarce. A field experiment was conducted in the 1992 wet season (WS), the 1993 dry season (DS) and the 1993 wet season to compare GM species and urea as sources of N for rice, to monitor N release and uptake during the season, and to verify the effect of the chemical composition of GM on rice yield (including the residual effect on dry season rice). Ten species were compared, with two controls (with and without deep‐placed urea supergranules). Nitrogen from urea or GM crops was applied at the rate of 80 kg N ha−1. Most GM species performed as well as urea supergranules. Cowpea [Vigna unguiculata (L.) Walp.], soybean [Glycine max (L.) Merr.], and sorghum [Sorghum bicolor (L.) Moench] outyielded the urea control in the 1992 wet season. Residual effects of GM incorporation on rice grain yield during the 1993 dry season were generally modest. Rice grain yield response to GM application was comparable for both the 1992 and 1993 wet seasons (r2 = 0.83**). In microplots without rice plants, there was limited GM‐N mineralization past 30 days after transplanting (DAT). Soil NH+4‐N with rice increased until about 20 DAT, and then decreased sharply, because of rice N uptake. At 50 DAT, soil NH+4‐N reached very low levels in all treatments. Rice N uptake between 31 and 52 DAT was explained by the size of early‐season soil NH+4‐N pool (r2 = 0.83**). Higher N uptake rates by rice with GM than with urea from 52 to 69 DAT indicate a better synchrony between GM‐N availability and rice N uptake. The C/N ratio of GM species influenced rice N uptake, but only early in the season.

Zhou, Xiaomin; Leibovitch, Stewart; MacKenzie, Angus F.; Madramootoo, Chandra A.; Dutilleul, Pierre; Smith, Donald L.

doi: 10.2134/agronj1998.00021962009000020006xpmid: N/A

The high cost of labeled N fertilizer places practical limitations on measuring the fate of applied N. Applying of the labeled 15N to a microplot within a larger plot can reduce the cost. The objective of this study was to assess microplot dimensions required to produce reliable 15N data and cropping system effects on corn 15N uptake under a regime of monocropped corn (Zea mays L.) and corn intercropped with annual Italian ryegrass (Lolium multiflorum Lam.). Nitrogen was applied to large plots (15 by 75 m) at 270 kg N ha−1 on a fine, silty, mixed, nonacid, frigid Typic Humaquept soil during the 1993 and 1994 growing seasons. Enriched N fertilizer was applied to 1.15 by 1‐m2 confined microplots located in opposite halves of the large plot in each year of the study. Corn plants inside the confined microplots were sampled at 0.1, 0.3, and 0.5 m from the end borders of each microplot. In 1993, monocropping resulted in increases in leaf, stalk, and total dry matter production of 22, 41, and 30%, respectively, within microplots and relative to intercropped corn. There were no cropping system effects for these parameters in 1994. Monocropping increased atom % 15N enrichment in corn grain and stalks and increased fertilizer N recovery in all plant tissue compared with intercropping in both years. There were no differences in atom % 15N enrichment and fertilizer N recovery for plants harvested at the three sampling positions. These results suggest that a confined microplot with an area as small as 0.4 by 1.15 m can provide a reliable measure of fertilizer N recovery for corn plants in monocrop or intercrop systems. Any or all of the five plants within the microplot could be used to supply a reliable estimation of 15N recovery by corn plants.

Wiedenfeld, Robert P.

doi: 10.2134/agronj1998.00021962009000020007xpmid: N/A

Nitrogen fertilizer recommendations have been developed for sugarcane (Saccharum officinarum L.) based on numerous fertility trials, with the primary variables affecting those recommendations being soil type and crop age. Cropping history influences subsequent crop responses to N fertilization, but such effects have not been determined for sugarcane. The objective of this research was to evaluate previous‐crop effects on sugarcane growth and response to N fertilization. Eight 2‐yr previous‐crop treatments consisted of N‐fertilized and unfertilized corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and cotton (Gossypium hirsutum L.); unfertilized soybean [Glycine max (L.) Merr.]; and fallow. These treatments were followed by sugarcane grown for 3 yr at four different levels of N fertilizer application. Previous‐crop treatments containing corn and sorghum contributed more biomass back to the soil than cotton or soybean. None of the crops grown prior to sugarcane responded to N fertilization, resulting in 90% of the N fertilizer applied remaining in the soil. Sugarcane yield and quality in the plant‐cane crop were affected primarily by previous‐crop treatments, in the first ratoon by both previous crop and N fertilizer application, and in the second ratoon primarily by N fertilizer application. Sugarcane responses to N fertilization were generally lowest following those treatments which had the most N returned from plant residue, or the most measured residual N. Inorganic soil N measurements correlated better with sugarcane responses to N in the plant cane crop, while mineralizable soil N levels correlated better with sugarcane responses to N in the first ratoon crop. Soybean resulted in low inorganic and mineralizable soil N, yet sugarcane following soybean failed to respond to N fertilizer application, indicating that N following soybean is less readily released but does later become available.

