The Evolution Of Wheat Cultivars Productivity On The Loess Tableland

We tested the data of wheat cultivar regional experiments and meteorology to assess the synergistic effect between yield and atmospheric precipitation during 1972-2008 on the Loess Tableland. Meanwhile, eight dry-land winter wheat cultivars(Triticum aestivum L.), representative of those widely cultivated from the 1940 s to the 2010 s in this region, were selected and grown in field during the growing seasons of 2007-2009 and 2012-2014. The lab analysis was conducted, so as to identify the morphological and physiological traits associated with yield progress. The photosynthetic characteristics of leaves, responses of wheats to drought, efficiency of dry-matter and nutrient translocation and contribution of them to the grains were studied, and findings are as follows:1 The yield of winter wheat on the Loess Tableland increased significantly with cultivar replacement. However, the high fluctuation of annual precipitation and seasonal precipitation resulted in high fluctuation of yield, which in the normal years, wet years and dry years was 4311.9 kg ha-1, 4361.0 kg ha-1 and 3641.6 kg ha-1, respectively. Additionally, it was impossible to eliminate the fluctuation in the present days, the yield was only fluctuated at a high level by modern agriculture technology. Although a significant increase in the yield of winter wheat, the increase was still not big enough compared with other regions both in China and abroad. Hence, we should further increase grain numbers, thousand-grain weight and the distribution ratio of dry matter translocation to increase yield.2 The yield of winter wheat increased 7 times from the 1940 s to the 2010 s in this region. But there was no significant correlation between yield and net photosynthetic rate, when the all cultivars representing the germ plasm typically grown on same environment. The grain numbers and thousand-grain weight were the key factors to restrict yield increased, not be limited by the products of photosynthesis. It suggested that there may be enough photosynthetic capacity or other factors to restrict yield increased. A significant positive correlation was observed between yield and grain number per unit area(r=0.855, P<0.05), harvest index(HI)(r=0.885, P<0.01) and thousand-grain mass(r=0.879, P<0.01). Hence, the sink strength was the key factor to yield increased, not the leaf net photosynthetic rate.3 Although the yield in modern cultivars decreased the most with drought stress, it could accumulate more dry matter and still higher than the previous cultivars. The contribution of pre-anthetic assimilates to the grains was higher under unstressed than under stressed conditions. Water stress significantly decreased the duration(averages of 47.4-41.7 d) and the rates of grain filling(averages of 0.03-0.02 g d-1). Yield was reduced, largely due to a decrease in the number of spikes per ha, which decreased by an average of 39% under water stress.4 The post-anthesis N, P and K concentrations showed an increased trend with cultivar replacement. The N, P and K concentration in aboveground plants in modern cultivars was 26%, 24% and 21% higher than in old and 12%, 14 % and 7% higher than in intermediate cultivars, respectively. Generally, similar to the pattern of the nutrient concentrations, N had similar accumulation ranges with K, whereas P accumulation was significantly lower for the same growth period. All the wheat cultivars exhibited significantly larger fractions of N, P, and K that accumulated between sowing and anthesis in the grown seasons. The old cultivars had a higher ratio of N and P accumulation than others between sowing and anthesis, followed by intermediate and modern cultivars. The N, P and K concentration and accumulation of winter wheat on the Loess Tableland increased significantly with cultivar replacement. Effects of growth period and cultivar on either concentrations or the accumulations of N, P, and K in straw and grain were highly significant in both grown seasons with the exception of a non-significant effect(P< 0.05) of cultivar on P and K concentration in grain in 2013 and P concentration in leaf in 2014.5 The yield water-use efficiency increased significantly with cultivar replacement. It was 62% higher in modern cultivars than in old and 25% higher than in intermediate cultivars, respectively. With increasing precipitation, the yield water-use efficiency was also increased. It increased the most in modern cultivars as 175%, followed by intermediate and modern cultivars.