A five-year study to investigate the potential interaction of conservation tillage with reduced irrigation amounts was conducted near Dawson, GA on peanut ( Arachis hypogaea L.). Conventional tillage was compared to two conservation tillage programs (wide-strip and narrow-strip tillage) under four irrigation levels (100, 66, 33, and 0% of a recommended amount). Peanut yield did not exhibit a tillage by irrigation interaction as expected, although the main effects of irrigation and tillage were each significant by year due to weather variations. Peanut yield in narrow-strip tillage or wide-strip tillage were individually superior to conventional tillage in three seasons out of five, however only in one year did both conservation tillage systems outperform the conventional system. No detrimental effects on yields could be attributed to conservation tillage. Peanut quality and digging loss were dependent on the tillage by year effect as well as the main effect of irrigation. Irrigation increased total sound mature kernels (TSMK) 2% versus non-irrigated (0% irrigation level); tillage was not significant each year of the study but increased TSMK 2% in three of five years. Digging losses were greater in plots with increased yield potential such as those receiving irrigation. Net economic returns revealed a moderate trend towards sustained profitability under reduced irrigation levels through narrow-strip tillage and to a lesser extent, wide-strip tillage. Under conventional tillage systems, returns decreased with decreasing amounts of irrigation applied.

Information is needed on the role of cover crops as a weed control alternative due to the increase in adoption of conservation-tillage in peanut production. Field experiments were conducted from autumn 1994 through autumn 1997 in Alabama to evaluate three winter cereal cover crops in a high-residue conservation-tillage peanut production system. Black oat ( Avena strigosa Schreb.), rye ( Secale cereale L.), and wheat ( Triticum aestivum L.) were evaluated for their weed-suppressive characteristics compared to a winter fallow system. Three herbicide systems were utilized: no herbicide, preemergence (PRE) herbicides followed by (fb) postemergence (POST) herbicides, and PRE fb sequential POST herbicides. The PRE fb POST herbicide input system consisted of pendimethalin at 1.12 kg ai/ha fb an additional early POST application of paraquat at 0.14 kg ai/ha plus bentazon at 0.56 kg ai/ha. The PRE fb sequential POST herbicide input system contained the aforementioned herbicides fb 2,4-DB at 0.22 kg ai/ha plus chlorimuron at 0.14 kg ai/ha applied late POST. No cover crop was effective in controlling weeds without a herbicide program. However, when black oat or rye was utilized with PRE fb POST herbicides, weed control was similar to the high input system in two out of three years. Yield increased in 14 of 27 comparisons following conservation-tilled peanut using the Brazilian cover crop management system, compared to a winter fallow system. Yields never decreased following a winter cover crop compared to winter fallow. The winter fallow, high herbicide input system yielded between 7 and 26% less peanut compared to the highest yielding system that included a winter cover crop. The Brazilian system using black oat or rye cover crop has potential to increase peanut productivity and reduce herbicide inputs for peanuts grown in the Southeast.

The ability to measure plant water use directly could address a myriad of problems in peanut production from irrigation scheduling to aflatoxin management. One of the most effective methods of measuring plant water use is via the sap flow method; however this technique has not been tested in peanut in a field setting. In this study, sap flow collars were installed on peanut plants growing under overhead irrigation (OH), subsurface drip irrigation (SDI), and non-irrigated (NI) production. Using this experimental set-up the following objectives were addressed: 1) determine if the technique of sap flow measurement could be successfully utilized in peanut; 2) determine if daily peanut stem water flow, biomass partitioning, and carbon isotope discrimination differed among irrigation treatments, and 3) determine what environmental parameters were most closely correlated with peanut stem water flow. Peanut stem water flow was successfully measured during a two week period coinciding with active pod fill. Mean daily flow rates ranged from 4–6 g/hr in irrigated treatments and from 1–2 g/hr in the dryland treatment. Significant differences among irrigation treatments existed in daily water use patterns, average daily water use, and cumulative daily water use based on plant sap flow. Soil moisture, soil temperature, and canopy surface temperature were significantly correlated with plant sap flow. Significant differences also existed among irrigation treatments in plant size with SDI plants having more leaf mass, longer internodes, and overall larger canopies than either the OH or NI plants. Even though SDI plants had much greater aboveground biomass than plants in the other treatments, yields did not differ between irrigation methods indicating SDI plants may have had lower water-use efficiencies than either OH or NI plants. However, seasonal water-use efficiency measurements represented by carbon isotope discrimination results did not definitively show this. This study has shown the efficacy of sap flow measurement in peanut and the potential applications of this technique in future irrigation studies.

Legumes typically mineralize rapidly and can contribute to nitrogen (N) requirements of succeeding crops, but limited information exists on the mineralizable N content of peanut ( Arachis hypogaea L.) residue. The objective of this study was to determine net N mineralization from two types of peanut residue for two soil types. Aboveground peanut residue (cv. Georgia Green) was collected 1 d prior to digging (PRE) and immediately after peanut threshing (POST). Leaf and stem residues were mixed and analyzed for carbon (C), N, lignin, and cellulose. Peanut residue equivalent to 4.5 Mg/ha was applied to a Greenville fine sandy loam (fine, kaolinitic, thermic Rhodic Kandiudults) and a Tifton loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudult) and aerobically incubated for 98 d in the dark at 25 C to determine C and N mineralization. Each soil was incubated simultaneously, with and without residue. PRE harvest residue had lower C, lignin, and cellulose concen-trations, but higher N concentrations than POST harvest residue. Differences in residue quality corresponded to differences in cumulative C mineralized and C turnover for the Tifton soil, but did not result in differences for cumulative N mineralized or relative N mineralized within either soil type. These data indicate that peanut residue will not supply significant amounts of N to a subsequent crop for these two soil types.