Search

Early planting (late April to early May) is recommended for increasing soybean [Glycine max (L.) Merr.] yield but a full understanding of the physiological response is lacking. Carbon dioxide exchange rate (CER) was measured on soybean planted between 18 April and 29 May to determine if CER could resolve this yield difference. During the season CER was measured twice weekly on individual leaves. Total carbon fixation, dry matter accumulation, and radiation use efficiency (RUE) were calculated for the growth periods R1 to R3 and R3 to R6. During the early vegetative stages CER (before flowering) declined for all planting dates and reached a minimum of 0.566 (late planting) to 0.629 (optimal planting) mg C[O.sub.2] [m.sup.-2] [s.sup.-1] by approximately R2 (late flowering) followed by a linear rate increase to a maximum of 1.23 mg C[O.sub.2] [m.sup.-2] [s.sup.-1] by R5 to R6 (early seed fill). The optimal first week of May planting increased main-stem node number, average CER during R1 to R6, total carbon fixation, and dry matter but did not increase seed yield. Overall, yield and seed number were positively related to CER between R3 and R6. These data demonstrate that (i) CER was controlled by plant growth stage and was independent of the date that growth stage occurred and (ii) early planting did not consistently increase the CER rate during the R3 to R6 growth stage, limiting yield improvement. Factors other than CER are more likely to explain the reported positive yield response to early planting. doi: 10.2135/cropsci2010.02.0107

Regional-level recurring spatial patterns of yield variability are important for commercial activities, strategic agricultural planning, and public policy, but little is known about the factors contributing to their formation. An important step to improve our understanding is recognizing regional spatial patterns of yield variability in association with regional environmental characteristics. We examined the spatial distribution of county-level mean yields and CVs of mean yields of four functionally different crops--corn (Zea mays L.), soybean [Glycine max (L.) Merr.], alfalfa (Medicago sativa), and oat (Avena sativa L.)--in Iowa using Moran's Index of spatial autocorrelation. Patterns of association with 12 county-level climatic, edaphic, and topographic environmental characteristics were examined using partial least squares regression. Two distinct geographic provinces of yield stability were identified: one in the northern two-thirds of the state characterized by high mean yields and high yield constancy, and one in the southern third of the state characterized by Iow mean yields and low yield constancy. Among eight partial least squares regression models, which explained 50 to 81% of variation of mean yields and yield CVs, mean organic matter and mean depth to seasonally high water table had greatest relative importance to mean yields of grass crops and legume crops, respectively. Among the CV models, variables describing water availability were of greatest relative importance, with less distinct differences between grass and legume crops. Partial least squares regression is a potentially powerful tool for understanding regional yield variability.

Determining the extent of change in fresh versus field-cured grass hay quality, mineral, and N[O.sub.3]-N concentrations under rain-free conditions provides valuable information to hay producers. The objectives of this research were to evaluate the effect of fresh vs. field-cured forage on crude protein (CP), neutral detergent fiber (NDF), total digestible nutrients (TDN), P, K, Ca, and N[O.sub.-3]-N concentrations of orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromus inermis Leyss.), and timothy (Phleum pratense L.), and to determine if interactions with N rate exist. At the low N rate in 1999 and 2000, orchardgrass CP in fresh and field-cured forage, NDF, and TDN concentrations were different. Orchardgrass P and K concentrations were lower in field-cured compared with fresh forage, but differences were inconsistent across N rates. In contrast, smooth bromegrass K (23 vs. 27 g [kg.sup.-1]) and Ca (4.3 vs. 6.2 g [kg.sup.-1]) concentrations were greater in field-cured compared with fresh forage in 1999 across N rates. Tissue N[O.sub.-3]-N concentration was greater in field-cured orchardgrass at all N rates and at the Iow N rate in smooth bromegrass in 1999. Interactions between N rate and fresh vs. field-cured smooth bromegrass were detected for all variables in 1999 and orchardgrass K concentration in 2000. These results demonstrate that changes in grass quality, mineral, and tissue N[O.sub.-3]-N concentrations occur under rain-free field curing conditions. Consequently, forage scientists conducting research on grass hay quality indices and mineral content should sample subsequent to field-curing to provide accurate results., COOL-SEASON GRASSES are commonly grown in the northeast USA for hay production because of their tolerance of poor drainage, lower establishment and maintenance costs, and faster drying rates than legumes. [...]

