Crop Rotation, Residue Durability, and Nitrogen Fertilizer Effects on Winter Wheat Production

Abstract

Alternative rotation crops and residue surface cover are needed for sustainable cropping systems. In two large‐scale field trials near Genesee, ID, ‘Gisilba’ condiment mustard ( Sinapis alba L), ‘Columbia’ dry pea ( Pisum sativum L.), and ‘Crimson’ lentil ( Lens culinaris Medik.) spring crops were evaluated for their agronomic effect on subsequent ‘Madsen’ winter wheat ( Triticum aestivum L.) during 1994–1995 and 1995–1996. After harvesting the spring crops, a chisel (applying 55 lb N/acre, 30 lb P/acre, and 20 lb S/acre) and two passes with a field cultivator with a harrow attachment prepared the seedbed for planting with winter wheat. Crop residue level and retention was measured over winter as the wheat crop became established. In the spring of each second year, incremental levels of N fertilizer (from 0 to 200 lb/acre) were applied to the winter wheat on a small plot section of each large plot using a split‐plot arrangement. Residues from the three spring crops showed very little winter decomposition. Mustard residues maintained a surface cover above 50%, greater than the 30% for pea and 25% for lentil. Winter wheat yields were 109 bu/acre following pea, 109 bu/acre following lentil, and 102 bu/acre after mustard in 1994–1995, but no significant differences were found in 1995–1996. Winter wheat test weight was statistically higher following lentil, but no differences in grain protein content or seed weight were observed. There were no significant differences in residual soil inorganic N among the spring crops and N fertilizer response regression equations of the subsequent winter wheat were not significantly different among previous crops. This information shows mustard, pea, and lentil can be beneficial rotational crops prior to winter wheat. Mustard is superior in residue production and could be a valuable alternative crop to pea and lentil in sustainable cropping systems that optimize crop production while reducing problems of soil loss. Research Question Winter wheat producers in the Palouse region of the Pacific Northwest typically grow dry pea or lentil as a previous crop. Concerns about soil losses that occur due to inadequate crop residues from these spring‐planted grain legumes have resulted in experimentation with alternate spring crops such as mustard. This study evaluates: the amount and durability of crop residues from mustard, pea, and lentil grown prior to winter wheat; the effects of mustard, pea, and lentil on the yield and quality of the subsequent winter wheat crop; and the effects of N application on winter wheat grown in rotation with mustard, pea, and lentil. Literature Summary In this annual cropping region, the most serious soil erosion occurs during winter in low‐residue grain legume fields sown to winter wheat. Crop management practices that result in 30 to 50% residue surface cover have been identified as a critical factor in preventing soil losses. Previous studies have shown improved agronomic performance of winter wheat when grown in rotation with pea, especially during dry years. Rotational benefits of Brassicas , such as mustard, when grown preceding winter wheat have been demonstrated in comparison with continuous cereal cropping systems. Interactions among applied N, crop residues, soil moisture, and residual soil N have been shown to affect the N response of winter wheat to previous crop. Study Description Field‐scale experiments were conducted over two 2‐yr cycles near Genesee, ID, during 1994–1995 and 1995–1996. In both experiments, dry pea, lentil, and mustard were seeded (25 ft by 500 ft plots in 1994, 16 ft by 600 ft plots in 1995) in a four replicate, randomized complete block design the spring of the first year and seeded over with winter wheat in the fall. Spring barley was grown the year prior to the experiment spring crop year. Spring crop production, residue production, and winter durability of pea, lentil, and mustard residues were evaluated. Fertilizer N rates of 0, 40, 80, 120, 160, and 200 lb/acre were spring‐applied on a section of the winter wheat plots using a split‐plot arrangement. Agronomic performance of winter wheat was compared across previous spring crop and N fertilizer rates. Applied Questions How did the spring‐planted pea, lentil, and mustard crops compare in seed production, crop residue production, and durability? Pea and lentil had higher seed yields but lower residue production than mustard in both 1994 and 1995 (Table ). Pea had the highest seed yield in both years, however, the residue produced from pea was slightly lower than from lentil and much lower than from mustard. Residue surface cover from the three spring crops changed little over winter. Pea and lentil residues fell below the minimum 30% surface cover after January and mustard residues remained above the desired 50% surface cover throughout the winter. What influence did the previous spring crop have on winter wheat production and quality? Winter wheat yield following pea, lentil, or mustard were not different when averaged over years (Table ). Winter wheat seed test weights were highest following lentil. Previous spring crop did not influence grain protein content or seed weight of winter wheat. Was there a difference in winter wheat N response depending on the preceding spring crop? Winter wheat showed similar seed yield response to N fertilizer regardless of the previous spring crop. Test weight of winter wheat seed declined as N applications increased and the highest test weights were observed following lentil. Winter wheat seed size and protein content also responded similarly to N regardless of previous spring crop. Linear plateau regression analysis revealed optimum N fertilizer rates of 120 lb/acre for winter wheat following pea or lentil, and 160 lb/acre following mustard. Average seed yield, residue production, and after‐seeding residue surface cover persistence of three spring crops grown during 1994 and 1995 at Genesee, ID during 1994 and 1995. Crop yield Overwinter residue Spring crop Seed Residue Oct Dec Feb Mar ‐‐‐‐‐‐‐ lb/acre ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐ % surface cover ‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Mustard 1100 5610 58 59 62 61 Pea 3080 3090 33 31 30 28 Lentil 2160 3720 28 28 26 26 Average 2110 4140 40 38 36 35 LSD (0.05) 430 820 10 6 7 3 Average winter wheat performance following three spring crops grown during 1994 and 1995 at Genesee, ID. Spring crop Seed yield Test weight Grain protein Seed weight bu/acre lb/bu % seeds/lb Mustard 106 60.2 10.1 12 200 Pea 111 60.1 10.6 12 000 Lentil 113 60.4 10.5 11 900 Average 110 60.2 10.4 12 100 LSD (0.05) ns 0.2 ns ns