Gutiérrez‐Boem, Flavio H.; Thomas, Grant W.

doi: 10.2134/agronj1998.00021962009000020008xpmid: N/A

Plant leaf area affects both plant growth and yield. Although the effects of phosphorus and water availability on leaf area development have been studied as isolated factors, little work has been done on their possible interactions. A pot experiment was conducted to investigate the effects of both P and water availability on early leaf appearance and expansion in soft red winter wheat (Triticum aestivum L.), and to determine whether the effect of water deficit changes at each level of P nutrition and whether the soil water content affects plant P uptake. The soil was a Lonewood loam (fine‐loamy, siliceous, mesic Typic Hapludult), which had an available P level of 8.2 mg P kg−1 (Mehlich III). Additional P was applied at 0, 10 and 20 mg P kg−1 soil. Water treatments consisted of keeping soil‐water content at 80% (well watered) and 53% (stressed) of the 10 kPa soil‐water content. Plant development, leaf appearance and expansion, and stomatal resistance were measured during the experiment. At harvest (38 d after emergence), leaf area, aboveground biomass, and P concentration were measured. Phosphorus and water availability exhibited a significant interaction on tiller and leaf appearance, which were reduced by water stress but only at 0 applied P. As individual factors, P and water influenced different plant features. Lack of applied P decreased the rate of leaf appearance and, therefore, the final number of leaves and leaf area per plant. Water deficit reduced individual leaf area and, at 0 applied P, reduced rate of leaf appearance, number of simultaneously expanding leaves, and final number of leaves. Phosphorus uptake was increased only with added soil P, and not by water stress. The ability of plants to cope with mild water stress was enhanced by adequate P nutrition.

Crozier, Carl R.; King, Larry D.; Volk, Richard J.

doi: 10.2134/agronj1998.00021962009000020009xpmid: N/A

Legume cover crops have been studied in the southeastern USA, but there have been no 15N tracer studies comparing movement of legume N and fertilizer N for this region. Our study used l5N‐enriched crimson clover (Trifolium incarnatum L.) (135 kg N ha−1) and either 15NH4NO3 or NH154NO3 (70 kg total N ha−1) to quantify N movement through soil inorganic and organic N pools and into corn (Zea mays L.). Clover N mineralized rapidly, with 45% of the initially applied N detectable as inorganic N at 18 d following incorporation. Rapid nitrification of enriched NH+4 occurred, but, since the soil NO‐3 pool was larger in this treatment than in the enriched NO‐3 treatment (presumably due to chance), the relative enrichment of the soil NO‐3 pool was less than with the application of enriched NO‐3. At anthesis, 25% of the N in corn had been derived from the NO‐3 source, while only 11% had been derived from the NH+4 source (P < 0.05). At physiological maturity in 1990, the first growing season, 38 to 44% of each enriched source could be accounted for. By physiological maturity in 1991, 60% of the clover source but only 28 to 36% of the fertilizer sources could be accounted for. This study demonstrates the substantial amounts of endogenous soil N mineralization, inorganic N immobilization, and legume N persistence in these cropping systems.

Peng, Shaobing; Cassman, Kenneth G.

doi: 10.2134/agronj1998.00021962009000020010xpmid: N/A

Measurements of the N uptake rate of rice (Oryza sativa L.) have usually been conducted over a period of 7 to 14 d. Such a sampling interval may not accurately determine the maximum rate, since information concerning N uptake dynamics during the first week after N topdressing is limited. In this study, N uptake dynamics and fertilizer N recovery efficiency following N topdressing were determined with more frequent samplings. Field experiments were conducted at International Rice Research Institute (IRRI) and at the Philippine Rice Research Institute (PRRI) during the 1995 dry season. Treatments consisted of 0, 50, and 100 kg N ha−1 applied at midtillering (MT) or panicle initiation (PI). Tissue N concentration and N uptake were measured 0, 2, 4, 6, 9, and 14 d after N application. Fertilizer N recovery efficiency was estimated using the difference method. At PI, maximum N uptake rates of 9 to 12 kg ha−1 d−1 were measured over the 4‐d period following application of 100 kg N ha−1, which is up to double the previously reported maximum value of 6 kg ha−1 d−1. The much larger estimates of maximum N uptake rates in our study probably resulted from more frequent sampling than in previous studies. Nitrogen uptake rates at PI were similar, regardless of N rate at MT. Recovery efficiency of N applied at PI reached 74 to 78%, and was significantly higher than that at MT. Recovery efficiency was relatively insensitive to the amount of N applied at MT and PI, which suggests that high N fertilizer efficiency can be achieved with large rates of applied N when growth conditions are favorable.