difference in nutrients applied vs. crop nutrient requirements results in the soil buildup of excess nutrients, es-A common problem when broiler litter is applied to pastures in pecially P (Sims, 1995). Water quality problems can the southeastern USA is the buildup of soil P because of the difference occur if P enters surface water in runoff (Sharpley et in N-P-K ratio of the broiler litter and forage crop requirements. A study was conducted to test the theory that if the N requirement of al., 1993). the forage crop is only partially met by the broiler litter, application Perennial pastures are an ideal recipient of animal of commercial N fertilizer would stimulate plant growth to remove manure (Edwards, 1996). Annual land preparation and excess soil P and K. A small-plot study was conducted for 2 yr combinplanting are not required. The forage sod protects the ing 9 Mg ha Ϫ1 broiler litter applied in October with various combinasoil from erosion and provides a firm surface for manure tions of 56 kg N ha Ϫ1 applied in December, March, May, and July to application equipment and grazing animals during wet an annual ryegrass (Lolium multiflorum L.)-'Coastal' bermudagrass weather. In the southeastern USA, mixtures of cool-[Cynodon dactylon (L.) Pers.] pasture system. Yield increased from and warm-season forages provide a year-long growing 8.9 to a maximum of 13.4 Mg ha Ϫ1 when 56 kg N ha Ϫ1 was applied up season and sink for N mineralized from animal manure to three times a year. Nitrogen uptake was directly related to the amount throughout the year. Essentially, all of the P and K in of N fertilizer applied, with a maximum of 285 kg N ha Ϫ1 removed following four applications. The most P and K was removed when N was broiler litter is available for plant uptake (Wilkinson, applied in December and March or March and May. These treatments 1979).removed 23% more P and 43% more K than when no commercial

No abstract

Effective comparisons of natural grasslands and improved pasture require a robust model for plant growth, soil water balance, runoff, soil erosion, and climatic impacts. Our first objective was to develop plant parameters in the field that enabled the ALMANAC model to simulate growth of coastal bermudagrass [Cynodon dactylon (L.) Pers.]. Pensacola bahiagrass (Paspalum notatum Flü gge var saurae Parodi), and some common native, warm-season grasses. Parameters included leaf area, light interception, biomass growth, and nitrogen concentration. The maximum leaf area index values of coastal bermudagrass and bahiagrass were near 2.2. Those for native grasses other than switchgrass (Panicum virgatum L.) were much less. Mean values for light extinction coefficient ranged from 0.7 to 2.1. Radiation use efficiency values for four of the five measured grass species were between 1.0 and 2.0 g MJ 21 . Grass [N] values showed similar patterns of seasonal change among species. Our second objective was to use these grass parameters to simulate biomass production of coastal bermudagrass, bahiagrass, and some native grasses on representative soils in several counties in a number of regions of Texas. Counties and soils that were simulated represented a diversity of sites in Texas where improved grasses and native grasses are grown. The ALMA-NAC model reasonably simulated biomass means and SDs for native grasses, coastal bermudagrass, and bahiagrass. The model is a realistic tool to simulate effects of soil type and weather on native and improved grass productivity on such diverse sites.

Understanding the growth pattern of cool‐season annual clovers is necessary to develop management practices that maximize forage production and identify compatible grass associations and farming systems. Plant density, light interception, shoot yield, and root yield of arrowleaf (Trifolium vesiculosum Savi.), crimson (T. incarnatum L.), rose (T. hirtum All.), and subterranean (T. subterraneum L.) clovers were compared for 3 yr on a sandy loam at Overton, TX. Clovers were sampled every 2 wk when uncut, and after being cut once or twice. Initial plant densities ranged from 200 to 250 m−2 and then declined to 100 to 150 m−2 during the growing season. The uncut treatment resulted in 3‐yr average maximum shoot yields of 2480 g m−2 for arrowleaf, 1290 g m−2 for crimson, 1410 g m−2 for rose and 1000 g m−2 for subterranean clovers. Autumn growth and regrowth after cutting was greater for crimson and subterranean clovers than for arrowleaf and rose clovers. Crimson and subterranean clovers reached near 100% light interception 4 wk after cutting. Cutting usually decreased yield for all species except subterranean clover that increased with cutting because of a prostrate growth habit. When cut, rose clover always had one of the smallest shoot and root yields. Root yield increased for all clovers during the growing season when not cut and with no or small root yield decreases after cutting. Crimson and subterranean clovers are better suited for grazing and crop rotations because of their earlier maturity and response to defoliation.

During the past 25 yr, several different dallisgrass (Paspalum dilatatum Poir.) biotypes have been discovered, but little is known regarding their cytology and reproductive behavior. This study was undertaken to determine the cytology, method of reproduction, and fertility of three biotypes and the forage yield and quality of two of them. Two biotypes, Torres and Uruguaiana, were introduced from southern Brazil and the third, Uruguayan, was collected in Uruguay. All three are hexaploids with 2n = 6x = 60. The Torres biotype was meiotically irregular, with a mean chromosome association of 58.74 univalents and 0.63 bivalents per cell. Two accessions of the Uruguaiana biotype were studied; they had a mean meiotic chromosome association of 9.62 univalents, 25.17 bivalents, and 0.01 quadrivalents. Eleven accessions of the Uruguayan biotype were studied; their mean chromosome associations were 1.26 univalents, 29.28 bivalents, and 0.04 quadrivalents. It was proposed that the lack of chromosome pairing in the Torres biotype is genetically controlled. The genomic formulas of the Uruguaiana and Uruguayan biotypes are proposed to be AABBC1C2 and AABBCC, respectively. An examination of megasporogenesis and embryo sac development revealed that all three biotypes reproduce by apomixis, with apospory followed by pseudogamy. One Uruguayan accession was a facultative apomict with a small degree of sexuality. The forage yield potential and forage quality were determined for the Torres and Uruguayan biotypes, as well as for common dallisgrass. Torres produced less forage than the other two. Common dallisgrass produced less forage than the mean of the Uruguayan accessions in most environments. In vitro dry matter disappearance (IVDMD) differences among accessions were relatively small. Common dallisgrass did not differ in IVDMD from any of the Uruguayan accessions.