Numerous studies have evaluated growth, stand dynamics, and botanical composition of grass swards separately, but little information is available on the interaction of these factors. The objectives of this study were to determine the response of growth rate, tiller density, and botanical composition in orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromus inermis Leyss.), and timothy (Phleum pratense L.) to different N levels. Growth rates ranged from 8.6 to 1.54, 9.14 to 0.67, and 4.19 to 0.29 g dry matter (DM) [m.sup.-2] [d.sup.-j] in orchardgrass, smooth bromegrass, and timothy. Orchardgrass growth rates responded to changes in abiotic conditions, while smooth bromegrass and timothy expressed less plasticity under favorable growth environments. All species exhibited temporal fluctuations in tiller density. Orchardgrass and smooth bromegrass tiller densities were not closely associated with yield, presumably because of compensation in tiller weight. Nitrogen did not affect tiller density during the first production year, but orchardgrass tiller density was influenced by N throughout the second production year, including the fall growth period, when tiller density in all species was affected. Aggressive growth rates in orchardgrass reduced species diversity by 65% by the end of the second production year. Total diversity in smooth bromegrass decreased from 7.2 to 3.5 species 0.25 [m.sup.-2] compared with an increase in timothy from 1.5 to 5.7 species 0.25 [m.sup.-2] due to a combination of slow growth and reduced tiller density. Orchardgrass and smooth bromegrass are superior to timothy in Northeast hay production systems because of greater DM production and less weed competition., ALTHOUGH INHERENT ABILITIES of cool-season grasses allow them to adjust their growth rates in response to abiotic factors, it is often reported that growth rates of cool-season grasses are greatest [...]

Rotation effects on corn (Zee mays L.) growth have not been documented. Our objective was to evaluate dry matter (DM) and N accumulation of corn following corn, soybean [Glycine max (L.) Merr.], or wheat/red clover (Triticum aestivum L./Trifolium pretense L.) using moldboard plow, chisel, and ridge tillage under high (broadcast herbicides and 163 kg N [ha.sup.-1]) and low chemical management (banded herbicides and 95 kg N [ha.sup.-1]). In 1993, corn following soybean, compared with corn under high chemical management, had greater DM and N accumulation during vegetative development but similar N accumulation after silking (45 kg [ha.sup.-1]) and yield (7.6 and 7.2 Mg [ha.sup.-1], respectively). In 1994, corn following soybean, compared with corn under high chemical management, had similar DM and N accumulation during vegetative development, but greater N accumulation (59 and 35 kg [ha.sup.-1], respectively) after silking and yield (11.4 and 10.7 Mg [ha.sup.-1]). Corn following wheat/clover under both management systems, compared with corn following corn under high chemical management, had greater DM and N accumulation during vegetative development in 1994. Corn following wheat/clover under high chemical management had the greatest N accumulation after silking (79 kg [ha.sup.-1]) and yield (12.0 Mg [ha.sup.-1]), whereas the other two systems had the same N accumulation after silking and yield. Corn yield had linear responses to N accumulation after silking in 1993 ([r.sup.2] = 0.47) and 1994 ([r.sup.2] = 0.87). We conclude that N accumulation after silking influenced the yield response to rotation more than DM and N accumulation during vegetative development did., Corn, grown in rotation with other crops, yields more than continuous corn (Benson, 1985). Possible explanations for the corn yield increase under crop rotation include fewer pest problems (Benson, 1985), [...]

Biomass removal effects on soybean [Glycine max (L.) Merr.] light interception and yield under different row spacings have not been documented. Objectives for this study were to evaluate biomass removal, light interception, seed yield, and yield components of soybean under seven clipping treatments. Treatments in this study were clipping at V5, R1, R4, V5 + R1, V5 + R4, R1 + R4, and V5 + R1 + R4, and a control in 18- or 20-cm and 76-cm rows. In 1998, a dry year, biomass removal exhibited a negative linear relationship with seed yield in narrow rows ([r.sup.2] = 0.62). A row spacing-clipping interaction was observed. In wide rows, clipping at V5 or R1 produced a compensatory response by increasing yield 12 and 5%, respectively. Generally, soybean in 76-cm rows maintained seed yield by adjusting the number of pods or seed weight, except when clipping occurred at V5 + R4 or at three growth stages. In 1999, under severe moisture stress, row spacing influenced seed yield. Averaged across clipping treatments, narrow rows yielded 16% more (301 vs. 254 g [m.sup.-2]) than wide rows. Generally, soybean yield declined as clipping timing was delayed and as clipping frequency increased in narrow rows, except when clipping occurred at V5 + R1. Clipping at V5 and V5 + R1 did not affect yield in wide rows. All other clipping treatments suffered yield reductions ranging from 20 to 58%. A quadratic relationship ([R.sup.2] = 0.83) was observed between biomass removal and seed yield., SOYBEAN PRODUCERS suffer annual yield losses because of deer (Odocoileus virginianus) browsing. A report by Rutgers University Center for Wildlife Damage Control (unpublished, 1998) summarizing a survey of New Jersey [...]

While sowing cover crops in between cash crops is known to protect farm fields and enrich soils, many growers don't use the technique. In a survey of 3,500 Corn Belt [...]